Sulphur Chemistry in KOH-SO2 Activation of Fluid Coke and Mercury Adsorption from Aqueous Solutions by 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 © Copyright by Hui Cai 2010 Sulphur Chemistry in KOH-SO2 Activation of Fluid Coke and Mercury Adsorption from Aqueous Solutions 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 ...................................................................................................