A novel microporous membrane has been prepared by modifying an asymmetric SiC support using polydimethylsilane (PMS). One membrane, pyrolyzed at 573 K, possesses H 2 /N 2 selectivity of ∼100 and H 2 permeance of 8.9 × 10 −8 molؒm −2 ؒs −1 ؒPa −1 at 473 K. The other membrane, pyrolyzed at 873 K, has a lower H 2 /N 2 selectivity of ∼40 and lower H 2 permeance of 4.9 × 10 −9 molؒm −2 ؒs −1 ؒPa −1 at 473 K. Permeation in both membranes exhibits the characteristics of activated diffusion at elevated temperatures. A higher pyrolysis temperature results in a less-permeable membrane. The support preparation and the thermal events of PMS are analyzed. The effects of pyrolysis temperature on membrane property are discussed.

Asymmetric SiC membranes are modified by a SiH 4 /C 2 H 2 / Ar low-pressure chemical vapor deposition (LPCVD) system at a temperature of 800°C. The pore size of the membrane is reduced to increase its selectivity at the expense of its permeance. The chemical vapor deposition (CVD) modification, using a chamber to minimize the gas-phase reaction, is superior to that without a chamber, because the film-forming species of low sticking coefficients can improve the pore size at a lower cost of permeance reduction. With the knowledge of pore structure and CVD kinetics, the alteration of membrane properties can be properly predicted.