SUPEROXIDE RADICAL AND UV IRRADIATION IN ULTRASOUND ASSISTED OXIDATIVE DESULFURIZATION (UAOD): A POTENTIAL ALTERNATIVE FOR GREENER FUELS by Ngo Yeung Chan A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (ENVIRONMENTAL ENGINEERING) May 2010 Copyright 2010 Ngo Yeung Chan i ACKNOWLEDGMENTS I would like to dedicate my heartfelt gratitude to my advisor (former committee chairperson) Prof. T. F. Yen (1927 – 2010), for his selfless support, guidance and edification. I would like to thank also my committee chairperson, Prof. M. Pirbazari, and the committee members Prof. J. S. Devinny, Prof. J. J. Lee and Prof. K. S. Shing for their helpful advice and encouragement. I sincerely express my special thanks to Dr. M. Quinlan for his valuable suggestions and help. I definitely appreciate all the friendships and helps from my colleagues including Dr. M. W. Wan, Dr. O. Etemadi, Dr. S. S. Cheng, Dr. C. Y. Yang, and Dr. W. Fan. I would also thank T. Y. Lin, Y. Tung, and S. Angkadjaja for their excellent assistance. I would like to acknowledge Eco Energy Solutions Inc., Reno, Nevada and Intelligent Energy Inc., Long Beach, California for their financial support in this study; the U.S. Navy for the instrumental support of the ultrasonic device; and the U.S. Army for the instrumental support of the Horiba Sulfur in Oil Analyser. ii Last by not least, I express my special thanks to my parents Yin Man Wong and Ho Yee Chan, and my brother Ngo Fung Chan for their endless love and support. iii TABLE OF CONTENTS ACKNOWLEDGMENTS ii LIST OF TABLES ix LIST OF FIGURES xiii LIST OF ABBREVIATIONS xviii ABSTRACT xxii CHAPTER 1: INTRODUCTION 1 1.1 General Overview 1 1.2 Diesel Fuel 2 1.2.1 Diesel Fuel and Organic Sulfur Compounds (OSCs) 2 1.2.2 Diesel Fuel and Sulfur Regulations 6 1.3 Residual Oil 8 1.3.1 Residual Oil and OSCs 8 1.3.2 Residual Oil and Sulfur Regulations 14 1.4 Current Desulfurization Technologies 18 1.4.1 Hydrodesulfurization (HDS) 19 1.4.2 Adsorptive Desulfurization (ADS) 24 1.4.3 Biodesulfurization (BDS) 28 1.4.4 Oxidative Desulfurization (ODS) 31 1.5 Research Objectives 35 CHAPTER 2: THEORETICAL BACKGROUND 36 2.1 Introduction 36 iv 2.2 Ultrasound 37 2.2.1 Fundamentals of Ultrasound 37 2.2.2 Theory on Sonochemistry 38 2.2.3 Sonochemistry in Aqueous Phase 42 2.2.4 History of UAOD and Its Modifications 46 2.3 Oxidant Selection 52 2.3.1 Hydrogen Peroxide 53 2.3.2 Superoxide Anions 55 2.4 Acid Catalysis 57 2.5 Phase Transfer Catalysis 59 2.5.1 Overview of Phase Transfer Catalysis 59 2.5.2 Mechanism of Phase Transfer Catalysis 60 2.5.3 PTC Selection in UAOD Process 65 2.6 Ionic Liquids (ILs) 68 2.6.1 Overview of ILs and RTILs 68 2.6.2 Applications of ILs in Hydrocarbon Separation 74 2.6.3 Applications of ILs in Desulfurizaton 76 2.7 Ultraviolet Irradiation 79 2.7.1 Fundamentals of Photochemistry and UV Radiation 79 2.7.2 UV and Photochemical Reactions in Aqueous System 84 2.7.3 Photocatalysis and Titanium (IV) Oxide 86 2.7.4 Photolysis and Photo-Oxidation Desulfurization 88 CHAPTER 3: MODIFIED OXIDATIVE DESULFURIZATION USING SUPEROXIDE ON MODEL SULFUR COMPOUND STUDY 90 3.1 Introduction 90 3.2 Materials and Experimental Procedures 93 3.2.1 Chemical Preparation 93 3.2.2 Ultrasonic Reactor 94 3.2.3 Ultraviolet Lamp 95 3.2.4 Analytical Method 96 3.3 Experimental Design, Procedure, Results and Discussion 97 3.3.1 Use of Solid Oxidants in Oxidative Desulfurization 97 v 3.3.1.1 Solid Oxidants Selection 97 3.3.1.2 Experimental Procedure 98 3.3.1.3 Results and Discussion 99 3.3.2 Effect of Different Phase Transfer Catalysts 104 3.3.2.1 Phase Transfer Catalyst Selection 104 3.3.2.2 Experimental Procedure 106 3.3.2.3 Results and Discussion 107 3.3.3 Effect of Acid Catalysts 110 3.3.3.1 Acid Catalyst Combination 110 3.3.3.2 Experimental Procedure 111 3.3.3.3 Results and Discussion 112 3.3.4 Effect of Ionic Liquid 114 3.3.4.1 Ionic Liquid Dosage 114 3.3.4.2 Experimental Procedure 115 3.3.4.3 Results and Discussion 116 3.3.4.4 Ionic Liquid Selection 118 3.3.4.5 Experimental Procedure 119 3.3.4.6 Results and Discussion 120 3.3.5 Effect of Treatment Methods 121 3.3.5.1 Time of Ultrasonication 121 3.3.5.2 Experimental Procedure 122 3.3.5.3 Results and Discussion 123 3.4 Desulfurization Efficiency on Various Model Sulfur Compounds 125 3.4.1 Identification of Experimental Optimum Conditions 125 3.4.2 Experimental Procedure 127 3.4.3 Results and Discussion 128 3.5 Kinetic Studies of Desulfurization on Model Sulfur Compounds 129 3.5.1 Experimental Procedure 133 3.5.2 Results and Discussion 134 3.6 Preliminary Study on UV Assisted Desulfurization Process 142 3.6.1 Challenge in UAOD Processes 142 3.6.2 Experimental Procedure 143 3.6.3 Results and Discussion 144 3.7 Summary and Conclusion 145 vi CHAPTER 4: MODIFIED OXIDATIVE DESULFURIZATION USING KO2 AND H2O2 ON PETROLEUM FUEL 148 4.1 Introduction 148 4.2 Materials 150 4.3 Experimental Procedure and Analytical Method 151 4.4 Results and Discussion 152 4.4.1 Desulfurization of JP-8 152 4.4.2 Desulfurization of MGO 155 4.4.3 Desulfurization of Sour Diesel 157 4.4.4 Kinetic Studies of Desulfurization on Various Diesel Samples 159 4.4.5 Desulfurization of Heavy-Distillates 163 4.5 Summary and Conclusion 164 CHAPTER 5: QUALITATIVE ANALYSIS USING GC-SCD 166 5.1 Introduction 166 5.2 Materials 171 5.3 Experimental Procedure 172 5.3.1 Preparation of Model Sulfur Compound Solutions 172 5.3.2 Desulfurization of Feedstock 173 5.3.3 Analytical Method 174 5.3.4 Estimation of Retention Time of Different OSCs 176 5.4 Results and Discussion 179 5.4.1 Model Sulfur Compounds Identification 179 5.4.2 Characterization of Untreated Diesel Samples 184 5.4.3 Characterization of Desulfurized Diesel Samples 187 5.4.4 Characterization of Heavy-Distillates 197 5.5 Mechanism of Inorganic Sulfate Formation 203 5.6 Summary and Conclusion 205 CHAPTER 6: CONCEPTUAL MODEL FOR THE MODIFIED UAOD DESULFURIZATION PROCESS 208 6.1 Introduction 208 vii 6.2 Model Overview 209 6.3 Summary 212 CHAPTER 7: CONCLUSION AND RECOMMENDATIONS 213 7.1 Summary and Conclusion 213 7.2 Recommendations for Future Work 221 REFERENCES 224 viii LIST OF TABLES Table 1.1 Major types of OSCs in petroleum 5 Table 1.2 Sulfur content standards for diesel 7 Table 1.3 Classification of residual oil’s components 11 Table 1.4 Standard properties of residual oil 14 Table 1.5 Sulfur content standards for all marine-use fuel oils 17 Table 1.6 Chemical reactions for the Claus process and the contact process 20 Table 2.1 Sonochemistry in a cavitation bubble formed in water 43 Table 2.2 Chemical reactions initiated by ultrasound in water 44 Table 2.3 Comparison of the UAOD process and its modifications 50 Table 2.4 Oxygen-donor Oxidants 54 Table 2.5 Hydration of anion in chlorobenzene-aqueous system 64 Table 2.6 Standard electrode potentials for selected half-reactions 66 Table 2.7 Specific conductivities 69 Table 2.8 General properties of modern ionic liquids 70 Table 2.9 Toxicity of ionic liquids, expressed as EC50 in µM 71 ix Table 2.10 Ultraviolet Classification 82 Table 2.11 Energy per mole of photons 83 Table 3.1 Specifications of Ultrasonic Reactor VCX-750 listed in product catalogue 94 Table 3.2 Specifications of UV lamp UVLMS-38 listed in product catalogue 95 Table 3.3 Desulfurization efficiency with 30% wt. H2O2 as oxidant 99 Table 3.4 Desulfurization efficiency with KMnO4 as oxidant 100 Table 3.5 Desulfurization efficiency with NaO2 as oxidant 100 Table 3.6 Desulfurization efficiency with KO2 as oxidant 101 Table 3.7 Effect of surfactants on the UAOD process 105 Table 3.8 Desulfurization of DBT solution with TOAF as PTC 108 Table 3.9 Desulfurization of DBT solution with 18-crown-6 as PTC 109 Table 3.10 Desulfurization of DBT solution with respect to acid dosage 112 Table 3.11 Desulfurization of DBT solution with respect to acid catalyst applied 113 Table 3.12 Desulfurization of DBT solution with respect to IL dosage 116 Table 3.13 Desulfurization of DBT solution with respect to type of IL 120 Table 3.14 Desulfurization of DBT solution under magnetic stirring and ultrasound 124 x Table 3.15 Selected conditions for desulfurization in model compound studies with 10 minutes ultrasonication 126 Table 3.16 Desulfurization of various model sulfur compounds 128 Table 3.17 Selected conditions for desulfurization in model compound studies without ultrasonication 132 Table 3.18 Desulfurization efficiencies with respect to reaction time 134 Table 3.19 Rate constants for various model sulfur compounds using KO2 138 Table 3.20 Rate constants for various model sulfur compounds using H2O2 138 Table 3.21 Apparent activation energies for oxidation of BT and DBT 140 Table 3.22 Desulfurization of model sulfur compounds with UV 144 Table 4.1 Desulfurization of JP-8 using KO2 as oxidant 152 Table 4.2 Desulfurization of JP-8 using 30% wt.