Chapter 1 Activated Carbon and Its Surface Structure .............................. 1 1.1 Crystalline Structure of Activated Carbons .......................... 3 1.2 Porous Structure of the Active Carbon Surface ....................... 4 1.3 Chemical Structure of the Carbon Surface ............................ 7 1.3.1 Carbon-Oxygen Surface Groups .................................. 8 1.3.2 Characterization of Carbon-Oxygen Surface Groups ............. 10 1.3.2.1 Thermal Desorption Studies ........................... 11 1.3.2.2 Neutralization of Alkalies ........................... 17 1.3.2.3 Specific Chemical Reactions .......................... 21 1.3.2.4 Spectroscopic Methods ................................ 21 1.4 Influence of Carbon-Oxygen Surface Groups on Adsorption Properties ......................................................... 36 1.4.1 Surface Acidity of Carbons ................................... 38 1.4.2 Hydrophobicity ............................................... 38 1.4.3 Adsorption of Polar Vapors ................................... 39 1.4.4 Adsorption of Benzene Vapors ................................. 42 1.4.5 Immersional Heats of Wetting ................................. 43 1.4.6 Adsorption from Solutions .................................... 44 1.4.7 Preferential Adsorption ...................................... 45 1.4.8 Catalytic Reactions of Carbons ............................... 46 1.4.9 Resistivity .................................................. 46 1.5 Active Sites on Carbon Surfaces .................................... 46 1.6 Modification of Activated Carbon Surface ........................... 52 1.6.1 Modification of Activated Carbon Surface by Nitrogenation .... 53 1.6.2 Modification of Carbon Surface by Halogenation ............... 54 1.6.3 Modification of Carbon Surface by Sulfurization .............. 56 1.6.4 Activated Carbon Modification by Impregnation ................ 58 References ............................................................. 60 Chapter 2 Adsorption Energetics, Models, and Isotherm Equations .................. 67 2.1 Adsorption on a Solid Surface ...................................... 67 2.2 Adsorption Equilibrium ............................................. 69 2.2.1 Adsorption Isotherm .......................................... 69 2.2.2 Adsorption Isobar ............................................ 70 2.2.3 Adsorption Isostere .......................................... 70 2.3 Energetics of Adsorption ........................................... 71 2.3.1 Molar Energy of Adsorption ................................... 72 2.3.2 Molar Integral Enthalpy of Adsorption ........................ 72 2.3.3 Molar Integral Entropy of Adsorption ......................... 73 2.3.4 Heat of Adsorption ........................................... 73 2.3.5 Isosteric Heat of Adsorption ................................. 74 2.4 Adsorption Isotherm Equations ..................................... 77 2.4.1 Langmuir Isotherm Equation .................................. 78 2.4.1.1 Langmuir Isotherm for Dissociative Adsorption ....... 82 2.4.1.2 Langmuir Isotherm for Simultaneous Adsorption of Two Gases ........................................ 83 2.4.1.3 Applicability of the Langmuir Isotherm .............. 84 2.4.2 Brunauer, Emmett, and Teller (BET) Isotherm Equation ........ 85 2.4.2.1 Derivation of the BET Equation ...................... 86 2.4.2.2 Applicability of the BET Equation to Active Carbons ............................................. 91 2.4.2.3 Criticism of the BET Equation ....................... 92 2.4.2.4 Alternative Approach to Linearization of the BET Equation ............................................ 93 2.4.2.5 Classification of Adsorption Isotherms .............. 97 2.4.2.6 Type I Isotherms ................................... 100 2.4.2.7 Type II Isotherms .................................. 104 2.4.2.8 Type III and Type V Isotherms ...................... 105 2.4.2.9 Type IV Isotherm ................................... 111 2.4.3 Potential Theory of Adsorption ............................. 112 2.4.3.1 Dubinin Equation for Potential Theory .............. 116 2.4.4 Freundlich Adsorption Isotherm ............................. 120 2.4.5 Temkin Adsorption Isotherm ................................. 121 2.4.5.1 Derivation of the Isotherm for a Uniform Surface ... 122 2.4.6 Capillary Condensation Theory .............................. 123 2.4.6.1 Evidence in Support of the Capillary Condensation Theory ............................................. 124 2.4.7 Applicability of Langmuir, Freundlich or Temkin Isotherms to Adsorption Data ......................................... 125 2.4.7.1 Linearity of the Plot .............................. 125 2.4.7.2 Variation of Heat of Adsorption (q) with Surface Coverage (θ) ....................................... 126 2.4.7.3 Appropriate Range θ ................................ 126 2.4.8 Adsorption Hysteresis ...................................... 126 2.4.9 Theory of Volume Filling of Micropores (TVFM) .............. 131 2.4.9.1 Filling of Micropore Volume in Adsorption .......... 135 References ............................................................ 141 Chapter 3 Activated Carbon Adsorption from Solutions ............................ 145 3.1 Types of Isotherms for Adsorption from Solution Phase ............ 146 3.1.1 Preferential Adsorption .................................... 146 3.1.2 Absolute Adsorption ........................................ 146 3.2 Types of Adsorption Isotherms .................................... 146 3.2.1 Classification of Adsorption from Solutions ................ 148 3.2.2 Adsorption from Dilute Solutions ........................... 148 3.2.2.1 Potential Theory of Adsorption from Dilute Solutions .......................................... 159 3.2.3 Adsorption from Solutions at Higher Concentrations (Composite Miscible Solutions) ............................. 161 3.2.3.1 Derivation of Composite Isotherm ................... 161 3.2.3.2 Classification of Composite Isotherms .............. 164 3.3 Factors Influencing Adsorption from Binary Solutions ............. 167 3.3.1 Adsorbent-Adsorbate Interaction ............................ 168 3.3.2 Departures from Usual Composite Isotherm Shapes ............ 179 3.3.3 Porosity of the Adsorbent .................................. 183 3.3.4 Surface Heterogeneity ...................................... 183 3.3.5 Steric Effects ............................................. 184 3.3.6 Orientation of Adsorbed Molecules .......................... 184 3.4 Determination of Individual Adsorption Isotherms from Composite Isotherms ........................................................ 185 3.5 Thickness of the Adsorbed Layer .................................. 189 3.6 Chemisorption from Binary Solutions .............................. 192 3.7 Traube's Rule .................................................... 193 References ............................................................ 196 Chapter 4 Carbon Molecular Sieves ............................................... 201 4.1 Preparation of Carbon Molecular Sieves (CMS or MSC) .............. 202 4.2 Characterization of Carbon Molecular Sieve Carbons ............... 210 4.2.1 Characterization of Carbons by Adsorption of Organic Vapors ..................................................... 213 4.2.2 Characterization of Carbons by Immersional Heats of Wetting ................................................. 222 4.3 Adsorption by Carbon Molecular Sieves ............................ 227 References ............................................................ 238 Chapter 5 Activated Carbon Adsorption Applications .............................. 243 5.1 Liquid Phase Applications of Activated Carbon Adsorption ......... 244 5.1.1 Food Processing ............................................ 244 5.1.2 Preparation of Alcoholic Beverages ......................... 244 5.1.3 Decolorization of Oils and Fats ............................ 245 5.1.4 Activated Carbon Adsorption in Sugar Industry .............. 246 5.1.4.1 Decolorization with Powdered Activated Carbons ..... 247 5.1.4.2 Decolorization with Granulated Activated Carbons ... 249 5.1.5 Application in Chemical and Pharmaceutical Industries ...... 250 5.1.6 Activated Carbon for the Recovery of Gold .................. 251 5.1.6.1 Mechanism of Gold Recovery by Activated Carbon Adsorption ......................................... 252 5.1.6.2 Desorption of Gold from Active Carbon Surface ...... 259 5.1.6.3 Desorption of Gold Using Inorganic Salts ........... 260 5.1.6.4 Desorption of Gold by Organic Solvents ............. 260 5.1.7 Purification of Electrolytic Baths ......................... 261 5.1.8 Refining of Liquid Fuels ................................... 263 5.2 Gas-Phase Applications ........................................... 263 5.2.1 Recovery of Organic Solvents ............................... 263 5.2.2 Removal of Sulfur Containing Toxic Components from Exhaust Gases and Recovery of Sulfur .................. 267 5.2.2.1 Removal of Sulfur Dioxide from Waste Gases ......... 267 5.2.2.2 Removal of Hydrogen Sulfide and Carbon Disulfide ... 272 5.3 Activated Carbon Adsorption in Nuclear Technology ................ 277 5.4 Activated Carbon Adsorption in Vacuum Technology ................. 279 5.5 Medicinal Applications of Activated Carbon Adsorption ............ 279 5.6 Activated Carbon Adsorption for Gas Storage ...................... 289 References ............................................................ 292 Chapter 6 Activated Carbon Adsorption and Environment: Removal of Inorganics from Water ............................................................ 297 6.1 Activated Carbon Adsorption of Inorganics from Aqueous Phase (General) .................................................. 299 6.2 Activated Carbon Adsorption of Copper ............................ 304 6.2.1 Mechanism of Copper Adsorption ............................. 315 6.3 Activated Carbon Adsorption of Chromium .......................... 316 6.3.1 Mechanism of Adsorption of Cr(III) Ions .................... 325 6.4 Activated Carbon Adsorption of Mercury ........................... 326 6.5 Adsorptive Removal of Cadmium from Aqueous Solutions ............. 335 6.6 Activated Carbon Adsorption of Cobalt from Aqueous Solutions ..... 340 6.7 Activated Carbon Adsorption of Nickel ............................ 346 6.8 Removal of Lead from Water ....................................... 351 6.9 Adsorptive Removal of Zinc ....................................... 353 6.10 Activated Carbon Adsorption of Arsenic ........................... 355 6.11 Adsorptive Separation of Cations in Trace Amounts from Aqueous Solutions ........................................................ 358 6.12 Mechanism of Metal Ion Adsorption by Activated Carbons ........... 361 References ............................................................ 364 Chapter 7 Activated Carbon Adsorption and Environment: Adsorptive Removal of Organics from Water ................................................ 373 7.1 Activated Carbon Adsorption of Halogenated Organic Compounds ..... 374 7.2 Activated Carbon Adsorption of Natural Organic Matter (NOM) ...... 383 7.3 Activated Carbon Adsorption of Phenolic Compounds ................ 387 7.4 Adsorption of Nitro and Amino Compounds .......................... 402 7.5 Adsorption of Pesticides ......................................... 411 7.6 Adsorption of Dyes ............................................... 416 7.7 Activated Carbon Adsorption of Drugs and Toxins .................. 426 7.8 Adsorption of Miscellaneous Organic Compounds .................... 429 7.9 Mechanism of Adsorption of Organics by Activated Carbons ......... 434 References ............................................................ 436 Chapter 8 Activated Carbon Adsorption and Environment: Removal of Hazardous Gases and Vapors ............................................................ 443 8.1 Removal of Volatile Organic Compounds at Low Concentrations ...... 443 8.2 Removal of Oxides of Nitrogen from Flue Gases .................... 445 8.3 Removal of Sulfur Dioxide from Flue Gases ........................ 451 8.4 Evaporated Loss Control Device (ELCD) ............................ 452 8.5 Protection of Upper Respiratory Tract in Hazardous Environment ... 452 8.6 Activated Carbon Adsorption of Mercury Vapors .................... 461 8.7 Removal of Organosulfur Compounds ................................ 462 8.8 Adsorptive Removal of Miscellaneous Vapors and Gases ............. 463 References ............................................................ 470 Author Index .......................................................... 473 Subject Index ......................................................... 495