Pore size through silica based membranes prepared by using a counter diffusion chemical vapor deposition method was controlled precisely using silica precursors having organic functional groups including ethyltrimethoxysilane (ETMOS) propyltrimethoxysilane (PrTMOS) and hexyltrimethoxysilane (HTMOS). According to the thermal decomposition properties of the silica hydrolysis powder the decomposition temperature of HTMOS (400° C) was higher than those of ETMOS and PrTMOS. The pore sizes through the silica hybrid membranes deposited at 270° C were approximately 0.40 nm that were independent of the sizes of alkyl groups in the silica precursors. The alkyl groups in the membranes were partially decomposed during the deposition. These membranes were applied to hydrocarbon separation especially for propylene/propane system and methane/ethane system. Methane/ethane permeance ratio of 38 was achieved through the ETMOS derived membrane deposited at 300° C. The HTMOS derived membrane exhibited 414 permeance ration for propylene/propane. The activation energy of propane permeation was positive indicating that the high permeation ratio was due to molecular sieve permeation mechanism.
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