Preparation and Characterization of Microporous Activated Carbon from Biomass and its Application in the Removal of Chromium(VI) from Aqueous Phase Thesis submitted in partial fulfillment of the requirement for the degree of Doctor of Philosophy in Chemical Engineering by Ramakrishna Gottipati (Roll No – 507CH001) Under the guidance of Dr. Susmita Mishra Department of Chemical Engineering National Institute of Technology Rourkela, Odisha – 769008 January 2012 i Department of Chemical Engineering National Institute of Technology, Rourkela Odisha, India – 769008 Certificate This is to certify that the thesis entitled ‘Preparation and Characterization of Microporous Activated Carbon from Biomass and its Application in the Removal of Chromium(VI) from Aqueous Phase’ submitted by Ramakrishna Gottipati is a record of an original research work carried out by him under my supervision and guidance in partial fulfillment of the requirements for the award of the degree of Doctor of Philosophy in Chemical Engineering during the session July’2007 – January’2012 in the Department of Chemical Engineering, National Institute of Technology, Rourkela. Neither this thesis nor any part of it has been submitted for the degree or academic award elsewhere. Dr. Susmita Mishra Department of Chemical Engineering National Institute of Technology, Rourkela ii Acknowledgement I would like to express my deep and sincere gratitude to Dr. Susmita Mishra for her invaluable supervision and esteemed guidance. As my supervisor, her insight, observations and suggestions helped me to establish the overall direction of the research and to achieve the objectives of the work. Her continuous encouragement and support have been always a source of inspiration and energy for me. My sincere thanks are due to members of Doctoral Scrutiny Committee (DSC) and faculty members of Chemical Engineering Department for their suggestions and constructive criticism during the preparation of the thesis. I acknowledge all my friends, research scholars, and staff of Chemical Engineering Department for their support during my research work. I must acknowledge the academic resources provided by N.I.T., Rourkela and the research fellowship granted by Department of Science and Technology (DST) to carry out this work. Finally, I am forever indebted to my parents, sister and brother-in-law for their understanding, endless patience and encouragement from the beginning. Ramakrishna Gottipati iii DDDedicatedDedicated to My Family and Friends iv Contents Page No. List of Figures VII List of Tables XII Nomenclature XIV Abstract XVII Chapter – 1: Introduction 1 1.1. Role of Activated Carbon 1 1.2. Hexavalent Chromium [Cr(VI)] 3 1.3. Motivation 3 1.3.1. The Problem 3 1.3.2. Health Impacts 4 1.3.3. Status of clean-up Activity 4 1.4. Objectives 5 1.5. Scope of the Study 5 1.6. Organization of Thesis 6 Chapter – 2: Literature Review 7 2.0. Summary 7 2.1. Types of Carbon materials 7 2.2. Activated Carbon 9 2.2.1. Historical Background 9 2.2.2. Preparation of Activated Carbon 11 2.2.2.1. Physical Activation 11 2.2.2.2. Chemical Activation 12 2.2.3. Structure of Activated Carbon 13 2.2.3.1. Porous Structure 13 2.2.3.2. Crystalline Structure 13 2.2.3.3. Chemical Structure 17 I 2.2.4. Classification of Activated Carbon 18 2.2.4.1. Powered Activated Carbon 18 2.2.4.2. Granular Activated Carbon 18 2.2.4.3. Activated Carbon Fibers 19 2.2.5. Characterization of Activated Carbon 19 2.2.5.1. Gas Adsorption Isotherms 20 2.2.5.1.1. Qualitative interpretation of adsorption isotherms 20 2.2.5.1.2. Quantitative interpretation of adsorption isotherms 25 2.2.5.2. Spectroscopic Methods 27 2.3. Activated Carbon Applications 28 2.4. Chromium 30 2.4.1. Overview 30 2.4.2. Chemistry and Behavior 31 2.4.3. Environmental Occurrence 32 2.4.4. Toxicology 33 2.4.4.1. Effects of Short-term Exposure 33 2.4.4.2. Effects of Long-term Exposure 34 2.5. Chromium(VI) Removal by Activated Carbons from Aqueous Phase 35 2.5.1. Chromium(VI) Removal by Activated Carbons 35 2.5.2. Effect of Process Parameters 40 2.5.2.1. Effect of pH 40 2.5.2.2. Effect of Contact time and Initial Chromium(VI) Concentration 41 2.5.2.3. Effect of Adsorbent Dose 42 2.5.2.4. Effect of Temperature 42 2.6. Design of Experiments (DoE) 43 2.6.1. Fundamentals of DOE 43 2.6.2. Factorial Designs 44 2.7. Regeneration of Activated Carbon 45 II Chapter – 3: Materials and Methods 46 3.0. Summary 46 3.1. Materials 46 3.2. Methodology 46 3.2.1. Characterization of Precursor 46 3.2.1.1. Estimation of Cellulose 47 3.2.1.2. Estimation of Lignin 47 3.2.1.3. Thermogravimetric Analysis 47 3.2.1.4. Proximate Analysis 48 3.2.2. Preparation of Activated Carbon 48 3.2.2.1. Effect of Impregnation 49 3.2.2.2. Effect of Carbonization Temperature 49 3.2.2.3. Effect of Holding Time 50 3.2.3. Characterization of AC 50 3.2.3.1. Proximate Analysis 50 3.2.3.2. Ultimate Analysis 51 3.2.3.3. Yield 51 3.2.3.4. Bulk Density 51 3.2.3.5. Porosity Characterization 52 3.2.3.6. Determination of Surface Chemistry 53 3.2.3.7. Microscopy 53 3.2.3.8. Other Analyses 54 3.2.3.8.1. X-ray diffraction spectroscopy 54 3.2.3.8.2. Iodine number 54 3.2.3.8.3. Methylene blue number 55 3.2.4. Adsorption Experiments 55 3.2.5. Comparison and Regeneration 58 3.2.6. Modeling of Cr(VI) Adsorption 58 III Chapter – 4: Preparation and Characterization of Activated Carbon 59 4.0. Summary 59 4.1. Selection of Precursor 59 4.2. Preparation of AC 62 4.3. Effect of Process Parameters 62 4.3.1. Effect of Impregnation Ratio 62 4.3.1.1. Effect of Impregnation on the Yield of AC 63 4.3.1.2. Nitrogen Gas Adsorption – Desorption Isotherms 64 4.3.1.3. Surface Area and Pore Volume 68 4.3.1.4. Micropore Surface Area and Micropore Volume 71 4.3.2. Effect of Carbonization Temperature 74 4.3.2.1. Effect of Carbonization Temperature on the Yield of AC 74 4.3.2.2. Nitrogen Gas Adsorption – Desorption Isotherms 75 4.3.2.3. Surface Area and Pore Volume 78 4.3.2.4. Micropore Surface Area and Micropore Volume 81 4.3.3. Effect of Holding Time 84 4.3.3.1. Effect of Holding Time on the Yield of AC 4.3.3.2. Nitrogen Gas Adsorption – Desorption Isotherms 84 4.3.3.3. Surface Area and Pore Volume 88 4.3.3.4. Micropore Surface Area and Micropore Volume 90 4.4. Optimum Conditions and Comparison 93 4.5. Pore Size Distribution (PSD) 94 4.6. Fourier Transform Infrared spectroscopy (FTIR) 96 4.7. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) analysis 99 4.8. X – Ray Diffraction spectroscopy (XRD) 102 IV Chapter – 5: Adsorption of Chromium(VI) on Activated Carbon 104 5.0. Summary 104 5.1. Effect of Process Parameters 105 5.1.1. Effect of pH 105 5.1.2. Effect of Adsorbent Dose 110 5.1.3. Effect of Initial Chromium(VI) Concentration 115 5.1.4. Effect of Temperature 121 5.2. Adsorption Equilibrium Study 125 5.2.1. Langmuir Isotherm 125 5.2.2. Freundlich Isotherm 126 5.2.3. Temkin Isotherm 128 5.2.4. Dubinin – Radushkevich Isotherm 129 5.3. Adsorption Kinetic Study 131 5.3.1. Pseudo-First-Order Kinetic Model 132 5.3.2. Pseudo-Second-Order Kinetic Model 134 5.4. Adsorption Mechanism 138 5.4.1. Intra-Particle Diffusion 138 5.4.2. Boyd Model 141 5.5. Adsorption Thermodynamic Study 144 5.6. Role of Surface Chemistry 145 5.7. Energy Dispersive X-ray spectroscopy (EDX) 147 5.8. Comparison and Regeneration 149 5.8.1. Porous Characteristics 149 5.8.1.1. N 2 Adsorption – Desorption Isotherms 149 5.8.2. Chromium(VI) Adsorption 152 5.8.3. Regeneration of Spent AC 153 Chapter – 6: Modeling of Chromium(VI) Adsorption 155 6.0. Summary 155 6.1. Full Factorial Design 155 6.2. Designing of Experimental Matrix 156 6.3. Modeling of Chromium(VI) Removal by AC-PA 159 V 6.3.1. Pareto Plot 160 6.3.2. Main Effects 161 6.3.3. Interaction Effects 162 6.3.4. Normal Probability Plot 164 6.3.5. Optimization 164 6.3.6. Validation Experiments 165 6.4. Modeling of Chromium(VI) Removal by AC-ZC 166 6.4.1. Pareto Plot 167 6.4.2. Main Effects 168 6.4.3. Interaction Effects 169 6.4.4. Normal Probability Plot 171 6.4.5. Optimization 172 6.4.6. Validation Experiments 173 6.5. Modeling of Chromium(VI) Removal by AC-PH 173 6.5.1. Pareto Plot 175 6.5.2. Main Effects 176 6.5.3. Interaction Effects 177 6.5.4. Normal Probability Plot 181 6.5.5. Optimization 181 6.5.6. Validation Experiments 182 Chapter – 7: Conclusions and Future Perspective 184 7.0. Summary 184 7.1. Conclusions 184 7.2. Scope of Research 185 References 187 VI List of Figures Fig. No Title Page No 2.1. Major allotropic forms of carbon and some of carbon structures derived from these forms. 8 2.2. Graphical representation of pore structure in activated carbon.