Experimental study and numerical simulation of hydrogen/isobutane permeation and separation using MFI-zeolite membrane reactor

A composite alumina-MFI-zeolite membrane has been prepared by a pore-plugging method. Transport through this membrane is controlled by molecular size and adsorption properties, as expected for a defect-free zeolite composite layer. Single gas transport was studied for hydrogen and isobutane. In the studied temperature range, (323-723 K) for isobutane and (277-723 K) for hydrogen, transports were activated. Isobutane exhibited a flux maximum at 450 K, whereas hydrogen flux declined with temperature. These different permeation behaviors were modeled using Maxwell-Stefan equations taking into account only surface diffusion. Activation energies were obtained from the model by fitting the experimental data. They were calculated to be 31 kJ mol(-1) for isobutane and 1.9 kJ mol(-1) for hydrogen. The diffusion coefficients calculated at 323 K differed by four orders of magnitude. Separation experiments with a mixture of hydrogen and isobutane in a 293-723 K temperature range were performed. Typical permeation behavior was observed for a mixture of weakly and strongly adsorbed molecules. At room temperature, hydrogen permeation was hindered by stronger adsorbed isobutane molecules in the micropores, H-2/i-C4H10 Separation experiments showed a separation factor of 25 at 723 K, a typical temperature of the isobutane dehydrogenation in membrane reactors.