Zeolite membrane process for industrial CO2/CH4 separation

Zeolite membrane processes were designed for biogas upgrading for feed pressures ranging from 5 to 20 bar and compared with corresponding polymeric membrane processes. The mass transfer through zeolite membranes was estimated by a model accounting for adsorption and diffusion through the surface barriers and the interior of the pores, while the mass transfer through polymeric membranes was estimated using reported permeances for commercial polymeric membranes. The zeolite membranes displayed approximately three orders of magnitude higher permeance and up to 7 times higher selectivity. To reach a low methane loss, two and three membrane stages were needed for zeolite and polymeric membranes, respectively, because of the differences in selectivity. Due to the higher selectivity, the electricity need for the zeolite membrane process was only 50–60% of that for the corresponding polymeric membrane process. As a result of the much higher permeability, the zeolite membrane processes were much more compact than the equivalent polymeric membrane processes. The estimated cost for zeolite membranes prepared in small scale including modules was much lower than the cost for industrially produced polymeric membranes including modules.