Sulphur Chemistry in KOH-SO2 Activation of Fluid Coke and Mercury Adsorption from Aqueous Solutions

Hui Cai

A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Department of Chemical Engineering and Applied Chemistry University of Toronto

Hui Cai

Doctor of Philosophy

Department of Chemical Engineering and Applied Chemistry University of Toronto

2010

ABSTRACT

The technical feasibility of producing sulphur-impregnated activated carbons

(SIACs) from high-sulphur fluid coke by chemical activation was investigated. Using

KOH and SO2, the activation process was able to produce SIACs with controllable specific surface area (SBET), pore size distribution and sulphur content. The highest SBET was over 2500 m2/g and the highest sulphur content was 8.1 wt%.

K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy was employed to characterize the sulphur in fluid cokes and SIACs. The results revealed that the sulphur on fluid coke surface was mainly in the form of organic sulphide and thiophene (total 91-95 %), in addition to some sulphate (5 - 9%). The study of KOH- treated fluid coke suggested that KOH was effective in converting organic sulphide and thiophene to water soluble inorganic species which were readily removed by acid and water washing. SO2 treatment of fluid coke added sulphur to fluid coke through SO2- carbon reaction. Elemental sulphur was the main product, while part of the thiophene, sulphide and sulphate in the raw coke remained in the product. In KOH-SO2 activation,

- ii - disulphide, sulphide, sulphonate and sulphate were identified on SIAC surface; no thiophene was found, suggesting a complete removal of thiophene. Sulphur content in specific forms in SIACs was therefore controllable by varying the ratio of KOH, SO2 and fluid coke.

2+ SIACs produced from KOH-SO2 activation showed a comparable Hg adsorption capacity (43 – 72 mg/g) with those reported in the literature (35-100 mg/g) and that of a

2+ commercial SIAC (41 mg/g). Although a larger SBET often resulted in a greater Hg adsorption capacity, the benefit started to diminish when SBET was greater than about

1000 m2/g. A statistically significant and positive correlation was found between Hg2+ adsorption capacity and total sulphur content. Elemental sulphur and reduced sulphur were largely responsible for the enhanced Hg2+ adsorption.

- iii - ACKNOWLEDGEMENTS

I would like to express my deepest appreciation to my supervisor, Professor Charles Jia, for his guidance, patience and financial support. Without his trust in me and persistent help, this dissertation would not have been possible. I am also very grateful to my committee members, Professor Donald Kirk and Professor Charles Mims, for their valuable advice and encouragement during my studies.

In addition, I thank the following people for their helpful suggestions and technical assistance during the course of my research: Professor Shitang Tong, Dr. John Graydon, Sue Mao, Peter Brodersen (Surface Interface Ontario), Dan Mathers and Ying Lei Wania (ANALEST), Sal Boccia (Department of Material Science), Arstrid Jurgensen (Canadian Synchrotron Radiation Facility), Frank Huggins (University of Kentucky) and people on Ifeffit Mailing list who answered my questions.

I cannot find the words to thank my best friends at the University of Toronto: Chunbei, Olive, Stephanie and Ivy, who accompanied me and warmed my heart during the most difficult time of my life. I give my special thanks to Jasper, Jean, Johnny, Zhihua and Chunyan for their care, encouragement and support from afar. I am also thankful to my colleagues and other friends who have been helping and supporting me all the time.

My greatest thank you is given to my dearest parents, Chaoqun Cai and Shuyun Wang, as well as my son, Michael. They are the driving force behind my accomplishment. Their love is the source of my courage, making me stronger than I thought.

This work is dedicated to my late grandfather, who would be most delighted with this achievement.

- iv - TABLE OF CONTENTS

ABSTRACT...... II

ACKNOWLEDGEMENTS...... IV

TABLE OF CONTENTS...... V

LIST OF TABLES...... IX

LIST OF APPENDICES...... XIV

NOMENCLATURE ...... XV

CHAPTER 1 OVERVIEW...... 1 1.1 INTRODUCTION ...... 1 1.2 OBJECTIVES AND HYPOTHESIS ...... 3 1.3 ORGANIZATION OF THE THESIS ...... 4

CHAPTER 2 LITERATURE REVIEW ...... 5 2.1 OIL-SANDS FLUID COKE ...... 5 2.1.1 Production of Fluid Coke...... 5 2.1.2 Chemical Composition...... 7 2.2 ACTIVATED CARBON (AC) ...... 8 2.2.1 Raw Materials ...... 9 2.2.2 Production Processes ...... 9 2.3 ACTIVATION OF OIL-SANDS FLUID COKE...... 11 2.3.1 Previous Work on Fluid Coke Activation...... 11 2.3.1.1 Steam Activation ...... 12

2.3.1.2 SO2 Activation...... 12 2.3.2 Potential Processes for Fluid Coke Activation ...... 13 2.3.2.1 KOH Activation...... 13 2.3.2.2 Carbon Activation by Other Activating Agents ...... 16 2.3.2.3 Surface Modification of Activated Carbon ...... 17 2.4 CHARACTERIZATION OF SULPHUR COMPOUNDS IN CARBONACEOUS MATERIALS …………………………………………………………………………19 2.4.1 Total Organic Sulphur in Coal and Coke...... 19

- v - 2.4.2 Speciation of Sulphur in Coal and Coke...... 20 2.4.3 Application of X-ray Absorption Near Edge Structure (XANES) for Sulphur Speciation...... 22 2.4.3.1 The Theory of XANES ...... 22 2.4.3.2 Sulphur Characterization using XANES...... 24 2.5 APPLICATION OF ACTIVATED CARBON - MERCURY ADSORPTION FROM AQUEOUS SOLUTION ...... 25 2.5.1 Effect of Adsorption Conditions...... 25 2.5.2 Effects of Activated Carbon Properties ...... 27 2.6 SUMMARY...... 29

CHAPTER 3 PREPARATION OF SULPHUR-IMPREGNATED ACTIVATED CARBON FROM FLUID COKE WITH KOH AND SO2...... 30 3.1 INTRODUCTION ...... 30 3.2 EXPERIMENTAL...... 32 3.2.1 Materials ...... 32 3.2.2 Experimental Set-up and Activation Procedures ...... 32 3.2.3 Analytical Techniques and Methods...... 35 3.3 RESULTS AND DISCUSSION ...... 35 3.3.1 KOH Activation...... 35 3.3.1.1 Morphology of KOH activated carbon ...... 35 3.3.1.2 Effects of Activation Condition on Activated Carbon Properties36 3.3.1.3 Sulphur Removal during KOH activation...... 43

3.3.2 KOH-SO2 Activation of Fluid Coke...... 45

3.3.2.1 Morphology of KOH-SO2 Activated Carbon ...... 45 3.3.2.2 Effects of Activation Condition on Activated Carbon Properties46 3.3.2.3 Comparison between Two Fluid Cokes ...... 51 3. 4 CONCLUSIONS ...... 55

CHAPTER 4 SPECIATION OF SULPHUR IN FLUID COKE AND ITS ACTIVATION PRODUCTS...... 57 4.1 INTRODUCTION ...... 57 4.2 EXPERIMENTAL...... 59 4.2.1 Materials and Sample Preparation ...... 59 4.2.2 Model Sulphur Compounds and Model Sulphur Compound Mixtures. 60

- vi - 4.2.3 Analytical Techniques ...... 62 4.2.3.1 XANES...... 62 4.2.3.2 X-ray photoelectron spectroscopy (XPS)...... 66 4.3 TOTAL ELECTRON YIELD (TEY) RESULTS...... 67 4.3.1 Model Compounds...... 67 4.3.2 Mixture of Sulphur Compounds ...... 70 4.3.3 Repeatability ...... 73 4.3.4 Fluid Cokes Samples...... 74 4.3.5 Sulphur-impregnated Activated Carbons (SIACs) ...... 76 4.3.6 Comparison between XANES and XPS Results ...... 79 4.3.6.1 Comparison for Raw Cokes ...... 79 4.3.6.2 Comparison for SIACs ...... 81 4.4 FLUORESCENCE YIELD (FY) RESULTS ...... 82 4.5 CONCLUSIONS ...... 84

CHAPTER 5 MECHANISMS STUDY OF KOH-SO2 ACTIVATION OF HIGH SULPHUR FLUID COKES ...... 86 5.1 INTRODUCTION ...... 86 5.2 EXPERIMENTAL...... 87 5.2.1 Materials ...... 87 5.2.2 Analytical Methods...... 88 5.3 RESULTS AND DISCUSSION...... 88 5.3.1 Activation Mechanisms ...... 88 5.3.1.1 Role of KOH...... 88

5.3.1.2 Role of SO2 ...... 91

5.3.1.3 KOH-SO2 Activation ...... 95

5.3.2 Sulphur Transformation during KOH-SO2 Activation ...... 97 5.3.2.1 Sulphur Characterization of Raw Fluid Cokes...... 97 5.3.2.2 Changes in Sulphur Content ...... 98 5.3.3 Changes in Sulphur Species...... 101 5.3.3.1 The Role of KOH in Changing Sulphur Form ...... 101

5.3.3.2 The Role of SO2 in Changing Sulphur Form ...... 102

5.3.3.3 Changes in sulphur species after KOH-SO2 activation ...... 103 5.3.3.4 Effects of Activation Temperature ...... 108

- vii - 5.4 CONCLUSIONS...... 111

CHAPTER 6 ADSORPTION OF MERCURY ION FROM AQUEOUS SOLUTIONS USING COKE-DERIVED SIACS...... 113 6.1 INTRODUCTION ...... 113 6.2 EXPERIMENTAL...... 115 6.2.1 Adsorbents ...... 115 6.2.2 Mercury Ion Adsorption...... 116 6.3 RESULTS AND DISCUSSION ...... 117 6.3.1 Adsorption Conditions...... 117 6.3.2 Adsorption Isotherms...... 120 6.3.3 Adsorption Capacity ...... 125

6.3.3.1 Effect of SBET ...... 125 6.3.3.2 Effect of Total Sulphur Content ...... 128 6.3.3.3 Effect of Sulphur Form...... 129 6.3.4 Adsorption Kinetics ...... 133 6.4 CONCLUSIONS...... 136

CHAPTER 7 OVERALL CONCLUSIONS...... 138

RECOMMENDATIONS...... 140

REFERENCES ...... 142

APPENDICES ...... 152

- viii - LIST OF TABLES

Table 2-1 Analysis of Syncrude coke from stockpiles, wt% (Furimsky, 1998)...... 7 Table 2-2 XPS 2p3/2 binding energies of model sulphur compounds (Kelemen et al., 1990) ...... 21 Table 2-3 XPS sulphur 2p3/2 binding energy (Jiménez Mateos and Fierro, 1996; Chang, 1981) ...... 21 Table 2-4 Hg2+ adsorption capacities reported in the literature...... 26 Table 3-1 Properties of Syncrude and Imperial Oil fluid coke...... 32 Table 3-2 Calculated weight loss (weight loss) for KOH activation: 15 g KOH; 5 g coke; 700°C; KOH/coke = 3:1 ...... 38 Table 3-3 Elemental composition on the surface of raw cokes and their KOH activation products (700°C, 1-hour, KOH/coke ratio = 3:1) ...... 44 Table 3-4 Contents of C, O and S in raw coke FC-S and FC-I...... 51 Table 4-1 Activation processes and conditions of SIAC samples ...... 60 Table 4-2 Structures of sulphur model compounds used in this study ...... 60 Table 4-3 K-edge first inflection energies of sulphur compounds used in this study...... 69 Table 4-4 Composition of the mixture of sulphur model compounds by least-squares peak fitting, M-1...... 71 Table 4-5 Composition of the mixture of sulphur model compounds, M-1, determined by linear combination fitting...... 72 Table 4-6 XANES TEY analysis of experiments repeated by one researcher at one time73 Table 4-7 Averages of repeated measurements experiments for XANES TEY analysis . 74 Table 4-8 Composition of sulphur compounds in FC-S and FC-I from XANES analysis76 Table 4-9 Results of XPS analysis of samples FC-S and FC-I...... 80 Table 4-10 Comparison of XPS and XANES results for two SIAC samples...... 82 Table 4-11 Sulphur forms in the bulk of raw fluid cokes (FY results)...... 83 Table 5-1 Properties of raw cokes ...... 88 Table 5-2 Thermodynamic data calculated with FactSage for Eqs. 5-2 and 5-3...... 90 Table 5-3 Thermodynamic data calculated by FactSage for Equations 5-4 and 5-5...... 94 Table 5-4 Sulphur content and forms in the raw cokes ...... 98 Table 5-5 Changes of organic sulphur content in SIACs produced under the same condition with different raw cokes (KOH-SO2 activation: 700°C, 1 hour, KOH/coke: 3:1) ...... 100 2- Table 5-6 Removal of SO4 from washed sample by additional washing with deionized water...... 105 Table 6-1 Summary of the properties of SIAC samples...... 116 Table 6-2 pH values for effective adsorption of Hg 2+ observed in previous studies..... 118 Table 6-3 Properties of SIACs and their adsorption capacities of Hg2+ at 25ºC, with initial HgCl2 concentration of 100 ppm ...... 121 Table 6-4 Parameters of Langmuir and Freundlich models for the adsorption of Hg2+ on activated carbons at 25ºC...... 123 Table 6-5 Activation conditions and properties of S-KS-2 and I-KS-2...... 124 Table 6-6 Properties and Hg2+ adsorption capacities of 5 samples...... 130 Table 6-7 Adsorption constants of Hg2+ uptake by SIACs...... 135

- ix - LIST OF FIGURES

Figure 2-1 Simplified schematics of fluid coking process (Furimsky, 2000)...... 6 Figure 2-2 Cross-sectional image of a fluid coke particle ...... 6 Figure 2-3 a. Sulphur 2p3/2 binding energy and b. the spectrum of elemental sulphur (Wagner et al., 2007) ...... 22 Figure 2-4 K-edge XANES spectrum of sulphur in poly (phenylene sulphide)...... 23 Figure 3-1 Apparatus for fluid coke activation...... 33 Figure 3-2 Processes of fluid coke activation with KOH and SO2 ...... 34 Figure 3-3 Structure of fluid coke (left) and its change after KOH activation (centre and right)...... 36 Figure 3-4 Time dependence of SBET and weight loss of fluid coke in KOH activation (FC-S, temperature: 700°C, KOH/coke: 3:1, N2: 350 ml/min)...... 37 Figure 3-5 Time dependence of micropore surface area (micropore SA) and its percentage in KOH activated carbon (FC-S, temperature: 700°C, KOH/coke: 3:1, N2: 350 ml/min)...... 37 Figure 3-6 Temperature dependence of SBET and weight loss in KOH activation (FC-S, KOH/Coke: 3:1, activation time: 1 hr, N2: 350 ml/min)...... 39 Figure 3-7 Temperature effect on pore and micropore volume of KOH activation (FC-S, KOH/Coke: 3:1, activation time: 1 hr, N2: 350 ml/min)...... 41 Figure 3-8 Effects of KOH/coke ratio on SBET, weight loss and micropore surface area (SA) percentage in KOH activation (FC-S, temperature: 700ºC, activation time: 1 hr, N2: 350 ml/min)...... 42 Figure 3-9 Changes in total sulphur contents of KOH-activated coke with time...... 43 Figure 3-10 SEM images of a SIAC produced from KOH-SO2 simultaneous activation: A. at magnification of 1.5 K, B. at magnification of 300 K ...... 45 Figure 3-11 Effects of activation time on SBET, weight loss and micropore SA percentage in KOH-SO2 activation (Raw coke: FC-S, Temperature: 700°C, KOH/coke: 3:1, SO2: 30%)...... 46 Figure 3-12 Time dependence of sulphur content in KOH-SO2 activation (Raw coke: FC- S, Temperature: 700°C, KOH/coke: 3:1, SO2: 30%)...... 47 Figure 3-13 Effects of activation temperature on SBET, micropore SA and weight loss of KOH-SO2 activation (FC-S, KOH/coke ratio of 3:1, 1-hr activation, 30% SO2)...... 47 Figure 3-14 Comparison of the SBET of KOH and KOH-SO2 activated carbon (FC-S, KOH/coke ratio of 3:1, 1-hr activation)...... 48 Figure 3-15 Comparison of the weight loss during KOH and KOH-SO2 activation (FC-S, KOH/coke ratio of 3:1, 1-hr activation)...... 48 Figure 3-16 Temperature dependence of total sulphur content in KOH-SO2 activation (FC-S, KOH/coke: 3:1, Activation time: 1 hr, SO2: 30%)...... 49 Figure 3-17 Effects of KOH/coke ratio on SBET, weight loss and micropore SA percentage in KOH-SO2 activation (temperature: 700°C, activation time: 1 hr, SO2: 30%)...... 50 Figure 3-18 Effects of KOH/coke ratio on total sulphur content in KOH-SO2 activation (temperature: 700°C, activation time: 1 hr, SO2: 30%) ...... 51 Figure 3-19 SBET of SIACs produced from FC-S and FC-I using KOH and SO2 activation at different temperatures (KOH/coke: 3:1; activation time: 1 hr)...... 52

- x - Figure 3-20 SBET of SIACs produced from FC-S and FC-I using KOH and SO2 activation with various KOH/coke ratios (temperature: 700°C; activation time: 1 hr)...... 52 Figure 3-21 Micropore volume of SIACs produced from FC-S and FC-I using KOH and SO2 activation at different temperatures (KOH/coke: 3:1; 1-hr activation) ...... 53 Figure 3-22 Micropore volume of SIACs produced from FC-S and FC-I using KOH and SO2 activation with various KOH/coke ratios (700°C, 1 hr)...... 53 Figure 3-23 Weight loss of FC-S and FC-I during KOH and SO2 activation at different temperatures (KOH/coke: 3:1, 1 hr) ...... 53 Figure 3-24 Weight loss of FC-S and FC-I during KOH and SO2 activation with various KOH/coke ratios (temperature: 700°C, activation time: 1 hr)...... 54 Figure 3-25 Total sulphur content in SIACs produced from FC-S and FC-I using KOH- SO2 activation at different temperatures (KOH/coke: 3:1, 1 hr) ...... 54 Figure 3-26 Total sulphur content of SIACs produced from FC-S and FC-I using KOH- SO2 activation with various KOH/coke ratios (temperature: 700°C, activation time: 1 hr) ...... 55 Figure 4-1(a) Sulphur K-edge XANES spectra of inorganic model compounds ...... 67 Figure 4-1(b) Sulphur K-edge XANES spectra of organic sulphur model compounds ... 68 Figure 4-2 XANES K-edge absorption energies of different sulphur compounds...... 70 Figure 4-3 Least-square peak fitting of sulphur K-edge XANES TEY spectrum of sulphur model compound M-1...... 71 Figure 4-4 Linear combination fit of sulphur K-edge XANES TEY spectrum of the mixture, M-1, with model compounds...... 72 Figure 4-5 Representative structures of various types of organic sulphur compounds in petroleum (Zhou and Chriswell, 1996)...... 75 Figure 4-6 Sulphur K-edge XANES TEY spectra of two raw coke samples (FC-S and FC-I)...... 76 Figure 4-7 Sulphur K-edge XANES TEY spectra of FC-S and SIAC-S (produced from FC-S with simultaneous KOH and SO2 activation)...... 77 Figure 4-8 Sulphur K-edge XANES TEY spectra of FC-I and SIAC-I (produced from FC-I with sequential KOH and SO2 activation)...... 78 Figure 4-9 Spectra of SIACs produced from KOH-SO2 activation at different activation conditions...... 79 Figure 4-10 The XPS spectrum of S 2p region for FC-S...... 80 Figure 4-11 The XPS spectrum of S 2p region for FC-I...... 80 Figure 4-12 The XPS spectrum of S 2p for SIAC-S (Raw coke: FC-S: KOH and SO2 simultaneous activation: 700°C, KOH/coke: 3:1, activation time: 1 hour) ...... 81 Figure 4-13 The XPS spectrum of S 2p for SIAC-I (Raw coke: FC-I; KOH and SO2 simultaneous activation: 700°C, KOH/coke: 3:1, activation time: 1 hour) ...... 82 Figure 4-14 XANES sulphur K-edge FY spectra of FC-S and FC-I ...... 83 Figure 4-15 Sulphur K-edge XANES FY spectra of FC-S and KS-1-2 ...... 84 Figure 4-16 Sulphur K-edge XANES FY spectra of FC-I and SIAC-I ...... 84 Figure 5-1 Temperature dependence of equilibrium composition of the major components of the KOH-C system (initial composition: KOH = 0.9 kmol, C = 1 kmol, H2O = 0.1 kmol and N2 = 0.5 kmol)...... 90 Figure 5-2 Increase in sulphur content during SO2 treatment of KOH-activated carbon. 92 Figure 5-3 Scheme for SO2 reduced on carbon surface (Humeres et al., 2002)...... 93

- xi - Figure 5-4 Temperature dependence of equilibrium composition of the major components of the KOH-C-SO2 system (initial composition: KOH:C:SO2:N2 = 1:1:1:0.5)...... 96 Figure 5-5 Temperature dependence of sulphur content of FC-S (KOH-SO2 activation: 700°C, 1 hour, KOH/coke: 3:1) ...... 99 Figure 5-6 Effects of KOH/coke ratio on total sulphur content in activation products.... 99 (700°C, 1 hour) ...... 99 Figure 5-7 Sulphur forms in SO2 activated carbon (FC-S, 700°C, 1 hr) ...... 103 Figure 5-8 Change in sulphur species after KOH-SO2 activation (FC-S, 700°C, KOH/coke ratio of 3:1, 1-hr activation)...... 104 Figure 5-9 Change of sulphur species in FC-S after KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour) ...... 106 Figure 5-10 Change of grouped sulphur species in FC-S after KOH-SO2 activation with different...... 106 Figure 5-11 Change of sulphur species in FC-I after KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour) ...... 107 Figure 5-12 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour) ...... 108 Figure 5-13 Change in sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-S, KOH/coke ratio of 3:1, 1- hr activation) ...... 109 Figure 5-14 Change in sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-I, KOH/coke: 3:1, 1 hour, 30% SO2) ...... 110 Figure 5-15 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-S, KOH/coke ratio of 3:1, 1- hr activation). 110 Figure 5-16 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-I, KOH/coke: 3:1, 1 hour, 30% SO2)...... 111 2+ Figure 6-1 Typical curves for Hg adsorption from HgCl2 solutions...... 118 2+ Figure 6-2 Changes of pH during adsorption of Hg by SIACs produced from KOH-SO2 activation under different temperatures and KOH/coke ratios ...... 120 Figure 6-3 Langmuir isotherms of Hg2+ adsorption by different samples produced from FC-S at 25°C...... 121 Figure 6-4 Freundlich isotherms for Hg2+ uptake on different samples produced from FC- S at 25°C ...... 123 Figure 6-5 Langmuir isotherms of Hg2+ adsorption by SIACs produced from FC-S (S- KS-2) and from FC-I (I-KS-2) at 25°C...... 124 Figure 6-6 Freundlich isotherms of Hg2+ adsorption by SIACs produced from FC-S (S- KS-2) and from FC-I (I-KS-2) at 25°C...... 125 Figure 6-7 Comparison of Hg2+ adsorption capacities of SIACs with similar sulphur contents (0.1~0.6%) but different surface area...... 127 2+ Figure 6-8 Effect of SBET on Hg adsorption capacity ...... 127 2+ Figure 6-9 Data fitting of SBET vs. Hg adsorption capacity using exponential function ...... 128 Figure 6-10 Relationship between normalized S content and Hg2+ adsorption capacity 129 Figure 6-11 Sulphur form changes in sample S-KS-12 before and after Hg2+ adsorption ...... 130 Figure 6-12 Sulphur forms in SIAC samples used for Hg2+ adsorption...... 132

- xii - Figure 6-13 Relationship between sulphur forms in SIAC samples (S-KS-2, S-KS-16 and I-KS-16) and Hg2+ adsorption...... 132 Figure 6-14 Relationship between sulphur forms in SIAC samples (S-KS-2, S-KS-16 and I-KS-16) and Hg2+ adsorption...... 133 Figure 6-15 Pseudo-first-order kinetic plots for the adsorption of Hg 2+ on a SIAC sample (I-KS-1)...... 134 Figure 6-16 An example of fitting Hg2+ adsorption curve using OriginPro 7.5 ...... 135

- xiii - LIST OF APPENDICES

APPENDIX A PRELIMINARY STUDIES OF HYDROXIDE ACTIVATION OF FLUID COKE 152

APPENDIX B CALCULATIONS ...... 153

APPENDIX C CALIBRATION CURVES ...... 160

APPENDIX D REPEATABILITY...... 162

APPENDIX E SEM IMAGES FOR RAW COKES AND SIACS ...... 163

APPENDIX F SULPHUR SPECIATION: MORE DATA...... 165

APPENDIX G XANES SPECTRA ...... 166

APPENDIX H XPS SPECTRUM AND DATA ...... 178

APPENDIX I MERCURY ION ADSORPTION CURVE...... 182

- xiv - NOMENCLATURE

ACF Activated Carbon Fibres

FC-I I type of fluid coke

FC-S S type of fluid coke

FY Fluorescence Yield (mode of XANES analysis)

I-KS-1 Sample ID: raw coke – activation process – sample number, i.e., I type of fluid coke - KOH-SO2 activation – #1

S-KOH-1 Sample ID: S type of fluid coke - KOH activation – #1

SBET BET surface area

SEM Scanning Electron Microscope

SIAC Sulphur impregnated activated carbon

SIAC-BG SIAC sample provided by Barrick Gold Co.

TEY Total Electron Yield (mode of XANES analysis)

XANES X-ray Adsorption Near Edge Structure Spectroscopy

XPS X-ray Photoelectron Spectroscopy

- xv - CHAPTER 1 OVERVIEW

1.1 INTRODUCTION

Oil-sands fluid coke is a by-product of upgrading bitumen from the Athabasca oil sands deposits in northeastern Alberta. The coke is produced in the ‘fluid coking’ process where bitumen is fed into a fluidized bed of hot coke (~600°C) and the volatile materials are driven off. The coke consists of spherical particles formed from the non-volatile materials in the fluidized bed, and has an ‘onion skin’ internal structure. Although the fluid coke has a high carbon content (~85 wt.%), its sulphur content approaching 7 wt.% hinders its use as fuel for power generation due to the release of sulphur into the environment (Ityokumbul and Kasperski, 1994; Furimsky, 1998).

The fluid coke is currently being produced at a rate of over 10,000 tonnes per day, and is stockpiled onsite due to its limited usage. With the increase in the storage of fluid coke, it becomes urgent to find a means to utilize this type of coke. Efforts have been made to utilize fluid coke through desulphurization which removes sulphur and thus allows it to be used as fuel (Al-Haj-Ibrahim and Morsi, 1992; Ityokumbul and Kasperski, 1994; Furimsky, 2000). Potentially, fluid coke can be used as a starting material for producing activated carbon – a highly porous carbonaceous material, due to its high carbon content and ready availability.

Oil-sands fluid coke has been used to produce activated carbon only by two groups of researchers, including this group at the University of Toronto (DiPanfilo and Egiebor, 1996; Chen, 2002), among a few studies using other types of petroleum coke to produce activated carbon (Marsh and Yan, 1984; Otowa et al., 1997; Lee and Choi, 2000; Mitani et al., 2004; Wu et al., 2005). DiPanfilo and Egiebor (1996) used steam to activate the fluid coke, and obtained activated carbon with a BET surface area (SBET, the specific surface area determined by the standard BET method of nitrogen adsorption at 77 K) of 318 m2/g after 6 hours. Another process called “SOactive” was developed in this group, where fluid coke was activated through contacting with SO2 for several hours. The product, ECOcarbon, showed 2 particular effectiveness in mercury removal, even though its SBET was only around 370 m /g (Chen, 2002; Demou, 2003). The major disadvantages of these two processes are the long activation time and the relatively low surface area of the products compared to commercial

- 1 - activated carbon. Another drawback of steam activation of high-sulphur materials is the generation of H2S.

Activated carbon can be produced from a variety of carbonaceous materials by two processes: physical activation and chemical activation. Physical activation involves carbonization of a carbonaceous material followed by activation of the resulting char using

CO2, steam, or a mixture of both. On the other hand, chemical activation is a single step process where the carbonization and activation of the feedstock take place at the same time with the presence of chemical agents. Generally, activation of a carbonaceous material using activating agents results in products with high surface area (Marsh and Rodríguez-Reinoso, 2006). Since the challenge of fluid coke activation is to increase its surface area, chemical activation was considered in this study.

The most widely used activating agents in chemical activation are phosphoric acid, zinc chloride and sulphuric acid. Potassium sulphide, potassium hydroxides and carbonates of alkali metals, chlorides of calcium, magnesium and ferric iron have also been suggested (Bansal et al., 1988). Among these activating agents, potassium hydroxide (KOH) is particularly effective in producing activated carbon with high surface area (Otowa et al. 1997). It is known that alkali metal compounds can accelerate the reactions between carbonaceous materials and oxygen, carbon dioxide or water vapour (Marsh and Yan, 1984; Thomoson and Sy, 1987), hence, enhancing the activation process where carbon is removed from internal structures.

Sulphur-impregnated activated carbon (SIAC) is a type of activated carbon which has high sulphur content. SIAC has been proven to be effective for capturing mercury from flue gases, which is a serious issue for coal fired power plants (Korpiel and Vidic, 1997; Liu and Vidic, 2000). In addition, SIAC has shown great potential for mercury adsorption from aqueous solutions (Anoop Krishnan and Anirudhan, 2002; Ranganathan and Balasubramanian, 2002; Nabais et al., 2006). Fluid coke has a high sulphur content, which could be beneficial for producing SIAC. Studies by Vidic and co-workers suggested that the sulphur content and forms are important for vapour phase mercury uptake (Korpiel and Vidic, 1997; Liu et al., 1998; Kwon and Vidic, 2000; Liu and Vidic, 2000; Feng et al., 2006).

- 2 - However, the mechanisms of reactions between mercury and sulphur in different forms are not well understood.

The mechanism of chemical activation of fluid coke has not been fully understood, and moreover, there has been no research on the effect of sulphur in cokes on SIAC production and mercury adsorption. This is partially attributed to the lack of a reliable method for characterizing the sulphur form in petroleum coke and SIACs. The overall goal of this work was to lay a technological and scientific foundation for the development of an economically viable process that uses an industrial waste – the fluid coke, producing SIAC that can be used for industrial pollution prevention and other applications. Consequently, this process will add value to the natural resource – Canadian oil sands.

1.2 OBJECTIVES AND HYPOTHESIS

Technologically，the objective of this work was to establish the feasibility of utilizing the waste petroleum byproduct – high sulphur fluid coke for producing SIACs and applying the SIACs to aqueous Hg2+ uptake. Scientifically, this work attempted to better understand the roles of sulphur in the raw coke during chemical activation and the effects of sulphur in the SIAC on aqueous Hg2+ uptake. With the understanding of sulphur transformation during activation, sulphur functional groups in SIACs can be customized by controlling the activation process. Moreover, with appropriate forms of sulphur compounds in the SIAC, its mercury adsorption capacity can then be maximized.

Two key hypotheses were proposed and examined in this study:

1. High sulphur content in fluid coke enhances the activation process and affects the sulphur forms in its activation products.

2. Chemical states of sulphur in the activation products (i.e. SIACs) affect their capacity of mercury adsorption from aqueous solution.

Following specific tasks were carried out to achieve the objectives:

1. Selection of suitable activating agents for an effective activation of fluid coke

2. Experimental design of an efficient process to produce SIACs

- 3 - 3. Investigation of the effects of activation conditions on SIAC properties

4. Thermodynamic analysis for understanding the mechanisms of coke activation

5. Development of an analytical procedure for identifying and quantifying sulphur species in fluid cokes and SIACs

6. Investigation of sulphur transformation during fluid coke activation by comparing the sulphur forms in fluid coke and SIAC samples

7. Application of SIACs produced in this study for adsorbing Hg2+ from the liquid- phase, and establishment of the relationship between Hg2+ adsorption and SIAC properties

1.3 ORGANIZATION OF THE THESIS

The thesis is written in a format which includes 2 papers. It consists of five major parts: literature review, SIAC production, sulphur characterization, studies of activation mechanisms and SIAC application – mercury ion adsorption. The literature review in Chapter 2 provides the fundamental knowledge and background information relevant to this study. Chapter 3 describes the processes that were employed to prepare SIACs from fluid coke using KOH-SO2 activation, including the discussion of the effects of activation conditions on SIAC properties. In Chapter 4, XANES technique is described in details for sulphur speciation in fluid coke and its activation products. Sulphur speciation is crucial for understanding sulphur transformation during activation, and thus the activation mechanism of fluid coke can be further investigated (Chapter 5). Chapter 6 discusses the application of SIACs produced from fluid coke in Hg2+ uptake from aqueous solutions, which provides this study with more practical significance. The thesis ends with an overall conclusion section, recommendations for the future work, and the literature cited in this thesis.

- 4 - CHAPTER 2 LITERATURE REVIEW

2.1 OIL-SANDS FLUID COKE

Alberta's largest and most accessible source of bitumen is contained in an area encompassing more than 30,000 square kilometers. Among four oil sands areas located in the province, the Athabasca deposit alone contains over one trillion barrels of bitumen. Total reserves of bitumen in Alberta are estimated at more than 1.7 to 2.5 trillion barrels. Oil sand fluid coke is currently being produced at a rate of over 10,000 tonnes/day as a by-product from the upgrading of bitumen in northeastern Alberta. The use of fluid coke as fuel for power generation is hindered by its high ash and sulphur contents. It is currently being stockpiled in the existing 45 million tonne reserves.

2.1.1 Production of Fluid Coke

Synthetic crude is produced from bitumen which comes out of the mine as a mixture of bitumen, sand, and water. The bitumen must be extracted from this mixture, and mixed with diluents so that it can be pumped to the fluid coker. The production of gas oil and naphtha in the coker for subsequent blending into synthetic crude constitutes primary upgrading.

Fluid coking technology is employed at Syncrude Canada Limited for the upgrading of Athabasca bitumen to produce synthetic crude oil, with fluid coke produced as the by- product. This process, developed by Exxon, makes use of a fluidized bed of coke for cracking residual feeds. In the fluid coking process (Figure 2-1), heated coker feeds (bitumen) are sprayed into a fluidized bed of hot coke particles which are maintained at 20-40 psi and

500°C. The bitumen is cracked to gas oil, naphtha, and some other lighter products. It is the gas oil and naphtha that are eventually mixed to form synthetic crude oil at Syncrude. While the feed vapors are cracked, a liquid film forms on the coke particles. The particles grow by layers until they are removed and new seed coke particles are added. Overall, the bitumen is thermally cracked into lighter fractions that are recovered as synthetic crude oil with the fluid coke left behind (DiPanfilo and Egiebor, 1996). The large coke particles that form in the reactor are circulated back to the burner where they are used as a fuel and fed to the reactor again. Therefore, the coke is continuously recirculated between the burner and the reactor.

- 5 - Fluid coke is generated from the non-volatile materials during this process, with a smooth non-porous surface with an “onion like” internal structure (Figure 2-2).

Figure 2-1 Simplified schematic of fluid coking process (Furimsky, 2000)

Figure 2-2 Cross-sectional image of a fluid coke particle (http://mccoy.lib.siu.edu/projects/crelling2/atlas/PetroleumCoke)

- 6 - 2.1.2 Chemical Composition

By the proximate, ultimate and ash composition analyses, the chemical composition of fluid coke was obtained from previous studies (Furimsky, 1998). The most important difference between the oil-sands fluid coke and other petroleum cokes derived from conventional crude is the significantly higher content of sulphur in the former. In the latter case, the sulphur content is usually less than 2%. The results in Table 2-1 indicate a uniform composition of the coke samples over more than 15 years of operation. For example, key parameters such as ash, carbon and sulphur contents have exhibited little variation. Table 2-1 Analysis of Syncrude coke from stockpiles, wt% (Furimsky, 1998) Years 1979-1980 1980-1982 1982-1983 1983-1985 1985-1995 Property proximate Moisture 0.44 0.60 0.50 0.69 0.25 Ash 5.40 7.21 5.18 7.52 4.83 Volatiles 4.85 5.11 6.23 6.10 4.99 Fixed Carbon 89.31 87.08 88.09 85.69 89.95 Ultimate Carbon 82.73 80.73 81.80 80.94 83.74 Hydrogen 1.72 1.63 1.66 1.56 1.77 H/C 0.25 0.24 0.24 0.23 0.25 Nitrogen 1.75 1.70 1.98 1.73 2.03 Sulphur 6.78 6.63 6.84 6.15 6.52 Oxygen 1.18 1.50 2.04 1.41 0.88 Ash composition

SiO2 38.80 50.06 41.60 41.26 37.64

Al2O3 24.35 20.94 24.22 24.94 24.33 Fe2O3 9.72 8.18 9.26 12.14 11.42

TiO2 3.64 2.86 3.25 4.84 4.63 P2O5 0.25 0.21 0.23 0.35 0.40 CaO 4.26 2.58 4.20 1.63 2.94 MgO 1.62 1.29 1.44 1.40 1.46

SO3 3.59 2.73 2.65 1.87 2.88

Na2O 1.51 1.17 1.57 1.16 1.67 K2O 1.83 1.78 1.83 1.93 1.72 BaO 0.20 0.15 0.07 0.14 0.09 SrO 0.11 0.06 0.09 0.06 0.11

V2O5 4.46 3.20 4.86 3.21 4.94 MnO 0.26 0.21 0.25 0.29 0.27

Cr2O3 0.08 0.05 0.08 0.08 0.09 Lost on fusion 2.90 2.30 1.82 2.50 2.62 Total 98.66 98.55 98.57 98.63 98.35

- 7 - The high sulphur content of oil-sands fluid coke limits its use as a direct energy source. With the increase in the storage of fluid coke, it becomes urgent to find a means to utilize this type of coke. Efforts have been made to utilize fluid coke through desulphurization which removes sulphur from fluid coke and thus allows it to be used as fuel (Al-Haj-Ibrahim and Morsi, 1992; Ityokumbul and Kasperski, 1994; Furimsky, 2000). Potentially, fluid coke can be used as a starting material for producing activated carbon – a highly porous carbonaceous material, due to its high carbon content and ready availability.

2.2 ACTIVATED CARBON (AC)

Activated carbon is a type of carbonaceous material, which has a porous structure and a large internal surface area. These materials can adsorb a wide variety of substances, i.e. they are able to attract molecules to their internal surface. The volume of pores of the activated carbons is generally greater than 0.2 mL/g. The internal surface area is generally greater than 400 m2/g. The width of the pores ranges from 0.3 to several thousand nm (Bansal et al., 1988). Generally, the smaller the particle size of an activated carbon, the higher removable efficiency at the initial stage.

Activated carbons have been used since the early part of the 20th century. Due to their large surface area, activated and impregnated carbons are widely popular for many diverse applications, such as air purification, catalyst support, decolorization, deodorization, gold/metal recovery, liquid purification, emergency poison treatment and solvent recovery. Activated carbons are the most important carbon materials used in water treatment (Radovic et al., 2000). According to US Industry Study report (2004), US demand for activated carbon was forecast to rise 4.3% annually to 475 million pounds in 2008. Since activated carbon is used primarily in pollution control, its demand is heavily impacted by environmental regulations. In 2005, US Environmental Protection Agency (EPA) issued the Clean Air Mercury Rule to permanently cap and reduce mercury emissions from coal-fired power plants for the first time ever (EPA website). As environmental regulations become stricter worldwide, the demand for activated carbon is expected to increase.

The removal of pollutants from the aqueous phase or gas phase by activated carbon occurs by means of an adsorption process. The type of application and the adsorption

- 8 - capacity of an activated carbon depend on its properties, such as pore structure, surface area, density, and surface chemistry. By varying the manufacturing conditions such as temperature, activating agent and oxidant flow rate, activated carbon with different adsorptive properties can be produced from the same starting material (Bansal et al., 1988). The production of activated carbon generally involves two basic steps: pyrolysis and activation. Pyrolysis is used to remove volatile matter and increase the carbon content. Activation is used to develop the pore structure, surface area, and active surface functional groups.

2.2.1 Raw Materials

Activated carbon can be produced from a variety of raw materials. The raw materials have to be abundant and cheap, with high carbon content and low inorganic content. It has been reported that the raw materials for activated carbon production are usually of plant or fossil origin: wood, fruit stones or pits, coirpith, coconut shell, bagasse pith, coals, petroleum cokes, biomass material, waste tires, sago waste, furfural, sewage sludge, and so on (Laine and Calafat, 1991; Rodriguez-Reinoso, 1997; Namasivayam and Kadirvelu, 1999; Anoop Krishman and Anirudhan, 2002; Ekinci et al., 2002; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Skodras et al., 20071).

2.2.2 Production Processes

Properties of activated carbon will be different depending on the nature of the starting material and the effectiveness of the activation process. An activated carbon with high adsorption capacity can be obtained only by activating the carbonaceous material under such conditions that the activating agent reacts with the carbon. The activation reaction occurs in two steps. In the first step, the disorganized carbon is burned out preferentially when the weight loss does not exceed 10%. This results in the opening of the blocked pores. In the second step, carbon in the raw material starts reacting with the activating agent, producing active sites and wider pores (Bansal et al., 1988). The relative amount of external and internal oxidation depends on how well the pore structure developed in the carbonaceous material. The activation of chars with no developed pore structure only results in a decrease in the carbon particle size.

- 9 - Basically, there are two processes for preparation of activated carbon: physical activation and chemical activation. Physical activation involves carbonization of a carbonaceous material followed by activation of the resulting char using CO2, steam, or a mixture of both. On the other hand, chemical activation is a single step process where the simultaneous carbonization and activation of the feedstock take place in the presence of chemical agents.

Physical activation is the process through which the carbonized product develops an external surface area and a porous structure of molecular dimensions, as previously mentioned. This step is generally carried out at a temperature between 800 and 1100°C in the presence of suitable oxidizing gases such as steam, carbon dioxide, air or any mixture of these gases. The oxygen in the activating agent basically burns away the more reactive portions of the carbon skeleton as CO and CO2 (Lizzio and Bebarr, 1997). The extent of weight loss is dependent on the nature of the gas employed and the temperature of activation.

Pastor-Villegas and Duran-Valle (2001) prepared activated carbon from rockrose by carbon dioxide and steam activation. They found that activated carbon prepared by steam activation showed a total pore volume larger than those prepared by carbon dioxide activation. The main reactions involved in CO2 and steam activation are (Walker, 1996; Alcaniz-Monge et al., 1997):

For CO2 activation: C + CO2 ↔ 2CO 2-1

For steam activation: C + H2O ↔ H2 + CO 2-2

Chemical activation of carbonaceous materials has been the subject of considerable interest, because activated carbon with a well-developed pore structure can be produced in a single operation. Compared with physical activation, chemical activation has several advantages: (i) lower activation temperature, (ii) one step operation, (iii) higher yield, and (iv) high quality product: activated carbon with high surface area and well-developed micropore structure.

In chemical activation, the starting material is impregnated with the activating agent in the form of a concentrated solution. The chemical impregnated material is then extruded and pyrolyzed at 400-600°C in the absence of air. On calcination at 400-800°C, the impregnated

- 10 - chemicals dehydrate the raw material, which results in charring and aromatization of the carbon skeleton, and the creation of a porous structure. The temperature used in this process is usually lower than that needed in physical activation, which allows a better development of a porous structure. The pore size distribution of the final carbon product is determined largely by the degree of impregnation.

The most widely used activating agents in chemical activation are phosphoric acid, zinc chloride, and sulphuric acid, although potassium sulphide, potassium hydroxides and carbonates of alkali metals, chlorides of calcium, magnesium, and ferric iron have been suggested (Bansal et al., 1988). These activating agents are dehydrating agents which influence the pyrolytic decomposition and inhibit the formation of tar.

2.3 ACTIVATION OF OIL-SANDS FLUID COKE

2.3.1 Previous Work on Fluid Coke Activation

There are two major types of petroleum coke: delayed coke and fluid coke, which are named based on their production processes, i.e. the type of technology used for primary upgrading: delayed coking and fluid coking. The difference in the employed technology determines the difference in some of the properties of the produced cokes. The most common factor for both cokes is the prolonged exposure to temperatures higher than 500°C, which results in their well known graphite-like structures. Due to the processing conditions, fluid coke usually has a lower content of volatiles and lower H/C ratio, compared with delayed coke (Furimskyr, 1998).

Most research on activation of petroleum cokes has been conducted for delayed coke (Lee and Choi, 2000; Mitani et al., 2004) or other types of coke (Marsh and Yan, 1984; Otowa et al., 1997). Only two studies are known to prepare activated carbons from fluid coke, which were using steam and SO2 as the activating agents, respectively (DiPanfilo and Egiebor, 1996; Chen, 2002).

- 11 - 2.3.1.1 Steam Activation

DiPanfilo and Egiebor (1996) attempted to activate Alberta oil-sands fluid coke using a two-step pyrolysis and activation process. Steam was employed as the activating agent at atmospheric pressure and 850°C. The highest BET surface area of produced activated coke was 318 m2/g after 6-hour activation with a weight loss of over 50%. They also investigated the effect of pretreating fluid coke with KOH on its activation, and found that KOH treatment led to a greater weight loss but not higher surface area or greater porosity. The authors suggested that the addition of KOH could weaken the formation of micropores by widening micropores without developing more pores. Consequently, their activated carbons had much lower surface area and pore volume than most commercial activated carbons.

2.3.1.2 SO2 Activation

Recently, the Green Technology Group at the University of Toronto developed a process in which oil-sands fluid coke was activated using SO2 as the activating agent (Chen, 2002; Demou, 2003). The new process was named “SOactive”, and the activated form of the fluid coke was termed “ECOcarbon” for its unique structure and environmental application.

In SOactive process, fluid coke reacts with SO2 in a temperature range of 600 to 750°C for 2-13 hours. The highest specific surface area of activated coke produced was 368 m2/g after 10 hr activation at 700°C with 77 % weight loss (Chen, 2002)., Sulphur content in the activated coke reached as high as 20 wt%, and the sulphur concentrated in the activated part of the coke particles while the sulphur content of the unreacted cores remained unchanged.

The product of SOactive process, ECOcarbon, showed a great potential for mercury removal due to its relative high surface area and high sulphur content. Preliminary results (Chen, 2002) showed that at equilibrium the ECOcarbon adsorbed about the same amount of 2+ Hg as the commercial activated carbon, even though the SBET of ECOcarbon was less than a third of the SBET of commercial activated carbon.

In SOactive process, the activation and sulphurization of fluid coke take place in one single step, which is different from commonly used processes of SIAC production where activation and sulphurization are separate processes. However, the disadvantages of

- 12 - SOactive process seem to be the long reaction time and low specific surface area of the product compared with the commercial activated carbon.

2.3.2 Potential Processes for Fluid Coke Activation

2.3.2.1 KOH Activation

The effect of alkali and transition metal salts on the kinetics of gasification reactions of carbon has been extensively investigated for many years. A small amount of certain alkali metal compounds have a strong catalytic influence upon the reactions of carbonaceous materials with oxygen, carbon dioxide and water vapour (Marsh and Yan, 1984; Thomoson and Sy, 1987). This feature suggests a possible application of such catalyst for the production of activated carbon. Chemical activation usually needs a large amount of activating agents. If the physical activation can be catalyzed by a small amount of catalyst, it may be economically attractive. However, there are few studies on the catalysis of physical activation.

Laine and Calafat (1991) prepared activated carbon by CO2 activation from coconut shell impregnated with five kinds of potassium solutions: KCl, KNO3, KOH, K2CO3 and

K3PO4. Their results showed that all the potassium compounds except KCl are effective catalysts for activation of the coconut shell. Compared with the non-impregnated product, the BET surface area of activated carbon produced from coconut shell impregnated with potassium compounds (5 wt% K) increased by up to 115%, and the most effective compound was K3PO4. Supported by the study of Yuhn and Wolf (1984), the authors explained that except the chloride, other alkaline salts, such as sodium carbonate, nitrate and hydroxide, reacted with carbon to form surface carbonate species, which enhanced carbon activation.

DiPanfilo and Egiebor (1996) investigated the steam activation of fluid coke pretreated with potassium hydroxide. It was found that treatment with potassium hydroxide led to a higher rate of reaction which was indicated by a greater weight loss, but did not lead to higher surface area or greater porosity. The authors suggested that the addition of KOH could weaken the formation of micropores as it leads to a widening of the micropores rather than developing more pores.

- 13 - A process using potassium hydroxide as activating agent to produce activated carbon can provide a very high surface area of the activated carbon (Otowa et al., 1997). The carbonaceous feeds used in this process are preferably coal, coal coke, petroleum coke, or mixtures. Prior to processing, the feedstock is thoroughly mixed with solid KOH or KOH solution. The weight ratio of potassium hydroxide to carbonaceous feed used is between 1.5 and 5. The mixture of carbonaceous feed and potassium hydroxide is heated within a temperature range of 500 to 900°C for about 15 min to 2 hours. The activated carbon produced by this process usually had a very high BET surface area, which can reach 3000 m2/g and even higher (Bansal et al., 1988).

Wu et al. (2005) prepared activated carbon from two Chinese petroleum cokes (MPC-

Minxi coke and SPC-Shengli coke) using different activation methods with H2O, KOH and/or KOH + H2O as activating agents. The raw coke was soaked in concentrated KOH solution for 2 hours to load KOH and then activated at 800°C for various periods of time. 2 The activated carbon with the highest SBET of about 3000 m /g was produced when using

KOH + H2O activation for 25 min. Since the KOH/coke ratio was only 1~2, the SBET was much higher than that in other studies with the same KOH/carbon ratio. It is interesting that the BET surface area of activated carbon produced from MPC was consistently higher than that from SPC, which was most likely associated with the higher content of nickel, chromium, iron and manganese. To verify this finding, SPC was loaded with nickel and chromium (0.5 wt.%), and activated under the same conditions as that for unloaded SPC. The results showed that the surface area of activated carbon produced from nickel and chromium loaded SPC was consistently higher than that from original SPC coke. It was suggested that metals, such as nickel and chromium could act as catalysts in coke activation, although the catalytical mechanism of these metals was not understood.

Marsh and Yan (1984) studied the effect of KOH on different cokes, and found that oxygen in KOH can remove the cross-linking and stabilizing of carbon atom in crystallites. They proposed a model for the KOH activation process: with the addition of KOH to coke, the potassium may form alkalides such as –OK using the oxygen of the alkali salt. The presence of potassium and oxygen in the coke structure may cause separation of constituent lamellae by oxidation of crosslinking carbon atoms, and formation of functional groups on the edges of the lamellae may cause them to expand the totally flat form. When the

- 14 - potassium salts are removed by leaching with water from within the coke particle, the lamellae cannot return to their previous non-porous structure but remain apart to create the microporosity.

Ehrburger et al. (1986) in studying the physicochemical reactions during carbonization of coals with KOH and NaOH concluded that there were three major reactions between

KOH/NaOH and coal: formation of carbonate, evolution of CO2 and formation of CO. They also found that during the formation of carbonate, some surface salt complexes were formed which acted as active sites and enhanced the activation process.

Sodium hydroxide was also used as the activating agent by several researchers (Raymundo-Pinero et al., 2005; Lillo-Rodenas et al., 2006; Tseng, 2007; Maciá-Agulló et al., 2007; Hwang et al., 2008). It has been found that KOH activation usually gave higher porosity and surface area than NaOH (Lillo-Ródenas, et al., 2003; Macia-Agullo et al., 2007). The difference between the effects of KOH and NaOH in carbon activation could be associated with the intercalation process during activation. Macia-Agullo et al. (2007) observed the formation of K or Na metals during carbon hydroxide activation. The authors suggested that these reduced metals could be eliminated from the carbon matrix by evaporation, but part of them may also be intercalated in the carbon matrix. It was known that the intercalation process occurs easily in ordered carbon materials, that K metal produces intercalation compounds more extensively than Na metal, and that the intercalation compounds react violently with water producing hydrogen (Marsh et al., 1987; Greenwood and Earnshaw, 1994). Therefore, during hydroxide activation, K is more effective than Na. They also found that NaOH was more reactive with carbon (giving lower yield), while KOH was more selective (giving narrower micropore size), suggesting that in NaOH activation a portion of reacted carbon did not contribute to porosity development.

It has been proven that some experimental variables have a great effect on the porosity of the activated carbons prepared by hydroxide activation: the ratio of hydroxide to starting material, the method of mixing, the temperature and the type of flow gas during the activation (Laine and calafat, 1991; Lee and Choi, 2000; Bagreev and Bandosz, 2002; Lillo- Ródenas et al., 2004; Lillo-Rodenas et al., 2006; Maciá-Agulló et al., 2007). Generally, with

- 15 - higher hydroxide/carbonaceous material ratio and higher activation temperature, the surface area of activated carbonaceous materials is higher.

2.3.2.2 Carbon Activation by Other Activating Agents

ZnCl2 has been widely used as activating agent in chemical activation. An example is the preparation of granular activated carbons from peach stones using ZnCl2 activation at 500°C (Caturla et al. 1991). The authors suggested that the porosity created by this reactant was due to the spaces left by zinc chloride after washing, indicated by the increase in porosity with the increase in the ratio of ZnCl2 to the precursor. When the ratio was lower than 0.4, the activated carbon displayed mainly microporosity, while when the ratio was higher than 0.4, an increase in mesoporosity was observed. Other observations made about

ZnCl2 activation include: (i) the volume of micropores developed by ZnCl2 is related to the volume of ZnCl2 introduced into the precursor, (ii) the microporosity is uniform and, (iii)

ZnCl2 acts at temperatures even lower than 500°C (Marsh and Rodríguez-Reinoso, 2006)

Molina-Sabio and Rodríguez-Reinoso (2004) prepared granular activated carbons by impregnating peach stones with solutions of phosphoric acid with various concentrations, in order to obtain different degrees of activation, which was defined by the amount of phosphorus (P) incorporated into the particles, XP, gram of P/gram of precursor. The impregnated material was heated under a flow of nitrogen at 450 °C, and then washed with water. It was found that there was a rapid development of microporosity when the H3PO4 concentration was low, and micropores dominated when the XP was below 0.3. As the concentration of H3PO4 increased, mesoporosity started to develop and could reach a level greater than the microporosity. The yield decreased when the mesoporosity was developed. There was a phosphoric acid concentration range in which high microporosity and high yield could be achieved at the same time.

A comparison of porosities in H3PO4 activated carbons from white oak and yellow poplar with a H3PO4/wood ratio of 1.45 was conducted by Jagtoyen and Derbyshire (1998). Although these woods differed in their cellular structure, biopolymer composition, density and hardness, their activation products were very similar. They found that micropore development began at about 150 °C, reaching a maximum at about 350°C. Mesoporosity

- 16 - started to develop at about 250 °C, reaching a maximum at 500-550°C. Most of the increase in mesopore volume (>350°C) equalled the decrease in microporosity, suggesting that pore widening contributed to the increase in mesopore volume. Results also showed that the pore volumes were controlled by the activation temperature: increasing to maxima between 500- 550 °C and then decreasing. Thus, porosity changes are a function of both the ratio of reagent to wood volume and the activation temperature.

2.3.2.3 Surface Modification of Activated Carbon

Activated carbons have been used for many years quite successfully for adsorptive removal of impurities from exhaust gas and wastewater streams. However, for effective removal of certain impurities in gases, such as hydrogen sulphide and mercury, the adsorption capacities and the removal rates may be substantially improved by adding suitable chemicals onto the surface of activated carbon. When these chemicals are deposited on the internal surface of the activated carbon, the removal mechanism may change from physical adsorption to chemisorption.

It has been reported that activated carbon with surface modified by sulphur compounds can increase the adsorption of mercury from both aqueous and gas phases. Focusing on mercury removal, some studies have shown that sulphur-impregnated activated carbons (SIACs) have higher efficiencies than activated carbons that have no sulphur or low sulphur content (Henning and Schäfer, 1993; Korpiel and Vidic, 1997; Liu et al., 2000; Ranganathan and Balasubramanian, 2002; Feng et al., 2006). Sulphur compounds can be added onto a carbon surface either during, or subsequently after the production of activated carbons. Usually, sulphur impregnated activated carbon is produced by heating the activated carbon in the presence of elemental sulphur, or sulphurous gases, such as hydrogen sulphide and sulphur dioxide (Korpiel and Vidic 1997; Liu and Vidic, 2000; Hsi et al., 2002; Krishnan and Anirudhan, 2002). After the sulphur-impregnation treatment, SIACs have sulphur-containing compounds attached to their internal surface. Although these compounds may reduce the carbon pore volume, because of the sulphur deposition, their mercury adsorption capacity is increased under certain experimental conditions (Feng et al., 2006). This could be related to the active sites where the sulphur-containing compounds facilitate the adsorption of mercury, through the reaction between sulphur and mercury.

- 17 - Korpiel and Vidic (1997) impregnated an activated carbon with elemental sulphur to prepare SIACs, and found that for mercury vapor adsorption, SIACs produced at 200oC was not as effective as those produced at 600oC. This temperature dependence was suggested to be associated with sulphur distribution in the porous carbon structure. At higher impregnation temperatures, the distribution of the sulphur in SIAC was deeper and more uniform, which resulted in a major portion of the carbon surface area containing sulphur- active sites to be exposed to the mercury.

Liu et al. (2000) found that sulphur impregnation at elevated temperatures resulted in sulphur-containing compounds attached to the carbon surface in the form of short linear- chains. They also suggested that more sulphur on the carbon surface provided more active sites for mercury adsorption. In SIACs, the mercury is adsorbed via chemisorption through a very stable mercury-sulphur bond.

Mercury adsorption and desorption experiments in a fixed-bed reactor using SIACs as adsorbents was conducted by Karatza et al. (2000). Their results indicated that the amount of mercury adsorbed was not dependent on the mercury concentration, and that mercury desorption takes longer than the adsorption process. Surface analyses on the carbons after mercury adsorption showed that sulphur was not uniformly distributed and the sulphur-rich zones were concentrated with mercury. In the sulphur-free zones mercury was virtually negligible, which confirms the chemical nature of Hg adsorption by SIACs.

Although activated carbon impregnated with sulphur offers great potential for vapour Hg removal, other types of chemical-impregnated activated carbons were also investigated.

Zeng et al. (2004) used ZnCl2-impregnated activated carbon to remove elemental mercury from coal combustion flue gas. Their result showed that chloride impregnation significantly enhanced the adsorption capacity of mercury, and the Cl-containing functional group on + carbon surface might react with mercury to form various complexes, e.g. [HgCl] , [HgCl2] 2- and [HgCl4] .

- 18 - 2.4 CHARACTERIZATION OF SULPHUR COMPOUNDS IN CARBONACEOUS MATERIALS

In order to understand the roles of sulphur in coke activation and in the application of activated products, the forms of sulphur in both raw fluid coke and activated carbon have to be identified. However, the characterization of sulphur within a carbon matrix is a challenging task, particularly when the sulphur is organic in nature.

2.4.1 Total Organic Sulphur in Coal and Coke

Methods for total sulphur content in coal and coke are well established, including the wet chemistry method according to the ASTM standard and instrumental analysis using an elemental analyzer. However, the routine method for direct identification and quantification of organic sulphur in coal and coke has not been established, although great progress has been made from the 70s (Davidson, 1994, Olivella et al., 2002). It is widely accepted that X- ray absorption near edge structure spectroscopy (XANES) is the most powerful technique for organic sulphur speciation and quantification, and it has been used to directly determine the organic sulphur in coal (Gorbaty et al., 1990). However, XANES, with its need for a synchrotron source, can hardly be considered as a routine laboratory technique (Davidson, 1994). Therefore, more practical and economical techniques are still needed.

The generally adopted method for total organic sulphur determination is the ASTM method D 2492, which determines the organic sulphur by subtracting the sum of the sulphate and pyritic sulphur from the total sulphur. Its major drawback is that it may overestimate organic sulphur in coke. For instance, if elemental sulphur exists in the sample, it will be counted as organic sulphur.

Riley et al. (1990) modified the ASTM method to eliminate this bias. They extracted the coal sample with boiling 2 M HNO3 for 30 min, which removed essentially all inorganic sulphur. After washing and drying, the extracted sample was analyzed for moisture, ash, and total sulphur using the same methods as ASTM D 2492. The total sulphur after extraction is the total organic sulphur, and it was found to be less than that obtained by ASTM D 2492. On the other hand, the results from HNO3 acid extraction were in agreement with that measured for deeply cleaned samples from which mineral matter was physically removed. This confirmed their hypothesis that the organic sulphur content determined using ASTM method

- 19 - could mistakenly contain other forms of sulphur as well. The authors claimed that the accuracy of their method was much higher than that of ASTM D2492.

SEM-EDX has been studied extensively for its potential as a direct method for organic sulphur determination. Davidson (1994) reviewed several studies of SEM-EDX analysis used in this area. An overall agreement was achieved between SEM-EDX analysis and the ASTM method. However, the limitation of this method is that it cannot give specific structure information about organic sulphur forms which is important in coal and coke studies (Olivella et al., 2002).

2.4.2 Speciation of Sulphur in Coal and Coke

In an attempt to develop an easy and fast method for organic sulphur quantification, a chemical method based on selective oxidation has been developed. The method involves stepwise oxidation with perchloric acid-ferric perchlorate mixture (Zhou and Chriswell, 1996). The authors grouped organic sulphur in coal into three categories according to their reactivity: 1) easily oxidized ones, i.e. disulphides, 2) less reactive ones, e.g. aliphatic sulphides and thiols, 3) relatively stable ones, e.g. thiophene and aromatic sulphides. The various groups of sulphur compounds were oxidized in a stepwise manner with an HClO4 solution containing certain concentration of Fe(ClO4)3, and the amount of sulphate formed during each step was measured. For two coal samples, with 0.1M of Fe(ClO4)3, the sulphur recovered as sulphate represented the amount of easily oxidized sulphur compounds, which was comparable to the total inorganic sulphur measured by ASTM method. Higher Fe(ClO4)3 concentration (0.7 M) oxidized less reactive sulphur compounds, present as aliphatic sulphides, aliphatic thiols and aromatic thiols. The rest, by difference, stable towards

HClO4/Fe(ClO4)3 oxidation, was the stable sulphur compounds. By this means, sulphur with different oxidation states in coals were determined, yet no specific form could be identified. For Illinois No.6 coal, 3% of inorganic sulphur, 0.7% of less reactive sulphur and 1.3% of relatively stable ones were determined, while 1.1% of inorganic sulphur, 0.4% of less reactive sulphur and 1.5% of relatively stable ones were found in Bevier coal.

It has long been recognized that X-ray photoelectron spectroscopy (XPS) could provide useful information for characterizing sulphur compounds in coal and coke. However, the

- 20 - characterization of organic sulphur on coal surface by XPS is complex due to the presence of other forms of sulphur. Therefore, a set of spectra for known organic sulphur compounds in coal and petroleum coke is crucial. Kelemen et al. (1990) applied XPS methods to quantitatively determine sulphur forms using a variety of model compounds and petroleum- based material. The sulphur 2p3/2 binding energies of some model compounds are summarized in Table 2-2. Organic sulphides are oxidized to sulphoxides first which could be further oxidized to sulphone.

More information of sulphur 2p binding energies was reported by other researchers, as shown in Table 2-3. Comparing the values in Table 2-3 with those given in Table 2-2, there is a small difference, which indicates the uncertainty of XPS analysis in organic sulphur determination. The XPS handbook (Wagner et al., 2007) and NIST (National Institute of Standards and Technology) X-ray photoelectron spectroscopy online database suggested that there are overlaps between certain sulphur forms (Figure 2-3). Therefore, it is difficult to distinguish certain sulphur forms with similar oxidation state, such as thiophene and elemental sulphur. As mentioned earlier, another technique for sulphur characterization is X- ray Absorption Near Edge Structure (XANES) spectroscopy which is reviewed in the next section.

Table 2-2 XPS 2p3/2 binding energies of model sulphur compounds (Kelemen et al., 1990) Compound Binding energy (eV)

DBT sulphone (>SO2) 168.2

Polyphenylene ether sulphone (>SO2) 168.2 DL-Methionine sulphoxide (>SO) 165.8

164.2/162.1 6-Ethoxy-2-mercaptobenzothiazole ( ) 1,2-Benzodiphenylene sulphide (-S-) 164.0 Sulphur 163.7 Polyphenylene sulphide (-S-S-) 163.7

163.1 DL-Methionine ( )

- 21 - Table 2-3 XPS sulphur 2p3/2 binding energy (Jiménez Mateos and Fierro, 1996; Chang, 1981) Compound Binding energy (eV) Compound Binding energy (eV) Dibenzothiophenes 161.4 Thiophenes 164.5 Thiols (-SH) 162.9 Sulphoxide (>SO) 166.0

Thioether (-S-) 163.6 Sulphone (>SO2) 168.2

Disulphide (-S-S-) 164.2 Sulphonate(–SO3) 169.1 a. b.

Figure 2-3 a. Sulphur 2p3/2 binding energy and b. the spectrum of elemental sulphur (Wagner et al., 2007)

2.4.3 Application of X-ray Absorption Near Edge Structure (XANES) for Sulphur Speciation

2.4.3.1 The Theory of XANES When an X-ray hits a sample, the oscillating electric field of the electromagnetic radiation interacts with the electrons bound in an atom. Either the radiation will be scattered by these electrons, or absorbed to excite the electrons.

A narrow parallel monochromatic X-ray beam of intensity (I0) passing through a sample of thickness (x) will become reduced to intensity (I) according to the expression:

ln (I0/I) =  x 2-3

In this equation,  is the linear absorption coefficient, which depends on the type of atoms and the density of the material. At certain energies, the absorption increases drastically and gives rise to an absorption edge. Such edge occurs when the energy of the incident

- 22 - photons is just sufficient to cause excitation of a core electron of the absorbing atom to a continuum state, i.e. to produce a photoelectron. Thus, the energies of the absorbed radiation at these edges correspond to the binding energies of electrons in the K, L, M, etc, shells of the absorbing elements, and the absorption edges are labelled correspondingly.

When the photoelectron leaves the absorbing atom, its wave is backscattered by the neighbouring atoms, which gives information of the chemical environment. Sulphur has a rich XANES structure, with a 13 eV shift from S (-II) in sulphide to S (VI) in sulphate. Figure 2-4 shows the sudden increase in the x-ray absorption of the sulphur K-edge in poly (phenylene sulphide), with increasing photon energy.

An x-ray absorption spectrum is typically divided into 4 regimes: i) pre-edge, E < E0, ii) x-ray absorption near edge structure (XANES), where the energy of the incident x-ray beam is

E = E0 ± 10 eV, iii) near edge x-ray absorption fine structure (NEXAFS), in the region between 10 eV up to 50 eV above the edge, and iv) extended x-ray absorption fine structure (EXAFS), which starts approximately from 50 eV and continues up to 1000 eV above the edge. However, the name, XANES, is often used for both XANES and NEXAFS regimes.

NEXAFS XANES EXAFS

Edge Normalized Absorption

Figure 2-4 K-edge XANES spectrum of sulphur in poly (phenylene sulphide)

The minor features in the pre-edge region are usually due to the electron transitions from the core level to the higher unfilled or half-filled orbital. In the XANES region, transitions of core electrons to non-bound levels with close energy occur. Because of the high probability of such transition, a sudden rise of absorption is observed. Therefore, XANES is

- 23 - strongly sensitive to oxidation state and coordination chemistry of the absorbing atom. In

NEXAFS, the ejected photoelectrons have low kinetic energy (E-E0 is small) and experience strong multiple scattering by the first and even higher coordinating shells. In the EXAFS region, the photoelectrons have high kinetic energy (E-E0 is large), and single scattering by the nearest neighbouring atoms normally dominates.

There are two modes of analysis offered by XANES that have different sensitivities providing a thorough characterization of the surface and bulk properties of the samples: the fluorescence yield (FY) and the total electron yield (TEY) mode. The FY mode of detection is a bulk technique and can probe >800 nm of a sample, while the TEY mode probes ~50 nm (Nichollsa et al., 2004).

2.4.3.2 Sulphur Characterization using XANES XANES has been used by several groups of researchers as an aid to characterize sulphur in coal, soil and activated carbon. Kasrai et al. studied the presence of inorganic and organic sulphur compounds in five coal samples (Kasrai et al., 1996). A large amount of sulphur model compounds were used in their study. The XANES spectra of these model compounds were qualitatively interpreted. TEY and FY techniques were applied for recording the S L-edge and S K-edge spectra of coal samples, and described in detail. Their study showed S L-edge XANES could quantitatively identify alkyl sulphides, alkyl disulphides, aryl disulphides, aryl sulphides and heterocyclic sulphur. The conclusion from their study was that the S L-edge TEY and FY technique gave a sensitive probe for sulphur speciation in coal.

Sarret et al. (1999) used sulphur K and L-edge XANES spectroscopy to study asphaltene samples. Their results showed that in all the samples, dibenzothiophenes were the dominant forms of sulphur. In the least oxidized asphaltenes, minor species included disulphide, alkyl and aryl sulphides as well as sulphoxides. The study illustrated the advantages of XANES spectroscopy as a selective probe for determining sulphur species in a complex system, e.g. asphaltenes. Furthermore, they found that sulphur L-edge spectroscopy was more sensitive to the major forms of reduced sulphur, while K-edge spectroscopy was suitable for the quantification of oxidized sulphur compounds.

- 24 - Solomon et al. (2003) conducted a study to assess the potential of K-edge XANES spectroscopy to characterize the impact of deforestation and changes in land use on the amount, form, and distribution of sulphur in soil samples. Most reduced sulphur (sulphides, disulphides, thiols and thiophenes), intermediate (sulphoxides and sulphonates) and highly oxidized forms (ester-SO4-S) were found in soil samples. Their results showed that S K-edge XANES spectroscopy offered a significant potential to evaluate the influence of the change on the nature and distribution of S in terrestrial ecosystem.

Recently, Feng et al. (2006) studied sulphur in SIACs prepared for vapour phase mercury uptake. The sulphur forms deposited on the carbon surface were analyzed using XPS and XANES. The XANES analysis allowed the authors to identify elemental sulphur, thiophene, sulphoxide and sulphate.

2.5 APPLICATION OF ACTIVATED CARBON - MERCURY ADSORPTION FROM AQUEOUS

SOLUTION

Mercury is one of the most harmful pollutants in the environment, due to its toxicity, high volatility and potential bioaccumulation. The sources of mercury in the environment are mainly from industrial emissions and wastewater. In this study, mercury removal from aqueous solution was chosen as the first-stage application of activated carbon produced from oil-sand fluid coke, since activated carbon adsorption is widely used in wastewater treatment due to its high efficiency and ease of application.

2.5.1 Effect of Adsorption Conditions

When using activated carbon to remove mercury, it is believed that physical characteristics of activated carbon, such as surface area, pore size distribution and particle size, along with its chemical properties determine its performance (Namasivayam and Kadirvelu, 1999; Mohan et al., 2001; Anoop Krishnan and Anirudhan, 2002; Babic et al., 2002; Ekinci et al., 2002; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Budinova et al., 2008; Zhu et al., 2009; Zabihi et al., 2009). The effective adsorption conditions studied previously are listed in Table 2-4. Additionally, activated carbons can be chemically modified to enhance their capacity in adsorbing aqueous contaminants. For this

- 25 - treatment to be advantageous, the impregnated substance and the contaminant should possess a high chemical affinity at specific operating conditions (Henning and Schäfer, 1993; Chen, 2002).

Table 2-4 Hg2+ adsorption capacities reported in the literature Adsorbent Hg 2+ adsorption Adsorption conditions Reference Capacity (mg/g)

H2SO4 activated coir 40 - 130 pH: 5 Namasivayam and pith Initial conc.: 10 – 40 mg/L Kadirvelu, 1999 Carbon Dose: 0.2 – 0.4 g/L Air activated fertilizer 200 - 600 pH: 2 Mohan et al., 2001 waste Initial conc.: 200 – 2000 mg/L Carbon Dose: 1 g/L

H2SO4 activated and 40 - 60 pH: 5.5 Ranganathan and sulphide loaded Initial conc.: 10 – 100 mg/L Balasubramanian, coconut shell Carbon Dose: 0.5 g/L 2002 Steam activated 40 - 150 pH: 5.5 Ekinci et al., 2002 biomass and coal Initial conc.: 10 – 40 mg/L Carbon Dose: 0.2 g/L

CO2 activated viscose 6.4 – 7.6 pH: 2 - 6 Babić et al., 2002 rayon cloth Initial conc.: 15 – 1000 mg/L Carbon Dose: 2.5 g/L Steam activated 35 - 55 pH: 6 Anoop Krishman bagasse pith Initial conc.: 100 mg/L and Anirudhan, Carbon Dose: 2 g/L 2002

H2SO4 activated 40 - 150 pH: 5.5 Yardim et al., 2003 furfural Initial conc.: 10 – 40 mg/L Carbon Dose: 0.2 g/L

H2SO4 and 15 -50 pH: 5.0 Kadirvelu et al., (NH4)2S2O8 activated Initial conc.: 20 – 50 mg/L 2004 sago waste Carbon Dose: 1 g/L

H2SO4, H3PO4, and 40 - 130 pH: 5.0 Zhang et al., 2005 ZnCl2 activated Initial conc.: 80 mg/L organic swage sludge Carbon Dose: 0.1-10 g/L

K2CO3 activated 45 - 105 pH: 5.5 Budinova et al., waste antibiotic Initial conc.: 10-40 mg/L 2008 material Carbon Dose: 0.2 g/L

ZnCl2 activated 10 - 100 pH: 5.0 Zabihi et al., 2009 walnut shell Initial conc.: 9.7-107 mg/L Carbon Dose: 1 g/L

- 26 - 2.5.2 Effects of Activated Carbon Properties

A few studies were conducted to investigate the possibility of using different types of activated carbon to remove Hg2+ from aqueous solution. Most of them were focused on investigating the effects of experimental conditions on Hg2+ adsorption. It was reported that Hg2+ adsorption was strongly dependent on the agitation time, initial concentration of Hg2+, pH and activated carbon dosage (Namasivayam and Kadirvelu, 1999; Mohan et al., 2001; Anoop Krishnan and Anirudhan, 2002; Babic et al., 2002; Ekinci et al., 2002; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005).

Although the properties of activated carbon are also important in Hg2+ adsorption, the research on this topic has been rather limited. The properties investigated previously include surface area, pore size and pore volume, particle size and surface chemistry. Ekinci et al. (2002) produced three types of activated carbon from apricot stones, furfural and coals. These activated carbons were then used to remove Hg2+ from aqueous solution. Their results showed that Hg2+ removal correlated well with the BET surface area. An increase in BET surface area increased the adsorption of Hg2+. This finding was supported by the study conducted by Zhang et al. (2004), who used organic sewage sludge as the starting material to produce activated carbon and used this activated carbon to adsorb Hg2+. Their results indicated that the high-adsorption capacity of one of their samples could be attributed to its high BET surface area and high micro pore volume. Based on the calculation of diffusion coefficients for Hg2+ adsorption, Krishnan and Anirudhan (2002) proposed that the rate limiting step of Hg2+ adsorption is the pore diffusion process. Pore size and pore structure of activated carbon can significantly affect the pore diffusion process, thus they play important roles in the mercury adsorption process.

Particle size is another important property that attracts more attention than other properties of activated carbon for mercury adsorption. Generally, the capacity of Hg2+ removal decreases with increasing the adsorbent particle size (Mohan et al., 2001; Anoop Krishman and Anirudhan, 2002; Kadirvelu et al., 2004). According to Mohan et al. (2001), in a system with poor mixing, dilute concentration of adsorbate, small particle size of adsorbent and high affinity of adsorbate for adsorbent, external transport is the rate-limiting step. On the other hand, the intraparticle step limits the overall transfer for the system with

- 27 - high concentration of adsorbate, good mixing, large particle size of adsorbent, and low affinity of adsorbate for adsorbent.

The modification of carbon surface chemistry has been attempted in order to improve the performance of activated carbon in mercury removal. Nabais et al. (2006) modified the surface of activated carbon fibres with powdered elemental sulphur and H2S gas. It was found that the most important parameter for mercury uptake is the type of sulphur introduced rather than total sulphur amount. They suggested that H2S treatment leads to the formation of functional groups where the sulphur is more accessible to mercury than the functional groups formed during the reaction with powdered sulphur. However, the types of functional groups formed during modification processes were not identified. Ranganathan and Balasubramanian (2002) prepared sulphide-loaded activated carbon from coconut shells by chemical treatment with sulphide and thermal activation. The carbons with and without sulphide treatment were used for Hg2+ adsorption, and the results showed that the sulphide- loaded activated carbon was more effective. Although surface modification of activated carbon is promising for improving Hg2+ adsorption, the knowledge of what type of functional groups on SIAC surface is beneficial for Hg2+ adsorption is needed in order to improve SIAC properties.

Henning and Schäfer (1993) proposed that SIACs have a catalytic effect on the adsorption of mercury vapour. Normally, mercury and sulphur are not converted to mercury sulphide at ambient temperature. However, catalyzed by activated carbon, this reaction can occur on the internal surface of activated carbon at low temperature. This process plays a key role during mercury removal from gases. It was also suggested that four steps limited the kinetics of this process: first, the mercury vapour has to diffuse to the external surface of the activated carbon; second, it diffuses into the SIACs porous structure; third, mercury reaches the sulphur-containing active sites; and last, mercury sulphide forms through the chemisorption of mercury by the sulphur-containing active site.

Hsi et al. (2001) used elemental sulphur to impregnate activated carbon fibres (ACFs). Data showed that the sulphur impregnated on the fibres was in the form of elemental and organic sulphur (i.e. thiophene, sulphone, and a small amount of thiocarbonyl) and sulphate. Using these fibres to adsorb Hg vapour, they suggested that elemental sulphur was the main

- 28 - form of sulphur affecting Hg adsorption. However, they also mentioned that additional studies were needed to understand if the organic sulphur contributed to Hg adsorption. In a more recent study, Feng et al. (2006) investigated the importance of sulphur forms in SIAC for mercury vapour removal. They suggested that elemental sulphur, thiophene, and sulphate were likely responsible for mercury uptake, with elemental sulphur species being the most effective.

2.6 SUMMARY

Based on the literature review, it was found that the challenge of fluid coke activation is to increase the porosity of the activation products from fluid coke. From previous work, KOH activation has been proven to be an effective process for producing activated carbon with high porosity. Therefore, KOH could be considered as the activating agent. SO2 activation has been used in the previous study to produce activated carbon with high sulphur content, although the activated carbon had very low surface area. Combining KOH and SO2 could potentially yield activation products with high surface area and high sulphur content.

Since fluid coke has high sulphur content, as do many low ranking coals, it is important to understand if the high content of sulphur affects the activation process. However, no previous research on this topic has been found.

Another challenge of this work was to characterize the sulphur species in fluid coke and its activation products, which is crucial for understanding the activation mechanisms. From the literature review, XPS and XANES could be applied for sulphur analysis.

For the application of SIACs, Hg2+ removal from aqueous solution was considered, since previous studies showed that sulphur-impregnated activated carbon displayed a higher capacity of Hg2+ adsorption than virgin activated carbon, and suggested that the sulphur in SIACs could play a role during the adsorption. However, very little evidence has been found, and no correlation has been established between the properties of SIACs and their Hg2+ adsorption capacity.

- 29 - CHAPTER 3 PREPARATION OF SULPHUR-IMPREGNATED ACTIVATED

CARBON FROM FLUID COKE WITH KOH AND SO2

3.1 INTRODUCTION

Oil-sands fluid coke is currently being produced at a rate of over 10,000 tonnes per day as a by-product from the upgrading of bitumen in northeastern Alberta. The use of fluid coke as fuel for power generation is hindered by its high sulphur content, and therefore is currently being stockpiled in the existing 45 million tonne reserves. However, the high carbon content of fluid coke makes it an attractive material for producing activated carbon, especially for sulphur-impregnated activated carbon (SIAC), which has been proven to be effective for mercury adsorption from gases and aqueous solutions (Korpiel and Vidic, 1997; Liu and Vidic, 2000; Anoop Krishnan and Anirudhan, 2002; Ranganathan and Balasubramanian, 2002; Nabais et al., 2006).

Few studies have been conducted using high sulphur petroleum coke to produce activated carbon, and none of their products have high porosity and high surface area (Dipanfilo and Egiebor, 1996; Lee and Choi, 2000). DiPanfilo and Egiebor (1996) conducted a two-step pyrolysis and activation process to produce activated carbon from oil-sands fluid coke. Steam was employed as the activating agent at atmospheric pressure and 850°C. The 2 highest BET surface area (SBET) of activated coke was 318 m /g after 6-hour activation while the weight loss was over 50%. They also investigated the effect of pretreating fluid coke with potassium hydroxide on its activation and suggested that the addition of KOH could weaken the formation of micropores as it leads to a widening of the micropores rather than developing more pores. Chen (2002) developed a process in which the oil-sands fluid coke was activated using SO2 as the activating agent. Using this process, activated coke was produced with the highest specific surface area of 367.5 m2/g at 77.2% weight loss, after 10 hr activation at 700°C. Although the total sulphur content in the activated coke reached as high as 20 wt%, the process was not efficient.

A process using potassium hydroxide as activating agent can provide a very high surface area of the produced activated carbon (Marsh and Yan, 1984; Otowa et al., 1997, Lee and Choi, 2000; Mitani, et al., 2004; Wu, et al., 2005). The carbonaceous feeds used in this

- 30 - process are preferably coal, coal coke, petroleum coke, or mixtures. The activated carbon 2 produced by this process usually had a very high SBET, which could reach 3000 m /g and even higher (Otowa et al., 1997).

Laine and Calafat (1991) prepared activated carbon by CO2 activation from coconut shell impregnated with five kinds of potassium solutions: KCl, KNO3, KOH, K2CO3 and

K3PO4. Their results showed that all the potassium compounds except KCl were effective catalysts for activation of the coconut shell. Compared with the non-impregnated product, the

SBET of activated carbon produced from coconut shell impregnated with potassium compounds (5 wt% K) increased by up to 115%. Sodium hydroxide was also used as the activating agent by several researchers (Raymundo-Pinero et al., 2005; Lillo-Rodenas et al., 2006; Maciá-Agulló et al., 2007; Tseng, 2007; Hwang et al., 2008). It has been found that KOH activation usually gave higher porosity and surface area than NaOH activation (Lillo- Ródenas, et al., 2003; Macia-Agullo et al., 2007), which may be associated with the intercalation of metal Na or K produced from KOH/carbon or NaOH/carbon reactions into the carbon matrix. It is well known that the intercalation of alkali metals, such as Na and K, strongly depends on the crystallinity of the host carbon (Tanaike and Inagaki, 1997; Raymundo-Piñero et al., 2005). Raymundo-Piñero et al., (2005) found that K can be intercalated into graphite-like structures. The higher the structure order, the better the intercalation. On the other hand, Na can be only intercalated in highly defective carbons, i.e. carbon with non-graphitic structure. Therefore, NaOH is only effective with disordered materials whereas KOH was found effective with all of them. A preliminary study carried out by the author (Appendix A) confirmed that KOH activation of fluid coke provided the coke with higher surface area and higher pore volume than NaOH activation, which was in agreement with the fact that fluid coke has a highly graphitic structure (Furimskyr, 1998).

The objective of this study was to establish the technical feasibility of a process for producing SIAC from oil-sands fluid coke and to better understand the mechanism of fluid coke activation. To better control sulphur contents in the activated carbon, SO2 was used as a sulphur-impregnating agent. This study represented the first attempt to activate oil-sands fluid coke with KOH and SO2.

- 31 - 3.2 EXPERIMENTAL

3.2.1 Materials

Two types of fluid coke were used as raw materials: FC-S and FC-I. Some properties of these cokes are shown in Table 3-1, which were measured either according to ASTM methods (such as moisture, volatile and ash content) or by instruments (described in Section 3.2.3) Table 3-1 Properties of Syncrude and Imperial Oil fluid coke Property FC-S FC-I Size (μm) 212-300 212-300 2 SBET (m /g) 7.5 14.0 Proximate analysis Moisture (%) 1.01 0.98 Ash (%) 3.47 0.35 Volatiles (%) 5.35 3.58 Fixed carbon (%) 90.17 95.09 Ultimate analysis Carbon (%) 82.74 87.22 Hydrogen (%) 1.69 1.93 Nitrogen (%) 1.84 1.81 Oxygen (%) 6.40 3.43 Sulphur (%) 7.37 5.61

The activating agent, potassium hydroxide, was purchased from VWR International. Its KOH content is higher than 85% as indicated by the manufacturer, and the moisture is 12% from measurement. Purity of SO2 gas used in this study is 99.99%, and it was diluted with N2 gas (99.99%) when used in the experiments. Concentrated hydrochloric acid was purchased from EM Science, and diluted with deionized water to 1:20 solution (i.e. 5%) for washing activation products. Both KOH and HCl were reagent grade and were used without further purification.

3.2.2 Experimental Set-up and Activation Procedures

The experimental set-up for production of SIAC was designed based on that used by Chen (2002). The set-up mainly consisted of a stainless steel tube reactor (48 mm ID, 50 mm OD × 200 mm Length) placed in a vertical tubular furnace with a programmable temperature controller and a gas supply system consisting of gas cylinders and mass flow

- 32 - controllers connected to each gas cylinder. The exit gas from the furnace passed through an ice condenser before entering a scrubber containing 10% NaOH solution (Figure 3-1).

Figure 3-1 Apparatus for fluid coke activation

Two processes were used to produce activated carbon and SIACs: KOH-only activation and KOH and SO2 activation. In KOH-only activation, 5 grams of fluid coke were physically mixed with flake KOH in a KOH/coke mass ratio of 1:1 to 3:1. It should be pointed out that the ratio of KOH/coke in this study is mass ratio in grams, and a KOH/coke mass ratio of 1:1 in grams corresponds to a KOH/carbon molar ratio of about 1:4, since the coke consists 83% of carbon (measured using an elemental analyzer). The mixture was charged into the stainless steel reactor and placed in the tubular furnace. The height of the coke bed consisting of fluid coke powders was about 1 cm, and it was located at the centre of the tube furnace. To remove oxygen, the system was purged with nitrogen (purity: 99.99%) at 350 mL/min for 30 minutes prior to raising the temperature. A heating rate of about 13°C/min was used to bring the temperature to the pre-set level (600 - 900°C). The temperature was held for the selected time. During this period of time, N2 gas (99.99%) was passed through the reactor to provide an inert environment in the reactor. Upon the completion of KOH activation, the reactor was allowed to cool down and removed from the furnace. The solid product was transferred to a flask and washed with 200 mL of deionized water. It was then further washed with 200 mL of 5% HCl and 500 mL of deionized water, filtered, and dried at 110°C for 20 hours.

- 33 - In the KOH and SO2 activation, the fluid coke was mixed with KOH flakes with a mass ratio of 1:1 to 3:1 in the reactor, and the reactor was placed in the furnace. The system was purged with nitrogen gas at 350 mL/min for 30 minutes prior to raising the temperature to 600-900°C. Once at the selected temperature, the reactor was heated for a certain period of time, with 30% SO2 (70% of N2) gas at 500 mL/min. After activation, the product was taken out from the reactor, washed following the same procedure as in KOH-only activation. A flow sheet for these activation processes is shown in Figure 3-2.

For comparison purposes, SO2 activation based on previous study was employed to produce SIACs (Chen, 2002). In SO2 activation, 10 g of fluid coke was charged to the reactor, and the reactor was placed in the furnace. The system was purged with nitrogen at 350 mL/min for 30 minutes, and then fluid coke was heated to 700°C and hold for 1 hour with

30% SO2 gas (70% of N2 gas) passing through at 500 mL/min. After activation, the product was taken out of the reactor and washed using the same procedure as that in KOH-only activation. In this process, SO2 was the activating agent and also sulphur impregnating agent.

Raw material: fluid coke

Physically mixed with KOH flakes

30% SO2

Heating the mixture Heating the mixture (600~900°C, 0.5~3 hr) (600~900°C, 15 min~3 hr)

Solid product

Washed with 5% HCl and deionized water

Drying at 110°C for 20 hours

Activated carbon/SIAC

Figure 3-2 Processes of fluid coke activation with KOH and SO2

- 34 - 3.2.3 Analytical Techniques and Methods

An SA3100 Coulter surface area and pore size distribution analyzer was employed to determine the SBET and pore size distribution of raw cokes and activated products. A Hitachi S-5200 Scanning Electron Microscope (SEM) was employed to obtain topographical information for the surfaces of the raw and activated coke. X-ray photoelectron spectroscopy (XPS, Thermo Scientific Theta Probe) was used to analyze the elemental composition on the surface of fluid coke and their activation products.

Total sulphur content in coke and SIACs was determined using the Eschka method according to the ASTM standard (ASTM D3177) and/or an elemental analyzer (Vario EL III, German). The ASTM method is based on igniting 1 g of sample mixed with Eschka mixture, removing the combustible matter, and converting all sulphur compounds to sulphate. The sulphate can be extracted with hydrochloric acid solution and gravimetrically determined by precipitation with barium chloride. An elemental analyzer was also used to determine sulphur, carbon, hydrogen and nitrogen in the samples. The sulphur contents determined with the two methods were in good agreement with an average difference of 0.2%.

3.3 RESULTS AND DISCUSSION

3.3.1 KOH Activation

3.3.1.1 Morphology of KOH activated carbon

The structure of fluid coke was significantly changed after KOH activation (Figure 3- 3). Oil-sands fluid coke particle has a solid structure (also see Figure 2-2). Upon activation the solid particles of fluid coke were broken, and the layered structure became visible. High porosity is essential for activated carbon to have a high adsorption capacity of molecules. However, paths are needed to make internal pores accessible. Therefore, the opened structure of KOH activated fluid coke is beneficial for molecules diffusing into the internal surface of the carbon matrix and reaching the adsorption sites. The highest BET surface area (SBET) of KOH activated carbon was 2500 m2/g. The theoretical specific surface area was calculated in order to investigate the possibility of overestimation of this high surface area. Based on one

- 35 - graphene layer, the theoretical specific surface area is 5700 m2/g (detailed calculation in Appendix B-1).

Figure 3-3 Structure of fluid coke (left) and its change after KOH activation (centre and right)

3.3.1.2 Effects of Activation Condition on Activated Carbon Properties

Effects of activation time. Figures 3-4 and 3-5 show the changes in SBET, weight loss and the percentage of micropore surface area (micropore SA) with activation time at 700°C. The time zero was the time that the system reached the set temperature. However, it took about 50 min for the system to reach 700°C, and the surface area was developed during this period of time. Figure 3-4 shows that the SBET increased rapidly at the beginning, and stabilized after about half an hour, while the weight loss started to stabilize earlier. The development of surface area in KOH activation are mainly caused by two processes: i) carbon removal caused by the reaction between KOH and carbon (Marsh and Yan, 1984; Otowa et al., 1997, Lee and Choi, 2000; Mitani, et al., 2004; Wu, et al., 2005); ii) the removal of elemental K which produced from KOH-C reaction and intercalated into the carbon matrix (Tanaike and Inagaki, 1997; Raymundo-Piñero et al., 2005). Carbon removal is the major cause of the weight loss of fluid coke, while the removal of K does not contribute to the weight loss. With longer activation time, after the reaction between KOH and carbon completes, more surface area can be created by the removal of K. However, this would not result in a higher weight loss.

- 36 - 2500 60

50 2000

40 1500 /g) 2 30 (m

BET 1000 S 20 Weight loss (%) Weight BET surface area 500 10 Weight loss 0 0 15 30 60 120 180

Activation time (min)

Figure 3-4 Time dependence of SBET and weight loss of fluid coke in KOH activation (FC-S, temperature: 700°C, KOH/coke: 3:1, N2: 350 ml/min)

The change in pore volume followed the same trend as that of the SBET due to the positive correlation between the SBET and total pore volume. Apparently, surface area contributed from micropores (i.e. micropore surface area) increased at the beginning, and decreased afterwards, yet the percentage of micropore surface area in total SBET continuously decreased after 15 minutes.

70 1400

60 1200 /g)

50 1000 2

40 800

30 600

20 400 Micropore SA (m Micropore surface area percentage

Micropore SA percentage (%) 10 200 Micropore surface area 0 0 15 30 60 120 180 Activation time (min)

Figure 3-5 Time dependence of micropore surface area (micropore SA) and its percentage in KOH activated carbon (FC-S, temperature: 700°C, KOH/coke: 3:1, N2: 350 ml/min)

- 37 - It is generally accepted that activation starts with micropore formation, followed by pore enlargement (Gregg and Sing, 1982; Derbyshire et al., 1995; Williams and Reed, 2006). Three stages in the pore development process have been suggested: i) the opening of previously inaccessible pores through the removal of tars and disorganized carbon, ii) the creation of new pores by selective activation, and iii) the enlargement of the developed pores (Wigmans, 1989; Williams and Reed, 2006). Since most of new pores are created as micropores, the data shown in Figure 3-5 suggests that micropores (ca. 55%-60% in total specific surface area) were produced within 60 minutes, whereas mesopores and macropores were also produced by pore enlargement. After 60 minutes, micropore surface area decreased, suggesting that pore enlargement was more effective, and the creation of new pores may have stopped.

These results suggest that KOH was used up after about 60 minutes. To verify if KOH is consumed completely, the theoretical weight loss (weight loss) for KOH activation of FC- S at 700°C was calculated based on the mass balance and the reactions (Eqs. 3-1 and 3-2) that may take place during activation (Lillo-Ródenas et al. 2003; Lee and Choi, 2000).

6KOH + 2C → 2K + 3H2 + 2K2CO3 3-1

Coke-S + 2KOH → K2S + Coke-O + H2O 3-2

Table 3-2 Calculated weight loss (weight loss) for KOH activation: 15 g KOH; 5 g coke; 700°C; KOH/coke = 3:1 Percentage (%) Weight loss (g) Carbon removal by reaction with KOH 0.86 S removal 7.37 - 0.12 = 7.25* 0.36 Volatiles removal 4.34 - 0 = 4.34** 0.22 Moisture removal 1.01 0.05 Ash in raw coke – ash in the product 3.47-0.66 = 2.81 0.14 Estimated systematic error 1 0.05 Oxygen gain -0.19*** Total weight loss 1.49 (1.49/5 = 29.8%) Measured weight loss after 60 minutes 31.2% * Content in fluid coke – Content in activation product (i.e. activated carbon) ** The actual volatile content in the final product was 21%. However, volatile matters in the product were mostly produced by KOH-carbon reaction, which was included in carbon removal through the reaction with KOH. Therefore, it was assumed that the volatile matters in raw coke were all removed. *** Oxygen added to activated carbon by replacing sulphur in coke

- 38 - From calculation, it was found that consuming 15 g of KOH (KOH/coke = 3:1) would lead to a theoretical coke weight loss of about 30 % (Table 3-2 with assumptions and other details of calculation given in Appendix B-2), lower than the actual weight loss, which supports the suggestion that KOH was completely consumed after about 60 minutes. In other words, the yield of activated carbon (or the weight loss of the coke) is determined by the amount of KOH added. Clearly, KOH activation is a fast process but consumes a large quantity of KOH. For the activation process to be economical, KOH needs to be recovered, regenerated and reused. The difference between the calculated result (29.8%) and the measurement (31.2%) may be attributed to the possibly underestimated loss during sample handling and other reactions which were not included in the calculation but discussed in Chapter 5.

Effect of activation temperature. Fixed activation time and the ratio of KOH and fluid coke were used in this series of experiments for which results are shown in Figures 3-6 and 3-7. The result shows that the weight loss increased with the increase in activation temperature from 600 to 800°C, and became stable afterwards (Figure 3-6). Similar results were found by Molina-Sabio and Rodriguez-Reinoso (2004). They activated olive stones with KOH and found that the weight loss at 500 and 700°C is low (75-80%), whereas temperatures of 850 and 900°C lead to higher weight loss (85-90%).

3000 50 BET surface area 2500 Weight loss 40

2000

/g) 30 2 1500 (m

BET 20 S

1000 (%) loss Weight

10 500

0 0 600 700 800 900 Temperature (°C)

Figure 3-6 Temperature dependence of SBET and weight loss in KOH activation (FC-S, KOH/Coke: 3:1, activation time: 1 hr, N2: 350 ml/min)

- 39 - It was evident in the previous section that KOH was completely consumed within the first 30 minutes at 700°C. For activation at temperatures over 700°C, if the activation mechanism does not change, the weight loss should be the same for all temperatures. However, compared with the calculation in Table 3-3, the weight loss at 600 °C was much lower than the calculated value based on complete KOH consumption, while the weight losses at 800 and 900°C were substantially higher. With the increase in activation temperature, the reaction rate most likely increases, which should cause a faster consumption of KOH. Therefore, the low weight loss at 600°C could be partially caused by incomplete KOH consumption due to lower rate of reactions. Moreover, incomplete removal of volatile matters could be another cause of the low weight loss at 600°C. The volatile content in the raw coke and activated carbons were measured at 900-950°C according to ASTM standard method (D3175), assuming all volatile matter leaves the carbon in this range of temperature. Volatile matter in the activated carbon could be the residual volatiles from the raw coke and/or volatile products from KOH-carbon reaction as well as other possible reactions that are discussed in Chapter 5. Volatile products are bound into the carbon structure by the cross linking reactions before reaching pyrolysis temperatures (Williams and Reed, 2006). Theoretically, the amount of volatile matter left in an activated carbon sample should decrease with the increase in activation temperature, which is supported by the experimental result: the volatile matter in the activated carbon produced at 600°C (36%) is much higher than that in the activated carbon produced at 700°C (21%). These amounts are also much higher than that in the raw coke (~5%), suggesting that the source is the activation reaction. At lower temperatures more volatile matter will stay in the activated carbon and give lower weight loss. Consequently, at high temperatures, the removal of more volatile matter from the coke may enhance the enlargement of existing pores and creation of more new pores, which could be the reason for the higher SBET obtained at high temperatures (Figure 3-6). This effect becomes insignificant at a temperature around 900°C, due to the fact that most of the volatile matter is removed at that temperature. In addition, there is the possibility that different chemical reactions occur at higher temperatures, which may also cause the change in the weight loss and SBET, such as the decomposition of K2CO3 which is produced by KOH- Carbon reaction (Eq.3-1). This is discussed in Chapter 5.

- 40 - Figure 3-7 shows that the proportion of micropores in KOH-activated carbon decreased from 58% to 12% when the activation temperature increased from 600 to 900°C, while the total pore volume constantly increased. It was also observed that the micropore volume increased when the temperature increased from 600 to 700°C, but decreased when the temperature increased further. It suggests that the range of activation temperatures may have two domains, each of them corresponding to a particular activation mechanism. For the temperature at 600-700°C, the pore volume increases mainly by the creation of new micropores which is evident from the increased micropore volume. For 800-900°C, the pore volume increases through the enlargement of the already existing micropores; this phenomenon is evidenced by the decreased micropore volume, i.e. increased volume of mesopore and macropore. Higher temperatures should accelerate diffusion of KOH and enhance its mobility, which may be beneficial for the process of pore enlargement. This finding is particularly significant, since it provides a means for producing highly porous carbon materials that consist of mainly meso- and macropores.

1.4 Total pore volume 1.2 Micropore volume

1.0

0.8

0.6 Volume (mL/g) 0.4

0.2

0.0 600 700 800 900 Temperature (°C)

Figure 3-7 Temperature effect on pore and micropore volume of KOH activation (FC-S, KOH/Coke: 3:1, activation time: 1 hr, N2: 350 ml/min)

Effects of KOH/coke ratio. Figure 3-8 shows an increase in both SBET and weight loss with increasing KOH/coke mass ratio, which was caused by the fact that both SBET and weight loss are dependent on the amount of carbon reacting with KOH. It has been generally accepted that KOH activation of carbonaceous materials is initially caused by a redox reaction, where carbon is oxidized to CO and/or CO2, and K2CO3 is a potential by-product,

- 41 - thus, pores are created when the products leave the carbon matrix (Lillo-Ródenas et al., 2003). At the same time, KOH is reduced to metallic potassium (Marsh et al., 1984). Metal potassium can intercalate between the graphene layers of the carbon structure, and the following destructive removal of the intercalate can force apart the graphene layers, developing porosity and resulting in the expansion of the interlayer spacing (Marsh and Rodríguez-Reinoso, 2006). With more KOH, more metal potassium is produced, more intercalation occurs, and more pores and interlayer spacing are created. The expanded interlayer spacing could be favourable for a better distribution of the remaining KOH into the carbon matrix, and enhance porosity development (Maciá-Agulló et al., 2007).

100 BET surface area Micropore SA Weight loss 2500 80 2000

/g) 60 2 1500 (m

BET 40 S 1000

500 20 Weight loss / micropore SA (%)

0 0 123 KOH/coke ratio

Figure 3-8 Effects of KOH/coke ratio on SBET, weight loss and micropore surface area (SA) percentage in KOH activation (FC-S, temperature: 700ºC, activation time: 1 hr, N2: 350 ml/min)

It is interesting that micropore SA decreased from 90% to 60% when the KOH/coke ratio increased from 1 to 3 (Figure 3-8). This decrease in micropore percentage indicates that with high KOH/coke ratio, the enlargement of existing pores contributes more to porosity development than the creation of new pores. When more KOH is mixed with fluid coke, more KOH will be available for pore enlargement and new pore development through the reaction between KOH and fluid coke. More metallic K produced from the KOH-coke reaction intercalates into the carbon matrix and breaks down the carbon structure, which could enhance the enlargement of micropores. Along with temperature control, this finding

- 42 - provides another method for controlling pore size distribution which is critical to many applications of activated carbon. For instance, a pollutant uptake process which is controlled by the diffusion of adsorbate would benefit from larger pore size.

3.3.1.3 Sulphur Removal during KOH activation

KOH can also react with sulphur in fluid coke, and remove it from the carbon matrix. Figure 3-9 shows the total sulphur content in KOH-activated cokes produced with different activation times. Fifteen minutes after reaching the set temperature, the sulphur content in activated coke decreased from 7.37 % to 0.17%. The further increase in activation time did not result in substantial decrease in sulphur content. On a molecular basis, the rate of sulphur removal was substantially faster than that of carbon removal. In other words, the sulphur- containing species seemed to be more reactive towards KOH than carbon. As a sulphur atom is substantially larger than carbon, the removal of a sulphur atom is expected to contribute at least the same or more to the development of porosity than a carbon atom. The observed rapid removal of sulphur would lead to the conclusion that sulphur is beneficial to KOH activation of high sulphur fluid coke, particularly when the activation time is limited.

0.20

0.15

0.10

0.05 Total S content (%) S content Total

0.00 15 60 120 Activation time (min)

Figure 3-9 Changes in total sulphur contents of KOH-activated coke with time

According to Lee and Choi (2000), the reaction between sulphur in coke and KOH can be expressed by Eq.3-2. Combining Eqs. 3-1 and 3-2, an overall reaction could be proposed as Eq. 3-3.

- 43 - 4KOH + Coke-S → K2S + 2K + CO2 + 2H2O 3-3

Eq. 3-3 suggests that the final sulphur product from this process was K2S, which was identified experimentally recently (Yuan et al. 2009). Moreover, during acid washing of

KOH-activation products, the formation of H2S was evident, likely via the following equation.

K2S + 2HCl = H2S + 2KCl 3-4

Table 3-3 compares the elemental composition of two types of fluid coke (FC-S and FC-I) and their KOH activation products using same activation condition (FCS-AC and FCI- AC, respectively). Porosity development during chemical activation is mainly caused by the release of volatile matter and reaction products from the carbon matrix. Results in Table 3-3 show that a large amount of carbon was removed after activation, which could be a major contributor to the porosity development. At the same time, over 95% of sulphur was removed. There was also a substantial increase in oxygen content after activation. XPS analysis confirms the substantial increase in oxygen content after one hour activation at 700°C; the oxygen content on the coke surface increased from 8.6 to 16.9%. It can be noted that the activated product of FC-S (which had a higher sulphur content than FC-I) had a larger SBET (2215 m2/g) than that derived from FC-I (2074 m2/g).

Table 3-3 Elemental composition on the surface of raw cokes and their KOH activation products (700°C, 1-hour, KOH/coke ratio = 3:1) C H O N S Percentage (%) Raw FC-S 82.74% 1.69% 6.36% 1.84% 7.37% FCS-AC (FC-S after activation) 79.95% 0.06% 17.54% 2.28% 0.17% Raw FC-I 87.22% 1.93% 3.43% 1.81% 5.61% FCI-AC (FC-I after activation) 82.82% 0.00% 14.74% 2.25% 0.19%

Weight (g) 5g raw FC-S 4.137 0.085 0.318 0.092 0.369 3.49g FCS-AC (30.2% weight loss) 2.790 0.002 0.612 0.080 0.006 5g raw FC-I 4.361 0.097 0.172 0.091 0.281 3.68g FCI-AC (26.3% weight loss) 3.048 0.000 0.542 0.083 0.007

- 44 - It should be pointed out that oxygen contents in Table 3-3 were determined by difference, assuming C, H, O, N and S are major elements in fluid coke and activated carbon, based on XPS analysis. Therefore, these amounts could include the amount of other trace elements which may also play roles in porosity development.

3.3.2 KOH-SO2 Activation of Fluid Coke

Although the method of KOH activation can be used to produce activated carbon with high SBET, the sulphur in raw coke is essentially removed. If the sulphur in raw coke can be retained or recovered, not only may environmental pollution (e.g. sulphuric gas emission) be reduced, but also the SIAC production may be more economical. This section examines the feasibility of activating the coke using KOH and SO2 simultaneously.

3.3.2.1 Morphology of KOH-SO2 Activated Carbon

Figure 3-10 shows the SEM images for the pore structure of KOH-SO2 activation product (S-KS-4). This particular sample has a BET surface area of 2108 m2/g and 1.11 mL/g of pore volume. As shown in Figure 3-10a, the sample has the inherent layered structure with micron-sized cracks, which enhances the accessibility of internal pores. Figure 3-10b is an enlargment, showing a highly porous structure. Pores in the meso-pore size range (2-50 nm) are clearly visible, while for micropores a higher resolution is required.

A B

Figure 3-10 SEM images of a SIAC produced from KOH-SO2 simultaneous activation: A. at magnification of 1.5 K, B. at magnification of 300 K

- 45 - 3.3.2.2 Effects of Activation Condition on Activated Carbon Properties

Effect of activation time. SBET and sulphur content of activated coke continued to increase with activation time (Figure 3-11 and 3-12). While both KOH and SO2 could contribute to the development of porosity, only SO2 was able to add sulphur to the activated carbon. The change in SBET was small and different from that observed for the KOH-only activation where the supply of sole activating agent (KOH) was limited. In KOH-SO2 activation, however, there was a continued supply of activating agent (SO2). Since KOH was consumed rapidly and likely used up after one hour, SO2 should be responsible for the change in SBET in the later stage of activation. The substantial increase in sulphur content after the first hour supports this point.

Loading sulphur on activated carbon could cause a decrease in SBET due to the blockage of pores by products from the SO2 and carbon reaction (Chen, 2002). Interestingly, there was no significant change in SBET while there was a significant drop in micropore SA after one hour when KOH was mostly consumed. Apparently, SO2 was able to penetrate deeper into the inner part of coke particles through the pores created by KOH, creating additional new pores and enlarging the existing micropores. The enlargement of existing pores is consistent with the observed decrease in micropore volume (0.41 to 0.31 mL/g). Moreover, the sulphur products from SO2 seemed unable to deposit on the carbon surface and block micropores. However, further studies are needed to verify this, although there was evidence that the presence of KOH might change the fate of SO2 (details in Chapter 5).

2000 Weight loss Micropore SA BET surface area 80

1500 60 /g) 2

(m 1000 40 BET S

500 20 Weight loss/micropore SA (%) loss/micropore Weight 0 0 12 Activation time (hr)

Figure 3-11 Effects of activation time on SBET, weight loss and micropore SA percentage in KOH-SO2 activation (Raw coke: FC-S, Temperature: 700°C, KOH/coke: 3:1, SO2: 30%)

- 46 - 10 Total S content 8

Total S content (%) content S Total 2

0 12 Activation time (hr)

Figure 3-12 Time dependence of sulphur content in KOH-SO2 activation (Raw coke: FC-S, Temperature: 700°C, KOH/coke: 3:1, SO2: 30%)

Effect of temperature. As shown in Figure 3-13, when the temperature was increased 2 from 600 to 900°C, the SBET significantly increased (to 2500 m /g), and the weight loss increased and reached 67% at 900°C. The percentage of micropore SA decreased with the increase in activation temperature, particularly from 700 to 800°C. This behaviour is very similar to that observed for KOH-only activation, which was attributed to the creation of more new pores at lower temperature and the enhanced enlargement of existing pores at higher temperature.

3000 BET surface area Weight loss Micropore SA 80 2500

2000 60 /g) 2

(m 1500 40 BET S 1000

20 500 Weight loss/micropore SA (%)

0 0 600 700 800 900 Activation temperature (°C)

Figure 3-13 Effects of activation temperature on SBET, micropore SA and weight loss of KOH-SO2 activation (FC-S, KOH/coke ratio of 3:1, 1-hr activation, 30% SO2)

- 47 - Compared the SBET and weight loss of KOH-SO2 activated carbon with that of KOH- activated carbon (Figures 3-14 and 3-15), it was found that KOH-SO2 activated carbon has lower SBET but higher weight loss. The increase in weight loss suggests that SO2 had participated in the oxidation of carbon, even thought there is a possibility that SO2 may directly react with KOH and reduce the amount of KOH available for the coke. The reaction between KOH and SO2 induces production of K2SO3 and H2O, and K2SO3 can be further oxidized to K2SO4 (Lee and Park, 2002). Detailed discussion of KOH-SO2 reaction is in Chapter 5.

3000 KOH activation 2500 KOH-SO2 activation

2000 /g) 2 1500 (m BET S 1000

500

0 600 700 800 900

Activation temperature (°C)

Figure 3-14 Comparison of the SBET of KOH and KOH-SO2 activated carbon (FC-S, KOH/coke ratio of 3:1, 1-hr activation)

80 KOH activation KOH-SO2 activation 70

30 Weight loss(%) 20

0 600 700 800 900 Activation temperature (°C)

Figure 3-15 Comparison of the weight loss during KOH and KOH-SO2 activation (FC-S, KOH/coke ratio of 3:1, 1-hr activation)

- 48 - Since KOH removes sulphur from fluid coke as observed in KOH-activation, it is obvious that only SO2 is responsible for maintaining the sulphur content of fluid coke or adding sulphur to it. Total sulphur content decreased with the increase in activation temperature (Figure 3-16), which is in agreement with a previous study that sulphur-carbon bond becomes unstable at temperatures higher than 600°C (Furimsky, 2000). At higher temperatures more sulphur compounds leave the carbon matrix.

9 8 7 6 5 4 3 2 Total sulphur content (%) 1 0 raw coke 600 700 800 900 Activation temperature (°C)

Figure 3-16 Temperature dependence of total sulphur content in KOH-SO2 activation (FC-S, KOH/coke: 3:1, Activation time: 1 hr, SO2: 30%)

Effect of KOH/coke ratio. As shown in Figure 3-17, the increase in KOH/coke ratio resulted in an increase in SBET, which confirms the major role that KOH plays in pore development despite the possible reactions between KOH and SO2. Micropore SA percentage remained almost constant with the increase in KOH/coke ratio from 1:1 to 2:1, and decreased from 78% to 60% when KOH/coke ratio reached 3:1. This trend is different from that observed for KOH activation where micropore percentage continually decreased with the increase in KOH/coke ratio. It implies that SO2 plays a role in this change. One possibility is that at KOH/coke ratio of 1:1, a substantial proportion of KOH reacts with SO2, and leaves a small amount of KOH available for new pore creation via reacting with coke, 2 consistent with the observed low SBET (431 m /g) and weight loss. When the KOH/coke ratio increases to 2:1, more new pores are created, although there may not be enough KOH available for pore enlargement. With further increase in KOH/coke ratio, more metallic K

- 49 - produced from KOH-coke reaction intercalates into the carbon matrix and break down carbon structure, which enhances the enlargement of micropores and causes the drop of micropore percentage. However, no evidence could be found at this point, and this unusual trend in weight loss and micropore SA percentage is intriguing, thus, more in-depth studies are needed.

2000 100 BET surface area Weight loss Micropore SA 80 1500

/g) 60 2 1000 (m

BET 40 S

500 20 Weight loss/Micropore SA (%) loss/Micropore Weight

0 0 123 KOH/coke ratio

Figure 3-17 Effects of KOH/coke ratio on SBET, weight loss and micropore SA percentage in KOH-SO2 activation (temperature: 700°C, activation time: 1 hr, SO2: 30%)

No significant change was found in sulphur content (Figure 3-18) with different KOH/coke ratio, which confirms the effective role of KOH in porosity development and its inability to add sulphur. Sulphur content of KOH-SO2 activated carbon depends on the relative rate of two processes: 1) conversion of organic sulphur in the raw coke by KOH into water soluble inorganic species such as potassium sulphate and sulphide, which seems to be a fast process that removes sulphur, and 2) carbothermal reduction of SO2, which adds sulphur to the activated carbon. The amount of sulphur added should be determined by activation conditions such as temperature and activation time.

- 50 - 10

Total S content (%) 2

0 1 2 3

KOH/coke ratio

Figure 3-18 Effects of KOH/coke ratio on total sulphur content in KOH-SO2 activation (temperature: 700°C, activation time: 1 hr, SO2: 30%)

3.3.2.3 Comparison between Two Fluid Cokes

Table 3-4 shows the differences in elemental properties of FC-S and FC-I measured by elemental analyzer (for total amount) and XPS (for surface analysis). The higher oxygen content on the coke surface indicates that fluid coke may be oxidized since it has been exposed to the air. It should be pointed out that although sample FC-S was collected two years earlier than FC-I, its oxygen content on the surface is lower than that on the FC-I surface. Therefore, the higher oxygen content on the FC-I surface and its large difference in oxygen content between the bulk and the surface may suggest that FC-I could be oxidized easier than FC-S.

Table 3-4 Contents of C, O and S in raw coke FC-S and FC-I C (%) O (%) S (%) FC-S Total amount 82.7 6.4 7.4 On surface 85.1 8.6 3.6 FC-I Total amount 87.2 3.4 5.6 On surface 86.1 9.8 1.8

As shown in the following figures, overall, the behavior of both cokes in KOH-SO2 activation was quite similar in terms of the dependence on activation conditions. In most cases, however, the SIACs produced from FC-I had slightly higher SBET than that from FC-S (Figures 3-19 and 3-20), which is consistent with the inference that FC-I may be easier

- 51 - oxidized than FC-S. The micropore % of SIACs from FC-I seemed higher too (Figures 3-21 and 3-22), which may suggest that the penetration of activating agent into the inner part of the FC-I coke is easier. As shown in Table 3-1, the raw FC-I coke is more porous than FC-S. However, the weight loss of FC-I seems consistently lower than that of FC-S (Figure 3-23 and 3-24), which may be attributed to the lower volatile and ash contents of FC-I (Table 3-1). After activation the ash was removable by acid washing (Chen, 2002).

2500 SIACs from FC-S SIACs from FC-I 2000

/g) 1500 2 (m

BET 1000 S

500

0 600 700 800 Temperature (°C)

Figure 3-19 SBET of SIACs produced from FC-S and FC-I using KOH and SO2 activation at different temperatures (KOH/coke: 3:1; activation time: 1 hr)

2000 SIACs from FC-S SIACs from FC-I 1600

1200 /g) 2 (m

BET 800 S

400

0 123 KOH/coke ratio

Figure 3-20 SBET of SIACs produced from FC-S and FC-I using KOH and SO2 activation with various KOH/coke ratios (temperature: 700°C; activation time: 1 hr)

- 52 - SIACs from FC-S SIACs from FC-I 80 )

MIcropore volume (% 20

0 600 700 800 Temperature (°C) Figure 3-21 Micropore volume of SIACs produced from FC-S and FC-I using KOH and SO2 activation under different temperatures (KOH/coke: 3:1; 1-hr activation)

100 SIACs from FC-S SIACs from FC-I 80

Micropore volume (%) 20

0 123 KOH/coke ratio

Figure 3-22 Micropore volume of SIACs produced from FC-S and FC-I using KOH and SO2 activation with various KOH/coke ratios (700°C, 1 hr)

70 SIACs from FC-S SIACs from FC-I 60

Weight loss (%) 20

0 600 700 800 Temperature (°C)

Figure 3-23 Weight loss of FC-S and FC-I during KOH and SO2 activation under different temperatures (KOH/coke: 3:1, 1 hr)

- 53 - 40 From FC-S From FC-I

20 Weight loss (%) 10

0 123 KOH/coke ratio

Figure 3-24 Weight loss of FC-S and FC-I during KOH and SO2 activation with various KOH/coke ratios (temperature: 700°C, activation time: 1 hr)

The sulphur content of SIACs from FC-I was much lower than that from FC-S (Figures 3-25 and 3-26). Given the lower initial sulphur content and more porous carbon matrix of FC-I, the lower sulphur content in its activation product is expected.

9 8 SIACs from FC-S SIACs from FC-I 7 6 5 4 3

Sulphur content (%) content Sulphur 2 1 0 600 700 800 Temperature (°C)

Figure 3-25 Total sulphur content in SIACs produced from FC-S and FC-I using KOH-SO2 activation at different temperatures (KOH/coke: 3:1, 1 hr)

- 54 - 10 SIACs from FC-S SIACs from FC-I 8

4 Sulphur content (%) 2

0 123 KOH/coke ratio

Figure 3-26 Total sulphur content of SIACs produced from FC-S and FC-I using KOH-SO2 activation with various KOH/coke ratios (temperature: 700°C, activation time: 1 hr)

3. 4 CONCLUSIONS

It is feasible to activate oil-sands fluid coke using KOH. The highest SBET achieved was 2 2 2500 m /g, compared with the literature value of 370 m /g. The SBET of KOH-activated carbon increased with the increase in temperature (600 - 900°C). KOH/coke ratio (1:1 to 3:1) and activation time (15 – 180 min). Pore size distribution was found to be controllable. An increase in activation temperature from 600 to 900 °C lowered the volume percentage of micropores from 58% to 12%, while the increase in KOH/coke ratio from 1:1 to 3:1 resulted in a drop from 80% to 51%, without lowering total SBET.

The development of porosity seems to be controlled by the availability of KOH in the system. When the supply of KOH is sufficient, both creation of new pores and enlargement of existing pores are sustainable, resulting in the increase in SBET and decrease in micropore percentage. Under the studied conditions, even when KOH/coke ratio was 3:1, KOH was the limiting reagent, and ultimately controlled the yield of activation products.

Sulphur in the coke was more susceptible to the reactions with KOH than carbon, so that KOH was effective in removing sulphur from the coke. On a molecular basis, the rate of sulphur removal was substantially faster than that of carbon removal, suggesting that the high sulphur content in the coke may be beneficial to porosity development.

- 55 - SIACs were produced from fluid coke using KOH and SO2 simultaneously, for the first 2 time. The highest SBET achieved was over 2500 m /g, while the highest sulphur content was

8.1%. The properties of KOH-SO2 activated carbon were temperature and KOH/coke ratio dependent. The increase in activation temperature (600 – 900 °C) resulted in a higher SBET (1220 to 2500 m2/g), but lower micropore surface area percentage (70% - 34%) and lower sulphur content (7.3% - 3.5%). Increasing KOH/coke ratio from 1 to 3 resulted in an increase 2 of SBET from 430 to 1430 m /g and insignificant change in total sulphur content.

SO2 was effective in adding sulphur to carbon via carbothermal reduction of SO2, but it was less effective in creating pores than KOH. The temperature could affect sulphur addition positively or negatively, by accelerating the carbothermal reduction or by enhancing volatilization of reduced sulphur products. Consequently, the amount of sulphur added was controllable in the KOH-SO2-coke system.

- 56 - CHAPTER 4 SPECIATION OF SULPHUR IN FLUID COKE AND ITS ACTIVATION PRODUCTS

4.1 INTRODUCTION

In order to understand the roles of sulphur in coke activation and in mercury capture, the forms of sulphur in both raw fluid coke and SIACs have to be identified. However, the characterization of sulphur within a carbon matrix is a challenging task, particularly when sulphur is organic in nature. The commonly used wet chemistry method, ASTM D2492 and D3177, can only determine the amount of total sulphur, pyrite, sulphate, and, by difference, the organic sulphur in coal or coke. Thus, there are significant uncertainties in the quantification of organic sulphur, and the forms of organic sulphur cannot be identified (Taghiei et al., 1992; Davidson, 1994). XPS has been used to characterize sulphur in coal and coke (Kelemen et al., 1990; Mateos and Fierro, 1996; Liu et al., 2007). However, for non- conductive materials, e.g. coal and coke, XPS is prone to charge effects, thereby overestimating the presence of oxidized species (Olivella et al., 2002). In spite of the importance of sulphur speciation, the quantitative characterization of sulphur species in fluid coke and fluid coke-derived activate carbon has not been achieved.

Compared to the XPS technique, the first spectrum of which was recorded in 1907, X- ray absorption near edge structure (XANES) spectroscopy is a relatively new technique, which was first introduced in 1980. XANES has since been used by several groups of researchers as an aid to characterize sulphur in coal, soil, and activated carbon. Huffman et al. (1989) were among the early users characterizing sulphur species in coal with this technique. In their studies, samples derived from nine types of coal were examined, and sulphur K-edge XANES spectra for these samples were recorded. By least-squares peak fitting these spectra and correlating fitting results to the spectra of dibenzothiophene, benzo[b]thiophene, dibenzyl disulphide, thiophene-3-carboxylic acid, thiophene-2-acetic acid and thioacetamide, sulphur forms in these samples were quantitatively identified. The authors commented that their results were encouraging, yet it is clear that systematic studies of a wider range of standard sulphur compounds were desirable.

- 57 - Using XANES, Mehdi et al., (1992) investigated the transformation of sulphur species in coal during pyrolysis and oxidation. In situ sulphur K-edge measurement was performed on three types of coals, and the results showed that under relatively slow pyrolysis and oxidation conditions, degradation of organic disulphidic and sulphidic sulphur started at as low as 300°C, pyrrhotite was formed from pyrite at/over 400°C, and thiophenic sulphur remained stable over 500°C. In their study, least-squares peak fitting was applied to analyze the XANES spectra, and they stated that the accuracy of their method in the resulting sulphur percentage was ±5-10 %.

As suggested by Huffman et al. (1989), systematic studies of a wider range of standard sulphur compounds were needed so that the application of XANES in sulphur characterization could be more convincing. In 1996, Kasrai et al. made an effort to systematically study the presence of inorganic and organic sulphur compounds in coal using a wide range of standard sulphur compounds. Eighteen standard sulphur compounds were used and their XANES spectra were qualitatively interpreted. Total Electronic Yield (TEY) and Fluorescence Yield (FY) techniques were applied for recording the S L-edge and S K- edge spectra of coal samples, and described in detail. They concluded that the S L-edge TEY and FY techniques gave a sensitive probe for sulphur speciation in coal with an estimated error of ~10-15 %.

Sarret et al. (1999) used sulphur K and L-edge XANES spectroscopy to study asphaltene samples. The study illustrated the advantages of XANES spectroscopy as a selective probe for determining sulphur species in a complex system, e.g. asphaltenes. Furthermore, they found that sulphur L-edge spectroscopy was more sensitive to the major forms of reduced sulphur, while K-edge spectroscopy was suitable for the quantification of oxidized sulphur compounds.

Sulphur K-edge XANES spectroscopy was also used to characterize the organic sulphur compounds in humic substance extracts from mineral soils (Solomon et al., 2003). The technique provided information about the link between sulphur oxidation states, bioavailability of organic sulphur moieties and the shifts that occur following land use changes. However, it was not sensitive enough to differentiate betrween the reduced sulphur species such as sulphide, disulphide and thiols.

- 58 - Feng et al. (2006) studied the dependence of vapour phase mercury uptake on sulphur forms on sulphurized carbon surfaces. The sulphur forms deposited on the carbon surface were analyzed using XPS and XANES. The XANES analysis allowed the authors to identify sulphur forms, such as elemental sulphur, thiophene, sulphoxide, and sulphate.

Although it has been widely accepted that XANES is the most effective technique for determining organic sulphur in coal (Davidson, 1994), XANES has not been applied to characterize sulphur species in fluid coke and its activation products. The purpose of this study was to examine if the sulphur K-edge XANES could be suitable for identifying and quantifying sulphur species in fluid cokes and their activation products, SIACs. A procedure of fitting XANES spectra has to be established, since data analysis of this technique still needs to be improved. The outcome of this study will be used to better understand sulphur transformation during activation and the roles of sulphur in fluid coke activation and mercury removal.

4.2 EXPERIMENTAL

4.2.1 Materials and Sample Preparation

Two types of fluid coke were used: FC-S and FC-I. Fluid coke activation products (i.e.

SIACs) were produced using two processes: i) KOH activation followed by SO2 treatment

(e.g. SIAC-I) and ii) KOH and SO2 simultaneous activation (e.g. SIAC-S). Table 4-1 shows the activation conditions of these samples. In the first process, the fluid coke was mixed with

KOH and activated at 700°C for one hour (i.e. KOH-activation). After activation, SO2 was used to add sulphur to the KOH-activated fluid coke in order to produce SIACs. In the second process, fluid coke was mixed with KOH and activated with 30% of SO2 (70% of N2) passed through the reactor. Detailed activation processes were described in Chapter 3. The purpose of using two processes was to produce SIACs with more sulphur forms in order to examine what forms of sulphur that XANES can distinguish.

- 59 - Table 4-1 Activation processes and conditions of SIAC samples

SIAC Raw coke Temperature (°C) KOH/Coke Time (hr) Total S (%) SIAC-S FC-S 700 3:1 1 5.14 SIAC-I FC-I 700 3:1 1+1* 11.14 * Sample prepared by KOH activation (I hour) followed by SO2 treatment (1 hour)

4.2.2 Model Sulphur Compounds and Model Sulphur Compound Mixtures

In total, 25 sulphur model compounds were analyzed in this study. Some of them were provided by the Canadian Synchrotron Radiation Facility, while others were purchased from Sigma. The structures of these compounds are shown in Table 4-2. All these compounds were in the highest available purity and used without further treatment.

A model sulphur compound mixture was prepared, given that sulphur in fluid coke and SIACs are likely in a mixed form. The mixture was prepared by adding 0.1g of sulphur model compounds and 0.1 g of graphite in about 10 mL of deionized water to form slurry. After thorough mixing, the slurry was dried at room temperature (~25°C) under nitrogen protection for 24 hours. The dried mixture was ground to fine particles with particle size less than 200 mesh (74µm).

Table 4-2 Structures of sulphur model compounds used in this study Name Formula Structure

Elemental Sulphur S S8

DL-cysteine C3H7NO2S HS OH H2N

1-Phenyl-1H-tetrazole-5-thiol C7H6N4S

Thiophene-3-acetic acid C6H6O2S O S

OH 3-(2-thienyl) acrylic acid C7H6O2S S O

- 60 - Name Formula Structure

NH2 OH 3-(2-thienyl)-DL-alanine C7H9NO2S S O O

S OH H2N L-Cystine C6H12N2O4S2 NH2 HO S

S Benzyl disulphide C14H14S2 S

DL-Methionine C5H11NO2S

CH3 S-methyl-Lcysteine C4H9NO2S HO S NH2 S

4,4'-thiodiphenol C12H10O2S HO OH

Poly (phenylene sulphide) Poly (C6H4S) H3C S CH3

S-benzyl-L-cysteine C10H13NO2S S OH H2N

1,2-benzodiphenylene sulphide C16H10S S

H N Phenothiazine C12H9NS S S

Thianthrene C12H8S2 S NH2 O OH DL-Methionine sulphoxide C5H11NO3S S

CH3 O O

S Benzyl sulphoxide C14H14OS

O O S OH Anthraquinon-2-sulphonic acid C14H8O5S O

- 61 - Name Formula Structure

Diphenylamine-4-sulfonic acid, NaC H NO S sodium salt 12 10 3

DL-Methionine sulphone C5H11NO4S

O Sodium sulphite Na2SO3 NaO S O Na O

H3C Sodium n-dodecyl sulphate C12H25NaO4S O S ONa O O

Sodium sulphate Na2SO4 NaO S O Na O O

Sodium thiosulphate Na2S2O3 NaSS O Na O

4.2.3 Analytical Techniques

4.2.3.1 XANES

XANES analyses were performed at the Canadian Synchrotron Radiation Facility (CSRF) situated on the 1GeV electron storage ring, at Aladdin, University of Wisconsin. X- ray absorption spectra of Total Electron Yield (TEY) and Fluorescence Yield (FY) at the sulphur K-edge were recorded. The sampling depth of TEY mode at K edge of sulphur ranges from 4~50 nm depending on the matrix, which means it probes near-surface structure and can only detect the species on substrate surface. The FY mode of detection has a greater penetration, and the maximum analysis depth is larger than 50 ~ 800 nm (Kasrai et al., 1996; Saxena et al., 2001, Sarret et al., 2002; Frazer et al., 2003; Nichollsa et al., 2004). The K- edge data were recorded using the double-crystal monochromator (DCM) beamline with a resolution of ~0.7 eV. The TEY spectra at the S K-edge were recorded directly by monitoring the current from the sample, and a microchannel plate (MCP) detector was used for FY

- 62 - measurements.

At least two individual scans were recorded for each sample and digitally averaged to obtain a spectrum for analysis. The TEY spectra were used for quantitative estimation, since this technique does not suffer from self-absorption and thus no correction is required. The FY spectra were used to observe the difference in the form of sulphur compounds on the sample surface and in the bulk.

All spectra were analyzed using the software, Athena, following the suggested procedure (Ravel and Newville, 2005) with some conditions and constraints in order to obtain meaningful fits. First, for all spectra, the energy scale at the K-edge was calibrated by setting the strong absorption peak of elemental sulphur at 2472.0 eV. Second, the background was subtracted from all spectra using a linear fit of pre- and post- XANES contributions. The spectra were then normalized with respect to the individual step heights (or background) caused by the transition of ejected photoelectrons to the continuum. For FY spectra, self- adsorption correction was performed before data fitting.

There are two distinct approaches to fitting sulphur XANES spectra. One involves least-squares fitting based on a linear combination of XANES spectra of known sulphur species (i.e. linear combination fitting), the other is more generic and involves least-squares fitting of the spectrum to combinations of peak functions (e.g. Gaussian and Lorentzian) and background functions (i.e. peak fitting). The linear combination uses model compound spectra to construct synthetic spectra, which are then compared with that of the sample. In peak fitting, each spectrum was fitted with a number of Gaussian peaks and one or two arctangent steps. The Gaussian peaks represent the s → p electronic transitions and arctangent step functions represent the transition of ejected photoelectrons to the continuum. Although peak fitting is fairly straightforward in providing the information of peak composition in XANES spectra, it is necessary to use a number of conditions and constraints to obtain meaningful fits. The full width at half-maximum (FWHM) of each Gaussian component for S was loosely constrained within 1.0 – 2.5 eV. The FWHM is an expression of the extent of a function, given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value.

- 63 - Linear combination fitting is best when the researcher has the knowledge of the likely sulphur forms contributing to the spectrum, so that a proper set of standard species can be selected. However, in many situations, especially in fuel and environmental samples, one peak in the spectrum can be derived from a variety of sulphur compounds with similar functionality. When using the linear combination fitting, some sulphur forms may be missed if a wrong set of standard species are chosen. Therefore, in such cases peak fitting method is more suitable. The major drawback of peak fitting is the fact that one needs to assign the functional peaks to specific sulphur peaks which represent certain sulphur forms. The problem is that for one peak there may be several possible corresponding sulphur forms (Section 4.3.1). Moreover, where to locate the edge-steps relative to the peaks can be problematic, and the location of edge-steps can significantly influence the position and area of functional peaks.

Peak fitting has been widely applied to characterize sulphur forms in coal (Huffman et al., 1989 and 1991; Mehdi Taghiei et al., 1992; Olivella et al., 2002; Wiltfong et al., 2005), while application of linear combination fitting has not been studied so far. In this study, a fitting procedure that combines peak fitting and linear combination fitting was used. In addition, Principal Component Analysis was incorporated when analyzing sulphur forms in a series of SIAC samples that likely have the same sulphur forms but in various amounts. The step-by-step procedure of analyzing sulphur XANES K-Edge spectra is summarized below:

1. Merge two or more spectra collected from the same sample into one representative spectrum using the software: Athena in IFEFFIT XAS analysis software package.

2. Determine the position of pre-edge and post-edge in the spectrum, and normalize the spectrum by subtracting pre-edge and post-edge background. All spectra need to be normalized and saved as normalized spectrum file. The spectra in the following text all refer to normalized spectra.

3. Run least-squares peak fitting method (Software: Athena or SixPACK in IFEFFIT XAS analysis software package) to fit the spectrum.

3-1 Load spectra to the software

3-2 Open the peak fit window

- 64 - 3-3 Set parameters, including the peak number, function, position, area and height. Peak number has to be constrained, although the more peaks are used; the better fit can be obtained. A full width at half maximum (FWHM) rule has to be followed. In this study, five peaks were the maximum, and FWHM values were lower than 2.5 eV in all fittings.

3-4 Adjust parameters until a best fit is obtained. A high χ2 value usually means a good fitting.

3-5 Based on the peak positions, assign each peak to a possible sulphur form. There could be more than one form in respect to one peak. A collection of possible sulphur forms in a spectrum can be obtained after peak fitting.

4. Run linear combination fitting using the standard spectra of sulphur species identified through peak fitting (Software: Athena). Different combinations of selected sulphur species are tested with the combination fitting, the combination with lower χ2 value is chosen. The number of species in a spectrum was constrained to be lower than four.

5. Report analysis results based on linear combination fitting

The software calculated all combinations of these possible candidate spectra, and the fitting with low chi-square (χ2) was considered. The probability of chance occurrence of a given χ2 for an experiment with d degrees of freedom can be calculated. For same degree of freedom, a low χ2 means a higher probability.

However, using χ2 to evaluate the quality of a single fit has limitations. First, it was difficult to quantify the degree of freedom in the XANES spectrum. That number was certainly less than the number of data points measured. Nonetheless, when the chi-square was evaluated, the number of data points was used as the number of measurements. Second, the software cannot evaluate a measurement uncertainty for the XANES measurement. A value of one was used for uncertainty in the equation for χ2. Therefore, it means that χ2 tends to be very small, and as a result, it is not effective to evaluate the quality of a single fit. Relative changes in χ2 between each fitting are probably meaningful (Ravel, 2008); therefore, the change in χ2 was used as the indicator of the goodness of the fitting.

- 65 - For SIAC samples produced from the same procedure under different conditions, Principal Components Analysis (PCA) was conducted prior to linear combination fit using software SixPACK, developed by Sam Webb at the Stanford Synchrotron Radiation Laboratory. PCA uses the redundant information in a set of multivariate data to pick out patterns (relationships) in the variables and reduce the dimensionality of the data set without a significant loss of information. By using PCA, it was assumed that the SIAC samples prepared from same activation process may have similar sulphur forms, even though the activation conditions (such as temperature, time and KOH/coke ratio) were varied. It should be noted that PCA is a supplementary method to constrain and simplify the data analysis process, which is not necessarily applied. PCA can also verify if the right standard sulphur compounds were chosen. When this was needed, the following steps were applied:

1. Load spectra of the sample to SixPACK, and run component analysis. This gives the composite of a spectrum, i.e. the necessary components to form the spectrum.

2. Import the standard sulphur spectra to match the components. The software can identify which standard sulphur species may be a component which contributes to form the sample spectrum.

3. After matching all standard sulphur spectra, a collection of possible sulphur species is obtained and it can be combined with the collection of sulphur forms from peak fitting (see step 3-5) to run linear combination fitting.

It should be pointed out that analyzing XANES spectrum of sulphur species is a complex process and often requires the experience that can only be gained by hands-on practice.

4.2.3.2 X-ray photoelectron spectroscopy (XPS)

XPS (Thermo Scientific K-Alpha) was employed to characterize sulphur compounds in the coke and activated carbon, in order to compare the result with that of XANES. Survey and high resolution spectra of S (2p) were recorded using the XPS employing monochromatized Al K_X-rays. Binding energies (BEs) of peaks in the spectra were referred to the BE of C (1s) peak at 285.0 eV.

- 66 - 4.3 TOTAL ELECTRON YIELD (TEY) RESULTS

4.3.1 Model Compounds

Among the 25 model compounds, 21 are organic sulphur compounds, and belong to four categories- i) alkyl and aryl sulphides, ii) six-membered ring heterocyclic sulphur, iii) thiophenic sulphur, and iv) organic sulphur oxyanions. Inorganic model compounds include elemental sulphur, sodium thiosulphate, sulphite and sulphate. Sulphur K-edge XANES of 25 model compounds were recorded, and some spectra of these compounds are shown in Figures 4-1a and b. The zero of energy is taken at the first peak in the differential of the spectrum of elemental sulphur, and thus the relative energy is the absorption energy relative to elemental sulphur. The first large peak in the spectrum indicates the occurrence of an s → p transition (i.e. the edge, or “white line”). The transition of the photoelectron from the 1s level to hybridized 3p level reflects the oxidation state of the sulphur compound. The subsequent broader and smaller peaks in the range of 5-30 eV above the edge are formed from low-energy scattering resonances, which are features for a specific molecular structure. Therefore, each sulphur compound has a unique spectrum which can be used as a fingerprint for the electronic nature of the sulphur compound, and for distinguishing sulphur forms in pure compounds.

10 Sodium sulphate

8 Sodium thiosulphate

6 Sodium sulphite

Normalized absorption 4

2 Elemental sulphur

0 -10 0 10 20 30 40 Relative energy (eV)

Figure 4-1(a) Sulphur K-edge XANES spectra of inorganic model compounds

- 67 - 45

DL-methionine sulphone 35

30 anthraquinon-2-sulphonic acid

25 benzyl sulphoxide

20 Thianthrene Benzonaphthothiophene

Normalized Absorption Normalized 15 Poly (phenylene sulphide) 3-(2-thienyl) acrylic acid 10 thiophene-3-acetic acid DL-cysteine 5 Benzyl disulphide 0 -10 0 10 20 30 40 Relative energy (eV)

Figure 4-1(b) Sulphur K-edge XANES spectra of organic sulphur model compounds Table 4-3 lists the first inflection energy in the sulphur K-edge XANES spectra for all these model compounds. The first inflections of oxidized sulphur compounds are notably higher than those of reduced sulphur, with a total energy span of 10.1 eV from 2471.7 eV (elemental sulphur) to 2481.8 eV (sodium sulphate). Based on the electronic oxidation states recorded in the present study, the sulphur oxidation states and their associated sulphur species can be grouped into: i) reduced and elemental sulphur (2471.7 ~ 2475.0 eV), including: elemental sulphur, sulphide, disulphide, thiol and thiophene, and ii) moderately oxidized sulphur (2475 ~ 2481 eV), which include sulphoxide, sulphone, sulphonate, sulphite and thiosulphate, and iii) highly oxidized sulphur (> 2481 eV), representing sulphates.

The first inflection energy can be readily used to distinguish the forms of sulphur in pure compounds. However, some sulphur compounds may have similar absorption energies. For instance, thiophene-3-acetic acid, benzonaphthothiophene and 3-(2-thienyl)-DL-alanine have identical absorption energies of 2473.0 eV, since they are all thiophenic sulphur, despite their different atomic environment. Elemental sulphur and L-Cystine have same absorption

- 68 - energy of 2471.7 eV, yet they have different oxidation states. A chart was plotted to show the overlap of the absorption energies (Figure 4-2). The chart suggests that there are inherent limitations in distinguishing sulphur forms by XANES based on first inflection energy only. In this case, analyzing the complete XANES spectra of individual sulphur compounds could be beneficial.

Table 4-3 K-edge first inflection energies of sulphur compounds used in this study Compound First inflection energy (eV) Elemental Sulphur 2471.7 L-Cystine 2471.7 Benzyl disulphide 2472.0 1-Phenyl-1H-tetrazole-5-thiol 2472.2 S-benzyl-L-cysteine 2472.3 DL-cysteine 2472.3 DL-Methionine 2472.7 S-methyl-Lcysteine 2472.8 Thiophene-3-acetic acid 2473.0 Benzonaphthothiophene 2473.0 3-(2-thienyl)-DL-alanine 2473.0 Thianthrene 2473.2 3-(2-thienyl)acrylic acid 2473.2 Phenothiazine 2473.4 Poly (phenylene sulphide) 2473.7 4,4'-thiodiphenol 2474.0 Benzyl sulphoxide 2475.0 DL-Methionine sulphoxide 2475.4 Sodium sulphite 2477.6 DL-Methionine sulphone 2479.0 Sodium thiosulphate 2480.1 Diphenylamine-4-sulphonic acid 2480.2 Anthetaquinon-2-sulphonic acid 2480.4 Sodium n-dodecyl sulphate 2481.4 Sodium sulphate 2481.8

- 69 - sulphate sulphite sulphonate thiosulphate sulphone sulphoxide thiophene sulphide thiol disulphide elemental sulphur pyrite 2470 2472 2474 2476 2478 2480 2482 2484 Energy, eV Figure 4-2 XANES K-edge absorption energies of different sulphur compounds

4.3.2 Mixture of Sulphur Compounds

In order to evaluate the potential of XANES method in identifying sulphur species in carbonaceous materials, mixture of pure sulphur compounds with graphite was analyzed using XANES. Least-squares peak fitting was used to fit the spectra. Briefly, the spectrum was first normalized by calibrating the absorption energy and subtracting the background. It was then fitted with four Gaussian peaks and two arctangent steps. By varying the height and area of Gaussian peaks and arctangent steps, a fitting with χ2 of 1.96 was reached. The probability calculated from the χ2 was higher than 0.99, which loosely suggested a good fit.

Figure 4-3 shows the least-squares peak fitting of XANES TEY spectrum for the mixture of DL-methionine, sodium thiosulphate, sodium sulphate and graphite (code: M-1). The spectrum is fitted using four Gaussian curves and two arctangent step functions. According to the absorption energy listed in Table 4-3, the peaks can be assigned to: 2472.6 eV for sulphide or thiol, 2480.1 eV for sodium thiosulphate and 2481.7 eV for sodium sulphate. There is a small peak at 2471.2 eV, which does not match the first inflection energy of any model compounds. By checking the spectra of model compounds, the small peak was found to be the pre-edge peak of sodium thiosulphate (Figure 4-1a). In the least-squares method, only the primary peak of standard spectrum is considered. Therefore, the influence of secondary peaks in standard spectrum is neglected, although those small peaks may significantly affect the degree of fitting. The significant difference between the measured

- 70 - values from least-square peak fitting and the calculated values (Table 4-4) reveals the weakness of this method in fitting XANES spectra. However, this method is useful to determine the position of peaks which constitute the spectrum.

3.5 Data 3 Fit Atan 1 2.5 Atan 2 Gaussian peaks 2

1.5

1 Normalized absorption Normalized

0.5

0 -55 152535 Relative energy (eV)

Figure 4-3 Least-square peak fitting of sulphur K-edge XANES TEY spectrum of sulphur model compound M-1

Table 4-4 Composition of the mixture of sulphur model compounds by least-squares peak fitting, M-1 Component Amount S wt% in specific form (g) S form By Calculation By Measurement DL-Methionine 0.1 Sulphide 25.4 18.1 Sodium thiosulphate 0.1 Thiosulphate 47.9 18.8 Sodium sulphate 0.1 Sulphate 26.6 63.2 Graphite 0.1

Linear combination fit uses the entire spectrum of each standard sulphur compound to fit the sample spectrum using the linear combination principle. This method is ideal for quantifying the amount of known components in a sample. Therefore, when using this method, prior knowledge about types of compounds is required in order to choose appropriate standard sulphur compounds. Based on Gaussian peak positions in a least- squares peak fitted spectrum, several sulphur standards, including several organic sulphides, thiol, sodium thiosulphate and sodium sulphate, were chosen to perform a linear combination

- 71 - fit of the spectrum. Figure 4-4 shows the linear combination fitting curve of M-1 with these compounds. Fitting results are given in Table 4-5, indicating a good agreement between the actual and measured compositions of the mixture.

Table 4-5 Composition of the mixture of sulphur model compounds, M-1, determined with the linear combination fitting Component Amount S wt% in specific form (g) S form By By Relative Calculation Measurement Difference (%) DL-Methionine 0.1 Sulphide 25.4 25.5 0.4 Sodium thiosulphate 0.1 Thiosulphate 47.9 44.9 6.3 Sodium sulphate 0.1 Sulphate 26.6 29.4 10.5 Graphite 0.1 Average Difference 5.7

3.5

Data 3 Fit

DL-methionine 2.5 Sodium sulphate

2 Sodium thiosulphate

1.5

Normalized absorption 1

0.5

0 -5 0 5 10 15 20 25 30 35 40 Relative energy (eV)

Figure 4-4 Linear combination fit of sulphur K-edge XANES TEY spectrum of the mixture, M-1, with model compounds The linear combination fitting in the range of -5~13 eV seems not as good as the peak fitting, as there are two discrepancies between the fit and the data around 5 eV and 10 eV. This may be caused by the fact that the small secondary peaks of each standard spectrum can significantly affect the fitting and make the fitting more complicated than the primary peak- only least-square fitting described earlier. Moreover, the Gaussian and step functions in peak fitting are independent of each other. The heights, widths and positions can all be adjusted

- 72 - independently. The linear combination fitting, however, does not have this additional degree of freedom, since the complete spectra of model compounds are signatures of those respective compounds and should not be changed. Consequently, more spectra are needed to obtain the same number of degrees of freedom. However, since the linear combination fit incorporates the small features of each spectrum, it is more accurate in quantifying sulphur species when there is a preliminary knowledge of sulphur forms in a sample.

4.3.3 Repeatability

Table 4-6 shows the results of repeated XANES TEY analyses of the same batch of sample (S-KS-1-2 with total sulphur content of 5.14 wt.%) by two researchers on different days based on the same procedure. Results in Table 4-6 indicate that when the sample was analyzed by the same researcher on the same day, the results were repeatable, with the relative difference ranging from 2 to 15%. The difference between the results obtained by the two researchers was however much greater, which could be attributed to the heterogeneity of the SIAC sample. The amount of sample required for XANES analysis is less than 1 mg, while one batch is about 3~4 grams. Table 4-7 gives the averages of four measurements of the same sample by both researchers, showing large relative standard deviations for all but one species – sulphate. Sulphate is the most distinguishable form in all sulphur forms.

Table 4-6 XANES TEY analysis of experiments repeated by one researcher at one time S content in specific form (%) Sample Sulphide Disulphide Sulphonate Sulphate S-KS-1-2-J-1 1.68 0.27 0.45 2.72 S-KS-1-2-J-2 1.43 0.37 0.51 2.83 Average 1.56 0.32 0.48 2.78 Relative difference 8.0 % 15.6 % 6.3 % 2.0 % S-KS-1-2-E-1 1.05 0.65 0.30 3.14 S-KS-1-2-E-2 0.94 0.70 0.25 3.26 Average 1.00 0.68 0.28 3.20 Relative difference 5.5 % 3.7 % 9.1 % 1.9 %

- 73 - Table 4-7 Averages of repeated measurements experiments for XANES TEY analysis Sulphur content in specific form (%) Sample Sulphide Disulphide Sulphonate Sulphate S-KS-1-2-J-1* 1.68 0.27 0.45 2.72 S-KS-1-2-J-2* 1.43 0.37 0.51 2.83 S-KS-1-2-E-1** 1.05 0.65 0.30 3.14 S-KS-1-2-E-2** 0.94 0.70 0.25 3.26 Average 1.28 0.50 0.38 2.99 Standard deviation (SD) 0.34 0.21 0.12 0.25 Relative SD 26.8% 42.2% 32.5% 8.5% * Determined by Jenny Cai ** Determined by Eric Morris

4.3.4 Fluid Cokes Samples

It is generally known that more than 95% of the total sulphur in fluid coke is of organic nature (Furimsky, 1998), with small amounts of sulphate and pyritic sulphur, while elemental sulphur is rarely found in petroleum coke (Al-Haj-Ibrahim and Morsi, 1992). The forms of sulphur compounds in petroleum coke strongly depend on the nature of the coking feedstock (crude oil). Organic sulphur compounds identified in some crude oils include thiols (alkyl, cyclic, and aromatic), sulphides (alkyl, cyclic, and alkyl cycloalkyl), disulphides (alkyl, cyclic, and aromatic), and thiophenes (Al-Haj-Ibrahim and Morsi, 1992). Figure 4-5 shows the representative structures of some organic sulphur compounds identified in petroleum, many of which may also present in petroleum coke. According to Zhou and Chriswell (1996), petroleum sulphur compounds can be grouped into three categories based on their reactivity in oxidation as follows: i) easily oxidized ones, e.g. disulphides - #5, ii) less reactive ones including aliphatic sulphides, aliphatic and aromatic thiols - #1, 2, 3, 4 and 8, and iii) relatively stable ones, e.g. thiophenes and aromatic sulphides - #6 and 7. Since the activation process is essentially an oxidation process, this oxidation reactivity of sulphur compounds in petroleum coke is an important property which may determine their behaviour during carbon activation. The compounds with high reactivity may be easily removed during carbon activation, while the stable ones may be retained after activation.

- 74 -

1. alkane thiols; 2. cycloalkane thiols; 3. dialkyl sulphides; 4. alkyl cycloalkyl sulphides; 5. polysulphides; 6. cyclic sulphides; 7. thiophenes; 8. arene thiols; 9. alkyl aryl sulphides; 10. thiaindanes; 11. benzothiophenes; 12. thienothiophenes; 13. thienopyridines; 14. dibenzothiophenes; 15. naphthothiophenes; 16. benzonaphthothiophenes; 17. phenanthrothiophenes. Figure 4-5 Representative structures of various types of organic sulphur compounds in petroleum (Zhou and Chriswell, 1996)

Figure 4-6 shows the K-edge XANES TEY spectra of two raw coke samples (FC-S and FC-I). The spectra were analyzed using least-square peak fit and linear combination fit. Three types of sulphur were identified in these raw cokes: thiophene, sulphide, and sulphate, as shown in Table 4-7. The total sulphur contents were determined using an elemental analyzer.

- 75 -

Figure 4-6 Sulphur K-edge XANES TEY spectra of two raw coke samples (FC-S and FC-I)

The overall similarity revealed in Table 4-8 is expected as both samples are petroleum coke produced by fluid cokers. The difference in total sulphur content is also justifiable. Sample FC-I was produced from a fluid coker that treats a blend feed with lower sulphur content, while sample FC-S was produced from a coker whose feed was from a single source and had a higher sulphur content. It should be pointed out that XANES-TEY is a surface technique while the elemental analyzer determines bulk compositions. Sample FC-S was collected two years earlier than FC-I, which may explain the relatively high sulphate content in FC-S. No elemental sulphur was found in these raw cokes, consistent with the existing knowledge and coking conditions (> 600 ºC without oxygen).

Table 4-8 Composition of sulphur compounds in FC-S and FC-I from XANES analysis Sulphur content in specific form (% in total S) Raw coke Total S (wt%) Thiophene Sulphide Sulphate FC-S 7.37 53 38 9 FC-I 5.61 52 43 5

4.3.5 Sulphur-impregnated Activated Carbons (SIACs)

Sulphur forms in SIACs produced from fluid coke were also characterized using XANES analysis. It was found that sulphur forms changed after activation, and depending on the raw coke and activation processes, sulphur forms in SIACs were different. For example,

- 76 - Figure 4-7 shows the spectra of raw coke FC-S and SIAC-S which is a SIAC produced from

FC-S with simultaneous KOH and 30% SO2 (balanced with N2) activation. The total sulphur content of SIAC-S is 5.14%, which was determined using the elemental analyzer.

Similar to that of FC-S, there are two major peaks present in the spectrum of SIAC-S. The first one has lower energy and represents sulphur compound(s) of lower oxidation states, and the second peak with a small feature is representative of sulphur compounds of higher oxidation states. After activation - an oxidation process, the first peak of FC-S diminished in size, while the second peak grew much larger. Apparently, the activation process had resulted in a conversion of the sulphur in low oxidation states to that in high oxidation states, i.e. the oxidation of sulphur. Linear combination fitting of SIAC-S spectrum suggests four types of sulphur compounds in the sample: disulphide (5 % of total S), sulphide (33 %), sulphonate (9 %) and sulphate (53 %).

Another example shown in Figure 4-8 is the change of sulphur forms in a SIAC sample (SIAC-I) produced from FC-I. SIAC-I (Total sulphur: 5.61%) was produced with KOH activation and followed by SO2 treatment which is a different process from SIAC-S production. Fitting the spectrum of SIAC-I using model compound spectra suggests that three sulphur types of compounds exist in the sample: disulphide (58 % of total sulphur), sulphonate (29 %) and sulphate (13 %).

Figure 4-7 Sulphur K-edge XANES TEY spectra of FC-S and SIAC-S (produced from FC-S with simultaneous KOH and SO2 activation)

- 77 -

Figure 4-8 Sulphur K-edge XANES TEY spectra of FC-I and SIAC-I (produced from FC-I with sequential KOH and SO2 activation)

To determine the effect of activation conditions on sulphur chemistry, samples were prepared from FC-S under different conditions and analyzed with XANES. Figure 4-9 shows sulphur K-edge XANES spectra of SIACs produced using KOH and SO2 simultaneous activation with different temperatures and KOH/coke ratios. The overall similarity in the spectra is indicative of the same chemical activation process. However, the difference in relative peak size confirms the effect of activation conditions. Clearly, activation processes substantially changed the chemical states of sulphur in the coke samples. XANES is sensitive enough to reveal the change.

Using the software, SixPACK, these XANES spectra were analyzed by applying the principal component analysis to reduce the dimension of data sets (i.e. the standpoint of a data set). It was found that five specific components could provide the set of spectra with the cumulative percentage of total variance over 99.5%. Therefore, a maximum of five components were chosen for each spectrum in the XANES analysis. By applying the linear combination technique, the relative ratio of different sulphur species can be obtained from the spectra. With the total sulphur content measured using a sulphur analyzer, the sulphur content in specific form can be obtained. For samples shown in Figure 4-9, elemental sulphur, sulphide, disulphide, sulphonate and sulphate were identified and quantified. Detailed results will be reported and analyzed in the following chapter where changes in sulphur chemistry during activation are discussed.

- 78 -

Figure 4-9 Spectra of SIACs produced from KOH-SO2 activation at different activation conditions

4.3.6 Comparison between XANES and XPS Results

4.3.6.1 Comparison for Raw Cokes

X-ray photoelectron spectroscopy (XPS) has been widely used to reveal the chemical states of sulphur on the carbon surface (Davidson, 1994; Kelemen et al., 1990; Mateos et al., 1996). Although XPS is relatively convenient for characterizing sulphur oxidation states on a sample surface, it is difficult for XPS to distinguish certain sulphur species with similar oxidation states, such as thiophene and elemental sulphur (Moulder et al., 1992). Given the limitation and capability of both XANES and XPS, this section compares the results from XPS with XANES findings. High resolution XPS spectra of the S 2p region were recorded, and they were analyzed by peak fitting using Gaussian functions. Figures 4-10 and 4-11 show the XPS S 2p spectra of samples FC-S and FC-I. The sharp peak at 163.7 eV can be assigned to sulphide, disulphide, thiol or thiophene with a binding energy (BE) of S 2p3/2 in the range of 163.6 ~ 163.8 eV, while the second one matches sulphoxide with a BE around 166.0 eV. The small peak of oxidized sulphur species with a BE around 168.8 eV could be sulphate (Moulder et al., 1992; Wagner et al., 2007). As shown in Table 4-9, XPS analysis suggests that in FC-S 91% of sulphur was in the form of sulphide, disulphide, thiol or thiophene, while the XANES result (Table 4-8) indicates that 91 % of sulphur in FC-S was in the form of sulphide and/or thiophene. On the other hand, the sum of sulphoxide and

- 79 - sulphate obtained from XPS analysis (4% + 5% = 9%) is the same as the sulphate amount obtained from XANES analysis, although the XANES analysis was unable to distinguish sulphur in sulphate and sulphoxide forms due to their similar first inflection energy and low concentrations. For FC-I the agreement between XPS and XANES is reasonable but not as good as FC-S. Overall, XANES and XPS results are consistent and complementary to each other.

Figure 4-10 The XPS spectrum of S 2p region for FC-S

Figure 4-11 The XPS spectrum of S 2p region for FC-I

Table 4-9 Results of XPS analysis of samples FC-S and FC-I Sulphur content in specific form (% in total S) Raw coke Sulphide/thiophene Sulphoxide Sulphate FC-S 91 4 5 FC-I 85 10 5

- 80 - 4.3.6.2 Comparison for SIACs

The XPS spectra of sulphur 2p were measured for the activated coke to compare the results which were obtained from XANES analysis. Figure 4-12 shows that the sulphur 2p binding energy shifts to higher energy after KOH and SO2 activation (sample SIAC-S), suggesting an increase in the degree of oxidation of sulphur (Sugama, 1998). There are two sources of sulphur in activated coke: sulphur from SO2, the impregnating agent, and the original sulphur from the raw coke. When SO2 is relatively oxidative, KOH can oxidize sulphur in the raw coke and react with SO2. Sulphur transformation in FC-I activation exhibits a similar trend as FC-S (4-13).

Table 4-10 summarizes the results from XPS and XANES for two SIAC samples. The results showed that XPS results were in general consistent with XANES results, although XPS was unable to separate sulphide and disulphide while XANES couldn’t distinguish sulphonate and sulphate. However, the amount of sulphonate and/or sulphate from XANES is similar to their sum from XPS. The total amount of sulphide and disulphide from XANES is also close to that of sulphide and/or disulphide from XPS analysis. The difference between XANES and XPS results could also be caused by the difference in the depth of electron beam penetration (50 nm vs. 5 nm). The following section analyzes the effect of penetration depth.

Figure 4-12 The XPS spectrum of S 2p for SIAC-S (Raw coke: FC-S: KOH and SO2 simultaneous activation: 700°C, KOH/coke: 3:1, activation time: 1 hour)

- 81 -

Figure 4-13 The XPS spectrum of S 2p for SIAC-I (Raw coke: FC-I; KOH and SO2 simultaneous activation: 700°C, KOH/coke: 3:1, activation time: 1 hour)

Table 4-10 Comparison of XPS and XANES results for two SIAC samples Sulphur content in specific form (% in total S) SIAC Technique Sulphide disulphide Sulphonate Sulphate 61.7 SIAC-S XANES 32.7 5.3 (sulphonate and/or sulphate) 45.3 XPS 14.4 40.4 (sulphide and/or disulphide)

42.1 SIAC-I XANES 57.8 (sulphonate and/or sulphate) 46.1 XPS 11.1 42.8 (sulphide and/or disulphide)

4.4 FLUORESCENCE YIELD (FY) RESULTS

In the FY mode, the characteristic signal is generated from a deeper layer (50 ~ 800 nm) under the sample surface, and thus, FY analysis gives the sulphur composition in the deep layers which is usually considered to represent the bulk phase. Since the samples were exposed to the air for a long period of time, sulphur compounds on their surface could be oxidized and be different from the bulk phase. The analysis of FY should give a low content of oxidized sulphur such as sulphate, if air oxidation is important. Figure 4-14 shows

- 82 - XANES sulphur K-edge FY spectra of FC-S and FC-I. The results of spectra analysis revealed no oxidized sulphur (Table 4-11).

Figure 4-14 XANES sulphur K-edge FY spectra of FC-S and FC-I Table 4-11 Sulphur forms in the bulk of raw fluid cokes (FY results) Sulphur content in specific form (% in total S) Fluid coke Sulphide Disulphide Thiophene Thiol FC-S 37 38 11 14 FC-I 41 30 10 19

As shown in Figure 4-15, upon simultaneous KOH and SO2 activation, the sulphur forms in the bulk phase of Syncrude coke changed significantly. As expected, the activated coke (SIAC-S) contained a much greater amount of high oxidation state sulphur than the raw coke (FC-S). Analysis of the spectra suggests that elemental sulphur and thiosulphate were present in the bulk, along with sulphate. Elemental sulphur is a possible product of carbothermal reduction of SO2, and adsorbed on the internal surface of carbon after 2- 2- activation. Thiosulphate may form through sulphur-sulphite reaction (S + SO3 → S2O3 ) where sulphite is possibly formed from KOH and SO2 reaction (2KOH +SO2 → K2SO3 +

H2O). More discussion about reaction mechanisms is in Chapter 5. Comparing the sulphur content determined by XPS (i.e. sulphur content on carbon surface) and total sulphur content of the sample, the total sulphur content is much lower than that on the surface, consistent with the role of SO2 in adding sulphur.

- 83 - ― FC-S ― SIAC-S

Figure 4-15 Sulphur K-edge XANES FY spectra of FC-S and KS-1-2

As shown in Figure 4-16, KOH activation followed by SO2 treatment resulted in a similar shift to a high oxidation state for sulphur in FC-I. In the product (SIAC-I), i.e. activated coke, elemental sulphur and sulphate were identified.

― FC - I ― SIAC - I

Figure 4-16 Sulphur K-edge XANES FY spectra of FC-I and SIAC-I

4.5 CONCLUSIONS

K-edge X-ray absorption near edge structure (XANES) spectroscopy was employed to characterize sulphur in fluid cokes and their activation products (SIACs). To simulate the coke samples and validate the analytical technique, a mixture of pure sulphur compounds and

- 84 - graphite was prepared and examined with XANES; the results showed good agreement between the actual and measured sulphur contents in specific forms.

XANES results were found to be consistent with and complementary to XPS results. While both techniques can differentiate reduced sulphur and oxidized sulphur, XANES is more capable of distinguishing sulphur species at low oxidation states, and XPS is quite suitable for sulphur species with a high oxidation state. However, even for XANES it is difficult to distinguish directly organic sulphide and thiophene without analyzing secondary peaks.

A procedure for analyzing XANES spectrum was proposed, which combined the methods of least-squares peak fitting and linear combination fitting for all spectra, as well as principal component analysis for spectra of samples produced under similar conditions.

Different results for the same sample were obtained using the Total Electron Yield (TEY) and Fluorescence Yield (FY) modes of XANES. The results were qualitatively reasonable, suggesting the applicability of XANES in surface (4~50 nm beneath the surface) and bulk phase (50~800 nm max depth) sulphur speciation.

- 85 - CHAPTER 5 MECHANISMS STUDY OF KOH-SO2 ACTIVATION OF HIGH SULPHUR FLUID COKES

5.1 INTRODUCTION

As mentioned in Chapter 3, a petroleum industry waste material - oil-sands fluid coke is currently being produced and stockpiled onsite at a rate of over 10,000 tonnes per day. Although the fluid coke has a high carbon content, its high sulphur content precludes its use as a fuel for power generation due to the consequent sulphur introduction to the environment (Ityokumbul and Kasperski, 1994; Furimsky, 1998). With the increase in the storage of fluid coke, it becomes urgent to find means to utilize it. One possibility is to use fluid coke as a starting material for producing activated carbon (AC), given its high carbon content and ready availability.

A unique process using KOH and SO2 simultaneously to activate oil-sands fluid coke was developed in this study. In this process, KOH acted as an activating agent; SO2 simultaneouslly acted as both activating and sulphur-impregnating agent. After one-hour 2 activation, the highest SBET achieved was over 2500 m /g, while the highest sulphur content was 8.1%.

KOH and SO2 simultaneous activation was used for the first time to activate the carbonaceous material, and the KOH-SO2-carbon system could be more complex than the system with the single activating agent. Therefore, its activation mechanism is largely unknown, especially since sulphur chemistry is involved. The chemistry of KOH activation has been investigated by several researchers. Marsh et al. (1984) studied the effect of KOH on different cokes, and found that the oxygen in the KOH can remove the cross-linking and stabilizing of carbon atom in crystallites. They proposed a model for the KOH activation process: with the addition of KOH to a carbon matrix, the potassium may form alkalides such as –OK. The presence of potassium and oxygen in the coke structure may separate the constituent lamellae by oxidizing the cross-linked carbon atoms, and thus functional groups formed on the edges of lamellae may destroy their flat form. When the potassium salts are removed from the carbon matrix by leaching with water, the lamellae cannot return to their previous non-porous structure, and this creates the microporosity. Lillo-Ródenas et al. (2003

- 86 - and 2004) suggested that during KOH activation of anthracite, the KOH reacted with carbon to form metallic potassium and potassium carbonate, releasing hydrogen at the same time. Their findings were supported by the thermodynamic calculation and temperature programmed desorption (TPD) measurements. For instance, some reaction products such as

H2 and K2CO3 were quantified by TPD. Using X-ray diffraction (XRD), Raymumdo-Piñero et al. (2005) observed that carbon oxidation started at around 400°C, forming K2CO3, during

KOH activation of carbon nanotubes. All KOH transformed to K2CO3 at 600°C, and K2O was detected at 700°C. At 800°C, only K2O was detected, suggesting that K2O was the final product of KOH-carbon reaction. Although metallic K was expected to form by the K2O - carbon reaction, no metallic K was found by XRD. Vapour phase reactions were then carried out, which showed that metallic K produced by KOH reduction was intercalated between the graphitic type layers. This was the key for developing the porosity of the carbon nanotubes.

With SO2 introduced into the KOH-carbon system, the reactions among KOH, SO2 and carbon may take place simultaneously, and the activation mechanism could be complicated. The objective of this study was to further understand the mechanisms of chemical activation in particular the activation chemistry. Since the raw materials and products all have high sulphur contents, more attention was paid to the roles of sulphur in fluid coke and in SIACs during the activation process.

5.2 EXPERIMENTAL

5.2.1 Materials

Fluid cokes (FC-S and FC-I) obtained from two sources were activated with KOH and/or SO2. The properties of the raw FC-S and FC-I are given in Table 5-1, noting higher sulphur and oxygen contents and a lower SBET in FC-S. In KOH-SO2 activation, the fluid coke was mixed with KOH in the ratios of 1:1 to 3:1, and the mixture was heated at 600-

900°C for 15-120 min, with 30% SO2 blown through it. The detailed activation process is described in Chapter 3. KOH-only and SO2-only activations of fluid coke were also carried out, which provided the supporting evidence for understanding the roles of KOH and SO2 in

KOH-SO2 activation. KOH-only activation took place by following the same procedure as

KOH-SO2 activation, except nitrogen gas was used instead of 30% SO2. In SO2-only

- 87 - activation, fluid coke without mixing with KOH was heated in 30% of SO2. The remaining steps for KOH-only, SO2-only and KOH-SO2 activations were the same.

Table 5-1 Properties of raw cokes 2 Raw material SBET (m /g) C (%) O (%) S (%) FC-S 7.5 82.74 6.40 7.37 FC-I 14.4 87.22 3.43 5.61

5.2.2 Analytical Methods

Elemental analysis including total sulphur content in fluid cokes and their activation products were determined using an elemental analyzer (Vario EL III). Organic sulphur was determined using the method developed by Riley et al. (1990), in which 2 M nitric acid was used to extract inorganic sulphur from the sample. One gram of sample was mixed with 50 mL 2 M nitric acid and heated to a gentle boil for 30 minutes. After washing and drying, the total sulphur in the extracted sample was determined, which was considered as the total organic sulphur. XPS (Thermo Scientific Theta Probe) was used to measure the oxygen and sulphur contents in the surface of fluid cokes and their activation products.

Sulphur forms were identified using K-edge X-ray absorption near edge structure (XANES) spectroscopy, and the experiments were conducted in the Canadian Synchrotron Radiation Facility located at the University of Wisconsin, USA. The procedures for data collection and analysis of XANES were described in Chapter 4. The XANES analyses focused on the surface sulphur species by using total electron yield (TEY) mode only. The K- edge TEY mode can probe up to 50 nm beneath the substrate surface (Kasrai et al., 1996).

5.3 RESULTS AND DISCUSSION

5.3.1 Activation Mechanisms

5.3.1.1 Role of KOH

It was suggested that the main reactions between KOH and carbon included the oxidation of carbon to CO2 by KOH, the formation of carbonate from KOH and CO2 (Eqs. 5-

- 88 - 1 and 5-2) and the reduction of KOH to elemental K and hydrogen gas (Eq. 5-3) (Lillo- Rόdenas et al., 2003 and 2004; Raymundo-Piñero et al., 2005)

4KOH + C → 4K + CO2 + 2H2O 5-1

2KOH + CO2 → K2CO3 + H2O 5-2

6KOH + 2C → 2K + 3H2 + 2K2CO3 5-3

Thermodynamic data of these reactions were obtained using FactSage (commercialized thermodynamic calculation software). The large negative ∆G° values for Eq. 5-2 (Table 5-2) suggest that the formation of carbonate is thermodynamically favourable, particularly at lower temperatures due to the negative ∆H° which represents an exothermic reaction. On the other hand, the reduction of KOH by carbon to K and hydrogen gas (Eq. 5-3) is more favourable at higher temperatures from 600 to 900°C, as indicated by the negative ∆G° and positive ∆H° (Table 5-2). However, the reduction to K only (Eq. 5-1) has a positive ∆G° and is much less favorable thermodynamically. Accordingly, the most feasible products of KOH- carbon reactions would be K2CO3, elemental K and H2 gas. K2CO3 would remain in solid form at the temperature lower than 891°C – the melting point of K2CO3, and decompose at higher temperatures. Since K has a melting point of 64°C and a boiling point of 774°C, K would be in a molten form and could leave the reactor as vapour at higher temperatures. The formation of metallic K has been reported in previous studies (Otowa et al., 1997; Lillo- Ródenas et al., 2003; Maciá-Agulló et al., 2007). However, a portion of metallic K produced by KOH-carbon reaction may remain in the carbon by intercalating to the carbon matrix (Marsh et al., 1984; Greenwood et al., 1994; Raymundo-Piñero et al., 2005). As suggested by Raymumdo-Piñero et al. (2005), the removal of intercalated metallic K from graphitic- type layers may largely contribute to the development of carbon porosity.

KOH activation was studied using simulation software HSC Chemistry. The strong temperature dependence of equilibrium compositions for the KOH-carbon system (molar ratio = 0.9:1) is shown in Figure 5-1. The HSC indicated the same major products as predicted by FactSage for temperatures between 600 to 900 °C - K2CO3, elemental K and H2 gas. It suggests the feasibility of forming KH and CH4 at lower temperatures and CO at higher temperatures. It also predicts the thermo-decomposition of K2CO3 at higher

- 89 - temperatures. The reaction KOH + H2 → KH + H2O is thermodynamically feasible at temperatures below 500°C, and also the reaction C + 2H2(g) → CH4(g). Yet the kinetics of these reactions are largely unknown.

Table 5-2 Thermodynamics data calculated with FactSage for Eqs. 5-2 and 5-3 Temperature (°C) ∆G° (kJ/mol) ∆H° (kJ/mol)

2KOH + CO2 → K2CO3 + H2O 600 -103.6 -190 700 -93.7 -190 800 -83.8 -189 900 -74.1 -187

6KOH + 2C → 2K + 3H2 + 2 K2CO3 600 -2.6 128 700 -17.5 125 800 -36.9 283 900 -66.6 282

Figure 5-1 Temperature dependence of equilibrium composition of the major components of the KOH-C system (initial composition: KOH = 0.9 kmol, C = 1 kmol, H2O = 0.1 kmol and N2 = 0.5 kmol)

CO could be produced by the reaction between carbon and CO2, a decomposition product of K2CO3. Carbon and hydrogen gas could also reduce carbonate and form CO via

K2CO3 + 2C → 2K + 3CO and K2CO3 + 2H2 → 2K + 2H2O + CO (Ao et al., 2008). It is therefore feasible for K2CO3 to react directly with carbon and act as an activating agent at a

- 90 - sufficiently high temperature. Assuming the reduction of K2CO3 by hydrogen is negligible, the overall reaction becomes KOH + C → K + 0.5H2 + CO, where KOH/C ratio is 1:1, much lower than 3:1 as required by the reaction that produces K2CO3 (Eq. 5-3). Consequently, the theoretical weight loss for a given KOH/coke ratio during the activation may change with different temperatures, in this case, increase with the increase in activation temperature. This could be another reason for greater weight loss during the activation at higher temperatures of 800-900°C (Figure 3-6 in Charpter 3).

In summary, the activation at high temperatures could be advantageous for several reasons. First, less KOH may be required to remove the same amount of carbon and create pores, since K2CO3 may decompose and act as an activating agent. Second, more metallic K can be produced with the same amount of carbon consumed. Metallic K may contribute additionally to the development of pores via intercalation. Third, upon reaction with water, metallic K is converted into KOH which may be reused in the activation. Lastly, CO and hydrogen may be used as fuel.

5.3.1.2 Role of SO2

In order to determine if SO2 can add sulphur to the coke, SO2 was used to treat the fluid coke. At 700°C, 30% of SO2 in the N2 gas phase was used to treat fluid coke for one hour, in the absence of KOH. The result showed that the sulphur content of this SO2-treated product was 9.34 %, which was higher than that in the raw coke FC-S (7.37 %). Since there was a substantial weight loss after activation, sulphur enrichment from the loss of carbon can be a factor causing the changes in total sulphur content. The sulphur enrichment during SO2 treatment of fluid coke was calculated based on the carbon weight loss and sulphur content in the raw coke. The raw coke has 7.37% of sulphur, and the coke weight loss after 1-hour activation was 9.9%. Sulphur content in the activation product should be 8.18% if only carbon was oxidized and removed. If sulphur in the coke is also removed, the sulphur content in the activated product would be lower than 8.18%. However, total sulphur content in the product was 9.34%, which indicates that sulphur was added through other pathways. Since

SO2 was the only external source of sulphur in the system, the additional sulphur should be from SO2.

- 91 - Another series of experiments, KOH-SO2 sequential activation of fluid coke, were carried out to investigate if SO2 can add sulphur to the coke. In this process, KOH was first used to activate fluid coke in a flow of N2 gas for 1 hour, and then 30% of SO2 was introduced into the system for 0.5 to 2.5 hours. Since KOH was mostly consumed and the original sulphur was mostly removed after 1-hour KOH activation (Section 3.3.1.2), the increase in sulphur content of the final product after SO2 treatment must be from SO2 (Figure 5-2).

4 Total sulphur (%) 2

0 00.511.522.53 Treatment time (hr)

Figure 5-2 Increase in sulphur content during SO2 treatment of KOH-activated carbon

The interaction between sulphur dioxide and different types of carbons has been studied under a variety of conditions and with different objectives. Humeres et al. (2002) studied the reduction of SO2 on four types of carbonaceous materials. Their results showed that the reactivity of the different carbons to SO2, as measured by the second-order rate constants, followed the sequence of decreasing crystallinity: graphite < coke (7.34% ash content) < coke (11.73% ash content) < charcoal. The authors proposed a path (Figure 5-3) by which

SO2 reacts with carbon. First, a SO2 molecule is adsorbed onto carbon site A (CA) where SO2 reacts with C, and produces CO2 and S. Second, CO2 can undergo reduction to CO on site CB, or reacts with S on site CC to form CS2. Consequently, CO can also react with S, producing COS. However, there is not sufficient evidence supporting this point. An interesting finding worth pointing out is that the SO2-charcoal reaction was controlled by diffusion at temperatures above 700°C, while the reaction was kinetically controlled at lower

- 92 - temperatures. Fluid coke in the present study, FS-C, has 3.4% of ash, which is like a graph with low reactivity to SO2.

Figure 5-3 Schematic for SO2 reduced on carbon surface (Humeres et al., 2002)

Puri and Hazra investigated the interaction of various charcoals with SO2 at 600°C (Puri and Hazra, 1971). They found that sulphur was fixed partly by addition at unsaturated sites and partly by substitution through interaction with certain oxygen groups which came off as carbon monoxide upon high temperature evacuation. The fixation of sulphur strongly depended on the oxygen and hydrogen content, extent of surface unsaturated sites, and pore structure of charcoal. The carbon-sulphur complex resulting from the fixation of sulphur on charcoal was highly stable, and most of the fixed sulphur can be removed at 1200°C. A similar study was conducted by Chang (1981). At 600°C, carbon-sulphur surface compounds were prepared by reactions between four types of sulphurizing agents and several types of carbonaceous material, such as activated carbon, carbon black, coke, and petroleum pitches.

Among these sulphurizing agents, SO2 exhibited a greater ability to impregnate carbon than

CS2, H2S and SOCl2. The carbon-sulphur compounds were disordered materials, which were stable in bases. After an initial loss of several percent of sulphur, they became stable in strong acid. The possible C-S surface groups were thiocarbonyls (C=S<) and thiolactones S (S=C< ). C

More attention has been paid to the interaction between SO2 and activated carbon, since activated carbon has been widely used for desulphurization of industry gases. Zawadzki

(1987) carried out an IR spectroscopic study on the bond characteristic of SO2 molecules adsorbed on the surface of carbon films. No evidence was found for any stable surface carbon-sulphur complexes from 25 to 600°C. The author concluded that sulphur might be fixed to the carbon surface mainly as polymerized sulphur, held in the micropores of carbon.

Stacy et al. (1968) found that an oxygen-free carbon surface had limited total SO2 adsorption

- 93 - capacity. Furthermore, they suggested that the adsorption of SO2 was mostly physical adsorption between 50 and 300°C, while physical adsorption was negligible above 300°C.

Another study of SO2 reduction on activated carbon was carried out by Humeres et al. (2003). Their results indicated that the reaction product depended on whether the reaction was diffusion-controlled or kinetically controlled. Two types of sulphur bound to carbon were observed: non-oxidized sulphur (sulphide and/or disulphide) and oxidized sulphur (sulphone and sulphoxide).

It has been commonly accepted that SO2 reacts with carbon to form elemental sulphur,

CO2 and CO, as well as other intermediate products (Stacy et al., 1968; Zawadzki, 1987; Humeres et al., 2002 and 2003; Bejarano et al., 2003). The overall reaction is shown in Eqs. 5-4 and 5-5. However, at the temperature in this study, 600-900°C, theoretically, elemental sulphur would evaporate, since its boiling point is 445°C. If this is the case, no sulphur could be added to coke. However, the evidence of sulphur content increase in activation products suggested that certain forms of sulphur might be retain in the carbon matrix after SO2-carbon reaction.

SO2 + 2C → S + 2CO 5-4

SO2 + C → S + CO2 5-5

Thermodynamic data of Eqs. 5-4 and 5-5 were calculated using FactSage to verify the possibility of these reactions. The large negative ∆G° values shown in Table 5-3 suggest that both reactions are thermodynamically favorable at 600 to 900°C. The enthalpy of activation (∆H°) for formation of CO (Eq. 5-4) was found to be positive indicating that the reaction occurs with the absorption of heat (endothermic nature), while the formation of CO2 (Eq. 5-5) is an exothermic reaction.

Table 5-3 Thermodynamics data calculated by FactSage for Equations 5-4 and 5-5

SO2 + 2C → S(g) + 2CO SO2 + C → S(g) + CO2 Temperature (°C) ∆H° (kJ/mol) ∆G° (kJ/mol) ∆H° (kJ/mol) ∆G° (kJ/mol) 600 86.1 -80.4 -85.7 -98.3 700 86.2 -99.5 -84.7 -99.8 800 86.2 -118.6 -83.7 -101.4 900 86.1 -137.7 -82.8 -103.1

- 94 - When SO2 is reduced to elemental sulphur as shown in Eqs. 5-4 and 5-5, the elemental sulphur can also react with carbon and add sulphur into the carbon matrix. Experiments were conducted to investigate if elemental sulphur can add sulphur to fluid coke, using elemental sulphur as the sulphur impregnating agent to treat a KOH-activated carbon. In this process, one gram of elemental sulphur was mixed with 1 g of the KOH-activated carbon with around 0.1% of sulphur content. The mixture was charged into the stainless steel reactor, and placed in a tube furnace. Under nitrogen gas (>99.99%) protection, the mixture was heated at 700 – 800°C for one hour. After the furnace cooled down, the activation product was then removed and kept in a desiccator for further analysis. The results show that after impregnation at 700°C and 800°C for one hour, the sulphur contents in the samples increased to 11.95% and 9.82%, respectively. XPS analysis showed that the main sulphur forms in these samples were elemental sulphur, sulphide, sulphoxide and sulphate. This result is in good agreement with previous finding reported by Feng et al. (2006) who used elemental sulphur to impregnate sulphur into carbon at 600°C and found elemental sulphur, sulphide, thiophene, sulphonate and sulphate in the sulphur-impregnated carbon. This confirmed that SO2 can indirectly react with coke and add sulphur to the carbon matrix, even in the form of elemental sulphur.

5.3.1.2 KOH-SO2 Activation

As shown in Figure 3-14, the weight loss increased with the increase in activation temperature, and reached 67% at 900°C, much higher than that was observed in the KOH- only system. Thermodynamic analysis shows a more complicated composition in KOH-C-

SO2 system than that in KOH-C system (Figure 5-4). At the temperature from 600 to 900C,

K2S, K2SO4 and K2CO3 are possible solid products, while CO, CO2, COS, H2O, H2 and S are possible gaseous products. Experiments conducted by the author’s co-workers identified K2S,

K2SO4 and K2CO3 in the activated coke, while CO, CO2, S, H2O and H2 were observed in the exit gas from the reactor (Kim, 2008; Yuan et al., 2009). There was indirect evidence of elemental K in the gas leaving the reactor during KOH activation, and it could be also produced during KOH-SO2 activation. However, in the presence of H2S and elemental S, elemental K could be converted to K2S readily.

- 95 - The formation of elemental S and COS was due to the reaction between SO2 and carbon. Clearly, SO2 had participated in the oxidation of carbon in a substantial way, even though there was the possibility of direct reaction between SO2 and KOH.

N2(g)

Figure 5-4 Temperature dependence of equilibrium composition of the major components of the KOH-C-SO2 system (initial composition: KOH:C:SO2:N2 = 1:1:1:0.5)

Reactions between KOH and SO2 can produce K2SO3 (Eq. 5-6), and disproportionation of sulphite yields K2SO4 and elemental sulphur (Eq. 5-7) (Lee et al., 2002). During the experiment in this study, it was observed that elemental sulphur condensed at the outlet of the reactor, and a great amount of K2SO4 was found in the washing solution of activation products. According to FactSage database, both reactions have negative ∆G° (-158 to -132 kJ) values and are thermodynamically favourable at 600 to 900°C. These reactions suggest that

KOH may change the reaction pathway of SO2 and its final product. As K2SO3 and S co- exist, the formation of K2S2O3 may also be possible (Eq. 5-8).

2KOH + SO2 → K2SO3 + H2O 5-6

2K2SO3 + SO2 → 2K2SO4 + S 5-7

K2SO3 + S → K2S2O3 5-8

- 96 - The sulphur content decreased with the increase in activation temperature (Figure 3-17). At 900°C, the S content was only 3.5%, indicating that it is difficult for the sulphur compounds to remain in the activation product. The low sulphur content is expected, given the temperature dependence of sulphur addition discussed in the Section 3.3.3.2. At 600°C, there are at least two possible reasons behind the observed high sulphur content (> 7%), first, inefficient removal of organic sulphur in the coke by KOH, and second, inefficient removal of sulphur products from carbothermal reduction of SO2. Although without KOH the rate of carbothermal reduction of SO2 at 600°C would be low (Chen, 2002), the rate could be increased due to KOH. Lua and Guo (2001) identified alkaline functional groups such as pyrone and other keto-derivatives of pyran on the surface of KOH-activated oil-palm waste- derived carbon. These functional groups on the carbon surface may enhance the adsorption of acidic gases (e.g. SO2) onto the carbon surface (Stacy et al., 1968). Lee et al. (2002) studied the adsorption of SO2 on a KOH-impregnated activated carbon. They found that

KOH provided a strong basic functional adsorption site to allow selective adsorption of SO2. In addition, previous studies also suggested that the number of basic surface sites with good

SO2 selectivity on the surface of the adsorbent can enhance the adsorption of SO2 (Davini, 1990; Carrasco-Maríin et al., 1992). Therefore, the modification of the carbon surface by

KOH may enhance the adsorption of SO2 on the coke surface and consequently enhance the reaction between SO2 and carbon. Sulphur speciation could shed some light on this.

5.3.2 Sulphur Transformation during KOH-SO2 Activation

5.3.2.1 Sulphur Characterization of Raw Fluid Cokes

Table 5-4 summarizes the sulphur characteristics of two raw cokes. The total sulphur content of raw coke FC-S is 7.37%, including 7.23% organic sulphur, i.e. 98 % of sulphur is organic. FC-I has 5.61% total sulphur with 96 % being organic sulphur. As expected, the sulphur in fluid cokes is organic in nature. Despite the difference in total sulphur content between the two cokes, the types of surface sulphur species are rather similar – over 90% thiophene and sulphide and less than 10% of sulphate. This result is consistent with the existing knowledge about sulphur in petroleum coke (Al-Haj-Ibrahim and Morsi, 1992; Furimsky, 1998). The small amount of sulphate found in the fluid cokes could be caused by the oxidation of sulphur during storage under air. The sulphur species in petroleum coke

- 97 - strongly depends on the nature of the coking feedstock. It has been reported that thiol, sulphide, disulphide and thiophene are found in four crude oils (Ai-Haj-Ibrahim and Morsi, 1992).

Table 5-4 Sulphur content and forms in the raw cokes Raw material Total S Organic S Compositions of Surface Sulphur (wt %) (%) (%) Thiophene Sulphide Sulphate FC-S 7.37 7.23 52.3 43.2 4 FC-I 5.61 5.39 53 38 9

5.3.2.2 Changes in Sulphur Content

In KOH-SO2 activation, KOH was mixed with the coke at the beginning of the activation while the SO2 gas flow was maintained during the whole activation process. Depending on the activation conditions, KOH can be completely used up within one hour. In other words, the reactions in the KOH-SO2-coke system varied with activation time. Therefore, in the early stage of activation, there were reactions between KOH and the coke, between SO2 and the coke, and between KOH and SO2. While the reactions between KOH and the coke converted organic sulphur into water soluble inorganic sulphur, the reactions between SO2 and coke produced elemental sulphur that could remain in the carbon matrix.

With the strong potential of the reactions between KOH and SO2, it is anticipated that KOH suppresses the addition of sulphur via SO2. It should be pointed out that the sulphur forms in SIACs were measured after washing, and thus the washing effect has to be considered. For example, theoretically sulphate will be readily removed by washing while elemental sulphur may remain.

Figure 5-5 shows the temperature dependence of the sulphur content of activated FC-S. Regardless of the temperatures, the sulphur content in the activated carbon is always lower than that of the raw coke, demonstrating the ability of KOH to remove sulphur even under

SO2. When the temperature increased from 600 to 900°C, however, the total sulphur content decreased from 7.3% to 3.5%. There are at least three factors that influence the final sulphur content in an activation product - sulphur removal by KOH, sulphur addition by SO2, and sulphur enrichment by carbon weight loss.

- 98 - As discussed in Chapter 3, in the absence of SO2, sulphur in the coke is expected to be removed completely by KOH after activation and acid washing. Therefore, any residual sulphur must be attributed to the reaction between SO2 and the coke which produces elemental sulphur. It has been demonstrated that elemental sulphur can remain in the carbon matrix even at temperatures that are much higher than its boiling point (445°C). At higher temperatures, however, the ability of elemental sulphur to attach to carbon is likely reduced, resulting in lower sulphur contents in the activated carbons.

2 Totalsulphur content (%) 1

0 raw coke 600 700 800 900 Activation temperature (°C)

Figure 5-5 Temperature dependence of sulphur content of FC-S (KOH-SO2 activation: 700°C, 1 hour, KOH/coke: 3:1)

10 SIACs from FC-S 8 SIACs from FC-I

2 Total sulphur content (%)

0 0123 KOH/coke ratio

Figure 5-6 Effects of KOH/coke ratio on total sulphur content in activation products (700°C, 1 hour)

- 99 - As shown in Figure 5-6, the sulphur content in the activated carbon decreased with the increase of KOH/coke ratio for both FC-S and FC-I. This result was expected since first

KOH removes sulphur; secondly KOH consumes SO2 and therefore suppresses the sulphur addition.

Higher sulphur contents can be achieved by prolonging the activation process. When FC-S was activated for 2 hours at 700°C, the sulphur content reached 8.1%, compared with 5.1% for 1 hour activation. Prolonging the activation process leads to an increase in the time when there is no longer any KOH in the system. Without KOH, the sulphur addition via SO2 should be more efficient (Figure 5-2). With longer activation times, however, the weight loss increases, which means lower yields and higher energy consumptions.

Table 5-5 shows the change in organic sulphur content in the coke before and after activation with KOH and SO2 at 700°C for one hour. The results confirm the observation that KOH converts organic sulphur to inorganic sulphur. Since under the similar conditions but without SO2 in the system, the sulphur content in the activated carbon should be less than 0.2% (details in Chapter 3) and mainly in the form of sulphate, the results shown in Table 5-5 suggest that SO2 has a negative effect on the conversion of organic sulphur by KOH.

According to thermodynamic calculations the reaction between KOH and SO2 is highly favorable. Apparently, sulphur in FC-I seems more susceptible to reaction with KOH, more sulphur in FC-I was removed and less organic sulphur remained. This difference may be attributed to the greater initial porosity of FC-I.

Table 5-5 Changes of organic sulphur content in SIACs produced under same condition but different raw cokes (KOH-SO2 activation: 700°C, 1 hour, KOH/coke: 3:1) Sample Total S (%) Organic S in total S (%) FC-S Raw coke 7.37 98.1 Activated coke 5.14 31.1 FC-I Raw coke 5.61 96.1 Activated coke 2.46 15.4

Since KOH-SO2 activated carbon was washed with acid and deionized water, the only inorganic sulphur which is not very acid-soluble is elemental sulphur. This may suggest that in the activated carbon, inorganic sulphur would be mainly in the form of elemental sulphur.

However, only a small amount of elemental sulphur was found in some KOH-SO2 activated

- 100 - carbons, depending on their activation conditions. On the other hand, a large amount of sulphate was found in most activated carbons, suggesting that inorganic sulphate may remain in the activated carbon, even after washing with acid and water. This is further discussed in the next section.

5.3.3 Changes in Sulphur Species

5.3.3.1 The Role of KOH in Changing Sulphur Form

In order to understand how KOH affected the changes in sulphur form without the interference from SO2, samples activated with KOH only were analyzed for total sulphur content and composition. It was found that after one-hour KOH activation at 600~900°C, with KOH/coke ratio of 1:1 - 3:1, the total sulphur dropped to around 0.1 ~ 0.3 wt%, and after acid washing the only sulphur species identified on the surface was sulphate. This suggests that KOH is very effective in converting organic sulphur in the coke to water soluble inorganic species. The reactions occurring in this process have been suggested (Lee and Choi, 2000; Lillo-Ródenas et al., 2003) to be

2C + 6KOH → 2K + 3H2 + 2K2CO3 5-9

Coke-S + 2KOH → K2S + Coke-O +H2O 5-10

Equations 5-9 and 5-10 present the overall reactions between KOH and carbon and between KOH and sulphur. Eq. 5-10 suggests that the final product of inorganic sulphur from this process is K2S, and the removal of organic sulphur in the coke (Coke-S) is companied by the addition of oxygen to the coke. Although K2S was not directly identified in this study, a strong H2S odour produced during acid washing supports the theory of K2S formation. Alkali metal sulphides are not very stable in air and are readily oxidized by oxygen to sulphur oxides. Elemental analysis revealed that the oxygen content in fluid cokes increased from

6.4% to 12.9% and 3.4% to 11.8% for FC-S and FC-I, respectively, after 1-hour KOH-SO2 activation at 700°C, with KOH/coke of 3:1, which was expected according to Eq. 5-10. Actual forms of oxygen-containing groups in the activated carbon are still unknown, although the residual carbonate can certainly contribute to the oxygen in the activated carbon.

XANES analysis showed that the sulphur in KOH-activated carbon after washing was mainly in the form of sulphate. Zhang et al. (2008) activated high sulphur petroleum coke

- 101 - 2- 2- with KOH at 650-900°C, and found SO3 and SO4 in the collected washing solution of the absorbents. They concluded that K2SO3 and K2SO4 were the sulphuric products from KOH 2- activation. However, SO4 is the most stable oxidation product of sulphide, and it is possible that oxidation of alkaline metal sulphide takes place during and after acid washing. Acidified aqueous sulphite is readily oxidized by air at ambient conditions (Kuo et al., 2006).

Thiophenic sulphur is a major component of the organic sulphur in coal, its proportion is in the range of 55 to >90% (Sugawara et al., 1995). It is widely accepted that thiophenic sulphur is much more stable than the other organic sulphur such as sulphides in coal, and therefore is most difficult to remove (Ai-Haj-Ibrahim and Morsi, 1992; Gryglewicz, 1996). Under the catalysis of KOH, only 70% ~ 86% of total sulphur in the coal could be removed by pyrolysis in N2 up to 1000°C (Sugawara et al., 1995; Liu et al., 2005). Apparently, the removal of organic sulphur from oil-sands fluid coke with KOH was not a difficult process. The thiophenes do make up most of the sulphur present in petroleum cokes; however, it has been suggested that it is always possible to find compounds that react more readily with them than with the aromatic or other compounds in the coke structure (Ai-Haj-Ibrahim and Morsi, 1992), although the reason behind this easy removal is not clear.

In addition to thiophene, organic sulphur in the carbon matrix can take the forms of thiol, sulphide and disulphide (Ai-Haj-Ibrahim and Morsi, 1992). According to (Mukherjee, 2003; Baruah and Khare, 2007), upon reacting with KOH, even at 95°C, these organic sulphur species can be converted to inorganic sulphide and/or sulphur oxides through the following reactions.

Thiol: RSH + 2KOH → K2S + 2H2O + R’CH=CH2 5-11

Sulphide: RCH2SCH2R’ + 2KOH → RCH=CH2 + R’CH=CH2 + K2S + 2H2O 5-12

- - Disulphide: 2RSSR + 4OH → 3RS + RSO2 + 2H2O 5-13

5.3.3.2 The Role of SO2 in Changing Sulphur Form

The fluid coke, FC-S, was treated with SO2 only at 700°C for 1 hour, and the total sulphur content increased from 3.73% to 9.34%. Figure 5-7 shows the sulphur species identified on the surface of SO2 activated coke using XANES. The identification of elemental sulphur is consistent with the overall reaction of carbothermal reduction of SO2 (SO2 + C = S

- 102 - + CO2), although previous studies (Puri and Hazra, 1971; Feng, 2002; Bejarano et al., 2003) also demonstrated the feasibility of forming products other than elemental sulphur, such as sulphoxide, sulphone and sulphate. In this study, it was found that in addition to elemental sulphur, SO2 was able to add some sulphoxide to the carbon. Oxidization of organic sulphur compounds to sulphoxides could occur by the reaction as shown in Eq. 5-14; however, sulphoxide is not stable at high temperature and further transforms to sulphone easily (Ali et al. 2006). Thiophene and sulphide identified in the activated carbon were most likely from the raw coke. There seemed to be a decrease in thiophene content after the reaction with SO2 while the change in sulphide content was minimal. The sulphur atom in thiophene is relatively unreactive; however, the carbon atoms at the 2- and 5-position are highly susceptible to attack by electrophiles. Therefore, the removal of thiophene could be caused by the pi bond removal (Eq. 5-15) as proposed by Jaimes et al. (2009).

2R-S-R’ + SO → 2R-S(O)-R’ + S 2 5-14

5-15 + H2S

4.5 Elemental S Sulphide Thiophene 4.0 Sulphoxide Sulphate 3.5 3.0 2.5 2.0

1.5 1.0

0.5 Sulphur content in specific form (%) form inspecific content Sulphur 0.0 Raw coke SO2 activation

Figure 5-7 Sulphur forms in SO2 activated carbon (FC-S, 700°C, 1 hr)

5.3.3.3 Changes in sulphur species after KOH-SO2 activation

When using KOH and SO2 at the same time, the system became more complex and more types of sulphur species were produced. In order to simplify the system, PCA was applied in the analysis of XANES data (see Chapter 4 for details), and it was found that five

- 103 - components (i.e. elemental sulphur, sulphide, disulphide, sulphonate, and sulphate) would be sufficient for fitting all the spectra of SIACs produced by KOH-SO2 activation but under different activation conditions. By this means, sulphur in other forms with small amounts may be neglected.

Figure 5-8 shows the sulphur species identified in the raw coke and its KOH-SO2 activation product. The SIAC sample was produced at 600°C for 1 hour with KOH/coke ratio of 3:1, and its sulphur content (7.31%) was similar as that of the raw coke (7.37%). Thiophene in the raw coke was completely removed after activation, suggesting that KOH was able to react with organic sulphur in the coke under the condition studied despite the presence of SO2. Interestingly, no elemental sulphur was detected in the activated product, suggesting that KOH was able to prevent the formation of elemental sulphur. Given the high KOH/coke ratio and the relatively low temperature, it is reasonable to expect a much suppressed carbothermal reduction of SO2.

Organic sulphide in fluid coke may be converted to inorganic sulphide through the reaction shown as Eq. 5-12, and removed by washing with deionized water. The existence of sulphonate in the activation product may also suggest the formation of sulphoxide, which could be produced from the reaction between SO2 and sulphide in fluid coke (Eq. 5-14). Sulphoxide can be further oxidized to sulphonate through Eq. 5-16 (Jaimes et al., 2009).

3[RSO‾] → RSO3‾ + 2RS‾ 5-16

4.5 Sulphide Thiophene Disulphide 4.0 Sulphonate Sulphate 3.5 3.0

2.5

2.0

1.5 1.0

0.5 Sulphur content in specific form (%) form in specific content Sulphur 0.0 Raw coke S-KS-12

Figure 5-8 Change in sulphur species after KOH-SO2 activation (FC-S, 700°C, KOH/coke ratio of 3:1, 1-hr activation)

- 104 - Since potassium sulphate is rather water-soluble, the large quantity of sulphate identified in the washed carbon sample was not expected. One possibility is that the washing procedure might not be adequate. Another possibility is that sulphate in the activated carbon may behave differently from bulk-phase potassium sulphate. To verify this, 0.05 g of the sample (S-KS-12), which had been washed with HCl and deionized water after activation, was washed again with deionized water for 4 times (25 mL deionized water and 1 hour per time). The wash solutions were then analyzed using ion chromatography for sulphate concentration. Results in Table 5-6 suggests that the washing procedure was fairly adequate, since the total amount of sulphate removed was only 0.231 mg (0.077 mg of sulphur as sulphate), while the initial amount of sulphur in the form of sulphate is (50 mg x 2.5% = 1.25 mg), suggesting that the second reason might be true.

2- Table 5-6 Removal of SO4 from previously washed sample by additional washing with deionized water 2- 2- Sample Time SO4 Concentration in Sulphate removed S in form of SO4 wash solution (mg/L) (mg) (mg) S-KS-12 1st 9.04 0.226 0.075 2nd 0.20 0.005 0.002 3rd 0 0 0 4th 0 0 0

Figure 5-9 shows the change in sulphur species with KOH/coke ratio. With the increase in KOH/coke ratio the amount of elemental sulphur in the activated carbon decreased, which supports the argument that KOH suppresses the formation of elemental sulphur. Thermodynamically, the reaction between elemental K and elemental S is also feasible. The standard Gibbs free energy change of 2K + S → K2S is -195 kJ/mol at 700°C. This reaction may also consume elemental sulphur produced from carbothermal reduction of

SO2. The decrease in disulphide amount and increase in sulphate amount suggested that with the increase in KOH/coke ratio, more reduced sulphur (e.g. disulphide) was oxidized to oxidized sulphur. One possible reaction is as shown in Eq. 5-13. The increase in sulphate may also be caused by the enhanced reaction between KOH and SO2 with the increased amount of KOH.

- 105 - 3.0 Elemental S Sulphide Disulphide 2.5 Sulphonate Sulphate

2.0

1.5

1.0

0.5 Sulphur content in specific form (%) 0.0 1:1 2:1 3:1 KOH/coke ratio

Figure 5-9 Change of sulphur species in FC-S after KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour)

When the sulphur species were grouped according to their oxidation state (Figure 5-10), with the increase in KOH/coke ratio, the amounts of reduced and elemental sulphur decreased along with an increase in oxidized sulphur. This is in good agreement with the strong oxidizing ability of KOH. At a KOH/coke ratio of 3:1, no elemental sulphur was detected in the activated carbon.

4 Elemental S Total sulphide and disulphide 3 Total sulphonate and sulphate

1 S content in specific form (%) form specific in content S

0 1:1 2:1 3:1 KOH/coke ratio

Figure 5-10 Change of grouped sulphur species in FC-S after KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour)

- 106 - Changes in sulphur form after activation for FC-I are shown in Figure 5-11. Since the sulphur content decreased dramatically with the increase in KOH/coke ratio, the amount of each sulphur form was not comparable. For instance, sulphate amount seemed to decrease with the increase in KOH/coke ratio. However, the percentage of sulphate amount in total sulphur actually increased from 41% (KOH/coke = 1:1) to 62% (KOH/coke = 3:1). Elemental sulphur was produced in a large amount when there was no KOH present in the system; with KOH/coke ratio increasing, the amount of elemental sulphur was reduced. The decrease in total amount and percentage of sulphide and disulphide is in agreement with the finding in FC-S activation in which with higher KOH/coke ratio, less reduced sulphur was produced. Again, a KOH/coke ratio of 3:1 was able to prevent the formation of elemental sulphur.

Grouping sulphur species in SIACs produced from FC-I according to sulphur oxidation states showed that all groups of sulphur species generally reduced in amount (Figure 5-12). This may be caused by the efficient removal of sulphur from the raw coke, and no increase in any sulphur species can be observed.

3.0 elemental S sulphide 2.5 disulphide sulphonate sulphate 2.0

1.5

1.0

S content in specific form (%) form specific in S content 0.5

0.0 1:1 2:1 3:1 KOH/coke ratio

Figure 5-11 Change of sulphur species in FC-I after KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour)

- 107 - 5 Total sulphide and disulphide 4 Total sulphonate and sulphate Elemental S 3

1 S content in specific form (%) form in specific content S

0 1:1 2:1 3:1 KOH/coke ratio

Figure 5-12 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation with different KOH/coke ratios (700°C, 1 hour)

5.3.3.4 Effects of Activation Temperature

So far, it has been established that after KOH-SO2 activation and acid washing, reduced organic sulphur such as thiophene and sulphide are converted to oxidized sulphur such as sulphonate and sulphate. These changes are often companied by the decrease in total sulphur and organic sulphur since many oxidized inorganic sulphur species are water soluble. Figure

5-13 shows the temperature dependence of KOH-SO2 activation. When the temperature increases, the most notable trend is the decrease in the amount of sulphate and sulphonate. There are at least two possible reasons behind the decrease. First, at higher temperatures, less sulphur is converted to sulphate and sulphonate. Second, the sulphate and sulphonate formed at higher temperatures are more easily removed during acid washing. However, to draw any clear conclusion more work is needed.

- 108 - 3.5 Sulphide Disulphide 3.0 Sulphonate Sulphate

2.5

2.0

1.5

1.0

0.5 Sulphurcontent in specific form (%) 0.0 600 700 800 Activation temperature (°C)

Figure 5-13 Change in sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-S, KOH/coke ratio of 3:1, 1- hr activation)

The decrease in the amount of sulphonate and sulphate with the increase in activation temperature was also observed in FC-I activation (Figure 5-14). The total amount of sulphide and disulphide seems to increase with temperature. Little amount of elemental sulphur was produced at 600°C; however, with increasing activation temperature, the evaporation of elemental sulphur became easier, which may be the reason for the disappearance of elemental sulphur at higher temperatures. It is however not clear if this increase in reduced sulphur is related to the decrease in oxidized sulphur. The reaction between KOH and carbon in coke was faster at higher temperatures, which resulted in a greater weight loss. Apparently, the reaction between KOH and organic sulphur may respond to temperature change differently.

The changes in sulphur forms with the increase in activation temperature were also present in grouped sulphur forms according to their oxidation states as shown as in Figures 5- 15 and 5-16. There is a decrease in the amount of oxidized sulphur species (i.e. sulphonate and sulphate) and a general increase in the amount of reduced sulphur (i.e. sulphide and disulphide), with increasing temperature.

- 109 - 1.2 elemental S sulphide disulphide 1.0 sulphonate sulphate

0.8

0.6

0.4

S content in specific in S content (%) form 0.2

0.0 600 700 800 Temperature (°C)

Figure 5-14 Change in sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-I, KOH/coke: 3:1, 1 hour, 30% SO2)

5 Total sulphide and disulphide

4 Total sulphonate and sulphate

1 Scontent in specific form(%)

0 600 700 800 Temperature (°C)

Figure 5-15 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-S, KOH/coke ratio of 3:1, 1- hr activation)

- 110 - 2.5 Total sulphide and disulphide Total sulphonate and sulphate 2.0 Elemental S

1.5

1.0

0.5 S content in specificS in content (%) form 0.0 600 700 800 Temperature (°C)

Figure 5-16 Change in grouped sulphur species in SIACs produced by KOH-SO2 activation at different temperatures (FC-I, KOH/coke: 3:1, 1 hour, 30% SO2)

5.4 CONCLUSIONS

Elemental analysis showed that the two fluid coke samples contained 7.4 % and 5.6 % sulphur, respectively. Wet chemical analysis revealed that about 90 % of sulphur in the two samples was organic in nature; the remaining 10 % was in the form of inorganic oxides. XANES analysis indicated that over 50 % of the organic sulphur was in the form of thiophene while the rest was sulphide.

In the KOH-coke system, KOH removed most of the organic sulphur in the fluid coke, from 7.4% to less than 0.3% after one hour activation. The final forms of sulphur in the

KOH-activated carbon were likely K2S and K2SO4, while K2S was susceptible to oxidation during washing. After one hour KOH activation at 600-900°C, no thiophene was found in the activated products. Overall, KOH was very effective in converting organic sulphide/thiophene to water-soluble inorganic sulphur species.

Thermodynamic analysis predicts that the reactions between KOH and carbon produce

K2CO3, elemental K and H2 gas at temperatures between 600 to 900 °C. K2CO3, and H2 were identified in the activation products, while there was indirect evidence of the presence of

- 111 - elemental K. At higher temperatures, K2CO3 may become reactive towards carbon and act as an activating agent, which changes the KOH/C stoichiometric ratio of the overall reaction.

In the SO2-coke system, the carbothermal reduction of SO2 was able to produce elemental sulphur. A substantial amount of elemental sulphur was retained in the activated products despite the temperature being higher than the boiling point of elemental sulphur.

One-hour SO2 treatment of fluid coke at 700°C increased the sulphur content from 7.4% to

9.3%. Elemental sulphur, sulphide, thiophene, sulphoxide and sulphate were found in SO2- treated carbon. Unlike KOH, SO2 was not effective in converting organic sulphide and thiophene in the coke.

The thermodynamic analysis suggests that in KOH-SO2-C high-temperature system,

K2S, K2SO4 and K2CO3 are possible solid products, while CO, CO2, COS, H2O, H2 and S are possible gaseous products. Experiments identified K2S, K2SO4 and K2CO3 in the activated coke, when CO, CO2, S, H2O and H2 were observed in the exit gas from the reactor. The presence of K2SO4 suggests that a portion of the KOH reacted with SO2 and produced K2SO3 which was subsequently converted into K2SO4. This side reaction suppressed the formation of elemental sulphur, and could prevent the formation of elemental sulphur when the KOH/coke ratio was high. Sulphide, disulphide, sulphonate and sulphate were identified in the products of KOH-SO2 activation.

- 112 - CHAPTER 6 ADSORPTION OF MERCURY ION FROM AQUEOUS SOLUTIONS USING COKE-DERIVED SIACS

6.1 INTRODUCTION

Mercury is considered to be one of the most harmful pollutants in the environment, due to its toxicity, high volatility and potential bioaccumulation. The sources of mercury in the environment are mainly from industrial emissions and wastewater. According to US-EPA, coal-fired power plants are considered the major source of mercury emissions into the environment. Meanwhile, mercury is continually released into the aquatic environment from natural processes such as volcanic activity and weathering rocks. Industries mainly responsible for the dispersion of mercury are chlor-alkali, paint, pulp and paper, oil refinery, electrical, rubber processing and fertilizer (Anoop Krishnan and Anirudhan, 2002; Kadirvelu et al., 2004).

Commonly adopted methods to remove mercury ions from industrial wastewater include precipitation, ion exchange, alum and iron coagulation, activated carbon adsorption, electro deposition, and various biological processes (Kadirvelu et al., 2004). Among these methods, activated carbon adsorption is widely used due to its high efficiency and convenience to apply (Namasivayam and Kadirvelu, 1999; Mohan et al., 2000.; Anoop Krishnan and Anirudhan, 2002; Babić et al., 2002; Ekinci et al., 2002.; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Nabais et al., 2006; Budinova et al., 2008; Zhu et al., 2009; Zabihi et al., 2009). Sulphur impregnated activated carbon (SIAC) is a type of activated carbon with sulphur impregnated into the carbon matrix, which has been proven to be more effective in mercury adsorption than virgin activated carbon (Liu and Vidic, 2000; Mohan et al., 2001; Ranganathan and Balasubramanian, 2002.; Anoop Krishnan and Anirudhan, 2002; Feng et al., 2006).

A few studies have been conducted to investigate the possibility of using different types of activated carbon to remove Hg2+ from aqueous solution, most of them focused on investigating the effects of experimental conditions. It was reported that Hg2+ adsorption was strongly dependent on the agitation time, initial concentration of Hg2+, pH, and activated carbon dosage (Namasivayam and Kadirvelu, 1999; Mohan et al., 2001; Anoop Krishnan and

- 113 - Anirudhan, 2002; Babic et al., 2002; Ekinci et al., 2002; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Budinova et al., 2008; Zhu et al., 2009; Zabihi et al., 2009). Although the properties of the activated carbon itself are also important in Hg2+ adsorption, little research on this topic has been reported (Mohan et al., 2001; Ekinci et al., 2002; Kadirvelu et al., 2004; Zhang et al., 2005). The properties of activated carbon that were investigated included surface area, pore size distribution, particle size and surface chemistry.

Surface modification is of particular interest to change the carbon surface chemistry and to improve the performance of activated carbon for mercury removal. Mohan et al. (2001) used carbon disulphide to treat air-activated fertilizer waste, and observed an increase in the uptake of Hg2+ from wastewater. Ranganathan and Balasubramanian (2002) prepared sulphide loaded activated carbon from coconut shells by chemical treatment with sulphide and thermal activation. The carbons with and without sulphide treatment were used for Hg2+ adsorption, and the results showed that the sulphide loaded activated carbon was more effective. The studies of Hg2+ uptake from aqueous solution by steam-activated carbon and sulphurized steam-activated carbons revealed that the order of their adsorption capacity is: steam activated carbon in presence of SO2 and H2S > steam activated carbon in presence of

SO2 > steam activated carbon in presence of H2S > steam-only activated carbon (Anoop Krishnan and Anirudhan, 2002). It was suggested that Hg2+ adsorption capacity of activated carbons was associated with their sulphur content and pore volume. Nabais et al. (2006) modified the surface of activated carbon fibres with powdered elemental sulphur and H2S gas. It was found that the most important parameter for mercury uptake is the type of sulphur introduced rather than total sulphur amount. They suggested that H2S treatment leads to the formation of functional groups where the sulphur is more accessible to mercury than the functional groups formed during the reaction with powdered sulphur. However, the types of functional groups formed during the modification processes were not identified. Although surface modification of activated carbon is promising for improving Hg2+ adsorption, more work is needed to fully understand what types of functional groups on the surface of activated carbon are beneficial for Hg2+ adsorption.

In previous sections, SIACs production from oil-sands fluid coke was reported. In this section, the application of produced SIACs is explored. The purpose of this study was to

- 114 - evaluate the performance of SIACs produced from KOH-SO2 activation in mercury ion adsorption, and to investigate the effects of SIAC properties on mercury adsorption.

6.2 EXPERIMENTAL

6.2.1 Adsorbents

The adsorbents used to adsorb mercury ion from aqueous solutions were produced from oil-sands fluid coke using KOH and SO2 activation which was described in Chapter 3.

Briefly, in this process, KOH and SO2 were used to activate fluid cokes (FC-S and FC-I) and to add sulphur to the coke in one step. Activations were conducted at 600 – 900°C, for 15 – 120 min, with KOH/coke ratio of 1:1 to 3:1. Five KOH-activated carbons (No. 17-21 in

Table 6-1) which were activated without the presence of SO2, two SO2-activated carbons (No. 16 and 17) without presence of KOH and one commercial SIAC (SIAC-BG) were used for comparison purposes.

Table 6-1 shows the properties of these samples. The BET surface area (SBET) and pore size distribution of these samples was determined using a surface area and pore size analyzer (SA3100, Coulter). Total sulphur content was measured by an elemental analyzer (Vario EL III). Sulphur forms in SIAC samples before and after mercury adsorption were identified and quantified using X-ray absorption near edge structure (XANES) spectroscopy. XANES analyses were conducted at the Canadian Synchrotron Radiation Facility (CSRF) situated on the 1GeV electron storage ring, at Aladdin, University of Wisconsin. Detailed description for XANES analysis is in Chapter 4.

- 115 - Table 6-1 Summary of the properties of SIAC samples Pore volume Micropore No Sample S (m2/g) S (%) BET (mL/g) percentage (%) 1 S-KS-1 1451 0.75 41 8.10 2 S-KS-2 1222 0.62 64 7.31 3 S-KS-4 2108 1.11 30 4.84 4 S-KS-5 2505 1.39 28 3.50 5 S-KS-12 1174 0.59 67 5.14 6 S-KS-14 1753 0.87 84 2.70 7 S-KS-15 431 0.23 62 5.31 8 S-KS-16 1183 0.59 68 4.52 9 I-KS-1 1958 0.96 54 2.46 10 I-KS-2 1299 0.65 65 0.96 11 I-KS-3 2281 1.17 30 2.20 12 I-KS-12 1567 0.79 81 6.10 13 I-KS-15 410 0.22 62 7.41 14 I-KS-16 1183 0.59 72 3.48 15 S-KS-17 19 0.02 35 9.34 16 I-KS-17 13 0.02 56 8.04 17 S-KOH-2 2501 1.42 12 0.09 18 S-KOH-10 2088 1.05 51 0.12 19 S-KOH-12 1498 0.76 58 0.27 20 S-KOH-6 732 0.39 62 0.61 21 S-KOH-7 1695 0.86 52 0.17 22 SIAC-BG 664 0.35 28 8.11

6.2.2 Mercury Ion Adsorption

The procedure for determination of Hg2+ adsorption capacity was designed based on the

ASTM method, D3860-98. 0.1 g of activated carbon was added to 100 ml HgCl2 (from Aldrich) solution with initial mercury concentration of 100 mg/L. The suspension was shaken at 130 rpm and 25°C. The solution, 1 mL was sampled by a 10-mL plastic syringe at certain time intervals until 930 min or more. The sample solution was then filtered with a syringe filter (0.22 μm), diluted with deionized water, and analyzed by Inductively Coupled Plasma (ICP, Optima 7300, PerkinElmer). The plot of Hg2+ concentration in each sample vs.

- 116 - time gave the adsorption curve. The adsorption capacity was expressed as the amount of Hg2+ adsorbed, X, per unit weight of carbon, M, which was calculated by Eq. 6-1.

X/M = (CoVo-CV)/M 6-1 2+ Where Co = concentration of Hg before carbon treatment, mg/L, C = concentration of Hg2+ after carbon treatment, mg/L, 2+ Vo = volume of Hg solution before carbon treatment, L, and V = volume of Hg2+ solution after carbon treatment, L.

The adsorption isotherms of Hg2+ onto SIACs were determined by adsorbing Hg2+ from a series of HgCl2 solutions with different initial concentrations (50 – 400 mg/L). 0.1 g of

SIAC was dosed into 100 mL of HgCl2 solution, and the suspension was shaken at 130 rpm and 25°C over 20 hours. Samples were taken from the suspension afterwards, and analyzed using ICP to determine the equilibrium concentration of Hg2+.

6.3 RESULTS AND DISCUSSION

6.3.1 Adsorption Conditions

2+ Figure 6-1 shows typical curves of Hg adsorption by KOH-SO2 activated carbon at 25°C with initial mercury concentration of 100 mg/L and initial pH of 4.8. In Figure 6-1, sample S-KS-5 exhibits the highest adsorption capacity while sample S-KS-12 shows the lowest adsorption capacity. The decrease in Hg2+ concentration was the result of the adsorption of Hg2+ by SIACs. From the adsorption curves, it can be seen that Hg2+ adsorption mainly took place within 60 min, and after 100 min the Hg2+ concentration became the equilibrium value. The rapid uptake of Hg2+ at a short contact time and the continuous fashion of removal curves approaching saturation may be attributed to the saturation of a relatively small amount of adsorption sites. This suggests that monolayer coverage of Hg2+ may be formed on the carbon surface (Yardim et al., 2003). By calculation, for an uptake of 100 mg Hg2+ on the surface of 1 g activated carbon, the surface area needed by the 100 mg of Hg2+ is only about 1.5 m2. Compared to the surface area of an activated carbon, which is usually higher than 1000 m2/g, the surface area needed by Hg2+ ions is very small. Therefore, the formation of monolayer coverage of Hg2+ is possible.

- 117 - 120 S-KS-12 100 S-KS-16 S-KS-5 80

concentratiion (mg/L) 40 2+ 2+ Hg 20

0 0 100 200 300 400 500 600 700 800 900 1000 Adsorption time (min)

2+ Figure 6-1 Typical curves for Hg adsorption from HgCl2 solutions

Table 6-2 pH values for effective adsorption of Hg 2+ observed in previous studies Range of pH values for Reference Adsorbent effective adsorption Carrott et al., 1997 Steam activated peat and lignin <2.5 Namasivayam and H SO and (NH ) S O activated 2 4 4 2 2 8 >5 Kadirvelu, 1999 coirpith Mohan et al., 2001 Air-activated fertilizer waste 2.0 Ekinci et al., 2002 Steam activated furfural and coal 5-8 NH Cl/ZnCl impregnated and Babić et al., 2002 4 2 2.5-5 CO2 activated carbon cloth Anoop Krishnan and Steam activated and sulphurized 4-6 Anirudhan, 2002 activated bagasse pith

Yardim et al., 2003 H2SO4 activated furfural 4-8 H SO and (NH ) S O activated Kadirvelu et al., 2004 2 4 4 2 2 8 >4 sago waste H SO , H PO or ZnCl activated Zhang et al., 2005 2 4 3 4 2 >5 organic sewage sludge K CO activated waste antibiotic Budinova et al., 2008 2 3 5-9 material

Zabihi et al., 2009 ZnCl2 activated walnut shell 2-5

- 118 - Hg2+ adsorption by activated carbon is strongly dependent on adsorption conditions, which has been extensively studied (Namasivayam and Kadirvelu, 1999; Mohan et al., 2001; Anoop Krishnan and Anirudhan, 2002; Babic et al., 2002; Ekinci et al., 2002; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Budinova et al., 2008; Zhu et al., 2009; Zabihi et al., 2009). It is worth noting that Hg2+ adsorption by activated carbon is highly pH dependent. To control the pH of the solution during adsorption, buffer solution has to be added to the mercury solution. For instance, Zhu et al. (2009) used 0.01 M KH2PO4-NaOH to maintain a constant pH (~6). However, most researchers did not add buffer solution to control the pH throughout the adsorption process. Instead, adjusting the initial pH of the solution with dilute HCl or NaOH was commonly applied when conducting adsorption experiments (Carrott et al., 1997; Namasivayam and Kadirvelu, 1999; Mohan et al., 2001; Yardim et al., 2003; Kadirvelu et al., 2004; Zhang et al., 2005; Budinova et al., 2008; Zabihi et al., 2009), which means the variation of pH during Hg2+ adsorption was neglected. The pH values for effective adsorption of Hg2+ observed in previous studies are summarized in Table 6-2. The type of species of Hg2+ in the water solution strongly depends on the pH. According - to Knocke and Hemphil (1981), in the presence of Cl , at pH < 4.0, HgCl2 is dominant, and at pH > 4.0 Hg(OH)2 is the main form of mercury, based on the stability constant calculation. Using software PSEQUAD, Zekany and Nagyal (1985) found that the dominant mercury 2+ species is Hg at pH <3.0, Hg(OH)2 at pH >5, and both of these forms between the pH of 3- 5. Anoop Krishnan and Anirudhan (2002) suggested that for sulphurised activated carbon the 2+ interaction between Hg species such as HgCl2, (HgCl2)2, Hg(OH)2 and HgOHCl with surface sulphur groups is likely favoured in the pH range of 4-6.

In this study, the initial pH was in the range of 4.8-5.0, and it was monitored during Hg2+ adsorption. The pH was not controlled during Hg2+ adsorption, since the pH value was expected to be favourable for Hg2+ adsorption based on the literature review, with the consideration that the use of buffer solutions is not practical under real application conditions. Changes in pH during Hg2+ adsorption are shown in Figure 6-2. It was found that in all cases the pH significantly decreased. Since KOH was used in activating fluid coke, functional groups containing H+ may exist on the surface of activated carbon. During mercury adsorption, ion exchange may occur between H+ in activated carbon and Hg2+ or Hg(OH)+ in the solution. Therefore, the decrease in pH could be caused by mercury adsorption, since the

- 119 - more Hg2+ or Hg(OH)+ are adsorbed onto the carbon, the more hydrogen ions are released from the carbon into the solution (Namasivayam and Kadirvelu, 1999; Anoop Krishnan and Anirudhan, 2002; Kadirvelu et al., 2004).

4.5

3.5 pH

2.5 Control 1:1; 700C 2:1; 700C 3:1; 700C 3:1; 600C 3:1; 800C 2 0 50 100 150 Adsorption time (min)

2+ Figure 6-2 Changes of pH during adsorption of Hg by SIACs produced from KOH-SO2 activation under different temperatures and KOH/coke ratios

6.3.2 Adsorption Isotherms

The adsorption isotherms of Hg2+ onto SIACs were studied at 25°C (298 K). The data were fitted to Langmuir and Freundlich isotherms. The Langmuir equation has the linearized form:

Ce/qe = 1/ (Q0b) + (1/Q0) Ce 6-2

Where Ce is the equilibrium concentration of the solution, mg/L, and qe is the amount of adsorbate in activated carbon, mg/g. By calculating the intercept and the slope, Q0 (the adsorption capacity) and b (the Langmuir constant related to the energy of adsorption) can be obtained (Ranganthan and Balasubramanian, 2002; Ekinci et al., 2002). Figure 6-3 shows the 2+ linear plot of specific sorption (Ce/qe) against the equilibrium concentration (Ce) for Hg adsorption using two SIAC samples: S-KS-2 and S-KOH-6. All these samples were produced at 600°C with a KOH/coke ratio of 3:1. S-KS-2 was produced from KOH-SO2 activation for one hour, and S-KOH-6 was produced by KOH activation for 15 min.

- 120 - 8 S-KOH-6 7 S-KS-2 6 Linear (S-KOH-6) 5 Linear (S-KS-2)

3 Ce/qe (g/L) Ce/qe 2

0 0 100 200 300 400 Ce (mg/L)

Figure 6-3 Langmuir isotherms of Hg2+ adsorption by different samples produced from FC-S at 25°C

2 2+ The values of Q0, b and correlation coefficients (R ) of Hg adsorption are shown in 2+ Table 6-4. The higher Q0 of S-KS-2 indicates that it has higher adsorption capacity of Hg than S-KOH-6. The constant b in Eq. 6-2 is related to the free energy of adsorption (b ∝ e – ΔG/RT ), and can be used to calculate the dimensionless separation factor RL, which is defined as RL = 1/(1 + bC0), where C0 is the initial concentration (mg/L). According to Hall et al.

(1966), RL is an indicator of favourability of the isotherm. RL > 1 indicates an unfavourable adsorption; RL = 1 is for linear adsorption; 0< RL <1 indicates a favourable adsorption; RL = 0 indicates an irreversible adsorption. For both S-KS-2 and S-KOH-6, the R1 values are between 0 and 1 (0.51 and 0.28, respectively), suggesting a favourable adsorption of Hg2+ by these activated carbons.

Properties of SIAC S-KOH-6 and S-KS-2 and their adsorption capacities are summarized in Table 6-3. Comparing the properties of the two samples, it was found that S-

KOH-6 has much lower SBET and sulphur content, which results in its low Q0.

Table 6-3 Properties of SIACs and their adsorption capacities of Hg2+ at 25ºC, with initial HgCl2 concentration of 100 ppm 2 2+ SIAC SBET (m /g) Sulphur content (%) Hg adsorption capacity (mg/g) S-KOH-6 723 0.61 32.7 S-KS-2 1222 7.31 53.2

- 121 - Freundlich adsorption isotherm often fits the data on rough surfaces better than Langmuir equation, since it was modified from the Langmuir equation to account for surface roughness and inhomogeneity in the adsorbent, and adsorbate-adsorbate interactions. The Freundlich isotherm describes the relationship between the adsorbed amount per unit weight of the adsorbent and the equilibrium concentration of adsorbate. Its linear form is:

log qe = log KF + (1/n) log Ce 6-3

In this Eq. 6-3, qe is the amount of adsorbate adsorbed by activated carbon (mg/g) and

Ce is the equilibrium concentration of the adsorbate in solution (mg/L). KF is the constant indicative of the relative adsorption capacity of the adsorbent (mg/g) and 1/n is the constant indicative of the intensity of the adsorption (Soleimani and Kaghazchi, 2008). The logarithmic graph for Freundlich isotherm model of Hg2+ adsorption on S-KS-2 and S-KOH- 6 is shown in Figure 6-4.

The Freundlich constants 1/n and KF were calculated using the slopes and intercepts of 2+ the lines (Table 6-4). A small 1/n and large KF values of Hg adsorption by activated carbon usually indicate its high affinity to Hg2+ and adsorption capacity (Vazquez et al., 2002). However, since S-KOH-6 is more likely to follow the Langmuir model due to its higher correlation coefficient for the Langmuir model than that for Freundlich model, it cannot be concluded that S-KOH-6 has a higher adsorption capacity. On the contrary, S-KOH-6 has a lower adsorption capacity than S-KS-2 (Table 6-3). The values of 1/n for these samples are between 0 and 1, indicating that the surfaces of these samples are heterogeneous in nature (Zhang et al., 2005).

- 122 - 2.2 S-KS-2

2 S-KOH-6 Linear (S-KS-2) Linear (S-KOH-6) 1.8

Log qe 1.6

1.4

1.2 11.522.53 Log Ce

Figure 6-4 Freundlich isotherms for Hg2+ uptake on different samples produced from FC-S at 25°C

The corresponding Freundlich and Langmuir parameters along with correlation coefficients are given in Table 6-4. The correlation coefficients showed that the data of Hg2+ adsorption by S-KS-2 fit the Freundlich model better than the Langmuir equation, whereas for S-KOH-6, its adsorption data fits the Langmuir model better. The mercury adsorption process takes place at the liquid-solid boundary, and the diffusion process occurs in a complex matrix. The reaction is thus expected to be heterogeneous. The complex adsorption phenomenon may involve chemical interactions between the solute and the chemical groups on the activated carbon surface, besides other driving forces, such as electrostatic interaction, Van der waals and hydrophobic interactions (Gaspard et al., 2006). Since samples S-KS-2 have a high sulphur content, it is highly possible that chemical reaction takes place between mercury and sulphur functional groups on SIAC surface. However, for sample S-KOH-6, its sulphur content is only 0.6%, which may not react with mercury. Therefore, the better fit of the Freundlich model indicates that the surface of S-KS-2 is more heterogeneous due to the loading of sulphur, while the surface of S-KOH-6 is more homogeneous.

Table 6-4 Parameters of Langmuir and Freundlich models for the adsorption of Hg2+ on activated carbons at 25ºC Langmuir model Freundlich model 2 2 R Q0 (mg/g) b R KF (mg/g) 1/n S-KS-2 0.9303 112 9.6 × 10-3 0.9572 5.7 0.48 S-KOH-6 0.9702 54 0.026 0.9091 12.3 0.24

- 123 - Two SIACs, S-KS-2 and I-KS-2, produced from FC-S and FC-I, respectively, were used to investigate if there is difference between the adsorption behaviour of SIACs produced from different raw cokes. Both these samples were produce from KOH-SO2 activation at 600°C for 1 hour, with KOH/coke ratio of 3:1. Their properties are listed in Table 6-5.

Table 6-5 Activation conditions and properties of S-KS-2 and I-KS-2 Sulphur content SIAC Raw coke S (m2/g) Hg2+ adsorption capacity (mg/g) BET (%) S-KS-2 FC-S 1222 7.31 53.2 I-KS-2 FC-I 1299 0.96 51.9

Figure 6-5 and 6-6 show the fitting of Hg2+ adsorption data for S-KS-2 and I-KS-2 using the Langmuir and Freundlich isotherms. The corresponding Freundlich and Langmuir parameters for these samples are very similar, suggesting that there is no significant dependence of Hg2+ adsorption on the raw coke which was used for preparing SIACs.

4 2 3.5 R = 0.9303

2.5 R2 = 0.9292

2 I-KS-2 1.5 Ce/qe (g/L) Ce/qe S-KS-2 1 Linear (I-KS-2) 0.5 Linear (S-KS-2) 0 0 100 200 300 400 Ce (mg/L)

Figure 6-5 Langmuir isotherms of Hg2+ adsorption by SIACs produced from FC-S (S-KS-2) and from FC-I (I-KS-2) at 25°C

- 124 - 2.5

1.5

I-KS-2

Log qe Log 1 S-KS-2

2 0.5 Linear (S-KS-2) R = 0.9572 Linear (I-KS-2) R2 = 0.9516 0 0 0.5 1 1.5 2 2.5 3 Log Ce

Figure 6-6 Freundlich isotherms of Hg2+ adsorption by SIACs produced from FC-S (S-KS-2) and from FC-I (I-KS-2) at 25°C

6.3.3 Adsorption Capacity

SIACs produced in this study exhibit high Hg2+ adsorption capacity, ranging from 42.6 to 71.5 mg/g. In order to evaluate the SIACs produced in present study, a commercial SIAC- 2+ BG (obtained from Barrick Gold Corporation) was used to adsorb Hg from HgCl2 solution under the same experimental conditions. The Hg2+ adsorption capacity of SIAC-BG was 40.8 mg/g which is lower than that of all SIACs produced in this study. The known Hg2+ adsorption capacity which has been reported in the literature for similar adsorption conditions as that applied in this study was about 35-100 mg/g (Anoop Krishman and Anirudhan, 2002; Ranganathan and Balasubramanian, 2002; Kadirvelu et al., 2004; Zabihi et al., 2009). For the same adsorption conditions, SIAC properties, such as surface area, pore size distribution and surface chemistry, also affect the uptake of Hg2+. In this study, the highest capacity is 71.5 2 mg/g which belongs to the SIAC with the SBET of 1451 m /g, pore volume of 0.75 mL/g and sulphur content of 8.1%.

6.3.3.1 Effect of SBET

The SBET of SIACs may significantly affect the adsorption of mercury. Ekinci et al. (2002) used three types of activated carbon from apricot stones, furfural and coals to remove 2+ Hg from aqueous solution. Their results showed that the increase in SBET increased the

- 125 - adsorption of Hg2+. The finding is also supported by the study of Zhang et al. (2004), who used organic sewage sludge as the starting material.

2+ Although the correlation between the SBET of activated carbon and its Hg adsorption capacity was suggested, there was no strong evidence to support this point, since the adsorption capacity was also affected by other factors, such as pore structure and surface chemistry. In this study, results from a series of SIACs with similar sulphur content 2+ (0.1~0.6%) but various SBET showed that Hg adsorption capacity increased with the 2+ increase in the SBET (Figure 6-7). It is interesting that with higher SBET, the increase in Hg adsorption capacity slows down, which may be associated with the pore structure of SIACs. High porosity is usually contributed by micropores, and their small size may not be 2+ accessible to Hg , especially when other mercury species such as HgCl2 and HgOHCl exist

(Budinoca et al., 2008). Figure 6-8 reveals a positive linear correlation between the SBET and adsorption capacity. An F-test for this regression indicates that the regression is statistically significant (Detailed calculation in Appendix B-4-1). However, the straight line does not go through the origin, yet theoretically, the adsorption capacity should be zero if there is no surface area. Therefore, the plot of SBET vs. adsorption capacity was also fitted using non- linear function, i.e. an exponential equation (Figure 6-9). It was found that the enhancement 2 of SBET on adsorption capacity diminished when the SBET was higher than 1000 m /g. This is an important finding, which reveals that extremely high surface area of SIACs may not be necessary for a high Hg2+ adsorption. This is also supported by the calculation result that the coverage of Hg2+ ions on the SIAC surface is very small (~1.5 m2 for100 mg of Hg2+ in 1 g of SIAC). In fact, using SIACs with moderate specific surface area for Hg2+ adsorption can be more economically efficient, since a large amount of KOH is usually needed to produce SIACs with high surface area.

- 126 - 70

20 adsorptioncapacity (mg/g)

2+ 10 Hg 0 732 1498 1695 2088 2501

2 SBET (m /g)

Figure 6-7 Comparison of Hg2+ adsorption capacities of SIACs with similar sulphur contents (0.1~0.6%) but different surface area.

40 y = 0.0136x + 30.748 2 30 R = 0.7688

20 adsorption capacity (mg/g) capacity adsorption

2+ 10 Hg 0 0 500 1000 1500 2000 2500 3000

2 SBET (m /g)

2+ Figure 6-8 Effect of SBET on Hg adsorption capacity

- 127 -

2+ Figure 6-9 Data fitting of SBET vs. Hg adsorption capacity using exponential function

6.3.3.2 Effect of Total Sulphur Content

2 Mercury adsorption using SIACs with a narrow range of SBET from 1174 to 1958 m /g revealed that the more sulphur that was in the SIACs, the more mercury that could be removed. However, although the range of SBET was narrow, there were still differences in 2+ SBET among these samples, and the effects of SBET on Hg could not be neglected. Therefore, a weak correlation was observed between total sulphur content and Hg2+ adsorption capacity. In order to show the real correlation between total sulphur content and Hg2+ adsorption capacities, it is ideal to use SIACs with similar SBET. However, it is difficult to prepare SIAC 2+ samples with the same SBET but different sulphur contents, so the sulphur content and Hg adsorption capacity of each sample was normalized by its BET surface area. In this case, a reasonable assumption was made that sulphur distribution in SIAC is uniform. Figure 6-10 clearly shows that Hg2+ adsorption capacity increased with the increase in specific sulphur content. This change was caused by the fact that in coke activation there is normally a negative correlation between the SBET and total sulphur content. An F-test confirmed that the regression of total sulphur vs. adsorption capacity was significant (Appendix B-4-3). These results provide more evidence for a previous study (Anoop Krishnan and Anirudhan, 2002)

- 128 - which suggested that the Hg2+ adsorption capacity increases with the increase in sulphur content.

0.06 )

2 0.05

0.04

0.03

y = 0.3116x + 0.0277 0.02 R2 = 0.5266

adsorption capacity (mg/m 0.01 2+ Hg 0.00 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 S content (mg/m2)

Figure 6-10 Relationship between normalized S content and Hg2+ adsorption capacity

6.3.3.3 Effect of Sulphur Form

The adsorption of HgCl2 on activated carbon in aqueous solutions may occur via two 2+ mechanisms: i) adsorption of HgCl2, and/or ii) reduction of Hg by the surface functional group (Lopez-Gonzalez et al., 1982). Therefore, during mercury adsorption, interaction between Hg2+ and sulphur function groups on SIAC surface is possible. According to the Pearson theory, during an acid-base reaction, hard acids prefer to co-ordinate with hard bases and soft acids to soft bases. Hg2+ is a Lewis acid, and thus, the interaction of Hg2+ species such as HgCl2, (HgCl2)2, Hg(OH)2 and HgOHCl with surface sulphur groups (soft bases) is likely to favour the pH range 4-6 (Pearson, 1988; Anoop Krishnan and Anirudhan, 2002).

Little work has been done on the effective sulphur forms in mercury adsorption. Mohan et al. (2001) observed an increase in the uptake of Hg2+ with the adsorbent presoaked in carbon disulphide, and Feng et al. (2006) found that elemental sulphur was probably most effective for capturing vapour phase mercury, while thiophene and sulphate also showed positive correlations with mercury uptake.

- 129 - In Figure 6-10, it can be noticed that for similar sulphur contents some SIACs have higher adsorption capacities, while others have lower capacities, which may be associated with the sulphur forms. However, it is difficult to determine how sulphur forms affect the adsorption. Therefore, the changes in sulphur forms after adsorption were detected in order to provide information on the type of sulphur species which may be involved in the reaction between sulphur and mercury (Figure 6-11). Table 6-6 lists the properties and adsorption capacities of SIAC samples that were used in this section. Samples S-KS-12, S-KS-16 and I- KS-16 have high Hg2+ adsorption capacities, due to their high surface area. However, it is interesting that although they have similar SBET, their adsorption capacities decrease with the increase in sulphur content. Therefore, the effect of sulphur forms in SIAC was investigated with the consideration that sulphur forms may influence mercury adsorption as suggested by a previous study (Feng et al., 2006, Mohan et al. 2001).

Table 6-6 Properties and Hg2+ adsorption capacities of 5 samples 2 Sample SBET (m /g) S % Hg(II) capacity (mg/g) S-KS-12 1174 5.14 48.22 S-KS-16 1183 4.52 54.71 I-KS-16 1183 3.48 57.39 S-KS-17 19 9.34 22.34 I-KS-17 13 8.04 23.26

60 Sulphide Disulphide sulphonate Sulphate 50

10 S content in specific form (%) form specific in S content 0 S-KS-12 S-KS-12 control S-KS-12 Hg

Figure 6-11 Sulphur form changes in sample S-KS-12 before and after Hg2+ adsorption

- 130 - 0.1 g of sample S-KS-12 was added to 100 mL of deionized water, and shaken overnight, as in the Hg2+ adsorption experiment. By this means, the effect of water on sulphur form changes was investigated. After Hg2+ adsorption, sulphur forms in S-KS-12 Hg adsorbed sample and S-KS-12 control sample did not change (Figure 6-11), yet the amount of each form changed. It suggests that for S-KS-12 adsorption, sulphur form did not change much during the adsorption, or the change is too small to be detected. The large reduction in sulphate amount may be attributed to the solubility of sulphate in water, and the prolonged shaking time. As the result, the percentage of other sulphur species increased.

As shown in Table 6-6, S-KS-16 and I-KS-16 have high Hg2+ adsorption capacities. Figures 6-12 shows that the two samples all have high contents of disulphide and a certain amount of elemental sulphur, which may enhance the adsorption. Samples S-KS-17 and I-

KS-17 have extremely low SBET. However, their adsorption capacities are not very low (Table 6-6), which is due partially to their high sulphur content, and this may also be associated with the large amount of elemental sulphur and thiophene present in these two samples. These findings provided support to the previous studies in which disulphide, elemental sulphur and thiophene in SIACs were found to enhance mercury adsorption (Mohan et al., 2001; Feng et al., 2006). A plot in Figure 6-13 shows a strong dependence of Hg2+ adsorption on the total amount of sulphur in the forms of elemental sulphur and disulphide in samples S-KS-12, S-KS-16 and I-KS-16. This provides further evidence for the effect of these forms of sulphur on mercury adsorption.

- 131 - 4.0 Thiophene Elemental S 3.5 Sulphide disulphide 3.0 Sulphonate Sulphate

2.5

2.0

1.5

1.0

S content in specific form (%) form specific in content S 0.5

0.0 S-KS-12 S-KS-16 I-KS-16 S-KS-17 I-KS-17

Figure 6-12 Sulphur forms in SIAC samples used for Hg2+ adsorption

51 R2 = 0.9978 49 adsorption capacity (mg/g) adsorption 2+ 47 Hg 45 0.00.51.01.52.02.5 S content in forms of elemental S and disulphide (%)

Figure 6-13 Relationship between sulphur forms in SIAC samples (S-KS-2, S-KS-16 and I- KS-16) and Hg2+ adsorption

Most SIAC samples produced in this study have various specific surface areas. Therefore, the contents of reduced sulphur and oxidized sulphur in SIACs were normalized by the SBET to eliminate the effect of surface area and to investigate if there was a correlation between the amount of sulphur in different oxidation states and Hg2+ adsorption capacity. Normalized sulphur content in reduced/oxidized form vs. normalized Hg2+ adsorption capacity was plotted in Figure 6-14, and a strong linear relationship between normalized reduced sulphur and normalized Hg2+ adsorption capacity was found. An F-test was carried

- 132 - out to examine if the regression was significant. The result indicated that with 95% of confidence, the regression between reduced sulphur and adsorption capacity was significant. On the other hand, the regression between oxidized sulphur and adsorption capacity was insignificant (Appendix B-4-4). Therefore, a high content of reduced sulphur in SIACs may enhance Hg2+ adsorption.

0.14 ) 2 2 0.12 R = 0.7196 R2 = 0.9566

0.1

0.08

0.06 Reduced S 0.04

adsorption capacity (mg/m Oxidized S

2+ 0.02 Hg 0 0.00 0.05 0.10 S content in specific form (mg/m2)

Figure 6-14 Relationship between sulphur forms in SIAC samples (S-KS-2, S-KS-16 and I- KS-16) and Hg2+ adsorption

6.3.4 Adsorption Kinetics

Steps in the uptake of an organic/inorganic species by a porous adsorbent were suggested as (Boyd et al., 1947; Reichenberg, 1953):

1. Transport of the adsorbate to the external surface of the adsorbent (film diffusion)

2. Transport of the adsorbate within the pores of the adsorbent except for a small amount of adsorption that occurs on the external surface (particle diffusion)

3. Adsorption of the adsorbate on the internal surface of the adsorbent

It is generally accepted that the process of adsorption itself is very rapid and not the rate-limiting step in the uptake of organic/inorganic compounds. Usually, the adsorption rate is controlled by film diffusion or particle diffusion. When the system has poor mixing, dilute concentration of adsorbate, small particle size and/or high affinity of adsorbate for adsorbent, external transport (film diffusion) is the rate-limiting step. In contrast, the internal transport

- 133 - (particle diffusion) step limits the overall rate for those systems which have high concentration of adsorbate, good mixing, large particle size of adsorbent, and/or low affinity of adsorbate for adsorbent (Mohan et al., 2001). According to this, Hg2+ adsorption on SIACs in this study is more likely film-diffusion controlled.

In order to calculate the rate of mercury adsorption by SIAC, a pseudo first order rate expression was applied (Eq. 6-4). This equation has been commonly used to describe the behaviour of mercury adsorption from aqueous solutions (Mohan et al., 2001; Yardim et al., 2003; Zhang et al., 2005).

kt qqte(1 e ) 6-4

Where qt is the adsorption capacity at any time (t, min), mg/g, and qe is the equilibrium -1 capacity, mg/g. k is the pseudo first order rate constant, min . Since qt and qe can be calculated with Eq. 6-4, the slope of a logarithmic plot of [ ln(qqet ) ln q e] vs. t gives the adsorption rate constant, k (Eq. 6-5)

ln(qqet ) ln q e  kt 6-5

The plot as per Eq. 6-5 for a SIAC sample I-KS-1 is shown in Figure 6-15. A linear straight line plot in all cases was observed with correlation coefficients higher than 0.97, which indicates that the adsorption reaction can be approximated as pseudo-first-order.

2.5 test 1

2.0 test 2 Linear (test 1) R2 = 0.9671 2 1.5 Linear (test 2) R = 0.9761

1.0 Lnqe-Ln(qe-q)

0.5

0.0 0 10203040506070 Time (min)

Figure 6-15 Pseudo-first-order kinetic plots for the adsorption of Hg 2+ on a SIAC sample (I- KS-1)

- 134 - Experimental data of Hg2+ adsorption was fitted using software, OriginPro 7.5, with the exponential function in form of Eq. 6-4, and most of the correlation coefficients for these fittings were higher than 0.95 (Table 6-7). One example of the fit is given by Figure 6-16. Adsorption rate constants can be obtained from the equation given by the software.

Figure 6-16 An example of fitting Hg2+ adsorption curve using OriginPro 7.5

Table 6-7 Adsorption constants of Hg2+ uptake by SIACs Sample Rate constant, k (min-1) Correlation coefficient, R S-KS-1 0.024 0.9814 S-KS-2 0.035 0.9947 S-KS-4 0.044 0.9950 S-KS-5 0.057 0.9961 S-KS-12 0.048 0.9944 S-KS-14 0.017 0.9795 S-KS-15 0.032 0.9810 S-KS-16 0.060 0.9975 I-KS-1 0.030 0.9873 I-KS-2 0.026 0.9542 I-KS-3 0.102 0.9641 I-KS-12 0.010 0.9917 I-KS-15 0.051 0.9519 I-KS-16 0.049 0.9917

- 135 - The k values for SIACs produced in this study were in the range of 0.01 – 0.102 min-1 (Table 6-7). The highest k value given by sample I-KS-3 may be attributed to the high mesopore volume of this sample (0.82 mL/g in the range of 0.09 – 1.00 mL/g for all studied SIACs). Under similar adsorption conditions (25-29°C, pH of 5 -5.5 and initial mercury concentration of 40-80 mg/L), it was found that the k values obtained in this study were -1 similar to those from the commercial activated carbon SIAC-BG (0.11 min ), an H2SO4 -1 activated furfural (0.097 min ), as well as an H2SO4 and (NH4)2S2O8 activated coirpith (0.075 min-1) (Namasivayam and Kadirvelu, 1999; Yardim et al., 2003). They were much higher than the values obtained from activated carbon produced from organic sewage sludge -1 using H2SO4, H3PO4 and ZnCl2 (0.008-0.018 min ), and from an air-activated fertilizer waste (0.0102 min-1) (Mohan et al., 2001; Zhang et al., 2005). The k values obtained in this study -1 were lower than that from a ZnCl2 activated carbon produced from walnut shell (0.15 min ) (Zabihi et al., 2009). However, Zabihi et al. did not mention the initial concentration of their mercury solutions in kinetic study. Therefore, the higher k value from their work could be caused by a lower initial concentration, since generally the k value increases with the decrease in the initial Hg2+ concentration.

6.4 CONCLUSIONS

2+ The data of equilibrium Hg adsorption on KOH-SO2 activated carbon fits the Freundlich model, suggesting that the SIAC surface is heterogeneous and the process may be chemical adsorption dominant. Hg2+ adsorption capacity of SIACs ranges from 43 to 72 mg/g, which is comparable with those reported in literature (35-100 mg/g) and that of a commercial SIAC (41 mg/g).

2+ In general, Hg adsorption capacity increased with the increase in the SBET of SIAC, 2+ indicating that a high SBET was beneficial for Hg adsorption. However, the benefit started to 2 diminish when SBET was greater than about 1000 m /g, which may suggest that more active 2+ sites become inaccessible to Hg in the SIACs with higher SBET. A statistically significant and positive correlation was found between Hg2+ adsorption capacity and total sulphur content on a per unit SBET basis. Moreover, there was a positive correlation SBET-normalized reduced sulphur (i.e. sulphide, disulphide, elemental sulphur and thiophene) and Hg2+

- 136 - adsorption capacity, indicating that reduced sulphur played an important role in Hg2+ adsorption. Disulphide, thiophene and elemental sulphur could be the major forms of sulphur which were largely responsible for the enhanced Hg2+ adsorption by SIACs.

Pseudo-first order rate expressions can describe the Hg2+ adsorption behaviour of SIACs produced from fluid coke, with correlation coefficients higher than 0.95. The rate constants (0.01-0.102 min-1) were comparable with those from previous studies (0.008-0.15 min-1) and a commercial SIAC (0.11 min-1) under similar experimental conditions.

- 137 - CHAPTER 7 OVERALL CONCLUSIONS

Following conclusions are drawn from this study:

1. It is technically feasible to activate fluid coke with KOH. The highest specific surface 2 area (SBET) achieved was 2500 m /g, which is much higher than that in the literature (370 2 m /g). The SBET and pore size distribution of KOH-activated carbon were controllable by varying the activation conditions (i.e. activation temperature, time and KOH/coke ratio). High sulphur content in the raw coke may be advantageous to the activation.

2. KOH and SO2 in combination were able to produce sulphur-impregnated activated carbons with controllable porosity and sulphur content. The increase in activation 2 temperature (600 – 900°C) resulted in a higher SBET (1220 to 2500 m /g) and a lower sulphur content (7.3% to 3.5%). The effect of increasing KOH/coke ratio (1:1 - 3:1) was 2 similar, with SBET rising from 430 to 1430 m /g and sulphur content dropping from 5.3%

to 4.9%. Prolonging activation time from 1 hour to 2 hours increased the SBET and total

sulphur content with larger weight loss. Micropore SA percentage of KOH-SO2 activated coke decreased with the increase in activation temperature and time, from 70% to 34% and 63% to 50%, respectively.

3. K-edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy was employed to characterize sulphur in two fluid coke samples and their activation products. XANES results were found to be consistent with XPS results. While both XANES and XPS techniques could distinguish reduced sulphur and oxidized sulphur, XANES was more capable of differentiating some sulphur species at low oxidation states. A procedure which combined two data processing methods was proposed in this study to improve the accuracy and reliability of XANES analysis.

4. Elemental analysis showed that two coke samples contained 7.4 % and 5.6 % sulphur, respectively. Wet chemical analysis revealed that about 90% of sulphur in two coke samples was organic in nature; the remaining 10% was in the form of inorganic oxides. XANES analysis indicated that over 50% of the organic sulphur was in the form of thiophene while the rest was organic sulphide.

- 138 - 5. After activating with KOH at temperatures of 600-900°C for 1 hour with KOH/coke ratio of 3:1, the sulphur content in the fluid coke dropped from 7.4 % to less than 0.5 %. The only residual sulphur identified was sulphate, suggesting that KOH was effective in oxidizing organic sulphur to water soluble inorganic sulphate. On the other hand,

reactions between the coke and SO2 added sulphur to carbon, mainly in the form of elemental sulphur, while part of thiophene, sulphide and sulphate in fluid coke remained

in the product. Apparently, SO2 was unable to remove organic sulphur from the coke.

6. After activating the fluid coke with KOH and SO2 simultaneously, XANES analysis revealed disulphide, sulphide, sulphonate and sulphate on the surface of activation products. No thiophene and elemental sulphur were found when high KOH/coke ratios were used, suggesting that KOH was able to oxidize thiophene even in the presence of

SO2, while it was also able to prevent the formation of elemental sulphur - an anticipated

product of carbothermal reduction of SO2.

7. During KOH-SO2 activation of fluid coke under the studied conditions, the

thermodynamic analysis suggests that in KOH-SO2-C high-temperature system, K2S,

K2SO4 and K2CO3 are possible solid products, while CO, CO2, COS, H2O, H2 and S are

possible gaseous products. Experiments identified K2S, K2SO4 and K2CO3 in the

activated coke, when CO, CO2, S, H2O and H2 were observed in the gas phase.

2+ 8. The data of Hg adsorption on KOH-SO2 activated carbon fits the Freundlich model. Hg2+ adsorption capacity of these SIACs ranged from 43 to 72 mg/g, which is comparable with that reported in the literature (35-100 mg/g) and a commercial SIAC (41 2+ mg/g). There was a positive correlation between Hg adsorption capacity and SBET;

however the enhancement of SBET diminished when SBET was greater than about 1000 m2/g. A statistically significant and positive correlation was found between Hg2+

adsorption capacity and total sulphur content on a per unit SBET basis. Reduced sulphur (e.g. disulphide, elemental sulphur and thiophene) were largely responsible for the enhanced Hg2+ adsorption.

- 139 - RECOMMENDATIONS

The following suggestions need to be considered in future work:

1. For the characterization of sulphur forms in SIACs using XANES, spectra with higher resolution are recommended. With higher resolution, the smaller features of the spectra will be clearer, and the analysis will be more convincing. More efforts can be made on FY spectra analysis, which may reveal the sulphur transformation in the bulk of fluid coke. The comparison between FY and TEY results may provide more information to help understand the diffusion process of reactants and products during activation. In addition, the handling process of XANES analysis should be carefully designed, since the sulphur species on the coke and SIAC surfaces may change their forms due to the exposure to the air.

2. During fluid coke activation, it was found that the micropore volume changed under different activation conditions. However, this change was not well investigated. The pore size distribution in activated carbon may have a significant effect on the adsorption of mercury. Therefore, the dependence of pore size distribution on activation conditions needs to be further investgated, in order to produce SIACs with desired pore size distrivution for an effective mercury adsorption.

3. The KOH-SO2 activation mechanism needs to be further understood. More efforts need to be made on understanding the effect of sulphur in raw coke on porosity development of SIACs. More types of raw coke with different sulphur contents are needed to compare the difference in SIACs produced from different raw cokes and to understand the role of sulphur during activation. The reaction between KOH/SO2 and the sulphur in raw coke needs to be further studied. The breakage of coke-sulphur bond and the means of sulphur addition to the carbon matrix need to be investigated.

4. The adsorption of Hg2+ from aqueous phase using SIACs can be further studied. 2+ The relationship between the SBET of SIACs and Hg adsorption capacities is of great 2+ interest. In this study, it was found the effect of SBET on Hg adsorption became weaker in the range of high SBET. This may be associated with the pore size distribution in the SIACs. However, no evidence has been found, and more research is needed.

- 140 - 5. More effort can be made in understanding the interaction between activated carbon and mercury in aqueous solution. The amounts and types of oxygen functional groups on the SIAC surface and the surface charge of SIAC should be measured, which were previously suggested to play important roles in mercury uptake. Hg forms before and after adsorption may be analyzed using XANES or XPS to provide supporting evidence for the investigation of the interaction between sulphur in SIAC and mercury in the solution.

- 141 - REFERENCES

Ali, M.F., Al-Malki, A., El-Al, B., Martinie, G., Siddiqui, M.N., 2006. Deep desulphurization of gasoline and diesel fuels using non-hydrogen consuming techniques. Fuel 85, 1354-1363. Alcaniz-Monge, J., Cazorla-Amoros, D., Linares-Solano, A., 1997. Production of activated carbons: use of CO2 versus H2O as activating agent. A reply to a letter from P.L. Walker, Jr. Carbon 35 (10-11), 1665-1668. Al-Haj-Ibrahim, H. and Morsi, B.I., 1992. Desulphurization of petroleum coke: A review. Industrial Engineering Chemical Research 31, 1835-1840. Ahmadpour A. and Do, D.D., 1996. The preparation of active carbons from coal by chemical and physical activation. Carbon 34, 471-479. Anoop Krishnan, K. and Anirudhan, T.S., 2002. Removal of mercury (II) from aqueous solutions and chlor-alkali industry effluent by steam activated and sulphurised activated carbons prepared from bagasse pith: kinetics and equilibrium studies. Journal of Hazardous Materials 92, 161-183. Ao, X., Wang, H., Wei, Y., Li, K., Liu, M., 2008. Reduction behaviour of methane in alkali molten carbonates. Jounal of Fuel Chemistry and Technology 36, 455-461. Babić, B.M., Milonjić, S.K., Polovina, M.J., Čupić, S., Kaludjerović, B.V., 2002. Adsorption of zinc, cadmium and mercury ions from aqueous solutions on an activated carbon cloth. Carbon 40, 1109-1115. Bagreev, A. and Bandosz, T., 2002. A role of sodium hydroxide in the process of hydrogen sulphide adsorption/oxidation on caustic-impregnated activated carbons. Industrial Engineering Chemical Research 41, 672-679. Bansal, R.C., Donnet, J., Stoeckli, F., 1988. Active carbon. Marcel Dekker, New York and Basel. Baruah B.P., Khare, P., 2007. Desulphurization of oxidized india coals with solvent extraction and alkali treatment. Energy Fuels 21, 2156-2164. Bejarano, C., Jia, C.Q., Chung, K., H., 2003. Mechanistic study of the carbothermal reduction of sulphur dioxide with oil sand fluid coke. Industrial Engneering and Chemical research 42, 3731-3739. Boyd, G.E., Adamson, A.W., Meyers, L.S., 1947. The exchange adsorption of ions from aqueous solution by organic zeolites II, kinetics, Journal of the American Chemical Society 69, 2836. Budinova, T., Petrov, N., Parra, J., Baloutzov, V., 2008. Use of an activated carbon from antibiotic waste for the removal of Hg(II) from aqueous solution Journal of Environmental Management 88, 165-172 Calahorro, C.V., Garcia, A.M., Garcia, A.B., Serrano, V.G., 1990. Study of sulphur introduction in activated carbon. Carbon 28, 321-335. Carrasco-Maríin, F., Utrere-Hidalgo, E., Rivera-Utrilla, J., Moreno-Catstilla, C., 1992. Adsorption of SO2 in flowing air onto activated carbons from olive stones. Fuel 71, 578.

- 142 - Chang, C.H, 1981. Preparation and characterization of carbon-sulphur surface compounds. Carbon 19, 175-186. Chen, Y., 2002. Preparation, characterization and application of novel adsorbent from petroleum coke activated by sulphur dioxide. Thesis of M.A.Sc. University of Toronto. Chugh, Y.P. and Caudle, R.D., 1987. Processing and utilization of high sulphur coals II. Elsevier, New York, Amsterdam, and London. Cofer, C.G., Economy, J., 1995. Oxidative and hydrolytic stability of boron nitride – A new approach to improving the oxidation resistance of carbonaceous structures. Carbon 33, 389- 395. Coulter Corp., SA3100 Series Surface Area and Pore Size Analyzer, Product Manual, version 2.11; Coulter: Miami, Florida, 1996 Courcot, D., Pruvost, C., Zhilinskaya, E. A., Aboukaïs, A., 2004. Potential of supported copper and potassium oxide catalysts in the combustion of carbonaceous particles. Kinetics and Catalysis 45, 580-588. Davidson, R.M., 1994. Quantifying organic sulphur in coal. Fuel 73, 988-1005.

Davini, P., 1990. Adsorption and desorption of SO2 on active carbon: The effect of surface basic groups. Carbon 28, 565-571. Demou, E., 2003. The activation of oilsands fluid coke using sulphur dioxide as an activating agent at low temperatures. Thesis of M.A.Sc. University of Toronto. Denisov, E.T., Sarkisov O.M., Likhtenshtein, G.I., 2003. Chemical Kinetics: Fundamentals and Recent Developments. Elsevier. B.V. Amsterdam, Boston. DiPanfilo, R. and Egiebor, N.O., 1996. Activated carbon production from synthetic crude coke. Fuel Processing Technology 46, 157-169. Ekinci, E., Budinova, T., Yardim, F., Petrov, N., Razvigorova, M., Minkova, V., 2002. Removal of mercury ion from aqueous solution by activated carbons obtained from biomass and coals. Fuel Processing Technology 77-78, 437-443. Estrade-Szwarckopf, H., 2004. XPS photoemission in carbonaceous materials: A “defect” peak beside the graphitic asymmetric peak. Carbon 42, 1713-1721. Evans, M.J.B., Halliop, E., MacDoonald, J.A.F., 1999. The production of chemically- activated carbon. Carbon 37, 269-274.

Feng, W., 2002. Effects of O2 and H2O on carbonthermal reduction of SO2 by oil sand fluid coke. Masters Thesis, University of Toronto. Feng, W., Kwon, S., Feng, X., Borguet, E., Vidic, R. D., 2006. Sulphur impregnation on activated carbon fibres through H2S oxidation for vapour phase mercury removal. Journal of Environmental Engineering 132, 292-300. Feng, W., Borguet, E. and Vidic, R.D., 2006. Sulphurization of a carbon surface for vapour phase mercury removal – II: Sulphur forms and mercury uptake. Carbon 44, 2998-3004. Furimsky, E., 1998. Gasification of oil sand coke: Review. Fuel Processing Technology 56, 263-290.

- 143 - Furimsky, E., 2000. Characterization of cokes from fluid/flexi-coking of heavy feeds. Fuel Processing Technology 67, 205–230. Furuhata, K., Ikeda, H., 1999. Ionic cellulose derivatives: synthesis of sodium 6- deoxycellulose-6-sulphonate with high degree of substitution Reactive and Functional Polymers. Volume 42, 103-109 Gaspard, S., Altenor, S., Passe-Coutrin, N., Ouensanga, F., Broers, F., 2006. Parameters from a new kinetic equation to evaluate activation carbons efficiency for water treatment. Water Research 40, 3467-3477. Gorbaty, M.L.; George, G.N.; Kelemen. S.R., 1990. Direct determination and quantification of sulphur forms in heavy petroleum and coals. Fuel 69, 945–949. Greenwood, N.N., Earnshaw, A., 1994. Chemistry of elements, Pergamon Press, Great British, pp.313-314. Gregg, S.J. and Sing, K. S. W., 1982. Adsorption, surface area and porosity, 2ed, Academic Press, London. Hall, L. W., Wolff, N., Bradley, J. W. P., Jolly, D. W., 1966. Unusual reaction to suxametonium chloride. British medical Journal 2, 1305. Henning, K. D. and Schäfer, S., 1993. Impregnated activated carbon for environmental protection. Gas Separation & Purification 7, 235-240. Hsi, H., Rood, M.J., Rostam-Abadi, M., Chen, S., Chang, R., 2001. Effects of sulphur impregnation temperature on the properties and mercury adsorption capacities of Activated Carbon Fibers (ACFs). Environmental Science & Technology 35, 2785-2791. Hsi, H., Rood, M.J., Rostam-Adadi, M., Chen, S., Chang, R., 2002. Mercury adsorption and properties of sulphur-impregnated adsorbents. Journal of Environmental Engineering 128, 1080-1089. Huffman, G.P.; Huggins, F.E.; Shah, N.; Lu. F., 1991. Quantitative analysis of all major forms of sulphur in coal by x-ray absorption fine structure spectroscopy. Energy Fuels 5, 574–581. Huffman, G.P.; Huggins, F.E.; Mitra, S.; Shah, N.; Pugmire, R.J., 1989. Investigation of the molecular structure of organic sulphur in coal by XAFS spectroscopy. Energy Fuels 3, 200– 205.

Humeres, E., Moreira, R.F.P.M., Peruch, M.G.B., 2002. Reduction of SO2 on different carbons. Carbon 40, 751-760. Humeres, E., Peruch, M.G.B., Moreira, R.F.P.M. and Schreiner, W., 2003. Reactive intermediates of the reduction of SO2 on activated carbon. Journal of Physical Organic Chemistry, 16, 824-830. Hwang, H.R., Choi, W.J., Kim, T.J., Kim, J.S. and Oh, K.J. 2008. The preparation of an adsorbent from mixtures of sewage sludge and coal-tar pitch using an alkaline hydroxide activation agent. Journal of Analytical and Applied Pyrolysis 83 (2), 220-226. Ityokumbul, M.T., Kasperski, K.L., 1994. Reactivity of caustic treated oil sand coke residues. Fuel Processing Technology, 37, 281- 294.

- 144 - Jaimes, L., Ferreira, M.L., Lasa, H. (2009). Thiophene conversion under mild conditions over a ZSM-5 catalyst. Chemical Engineering Science 64 (11), 2539-2561. Jagtoyen, M., Derbyshire, F., Rathbone, R., Rimmer, S. (1995). Relationship between reflectance and structure of high surface area carbons. Fuel 74 (4), 610-614. Jagtoyen, M., Derbyshire F., 1998. Activated carbons from yellow poplar and white oak by H3PO4 activation. Carbon, 36, 1085-1097. Jiménez Mateos, J.M., Fierro, J.L.G., 1996. X-ray photoelectron spectroscopic study of petroleum fuel cokes. Surface and Interface Analysis 24, 223-236. Kadirvelu, K., Kavipriya, M., Karthika, C., Vennilamani, N., Pattabhi, S., 2004. Mercury (II) adsorption by activated carbon made from sago waste. Carbon 42, 745-752. Karatza, D., Lancia, A., Musmarra, D., Zucchini, C., 2000. Study of mercury adsorption and desorption on sulphur impregnated carbon. Experimental Thermal and Fluid Science 21, 150-155. Karr, C. Jr., 1978. Analytical methods for coal and coal products. Academic press, New York, San Francisco and London. Kasrai, M., Brown, J.R., Bancroft, G.M., Yin, Z., Tan, K.H., 1996. Sulphur characterization in coal from X-ray adsorption near edge spectroscopy. International Journal of Coal Geology 32, 107-135. Kawatra, S.K. and Eisele, T.C., 2001. Coal desulphurization, Taylor and Francis, New York. Kelemen, S.R., George, G.N., Gorbaty, M.L., 1990. Direct determination and quantification of sulphur forms in heavy petroleum and coals: 1. The X-ray photoelectron spectroscopy (XPS) approach. Fuel 69, 939-944. Kim, Y., 2008. A study involving reaction mechanism and products of activation of fluid coke using KOH. Project report. Knocke, W.R., Hemphil, L.H., 1981. Mercury (II) sorption by waste rubber. Water Research 15, 275-282. Korpiel, J.A. and Vidic, R.D., 1997. Effect of sulphur impregnation method on activated carbon uptake of gas-phase mercury. Environmental Science and Technology 31, 2319-2325. Krishnan, S. V., Gullett, B. K., Jozewick, W., 1994. Sorption of elemental mercury by activated carbons. Environmental Science & Technology 28, 1506-1512. Kropp, K.G. and Fedorak, P.M., 1997.A review of the occurrence, Toxicity, and biodegradation of condensed thiophenes found in petroleum. Can. J. Microbiol 44, 605-622.

Kuo, D.T.F., Kirk, D.W., Jia, C.Q., 2006. The chemistry of aqueous S(IV)-Fe-O2 system: state of the art. Journal of Sulphur Chemistry 27, 461-530. Kwon, S., Vidic, R.D., 2000. Evaluation of two sulphur impregnation methods on activated carbon and bentonite for the production of elemental mercury sorbents. Environmental Engineering Science 17, 303-313. Laine, J., and Calafat A., 1991. Factors affecting the preparation of activated carbons from coconut shell catalyzed by potassium. Carbon 29, 949-953.

- 145 - Lee, S.H. and Choi, C.S., 2000. Chemical activation of high sulphur petroleum cokes by alkali metal compounds. Fuel Processing Technology 64, 141-153. Lee, S.H., Rhim, Y.J., Cho, S.P., Baek, J.I., 2006. Carbon-based novel sorbent for removing gas-phase mercury. Fuel 85, 219-226. Lee, S., Park, Y., 2003. Gas-phase mercury removal by carbon-based sorbents. Fuel Processing Technology 84, 197-206. Lee, Y.W., Park, J.W., 2002. Adsorption characteristics of SO2 on activated carbon prepared from coconut shell with potassium hydroxide activation. Environmental Science and Technology 36, 1086-1092. Li, Y.H., Lee, C.W., Gullett, B.K., 2002. The effect of activated carbon surface moisture on low temperature mercury adsorption. Carbon 40, 65-72. Li, Y. H., Lee, C. W., Gullet, B. K., 2003. Importance of activated carbon's oxygen surface functional groups on elemental mercury adsorption. Fuel 82, 451-457. Lillo-Ródenas, M.A., Lozano-Castelló, D., Cazorla-Amorós, D., Linares-Solano, A., 2001. Preparation of activated carbons from Spanish anthracite II. Activation by NaOH. Carbon 39, 751-759. Lillo-Ródenas, M.A., Cazorla-Amorós, D. and Linares-Splana, A., 2003. Understanding chemical reactions between carbons and NaOH and KOH, An insight into the chemical activation mechanism. Carbon 41, 267-275. Lillo-Ródenas, M.A., Juan-Juan, J., Cazorla-Amorós, D., Linares-Solano, A., 2004. About reactions occurring during chemical activation with hydroxides. Carbon 42, 1365-1369. Liu, Q., Hu, H., Ahu, S., Zhou, Q., Li, W., Wei, X., Xie, K., 2005. Desulphurization of coal by pyrolysis and hydropyrolysis with addition of KOH/NaOH. Energy & Fuels 19, 1673- 1678. Liu, F., Li, W., Chen, H., Li, B., 2007. Uneven distribution of sulphurs and their transformation during coal pyrolysis. Fuel 86 (3), 360-366. Liu, W., Vidic, R.D., Brown, T.D., 1998. Optimization of sulphur impregnation protocol for fixed bed application of activated carbon-based sorbents for gas-phase mercury removal. Environmental Science and Technology 32, 531-538. Liu W., Vidic, R.D., 2000. Optimization of high temperature sulphur impregnation on activated carbon for permanent sequestration of elemental mercury vapors. Environmental Science and Technology 34, 483-488. Liu, W., Vidic, R., Brown, T., 2000. Impact of flue gas conditions on mercury uptake by sulphur-impregnated activated carbon. Environmental Science & Technology 34, 154-159.

Lizzio, A.A. and Debarr, J.A., 1997. Mechanism of SO2 removal by carbon. Energy and Fuels, 11, 284-291. Lopez-Gonzalez, J.D., Moreno-Castilla, C., Guerrero-Ruiz, A., Rodirguez-Reinoso, F., 1982. Effect of carbon-oxygen and carbon-sulphur surface complexes on the adsorption of mercuric chloride in aqueous solutions by activated carbon. Journal of Chemical Technology and Biotechnology 32, 575-579.

- 146 - Lua, A., Guo, J., 2001. Microporous Oil-Palm-Shell Activated Carbon Prepared by Physical Activation for Gas-Phase Adsorption. Langmuir 17. 7112-7117. Maciá-Agulló, J.A., Moore, B.C., Cazorla-Amorós, D. and Linares-Solano, A. (2007). Influence of carbon fibres crystallinities on their chemical activation by KOH and NaOH. Microporous and Mesoporous Materials 101, 397-405. Majid, A., Bensebaa F., L’Ecuyer P., Pieizier G. and Deslandes Y., 2003. Modification of the metallic surface of silver by the formation of alkanethios self-assembled monolayers with subsequent reaction with chlorosilanes. Reviews on Advanced Materials Science 4, 25-31. Marsh H., Yan, D.S., O’Grady, T.M., Wennerverg, A., 1984. Formation of active carbons from cokes using potassium hydroxide. Carbon 22, 603-611. Marsh, H., Murdie, N., Edwards, I.A.S., Boehm, H.P., 1987. in: P.A. Thrower (Ed.), Internations of carbons, cokes, and graphites with potassium and sodium. Chemistry Physics Carbon, 20, Dekker, New York, p213 Marsh H., Rodríguez-Reinoso, F., 2006. Activated Carbon. Elsevier, London. Mitani, S., Lee, S., Yoon, S., Korai, Y., Mochida, I., 2004. Activation of raw pitch coke with alkali hydroxide to prepare high performance carbon for electric double layer capacitor. Journal of Power Sources 133, 298-301. Mohan, D., Gupta, V.K., Srivastava, S.K., Chander, S., 2000. Kinetics of mercury adsorption from wastewater using activated carbon derived from fertilizer waste. Colloids and Surfaces A: Physicochemical and Engineering Aspects 177, 169-181. Molina-Sabio, M., Rodriguez-Reinoso, F., 2004. Role of chemical activation in the development of carbon porosity. Colloids and Surfaces A: Physicochem. Eng. Aspects 241, 15–25. Morimoto, T., Wu, S., Azhar Uddin, M., Sasaoka, E., 2005. Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S. Fuel 84, 1968- 1974. Moulder, J.F.; Stickle, W.F.; Sobol, P.E.; Bomben, K.D., 1992. Handbook of X-ray photoelectron spectroscopy. Perkin-Elmer Corporation: Eden Prairie. Mukherjee, S., Borthakur, P.G., 2003. Effect of leaching high sulphur subbituminous coal by potassium hydroxide and acid on removal of mineral matter and sulphur. Fuel 82, 783-788. Nabais, J.V., Carrott, P.J.M., Carrott, M.M.L.R., Belchior, M., Boavida, D., Diall, T., Gulyurtlu, I., 2006. Mercury removal from aqueous solution and flue gas by adsorption on activated carbon fibres. Applied Surface Science 252, 6046-6052. Nam, K.H., Gomez-Salazar S. and Tavlarides, L.L, 2003. Mercury adsorption from wastewaters using a thiol functional adsorbent. Industrial & Engineering Chemistry Research 42, 1955-1964. Namasivayam, C. and Kadirvelu, K., 1999. Uptake of mercury (II) from wastewater by activated carbon from an unwanted agricultural solid by-product: coirpith. Carbon 37, 79-84. Nichollsa, M.A.G., Bancroft, M, Norton, P.R., Kasrai, M., Stasio, G.D., Frazer, B.H., Wiese, L.M., 2004. Chemomechanical properties of antiwear films using X-ray absorption microscopy and nanoindentation techniques. Tribology Letters 17, 245-259.

- 147 - Olivella, M.A.; Palacios, J.M.; Vairavamurthy, A.; del Río, J.C.; de las Heras, F.X.C., 2002. A study of sulphur functionalities in fossil fuels using destructive- (ASTM and Py–GC–MS) and non-destructive- (SEM–EDX, XANES and XPS) techniques. Fuel 81, 405–411. Otowa, T., Nojima, Y., Miyazaki, T., 1997. Development of KOH activated high surface area carbon and its application to drinking water purification. Carbon 35, 1315-1319. Pastor-Villegas, J. and Dura´n-Valle, C.J., 2002. Pore structure of activated carbons prepared by carbon dioxide and steam activation at different temperatures from extracted rockrose. Carbon 40, 397-402. Pearson, R.G., 1988. Absolute electronegativity and hardness: application to inorganic chemistry. Inorganic Chemistry 27, 734-740. Perrin, A., Celzard, A., Albiniak, A., Kaczmarczyk, J., Marêché, J.F., Furdin, G., 2004. NaOH activation of anthracites: effect of temperature on pore textures and methane storage ability. Carbon 42, 2855-2866. Pingitore Jr., N.E.; Meitzner, G.; Love, K.M., 1995. Identification of sulphate in natural carbonates by x-ray absorption spectroscopy. Geochim. Cosmichim. Acta. 59, 2477–2483. Prodpran, P., Shenogin, S., Nazarenko, S., 2002. Gas transport behavior of semicrystalline syndiotactic polystyrene containing α and β crystalline forms. Polymer 43, 2295-2309. Puri, B.R. and Hazra, R.S., 1971. Carbon-sulphur surface complexes on charcoal. Carbon 9, 123-134. Qian, J., Skyllberg, U., Frech, W., Bleam, W.F., Bloom, P.R., Petit, P.E., 2002. Bonding of methyl mercury to reduced sulphur groups in soil and stream organic matter as determined by x-ray absorption spectroscopy and binding affinity studies. Geochimica et Cosmochimica Acta 66, 3873–3885. Radovic, L.R., Moreno-Castilla, C., and Rivera-Utrilla, J., 2000. Theme article - carbon materials as adsorbents for the removal of pollutants from the aqueous phase, in Chemistry and Physics of Carbon, vol. 27, edited by Radovic, L.R. Marcel Dekker, New York. Ranganathan, K. and Balasubramanian, N., 2002. Testing of sulphide loaded activated carbon for uptake of HgII from aqueous solution. Engineering Life Science 2, 127-129. Rao, M.M., Reddy, D.H.K.K., Venkateswarlu, P., Seshaiah, K., 2009. Removal of mercury from aqueous solutions using activated carbon prepared from agricultural by-product/waste Journal of Environmental Management 90, 634-643. Ravel, B., Newville, M. J., 2005. ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT. Synchrotron Rad. 12, 537–541. Ravel, 2008. Athena user’s guide. Document version 1.5 for Athena version 0.8.56, pp.118. Raymundo-Piñero, E., Azais, P., Cacciaguerra, T., Cazorla-Amoros, D., Linares-Solano, A. and Beguin, F., 2005. KOH and NaOH activation mechanisms of multiwalled carbon nanotubes with different structural organization. Carbon 43, 786-795. Reichenberg, D., 1953. Properties of ion-exchange resins in relation to their structure III. Kinetics of exchange. Journal of the American Chemical Society 75, 589-592.

- 148 - Riley, J.T., Ruba, G.M. and Lee, C.C., 1990. Direct determination of total organic sulphur in coal. In Geochemistry of Sulphur in Fossil Fuels. Edited by Wilson, L.O. and Curt, M.W. American Chemical Society, Washington, DC. Ros, A., Lillo-Rodenas, M.A., Fuente, E., Montes-Moran, M.A., Martin, M.J. and Linares- Solano, A., 2006. High surface area materials prepared from sewage sludge-based precursors. Chemosphere 65, 132-140. Ruczinski, W., Everett, D. H., 1992. Adsorption of gases on heterogeneous surfaces. Academic Press, London, San Diego, New York, Boston, Sydney, Tokyo and Toronto. Sarret, G., Gonnan, J., Kasrai, M., Bancroft, M., Charrie-Duhaut, A., Lemoine, S., Adam, P., Albrecht, P., Eybert-Berard, L., 1999. Chemical forms of sulphur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulphur K- and L-edge X-ray absorption near-edge structure spectroscopy. Geochimica et Cosmochimica 63, 3767-3779. Skodras, G., Diamantopoulou, Ir., Zabaniotou, A., Stavropoulos, G., Sakellaropoulos., G.P., 20071. Enhanced mercury adsorption in activated carbons from biomass materials and waste tires. Fuel Processing Technology 88, 749-758. Skodras, G., Diamantopoulou, Ir., Sakellaropoulos., G.P., 20072. Roles of activated carbon structure properties and surface chemistry in mercury adsorption. Desalination 210, 281-286. Soleimani, M. and Kaghazchi, T., 2008. The investigation of the potential of activated hard shell of apricot stones as gold adsorbents. Journal of Industrial and Engineering Chemistry 14, 28-37. Solomon, D., Lehannes, J., Martinez, C.E., 2003. Sulphur K-edge XANES spectroscopy as a tool for understanding sulphur dynamics in soil organic matter. Soil Science Society of America Journal 67, 1721-1731. Stacy, W.O., Vastola, F.J. and Walker, Jr., 1968. Interaction of sulphur dioxide with active carbon. Carbon 6, 917-923. Subramaniam, S., 2005. Effects of microwave treatment on sulphur dioxide-activation of oilsands fluid coke. Forth year thesis. Sugama, T., 1998. Polyphenylethsulphone adhesive for EPDM elastomer-to-stainless steel joints in a hydrothermal environment. Journal of Materials Science 33, 5095-5102. Taghiei, M.M.; Huggins, F.E.; Shah, N.; Huffman, G.P., 1992. In situ x-ray absorption fine structure spectroscopy investigation of sulphur functional groups in coal during pyrolysis and oxidation. Energy Fuels 6, 293–300. Tanaike O.; Inagaki M., 1997. Ternary intercalation compounds of carbon materials having a low graphitization degree with alkali metals. Carbon 5: 831–836. Thomoson, W.J. and Sy, L.Y, 1987. Potassium catalyzed gasification of Kentucky oil shale char. Fuel 66, 223-227. Tseng, R.L., 2006. Mesopore control of high surface area NaOH-activated carbon. Journal of Colloid and Interface Science 303, 494-502.

- 149 - Tseng, R.L., 2007. Physical and chemical properties and adsorption type of activated carbon prepared from plum kernels by NaOH activation. Journal of Hazardous Materials 147, 1020- 1027. Vazquez, G., Gonzalez-Alvarez, J., Freire, S., Lopez-Lorenzo, M., Antorrena, G., 2002. Removal of cadmium and mercury ions from aqueous solution by sorption on treated pinus pinaster bark: kinetics and isotherm. Bioresource Technology 82, 247-251. Wagner, C.D.; Naumkin, A.V.; Kraut-Vass, A.; Allison, J.W.; Powell, C.J.; Rumble Jr. J.R. NIST X-ray photoelectron spectroscopy database. National Institute of Standards and Technology: Gaithersburg, 2007.

Walker, P.L. Jr., 1996. Production of activated carbons: use of CO2 versus H2O as activating agent. Carbon 34, 1297-1299. Wigmans, T., 1989. Industrials aspects of the production and use of activated carbons. Carbon, 27, 13-22. Williams, P.T., Reed, A.R., 2006. Development of activated carbon pore structure via physical and chemical activation of biomass fibre waste. Biomass and Bioenergy 30, 144– 152. Wiltfong, R.; Mitra-Kirtley, S.; Mullins, O.C.; Andrews, B.; Fujisawa, G.; Larsen, W., 2005. Sulphur speciation in different kerogens by XANES spectroscopy. Energy Fuels 19, 1971– 1976. Winterbottom J.M. and King M.B., 1999. Reactor design for Chemical Engineers. Stanley Thorns, London. Wu, M., Zh, Q., Qiu, J., Han, X., Guo, Y., Li, Z., Yuan, A., Sun, X., 2005. Preparation of porous carbons from petroleum coke by different activation methods. Fuel 84, 1992-1997. Yan, R., Ng, Y., Liang, D., Lim, C., Tay, J., 2003. Bench-scale experimental study on the effect of flue gas composition on mercury removal by activated carbon adsorption. Energy & Fuels 17, 1528-1535. Yan, R., Liang, D. T., Tsen, L., Wong, Y. P., Lee, Y. K., 2004. Bench-scale experimental evaluation of carbon performance on mercury vapour adsorption. Fuel 83, 2401-2409. Yardim, M.F., Budinova, T., Ekinci, E., Petrov, N., Razvigorova, M., Minkova, V., 2003. Removal of mercury (II) from aqueous solution by activated carbon obtained from furfural. Chemosphere 52, 835-841. Yehaskel, A., 1978. Activated carbon: Manufacture and regeneration. Noyes Data, New Jersey. Yuan, M.J., Cai, J.H., Jia, C.Q., 2009. Mechanism studies of KOH activation of fluid coke. In progress. Zabihi, M., Ahmadpour, A., Asl, A.H., 2009. Removal of mercury from water by carbonaceous sorbents derived from walnut shell. Journal of Hazardous Materials 167, 230- 236. Zekany, L., Nagyral, I., 1985. In: D.J. Leggett (Editor), Computational Methods for the Determination of Formation Constants, Plenum Press, London.

- 150 - Zawadzki, J., 1987. Infrared studies of SO2 on carbon-I. Interaction of SO2 with carbon films. Carbon 25, 431-436. Zeng, H., Jin, F., Guo, J., 2004. Removal of elemental mercury from coal combustion flue gas by chloride-impregnated activated carbon. Fuel 83, 143-146. Zhang, F., Nriagu, J.O., Itoh, H., 2005. Mercury removal from water using activated carbons derived from organic sewage sludge. Water Research 39, 389-395. Zhou, X. and Chriswell, C., 1996. Determination of forms of organic sulphur in coal by stepwise oxidation with perchloric acid-ferric perchlorate mixture. Fuel Processing Technology 46, 1996. Zhu, J., Yang, J., Deng, B., 2009. Enhanced mercury ion adsorption by amine-modified activated carbon Journal of Hazardous Materials 166, 866-872.

Online resources: http://mccoy.lib.siu.edu/projects/crelling2/atlas/PetroleumCoke/ χ2 calculator: http://www.fourmilab.ch NIST X-ray photoelectron spectroscopy database: http://srdata.nist.gov/xps/

- 151 - APPENDICES

APPENDIX A PRELIMINARY STUDIES OF HYDROXIDE ACTIVATION OF FLUID COKE

A-1 Effect of activating agents KOH and NaOH were used to activate fluid coke, and the results showed that both KOH and NaOH can activate fluid coke to produce activated carbon with high surface area. Moreover, KOH was more effective in terms of surface area development.

2500 /g 2 2000

1500

1000

500 BET surface area, m area, surface BET 0 SO2 Steam NaOH KOH

Chen DiPanfilo Present study and Egiebor

Figure A-1 Comparison of KOH and NaOH activation of fluid coke as well as previous studies

A-2 Effect of the flow gas Fluid coke was activated by KOH with a KOH/coke ratio of 3:1 at 800°C, in the flow of nitrogen and air, respectively. The results in Figure A-2 showed that the activated coke produced in the presence of air had a lower BET surface area and higher mean pore diameter.

3000 40 35 /g

2 2500 30 2000 25 1500 20 15 1000 10 500 Mean pore diameter, A A diameter, pore Mean BET surface area, m area, surface BET 5 0 0 in air in N2

Figure A-1 Fluid coke activated in air and in nitrogen

- 152 - APPENDIX B CALCULATIONS

B-1 Calculation of Theoretical Surface Area of a Single Graphene Layer

Figure B-1 Structure of a grapheme layer

For a single ring:

The area of one side is

½ 2 Aring = 3/2  3  X , where X is the carbon-carbon bond length, and X = 1.42 Ǻ

½ 2 ½ 2 2 -20 2 Thus, Aring = 3/2  3  X = 3/2  3  1.42 = 5.24 Ǻ = 5.24 x 10 m

1 g of carbon = 1g  12g/mol = 0.083 mol  0.083 mol  6.02  1023 = 0.5  1023 carbon

One ring has 6 carbon atoms, but each carbon atom is shared by three rings,

 (0.5  1023 carbon / 2 carbon per ring)  5.24  10-20 m2 = 1.31  103 m2 = 1310 m2

2 2 For 2 sides: 2Aring = 1310 m  2 = 2620 m /g

For one carbon atom:

1 g of carbon = 1g 12g/mol = 0.083 mol = 0.5  1023 carbon

Atomic radius of carbon is approximately 70 pm

2 -20 2 Acarbon = 4πR = 6.16  10 m

6.16  10-20 m2  0.5  1023 carbon/g = 3080 m2/g

Therefore, the total surface area of 1 gram of graphene layer is

3080 m2/g + 2620 m2 /g = 5700 m2/g

- 153 - B-2 Calculation of Weight Loss during KOH Activation

This calculation is for the results shown in Table 3-3, for KOH activation of fluid coke at 700C, 1 hour and KOH/coke ratio = 3:1. 15 g of KOH and 5 g of fluid coke were used.

1. Major carbon loss was caused by the reaction 6KOH + 2C = 2K + 3H2 + 2K2CO3

15 g of KOH was used in the experiment. Since the KOH has 12% of moisture, the KOH content in 15 g KOH is 13.2 g, i.e. 13.2 g  56 g/mol = 0.24 mol

2. Part of KOH is consumed by reacting with sulphur in coke through Coke-S + 2KOH =

K2S + Coke-O + H2O.

Sulphur in coke is 7.37%, and thus, 5 g coke × 7.37% = 0.37 g, i.e. 0.37 g / 32 g/mol = 0.012 mol of sulphur.

For 0.012 mol of S, 0.024 mol KOH is consumed and 0.012 mol O is added (0.012 mol × 16 g/mol = 0.19 g). Thus, there is 0.24 – 0.024 = 0.216 mol KOH is available for reacting with carbon.

3. For 0.216 mol KOH, 0.072 mol carbon is consumed, i.e. 0.072 mol × 12 g/mol = 0.86g

- 154 - B-3 Multivariate Analysis of Variance for SIAC Production

A multivariate analysis of variance (MANOVA) was conducted to verify whether changes in the independent variables (i.e. activation temperature, time and KOH/carbon ratio) have significant effects on the dependent variables (i.e. SBET and total sulphur). The multiple parameter equations for SBET and total S are shown in Eqs. 1 and 2. The positive variables in

Eq. 3-5 indicate that the SBET increases with the increase in the temperature, KOH/C ratio and activation time. On the other hand, total sulphur content decreases with the increase in the temperature and KOH/coke ratio, while increases with the increase of activation time. This is in good agreement with previous analysis.

Calculation:

The form of regression is: y = a1Temp + a2 KOH/C + a3Time + a4, where y is SBET or total S Results calculated by EXCEL:

SBET = 4.17 Temp + 639.48 KOH/C + 18.11 Time - 3195.07 (1) Regression Statistics Multiple R 0.939802361 Coefficients Standard Error R Square 0.883228477 Intercept 3195.067333 551.9911744 Adjusted R Square 0.858206008 X Variable 1 4.173953439 0.634850164 Standard Error 218.1936699 X Variable 2 639.475836 70.80073776 Observations 18 X Variable 3 18.11370899 167.2893426

S% = -0.0047Temp - 0.67KOH/C + 1.95 Time + 7.20 (2) Regression Statistics Coefficients Standard Error Multiple R 0.396760207 Intercept 7.202666667 5.138672969 R Square 0.157418662 X Variable 1 -0.004679894 0.005910035 Adjusted R Square -0.023134482 X Variable 2 -0.672497354 0.659108069 Standard Error 2.031238842 X Variable 3 1.945375661 1.557353201 Observations 18

- 155 - B-4 F-test for the significance of the correlation between SIAC properties and their Hg2+ adsorption capacity

2+ B-4-1 Regression of SBET and Hg adsorption capacity Data: 2 SBET (m /g) Hg(II) capacity (mg/g) 1 13 23.26 2 19 22.34 3 410 42.59 4 431 43.81 5 664 40.78 6 732 32.7 7 1174 48.22 8 1183 54.71 9 1183 57.39 10 1222 50.03 11 1299 51.86 12 1451 71.49 13 1498 46.77 14 1567 53.16 15 1695 52.03 16 1753 45.57 17 1958 60.15 18 2088 58.81 19 2108 63.3 20 2281 60.47 21 2501 59.33 22 2505 63.12

2+ Variable 1: SBET; Variable 2: Hg adsorption capacity Variable 1 Variable 2 Mean 1351.630455 50.08590909 Variance 553280.681 155.8669396 Observations 22 22 df 21 21 F 3549.698752 F Critical one-tail 2.084188623

At α = 0.05, F>Fcritical, the regression is significant

- 156 - B-4-2 Correlation between sulphur content and Hg2+ adsorption capacity Data: S% Hg(II) capacity (mg/g) 1 8.04 23.26 2 9.34 22.34 3 7.41 43.81 4 5.31 42.59 5 8.11 40.78 6 0.61 32.70 7 5.14 48.22 8 4.52 54.71 9 3.48 57.39 10 7.31 50.03 11 0.96 51.86 12 8.10 71.49 13 0.27 46.77 14 6.10 53.16 15 0.17 52.03 16 2.70 45.57 17 2.46 60.15 18 0.12 58.81 19 4.84 63.30 20 2.20 60.47 21 0.10 59.33 22 3.50 63.12

Variable 1: S%; Variable 2: Hg2+ adsorption capacity Variable 1 Variable 2 Mean 4.126818182 50.08590909 Variance 9.360632251 155.8669396 Observations 22 22 df 21 21 F 0.060055277 F Critical one-tail 0.479803022

At α = 0.05, F

- 157 - B-4-3 Correlation between normalized sulphur content and normalized Hg2+ adsorption capacity Data: normalized Normalized Hg(II) capacity S% (mg/g) 1 0.044 0.041 2 0.038 0.046 3 0.029 0.048 4 0.060 0.041 5 0.007 0.040 6 0.056 0.049 7 0.002 0.031 8 0.039 0.034 9 0.001 0.031 10 0.015 0.026 11 0.013 0.031 12 0.001 0.028 13 0.023 0.030 14 0.010 0.027 15 0.000 0.024 16 0.014 0.025

Variable 1: normalized S; variable 2: normalized Hg2+ adsorption capacity Variable 1 Variable 2 Mean 0.021979007 0.03450653 Variance 0.000399338 7.36213E-05 Observations 16 16 df 15 15 F 5.424216824 F Critical one-tail 2.403447072

At α = 0.05, F>Fcritical, the regression is significant

- 158 - B-4-4 Correlation between the content of reduced/oxidized sulphur and Hg2+ adsorption capacity

Normalized reduced S vs. Hg2+ capacity Normalized oxidized S vs. Hg2+ capacity

Normalized Hg 2+ Normalized Hg 2+ reduced S capacity oxidized S capacity Mean 0.611507186 0.285868 Mean 0.126234677 0.28586798 Variance 1.856598385 0.3183254 Variance 0.058157701 0.31832543 Observations 12 12 Observations 12 12 Degree of freedom 11 11 Degree of freedom 11 11

F0.95 5.832391008 F0.95 0.182698885 F0.95 Critical one- tail 2.81793047 F0.95 Critical one-tail 0.35487036

Thus, at α = 0.05, for reduced sulphur, F>Fcritical, the regression is significant. For oxidized sulphur, F

- 159 - APPENDIX C CALIBRATION CURVES

C-1 Temperature ramping rate of tube furnace

900

800

700

600

500

400

300 Temperature (°C) Temperature 200

100

0 0 102030405060 Time (min)

Figure C-1 Temperature ramping curve of tube furnace

C-2 Calibration curves for flowrate controllers

600

n 500

400

300 y = 1.1199x 200 R2 = 0.9999

Actual flowrate(mL/mi 100

0 0 100 200 300 400 500 600 Flowrate setting point (mL/min)

Figure C-2 Calibration curve for N2 flowrate controller

- 160 - 300

) 250

200

150 y = 1.0532x 100 2 R = 0.9995

Actual flowrate (mL/min flowrate Actual 50

0 0 50 100 150 200 250 300 Flowrate setting point (mL/min)

Figure C-3 Calibration curve for SO2 flowrate controller

C-4 Calibration curve for Hg 2+ analysis using ICP

60000

50000

40000

30000

Absorbance y = 537.93x - 1221.9 20000 R2 = 0.9979

10000

0 0 20406080100120 HgCl concentration (mg/L)

Figure C-4 Calibration curve for Hg 2+ analysis using ICP

- 161 - APPENDIX D REPEATABILITY

D-1 SIAC production

Sample Weight loss (%) SSA (m2/g) Micro. (%) S S-KS-1-2 31.4 1540 51.3 4.50% S-KS-1-3 39.8 1694 49.7 4.71% S-KS-1-4 35.0 1753 61.2 4.18% Average 35.4 1662 54.1 4.46% Error 1.2% 6.6% 11.5% 6.0% I-KS-1-1 31.7 1958 53.5 2.46% I-KS-1-2 28.3 1762 72.7 3.14% Average 30.0 1860 63.1 2.80% Error 5.7% 5.3% 15.2% 12.1% I-KS-2-1 23.9 1299 64.6 1.75% I-KS-2-2 16.3 1146 67.2 2.54% Average 20.1 1223 65.9 2.15% Error 18.9% 6.2% 2.0% 18.1%

D-2 SBET and total sulphur determination

2 SBET (m /g) Total sulphur content (%)

KS-2-1 I-KS-1 FC-I S-KS-1 1 1299 1958 1 5.45 8.23 2 1146 1567 2 6.13 7.99 3 1123 1929 3 5.95 8.59 4 1279 1899 4 5.17 8.15 5 1310 1789 5 5.61 8.10 Average 1231 1828 Average 5.66 8.21 SD 89.58 159.76 SD 0.38 0.23 Re SD 7.27% 8.74% Re SD 6.79% 2.78%

- 162 - APPENDIX E SEM IMAGES FOR RAW COKES AND SIACS

FC-I FC-S Figure E-1 SEM images for raw cokes

KOH-1 (×100) KOH-1 (×500)

KOH-1 (×15k) KOH-1 (×30k) Figure E-2 SEM images of KOH activated carbon KOH-1 with different resolutions

- 163 -

KNS-7 (× 3.5K) KNS-7 (× 200K)

Figure E-3 SEM images for KOH-SO2 sequential activated carbon KNS-7

KS-1-2 (× 250) KS-1-2 (× 1.5k)

KS-4 (× 200k) KS-4 (× 300k)

Figure E-4 SEM images with different resolution for KOH and SO2 simultaneous activated carbon

- 164 - APPENDIX F SULPHUR SPECIATION: MORE DATA

Fitting results of the composition of three model sulphur compound mixture are shown in Table 4-2. For mixtures M-1 and M-3, the differences between calculation and measurement results are not large, and the error is up to 15.6%, which is in agreement with the literature. However, for mixture M-2, the largest error is 24.2%. In this case, the possibility that sulphoxide, sulphonate, and sulphone may be oxidized during the mixing process or during exposure to the air after mixing should be considered. Therefore, the large error in this case may not reflect the real error of the XANES measurement, and the actual error should be much lower than the values shown in Table E-1.

Table F-1 Composition of model sulphur compounds

S wt% in specific form Component Amount Error S form Calculation Measurement (%) DL-Methionine 0.1g Sulphide 5.37 5.40 0.6 M-1 Sodium thiosulphate 0.1g Thiosulphate 10.13 9.50 6.2

Sodium sulphate 0.1g Sulphate 5.63 6.22 10.5

Graphite 0.1g Total sulphur 21.14 ---- Benzyl sulphoxide 0.1g Sulphoxide 2.78 2.44 12.2 Anthraquinon-2- 0.1g Sulphonate 2.22 2.10 5.4 M-2 sulphonic acid DL-Methionine 0.1g Sulphone 3.54 2.90 18.1 sulphone Sodium sulphate 0.1g Sulphate 4.51 5.60 24.2 Graphite 0.1g Total sulphur 13.05 ---- DL-Methionine 0.01g Sulphide 1.64 1.48 9.8 M-3 Sodium thiosulphate 0.01g Thiosulphate 3.09 2.94 8.1 Sodium sulphate 0.01g Sulphate 1.92 2.22 15.6 Graphite 0.1g Total sulphur 6.65 ---- Average Error 11.07

- 165 - APPENDIX G XANES SPECTRA

G-1 Model sulphur compounds (standards)

Name Category Energy (eV) TEY Spectrum FY Spectrum

Elemental Sulphur elemental 2471.66 sulphur

L-Cystine disulphide 2471.66

Benzyl disulphide disulphide 2472.00

1-Phenyl-1H- thiol 2472.25 tetrazole-5-thiol

S-benzyl-L-cysteine sulphide 2472.33

DL-cysteine thiol 2472.33

- 166 - DL-Methionine sulphide 2472.67

S-methyl-Lcysteine sulphide 2472.84

Thiophene-3-acetic thiophene 2473.01 acid

Benzonaphthothiop thiophene 2473.01 hene

3-(2-thienyl)-DL- thiophene 2473.01 alanine

Thianthrene sulphide 2473.18

3-(2-thienyl)acrylic thiophene 2473.18 acid

- 167 - Phenothiazine sulphide 2473.35

Poly (phenylene sulphide 2473.68 sulphide)

4,4'-thiodiphenol sulphide 2474.02

Benzyl sulphoxide sulphoxide 2475.03

DL-Methionine sulphoxide 2475.37 sulphoxide

Sodium sulphite sulphite 2477.55

2481.75

DL-Methionine sulphone 2479.01 sulphone

- 168 - Sodium thiosulphate 2480.09 thiosulphate

Diphenylamine-4- sulphonate 2480.25 sulfonic acid

Anthetaquinon-2- sulphonate 2480.42 sulfonic acid

Sodium n-dodecyl sulphate 2481.43 sulphate

Sodium sulphate sulphate 2481.77

- 169 - G-2 XANES TEY spectra of samples Sample IDs ID Sample Temp KOH/C Time ID Sample (°C) (hr) I-1 FC-I ------S-KNS-7 washed again S-KNS-7 washed again I-2 I-KOH-1 700 3:1 1 S-KS-1-2 washed again S-KS-1-2 washed again I-3 I-KNS-1 700 3:1 1+1 I-AW I-KS-1-2 I-4 I-KS-17 700 0 1 I-AW-2 repeated I-KS-1-2 I-5 I-KS-15 700 1:1 1 S-AW KS-1-4 I-6 I-KS-16 700 2:1 1 S-AW-2 repeated KS-1-4 I-7 I-KS-1 700 3:1 1 I-KS-16 Hg I-KS-16 mercury loaded I-8 I-KS-2 600 3:1 1 I-KS-17 Hg I-KS-17 mercury loaded I-9 I-KS-3 800 3:1 1 S-KS-1-2 Hg S-KS-1-2 mercury loaded S-1 FC-S ------S-KS-5 Hg S-KS-5 mercury loaded S-2 S-0-700 700 3:1 0 S-KS-16 Hg S-KS-16 mercury loaded S-3 S-KNS-7 700 3:1 1+2.5 S-KS-17 Hg S-KS-17 mercury loaded S-4 S-KS-17 700 0 1 SIAC Hg SIAC-BG mercury loaded S-5 S-KS-15 700 1:1 1 I-KS-1 repeated I-KS-1 S-6 S-KS-16 700 2:1 1 S-KS-1-2 repeated S-KS-1-2 S-7 S-KS-1-2 700 3:1 1 S-KS-1-2-2 Repeated S-KS-1-2 (again) S-8 S-KS-2 600 3:1 1 S-KS-17 repeated S-KS-17 S-9 S-KS-4 800 3:1 1 S-KS-17-2 repeated S-KS-17 (again) T18 SIAC-BG

- 170 -

- 171 - - 172 - - 173 -

- 174 - G-3 XANES FY spectra of samples

- 175 - - 176 -

- 177 - APPENDIX H XPS SPECTRUM AND DATA I-KS-2

S2p Scan 60 Scans, 16 m 33.0 s, 400µm, CAE 40.0, 0.10 eV 240 230 Elemental ID and Quantification 220 210 Name Peak BE At. % SF 200 S2p Scan C 190 S2p Scan A 164.14 1.82 1.670 180 S2p Scan B 165.32 0.75 1.670 170 S2p Scan D 160 S2p Scan C 168.81 65.53 1.670 S2p Scan A Counts / s (Resid. × 0.2) / s (Resid. Counts 150 S2p Scan B S2p Scan D 169.99 31.90 1.670 140 130 120

110 180 170 160 Binding Energy (eV)

I-KS-3

S2p Scan 60 Scans, 16 m 33.0 s, 400µm, CAE 40.0, 0.10 eV 300 280 Elemental ID and Quantification 260 Name Peak BE At. % SF S2pS2p Scan Scan C F 240 S2p Scan A 164.19 22.53 1.670 220 S2p Scan D S2p Scan B 165.37 13.47 1.670 200 S2p Scan A S2p Scan C 168.93 29.93 1.670 S2p Scan BG 180 S2p Scan D 170.11 15.43 1.670 S2p Scan E 160 S2p Scan H S2p Scan E 167.39 12.46 1.670 Counts / s (Resid. × 1) × (Resid. / s Counts 140 S2p Scan F 168.57 2.62 1.670 120 S2p Scan G 165.30 2.09 1.670 100 S2p Scan H 166.48 1.48 1.670 80 60 180 170 160 Binding Energy (eV) I-KS-15

S2p Scan 60 Scans, 16 m 33.0 s, 400µm, CAE 40.0, 0.10 eV 700 Elemental ID and Quantification Name Peak BE At. % SF 600 S2p Scan A 164.12 15.72 1.670

S2pS2p ScanScan HC S2p Scan B 165.30 9.26 1.670 500 S2p Scan J S2p Scan C 169.07 30.13 1.670 S2p Scan D 170.25 18.22 1.670 400 S2p ScanS2p DScan G S2p Scan E 165.14 2.15 1.670 S2p Scan A

300 S2p Scan F 166.32 1.34 1.670 S2pS2p ScanScan BE S2p Scan I S2p Scan G 168.11 9.74 1.670 Counts / s (Resid. × 2) × (Resid. s / Counts 200 S2p Scan F S2p Scan H 169.29 6.59 1.670 S2p Scan I 167.39 5.98 1.670 100 S2p Scan J 168.57 0.86 1.670

0 180 170 160 Binding Energy (eV)

- 178 - I-KS-16 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 600 Elemental ID and Quantification

500 Name Peak BE At. % SF S2p Scan A 164.05 26.78 1.670 S2p Scan A S2p Scan B 165.23 16.44 1.670 400 S2p Scan CH S2p Scan C 168.72 25.03 1.670 S2pS2p Scan Scan B E S2p Scan D 169.90 10.47 1.670 S2p Scan D 300 S2p Scan G S2p Scan E 164.89 3.07 1.670

Counts / s (Resid. × 1) / s (Resid. Counts S2p Scan F S2p Scan F 166.07 2.36 1.670 S2p Scan G 167.50 10.43 1.670 200 S2p Scan H 168.68 5.43 1.670

100 180 170 160 Binding Energy (eV) I-KS-17

S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 3000 Elemental ID and Quantification Name Peak BE At. % SF

S2p Scan A S2p Scan A 164.14 49.72 1.670 S2p Scan B 165.32 25.30 1.670

2000 S2p Scan H S2p Scan C 168.37 8.20 1.670

S2p Scan B S2p Scan D 169.55 2.20 1.670 S2p Scan E 166.02 5.49 1.670 S2p Scan F 167.20 1.74 1.670 S2p Scan E

Counts / s(Resid. × 2) 1000 S2p Scan G 162.65 3.86 1.670 S2pS2p ScanScan IC S2p Scan D S2p ScanS2p J Scan F S2p Scan H 163.83 1.06 1.670

S2p Scan G S2p Scan I 168.92 1.80 1.670 S2p Scan J 170.10 0.63 1.670

0 180 170 160 Binding Energy (eV)

S-KS-17 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 4000 Elemental ID and Quantification Name Peak BE At. % SF 3000 S2p Scan A S2p Scan A 164.09 54.19 1.670 S2p Scan B 165.27 21.13 1.670 S2p Scan C 168.75 4.64 1.670 S2p ScanS2p ScanB J 2000 S2p Scan D 169.93 1.64 1.670 S2p Scan E 165.88 5.13 1.670 S2p Scan E

Counts /s (Resid. ×2) S2p Scan F 167.06 3.75 1.670 S2p Scan C S2p Scan G 168.18 4.13 1.670 1000 S2pS2p Scan Scan H G S2p ScanS2p D Scan F S2p Scan H 169.36 1.69 1.670 S2p Scan I S2p Scan I 162.48 3.02 1.670 S2p Scan J 163.66 0.68 1.670 0 180 170 160 Binding Energy (eV)

- 179 -

KNS-7 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 900 Elemental ID and Quantification Name Peak BE At. % SF 800 S2p Scan A 164.04 18.57 1.670

700 S2p Scan C S2p Scan B 165.22 12.46 1.670 S2p Scan D S2p Scan C 168.46 32.09 1.670 600 S2p Scan A S2p Scan D 169.64 15.10 1.670

500 S2p Scan E 165.05 3.71 1.670 S2pS2p ScanScan BE S2p Scan F 166.23 3.04 1.670 400 S2p Scan G 169.54 11.05 1.670 Counts / s (Resid. × 0.5) S2p Scan F 300 S2p Scan H 170.72 3.98 1.670

200 100 180 170 160 Binding Energy (eV)

KS-2 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 1600 Elemental ID and Quantification 1400 Name Peak BE At. % SF S2p Scan A 164.11 30.83 1.670 1200 S2p Scan A S2p Scan B 165.29 15.51 1.670 1000 S2p Scan C 168.67 20.52 1.670 S2pS2p Scan Scan B H S2p Scan G S2p Scan D 169.85 9.16 1.670 800 S2p ScanS2p J Scan E S2p Scan C S2p Scan E 165.61 6.93 1.670 S2p Scan D 600 S2p S2pScan Scan I I S2p Scan J S2p Scan F 166.79 3.20 1.670 Counts / s (Resid. × 2) / s (Resid. Counts S2p Scan F S2p Scan G 163.67 5.92 1.670 400 S2p Scan H 164.85 1.11 1.670 200 S2p Scan I 167.61 4.68 1.670 S2p Scan J 168.79 2.14 1.670 0 180 170 160 Binding Energy (eV)

KS-4

S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 500 Elemental ID and Quantification

S2p Scan C 400 S2p Scan F Name Peak BE At. % SF S2p Scan A 164.19 14.34 1.670 S2p Scan D S2p Scan B 165.37 7.67 1.670 300 S2p Scan C 169.00 41.42 1.670 S2p Scan B S2pS2p Scan Scan G A S2p Scan D 170.18 24.05 1.670 S2p Scan E Counts / s (Resid. × 0.5) S2p Scan H S2p Scan E 167.40 6.55 1.670 200 S2p Scan F 168.58 0.95 1.670 S2p Scan G 165.25 3.07 1.670 S2p Scan H 166.43 1.95 1.670 100 180 170 160 Binding Energy (eV)

- 180 - KS-1-4 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 220 Elemental ID and Quantification

200 Name Peak BE At. % SF 180 S2p Scan A 164.24 15.83 1.670 S2p Scan B 165.42 12.32 1.670 160 S2p Scan C 168.59 45.35 1.670

140 S2p Scan D 169.77 26.50 1.670

Counts / s (Resid. × 0.2) 120

100

80 180 170 160 Binding Energy (eV)

S-KS-15

S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 700 Elemental ID and Quantification

600 Name Peak BE At. % SF S2p Scan A 164.07 22.91 1.670 S2p Scan CH 500 S2p Scan A S2p Scan B 165.25 12.63 1.670 S2p Scan C 168.97 26.94 1.670 S2p Scan BE 400 S2p Scan D S2p Scan D 170.15 12.60 1.670 S2p Scan G S2p Scan E 165.19 4.97 1.670

300 S2p Scan F 166.37 1.67 1.670 Counts / s (Resid. × 0.5) S2p Scan F S2p Scan G 167.81 12.57 1.670 S2p Scan H 168.99 5.71 1.670 200

100 180 170 160 Binding Energy (eV)

S-KS-16 S2p Scan 75 Scans, 20 m 41.3 s, 400µm, CAE 40.0, 0.10 eV 500 Elemental ID and Quantification Name Peak BE At. % SF

400 S2p Scan A 164.26 10.07 1.670 S2p Scan B 165.45 5.24 1.670 S2p Scan G S2p Scan D S2p Scan C 168.28 33.17 1.670 300 S2p Scan C S2p Scan D 169.46 14.10 1.670 S2p Scan H S2p Scan E S2p Scan E 170.08 8.01 1.670

200 S2p Scan A S2p Scan F 171.26 4.47 1.670 S2p Scan F S2p Scan B

Counts / s (Resid. × 0.5) / s (Resid. Counts S2p Scan G 168.85 15.90 1.670 S2p Scan H 170.03 9.04 1.670 100

0 180 170 160 Binding Energy (eV)

- 181 - APPENDIX I MERCURY ION ADSORPTION CURVE

Hg2+ adsorption curves (from Excel)

120 140 KOH-1-2 100 KOH-2 120 100 80

80 60 60 40 concentration (mg/L) concentration (mg/L) 2+

2+ 40 Hg Hg 20 20

0 0 0 50 100 150 200 0 50 100 150 200 Time (min) Time (min)

120 120 S-0-700 100 KOH-10 100

80 80

60 60

40 40 concentration (mg/L) concentration concentration (mg/L) concentration 2+ 2+ 20 20 Hg Hg

0 0 0 50 100 150 200 0 50 100 150 200 250 300 Time (min) Time (min)

- 182 - 140

120 120

100 100 KNS-5 KNS-6

80 80

60 60

40 40 concentration (mg/L) concentration (mg/L) 2+ 2+ 2+ 20 20 Hg Hg Hg

0 0 0 50 100 150 200 0 50 100 150 200 Time (min) Time (min)

120

100 KNS-7

40 concentration (mg/L) concentration 2+ 20 Hg

0 0 50 100 150 200 250 300 Time (min)

- 183 - 140

120 160 100 KS-1 140 Test 1 Test 2 KS-1--2 120 80 100

60 80

60 40 concentration (mg/L) concentration (mg/L)

2+ 40 2+ Hg 20 Hg 20

0 0 0 50 100 150 200 250 300 0 50 100 150 200 Time (min) Time (min)

120 120

100 KS-1-4 100 KS-2

80 80

60 60

40 40 concentration (mg/L) concentration concentration (mg/L) concentration 2+ 2+ 20 20 Hg Hg

0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Time (min) Time (min)

- 184 - 120 120

100 KS-4 100 KS-5

80 80

60 60

40 40 concentration (mg/L) concentration (mg/L) 2+ 2+ 20 20 Hg Hg

0 0 0 50 100 150 200 250 300 0 50 100 150 200 Time (min) Time (min)

120 120 S-KS-16 100 S-KS-15 100

80 80

60 60

40 40 concentration (mg/L) concentration concentration (mg/L) 2+ 2+ 20 20 Hg Hg

0 0 0 50 100 150 200 250 300 0 50 100 150 200 Time (min) Time (min)

- 185 - 120

100 I-KNS-1 test 1 test 2 120 I-KS-1

80 100

60 80

60 40 concentration (mg/L) concentration concentration (mg/L) concentration 40 2+ 2+ 20 Hg Hg 20 0 0 0 50 100 150 200 250 300 0 20 40 60 80 100 120 140 160 Time (min) Tme (min)

120 120

test 1 test 2 100 I-KS-1-2 100 I-KS-2

80 80

60 60

40 40 concentration (mg/L) concentration (mg/L) concentration 2+ 2+ 2+

20 Hg

Hg 20

0 0 0 50 100 150 200 250 300 0 20 40 60 80 100 120 140 160 Time (min) Time (min)

- 186 - 120 120

100 I-KS-3 100 I-KS-15

80 80

60 60

40 40 concentration (mg/L) concentration (mg/L) concentration 2+ 2+ 20 20 Hg Hg

0 0 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Time (min) Time (min)

120 120

100 Commercial SIAC 100 I-KS-16

80 80

60 60

40 40 concentration (mg/L) concentration concentration (mg/L) 2+ 2+ 20 20 Hg Hg

0 0 0 200 400 600 800 1000 0 50 100 150 200 Time (min) Time (min)

- 187 - Hg 2+ adsorption curve fitting (from OriginPro 7.5)

100 80 KOH-10 KS-1 70 80 60 Data: Data1_I 60 Data: Data1_G 50 Model: BoxLucas1 Model: BoxLucas1 Equation: Equation: 40 y = a*(1 - exp(-b*x)) 40 y = a*(1 - exp(-b*x)) Weighting: Weighting: 30 y No weighting y No weighting Y Axis Title

Y Axis Title Chi^2/DoF = 21.69375 20 Chi^2/DoF = 68.39293 20 R^2 = 0.97348 R^2 = 0.94298

10 a 79.59619 ±3.53406 a 96.75519 ±9.38294 0 b 0.04681 ±0.00538 b 0.02441 ±0.00468 0

-20 -10 -20 0 20 40 60 80 100 120 140 160 -20 0 20 40 60 80 100 120 140 160 X Axis Title X Axis Title

80 KOH-N2-2 80 KNS-5 70

60 60 Data: Data1_K 50 Data: Data1_B Model: BoxLucas1 Model: BoxLucas1 Equation: Equation: 40 40 y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) W eighting: Weighting: y No weighting 30 y No weighting Y Axis Title Y Title Y Axis 20 Chi^2/DoF = 40.26618 20 Chi^2/DoF = 11.66644 R^2 = 0.95522 R^2 = 0.98561 10 a 83.9697 ±6.61916 a 80.30277 ±2.65625 0 b0.0276±0.00448 0 b 0.04494 ±0.00377 -10 -20 0 20 40 60 80 100 120 140 160 -20 0 20 40 60 80 100 120 140 160 X Axis Title X Axis Title

- 188 -

I-KS-1 70 KS-1-2 80 60

60 50 Data: Data1_I Data: Data1_B Model: BoxLucas1 Model: BoxLucas1 40 Equation: Equation: y = a*(1 - exp(-b*x)) 40 y = a*(1 - exp(-b*x)) W eighting: Weighting: 30 y No weighting y No weighting q (mg/g) q (mg/g) 20 Chi^2/DoF = 2.89988 20 Chi^2/DoF = 13.9648 R^2 = 0.99444 R^2 = 0.98002 10 a 65.73001 ±1.11785 ± a 84.20259 3.91794 b 0.03717 ±0.00162 0 b 0.02739 ±0.00262 0

-10 -20 0 20 40 60 80 100 120 140 160 0 200 400 600 800 1000 Time (s) Time (s)

100 KS-5 80 S-KS-16

70 80 60 Data: Data1_B Model: BoxLucas1 Data: Data1_K 60 50 Model: BoxLucas1 Equation: Equation: y = a*(1 - exp(-b*x)) 40 y = a*(1 - exp(-b*x)) W eighting: 40 Weighting: y No weighting 30

y No weighting q (mg/g) q (mg/g)

20 Chi^2/DoF = 1.67245 Chi^2/DoF = 3.44401 R^2 = 0.99748 20 R^2 = 0.99612

10 a 86.33032 ±1.04305 a 75.71942 ±0.72161 b 0.05607 ±0.00209 0 b 0.05704 ±0.00169 0 -10 0 200 400 600 800 1000 0 200 400 600 800 1000 Time (s) Time (s)

- 189 -

I-KS-16 35 S-KS-17 80 30 Data: Data1_O Data: Data1_M 60 Model: BoxLucas1 25 Equation: Model: BoxLucas1 y = a*(1 - exp(-b*x)) 20 Equation: W eighting: y = a*(1 - exp(-b*x)) Weighting: 40 y No weighting 15 y No weighting

Y Axis Title Y Axis Title Chi^2/DoF = 5.82894 10 R^2 = 0.99173 Chi^2/DoF = 2.30586 20 R^2 = 0.9827 5 a 79.90136 ±1.45954 a 33.15611 ±1.21378 b 0.0468 ±0.00242 0 0 b 0.01999 ±0.0016

-5 0 200 400 600 800 1000 0 200 400 600 800 1000 X Axis Title X Axis Title

I-KS-17 100 35 KS-4

30 80

Data: Data1_V 25 Data: Data1_X Model: BoxLucas1 Model: BoxLucas1 Equation: 60 Equation: 20 y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) Weighting: W eighting: y No weighting 15 40 y No weighting

Chi^2/DoF = 2.51113 Y Axis Title Y Axis Title 10 Chi^2/DoF = 4.90652 R^2 = 0.98158 R^2 = 0.99456 20

5 a 33.47934 ±1.31312 ± b 0.01782 ±0.0015 a 86.14655 1.09095 b0.0436±0.00171 0 0 -5 -200 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 X Axis Title X Axis Title

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80 80 KS-2 I-KS-15 70 70

60 60 Data: Data1_Z 50 50 Model: BoxLucas1 Data: Data1_EE Equation: Model: BoxLucas1 40 y = a*(1 - exp(-b*x)) 40 Equation: W eighting: y = a*(1 - exp(-b*x)) y No weighting 30 30 Weighting: y No weighting Y Axis Title Chi^2/DoF = 3.72119 TitleY Axis 20 20 R^2 = 0.99417 Chi^2/DoF = 25.26526 R^2 = 0.94187 a 70.39127 ±1.03363 10 10 b 0.03226 ±0.00136 a 63.3166 ±2.51036 0 0 b 0.04139 ±0.00501

-10 -10 -200 0 200 400 600 800 1000 1200 1400 -200 0 200 400 600 800 1000 1200 1400 X Axis Title X Axis Title

80 100 S-KS-15 KNS-7 70 80 60 Data: Data1_DD 50 Data: Data1_BB Model: BoxLucas1 60 Model: BoxLucas1 Equation: Equation: 40 y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) Weighting: Weighting: 30 y No weighting 40 y No weighting

Y Axis Title Y Axis Title 20 Chi^2/DoF = 9.68854 Chi^2/DoF = 26.08174 R^2 = 0.96522 R^2 = 0.98097 20

10 a 64.65968 ±1.76014 a 82.47756 ±2.50885 b0.0271±0.00203 b 0.04402 ±0.00416 0 0 -10 -200 0 200 400 600 800 1000 1200 1400 -200 0 200 400 600 800 1000 1200 1400 X Axis Title X Axis Title

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100 60 S-0-700 I-KNS-1

50 80

40 60 Data: Data1_LL Data: Data1_E Model: BoxLucas1 Model: BoxLucas1 Equation: 30 Equation: y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) 40 Weighting: Weighting: y No weighting y No weighting q (mg/g) 20

Y Axis Title

Chi^2/DoF = 25.3703 Chi^2/DoF = 18.24092 20 R^2 = 0.93215 R^2 = 0.9736 10

a 57.09747 ±5.93321 a 75.96916 ±2.33621 b 0.01168 ±0.00239 0 b 0.03012 ±0.00261 0

0 50 100 150 200 250 300 -200 0 200 400 600 800 1000 1200 1400 Time (s) X Axis Title

100 60 I-KS-1-2 I-KS-3

50 80

40 Data: Data1_H 60 Data: Data1_JJ Model: BoxLucas1 Model: BoxLucas1 30 Equation: Equation: y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) Weighting: 40 W eighting: 20 y No weighting y No weighting q (mg/g)

Y Axis Title Chi^2/DoF = 34.20506 Chi^2/DoF = 23.25774 10 R^2 = 0.92719 20 R^2 = 0.96414

a 60.15881 ±6.62596 0 a 83.11768 ±1.93182 b 0.01219 ±0.00267 b 0.09774 ±0.01004 0 -10 0 50 100 150 200 250 300 -200 0 200 400 600 800 1000 1200 1400 Time (s) X Axis Title

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60 KS-1-4 70 Commercial SIAC

60 50

50 Data: Data1_B 40 Data: Data1_T Model: BoxLucas1 40 Model: BoxLucas1 Equation: Equation: 30 y = a*(1 - exp(-b*x)) y = a*(1 - exp(-b*x)) Weighting: 30 Weighting: y No weighting y No weighting q (mg/g)

20 Y AxisTitle 20 Chi^2/DoF = 38.19937 Chi^2/DoF = 28.25054 R^2 = 0.90821 R^2 = 0.91931 10 10 a 59.87041 ±5.57075 a 58.52349 ±2.44035 b 0.01633 ±0.00325 0 b 0.09039 ±0.01503 0 -10 0 50 100 150 200 250 300 0 200 400 600 800 1000 Time (s) X Axis Title

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