Post-synthesis defect abatement of inorganic membranes for gas separation

Simple, fast, and cost-effective defect abatement of inorganic gas separation membranes can be achieved by application of a continuous polymer layer. This polymer diminishes defect flow and is stable at a wide range of operating conditions. In the studies presented a thin layer of polydimethyl siloxane (PDMS) was applied to defective microporous silica and zeolite Y membranes. After application of PDMS, the H(2)/CO(2) and CO(2)/N(2) binary gas separation performance of both silica and zeolite membranes was found to improve significantly due to reduction in defect flow. At 30 degrees C, CO(2) selectivity of the silica membrane for a 1:1 CO(2)/N(2) mixture improved from 1.5 to 835 after application of PDMS. At higher temperatures, N(2) in the permeate could no longer be detected by gas chromatography, which translated into a selectivity of >1000. There was also an improvement in the selectivity for a 1:1 H(2)/CO(2) mixture at 30 degrees C from 1.9 without, to 66 with PDMS modification. Similar effects were found for supported zeolite Y membranes. The selectivity at 30 degrees C of a zeolite Y membrane for a 1:1 CO(2)/N(2) mixture was found to increase from 0.93 before, to >1000 at 30 degrees C after modification with PDMS. Along with the improved separation factors, a reduction in the overall permeance occurred due to reduced defect flow contributions. The H(2) permeance at 130 degrees C decreased from 8.5 x 10(-9) mol/(m(2) s Pa) for the uncoated silica membrane to 6.6 x 10(-9) mol/(m(2) s Pa) after PDMS application. The CO(2) and N(2) permeance values at 130 degrees C, however, decreased by almost two orders of magnitude. The decrease in overall permeance due to defect abatement is supported by transport calculations assuming simple expressions for solution-diffusion through the membrane and Knudsen flow through the defects. These calculations show that the application of PDMS leads to a decrease in the overall permeance but an increase in the H(2) selectivity for a wide range of defect area fractions (<10(-4)). (C) 2011 Elsevier B.V. All rights reserved.