High temperature permeation and separation characteristics of an all-silica DDR zeolite membrane

The permeation and separation characteristics of an all-silica DDR zeolite tubular membrane have been studied in the temperature range of 303–773 K and feed pressures up to 500 kPa. The permeation experiments are complemented by single component adsorption isotherms. The permeance of He, H2, CO2, CO and N2 monotonically decreases with increasing temperature. This behaviour could be described accurately for all components by a surface diffusion mechanism. Only in case of N2 and CO small deviations are observed above 600 K. Isobutane is not able to enter the DDR pores and passes only through a very small number of defects in the membrane. The single component permeance is about equal to the permeance of this component in a binary mixture. Only below 473 K the H2 permeance in a mixture with CO2 or isobutane is reduced in comparison with its single component permeance. The ideal H2/CO and CO2/CO selectivities range from 3 to 12 and 10 to 2 between 303 and 673 K, respectively. These mixture selectivities where always below 5 and much lower than the ideal selectivities because of non-differential operation along the membrane tube. The ideal H2/isobutane selectivity is >600 at 101 kPa feed pressure at all temperatures. The mixture selectivities at 101 kPa total feed pressure is ∼400 in an equimolar binary mixture. The high selectivities, high H2 and CO2 fluxes and stable membrane operation, also at high temperatures, makes this membrane a potential candidate for high temperature (reactive) separations that involve removal of H2 and CO2.