Development of hydrogen-selective triphenylmethoxysilane-derived silica membranes with tailored pore size by chemical vapor deposition

Amorphous silica membranes were developed, based on an in silico molecular design, to exhibit excellent hydrogen-selective performance for separating hydrogen from mixtures containing larger organic molecules, such as methylcyclohexane and toluene. Triphenylmethoxysilane (TPMS) was synthesized and used as a novel precursor to prepare membranes by the counter-diffusion chemical vapor deposition method. Under the optimized bubbler temperature and counter-diffusion chemical vapor deposition reaction time, the fresh membranes showed high reproducibility and high hydrogen permeance in the order of 10(-6) mol m(-2) s(-1) Pa-1 and high H-2/SF6 ideal selectivity of over 12,000 at 573 K. Moreover, the TPMS-derived membrane exhibited good stability after hydrogen regeneration, even after placement in a dehumidifier cabinet at room temperature for 90 days. Single gas permeation performance and normalized Knudsen-based permeance evaluation showed that the TPMS-derived membrane (three phenyl groups on the precursor) had a pore size of 0.486 nm, and exhibited looser structures with larger pore size than those of a diphenyldimethoxysilane (DPDMS)-derived membrane (two phenyl groups on the precursor). These results suggest that the pore size of silica membranes can be tailored with various structured silica precursors containing phenyl groups. (C) 2015 Elsevier B.V. All rights reserved.