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We have developed membrane reactors to dehydrogenate cyclohexane, using amorphous silica membranes with controlled pore sizes, and successfully operated them under pressures ranging from 1 to 8 atm. The membranes were prepared by chemical vapor deposition (CVD) using tetramethoxysilane (TMOS) or dimethoxydiphenylsilane (DMDPS). Both membranes had hydrogen-permselective properties. At 473-573 K, the TMOS-derived membranes showed hydrogen permeances on the order of 10 -8 mol m -2 s -1 Pa -1 , whereas the DMDPS-derived membranes showed permeances on the order of 10 -6 mol m -2 s -1 Pa -1 . Both membrane reactors produced hydrogen with conversions greater than equilibrium, and the DMDPS-derived membrane achieved higher conversion than the TMOS-derived membrane because of the greater hydrogen extraction effect of the DMDPS-derived membrane. In addition, it should be noted that this is the first report of successful operation of membrane reactors with highly hydrogen-permselective silica membranes under pressure.

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