Adsorption and Electrothermal Desorption of Volatile Organic Compounds and Siloxanes onto an Activated Carbon Fiber Cloth for Biogas Purification

Although biogases mainly consist of a mixture of carbon dioxide and methane, traces of volatile organic compounds are present, and these undesirable compounds must be removed during the purification process. Adsorption onto an activated carbon fiber cloth (ACFC) was investigated and, in particular, the feasibility of electrothermal desorption. Five compounds were chosen, and their desorption was assessed by monitoring the electric resistance of the material as a function of the temperature. The results were confirmed by thermogravimetric analysis. Toluene, dichloromethane, and isopropanol were entirely desorbed at 420 K, whereas siloxane D4 and ethyl mercaptan (ethanethiol) were partially removed. These conclusions were confirmed by dynamic adsorption measurements. Cycles of adsorption followed by electrothermal desorption were first carried out for a single component (toluene). Although there was a loss of adsorption capacity between the first and second cycles, a steady performance was reached, shedding light on the complete reversibility of the adsorption of toluene. On the. contrary, for the mixture of five organic compounds, a constant loss of adsorption capacity was measured after 3 cycles, which was attributed to the incomplete regeneration at 420 K of two organic compounds (ethanethiol and siloxane D4) from the ACFC from one cycle to another. The electrical consumption for the electrothermal desorption was highest at the beginning of the desorption and rapidly decreased as the temperature within the filter reached its set point. An average consumption was estimated at 1500 W kg(-1) of activated carbon fiber cloth.