Studies on Biogas Purification Using Activated Carbon and Zeolite

Abstract

Biogas generation from animal waste is inherent with a low biogas quality due to impurities such as CO2, CO, NOx H2 and H2S which requires gas clean-up. It was in view of this that the present study investigated the comparative studies on the kinetics of biogas purification using activated carbon (AC) and zeolite CBV 8014. The study focused on CO2 adsorption using AC and zeolite CBV 8014 for the purification of the produced biogas and developed the kinetic for adsorption by AC and zeolite CBV 8014. Surface morphology and functional group of the adsorbent before and after adsorption were also determined. Furthermore, model equations were developed for the upgraded biogas purity as a function of adsorption time and adsorbent dosage to predict biogas purity. The kinetic study of the adsorption by AC and zeolite CBV 8014 were evaluated using an improvised cylindrical column. The biogas produced from a mixture of chicken droppings and cow dung substrate (1:1) were characterized and found to contain CH4 gas (53.76%), CO2 (33.44%) and other gases in small quantity. Characterization of adsorbents showed that AC had a better pore structure compared to zeolite CBV 8014, however, adsorption studies 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 which show that zeolite CBV 8014 had strong affinity for CO2 adsorption. The percentage adsorption of the adsorbents was evaluated using a cylindrical glass column and the model equations developed well represent the experimental data. 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 less 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 adsorbents (AC and zeolite CBV 8014). The zeolite CBV 8014 has higher CO2 adsorption capacity than AC.