The objective of this research was to describe equilibrium between volatile organic compounds and granular activated carbon (GAC) during adsorption and desorption processes occurring in carbon beds used for air pollution control. A thermogravimetric analyzer measured the adsorption of methylisobutylketone (MIBK) onto a coconut based GAC at concentrations ranging from 55 to 10 300 ppmv and temperatures ranging from 25 to 105°C. The equilibrium adsorption data was first modeled by the two-parameter isotherms of Langmuir, Brunauer-Emmett and Teller, and Freundlich as well as the three-parameter isotherm of Dubinin-Astakhov. Also, a new three-parameter isotherm, created by adding a concentration-dependent term to the Freundlich equation, was introduced as the modified Freundlich isotherm. In both three-parameter isotherms, proper choice of the extra parameter allowed for a more accurate fit of the isotherm than did any of the two-parameter isotherms. Moreover, the authors have constructed a modified Freundlich polytherm and a Dubinin-Astakhov polytherm that properly described adsorption and desorption over the full range of test temperatures and concentrations.
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