Comparative studies on the kinetics of biogas purification using activated Carbon and Zeolite

Abstract

The study focus on CO2 adsorption using activated carbon and zeolite for the purification of the produced biogas and developed kinetic study for the AC and zeolite CBV 8014 adsorption. Furthermore, model equations were developed for the upgraded biogas purity as a function of adsorption time and adsorbent dosage to predict biogas purity. The adsorbents and kinetic study was evaluated using a cylindrical glass column. The biogas produced from chicken droppings and cow dung were characterized and found to contains CH4 gas (53.26%), CO2 (33.44%) and other gases in small quantity. The highest purity of 84.34% and 91.01% was obtained for AC and zeolite CBV 8014 respectively at 20 min adsorption time and the model equations developed well represent the experimental data. The adsorption capacity of the adsorbents was evaluated using a cylindrical glass column and was found to be in the order of zeolite CBV 8014 (91.01%) ˃ AC (84.34%) at 0 − 20 min adsorption time with adsorption increasing over time. The kinetic study of the biogas purification shows that the CO2 adsorption onto AC and zeolite CBV 8014 obeys the pseudo-second-order model, due to its regression coefficient (R2) value closer to unity. The equilibrium and kinetic study of CO2 adsorption onto AC and zeolite CBV 8014 shows that the magnitude of activation energy for both adsorbent are lesser than 40 kJ/mol, indicating the occurrence of physisorption mechanism. The intra-particle diffusion model also indicates that intra-particle diffusion is not the sole rate-limiting step in the adsorption process for both adsorbent (AC and zeolite CBV 804). The zeolite CBV 8014 has higher CO2 adsorption capacity than AC.