Studies on selective adsorption of biogas components on pillared clays: approach for biogas improvement

Comparative adsorptions of four gases (natural gas and landfill gas components), viz., CO2, CH4, C2H6, and N2, were studied on four different pillared clays (PILCs) to develop a selective material. Such material could be useful forthe separation/purification process of waste gases. These materials (PILCs) were prepared from two different natural montmorillonite clays, by pillaring with Al2O3 and ZrO2, separately and were characterized by means of nitrogen adsorption and XRD. The adsorption isotherms for pure component gases were determined for each PILC, up to 10(3) kPa. The isotherms data were explored to calculate the selectivity of PILCs for either gas in any binary mixture. It was observed that the surface area of the clays pillared with Al2O3 was higher than that of the clays pillared with ZrO2. At the highest studied equilibrium pressure, the order of maximum adsorption was found to be CO2 > C2H6 > CH4 > N2 for each material. With the help of adsorption modeling, the selective adsorption from binary mixtures was predicted at different equilibrium pressures and compositions. Among the four PILCs, a ZrO2 PILC was found to be the most suitable material, in terms of separation possibility. To further assess the efficiency of these materials in commercial processes, the adsorption capacity in terms of working capacity was also calculated at two different regeneration pressures, i.e., at 1.0 atm and 1.0 Torr.