Multicomponent hydrogen/hydrocarbon separation by MFI-type zeolite membranes

Separation of an eight-component simulated refinery gas mixture including hydrogen (approximately 84 mol%) and light hydrocarbons (C₁-C₄, 7.5 to approximately 0.3 mol%) by α-alumina-supported polycrystalline MFI zeolite membranes was studied at 25-500 °C and feed pressures of 0.1-0.4 MPa. The zeolite membrane showed excellent separation properties for rejection of hydrogen from the hydrogen/hydrocarbon mixture at <100 °C. At room temperature and atmospheric pressure on both feed and permeate sides, hydrogen permeation rate is almost zero, while the hydrocarbon permeation rate is 2-4×10^-4 mol·m^-2·s^-1. The zeolite membrane outperforms the microporous carbon membrane in terms of both selectivity and permeance for hydrocarbons over hydrogen. At 500 °C the zeolite membrane becomes permselective for hydrogen over hydrogen (C₁-C₄). In the whole temperature range iso-butane is nonpermeable (with a permeance below the GC analysis limit) through the zeolite membrane. Separation results of the zeolite membrane can be characterized by a solution-diffusion model considering competitive adsorption of hydrocarbons over hydrogen and configurational diffusion in the zeolite pores. The MFI-type zeolite membranes showed promise for applications in separation processes for hydrogen concentration/purification from various hydrogen/hydrocarbon mixtures (at lower temperatures) and in membrane reactors for dehydrogenation reactions (at high temperatures).