Modeling effects of moisture on adsorption capacity of activated carbon for VOCs

Activated carbon has long been used for removal or recovery of volatile organic compounds (VOCs) from exhaust gas streams. Moisture content in the gas streams has been shown to be unfavorable for adsorption of VOCs; however, limited quantitative models were found in the literature. This paper reports experimental data and proposes a model concerning the effect of moisture on the adsorption capacities of a granular activated carbon (GAG) for cyclohexane and normal hexane in air streams with relative humidities (RHs), equilibrium temperatures, and VOC concentrations in the ranges of 0-0.9, 33.6-76.4 degrees C, and 500-3,000 ppmv, respectively. Results show that within the experimental conditions the adsorption capacities of the GAC for the VOCs both in humid and dry air streams can be related to vapor pressures of the VOCs by the Langmuir model. Effect of RH on the VOC adsorption capacities are related to RHs of the air streams by the Freundlich-like model: q(VOC)/q(VOC,RH=0) = 1 - kRH(1/n). Some literature-cited data are also shown to be fit to the proposed model.