抄録
A hydrogen permselective membrane reactor was developed by using a counter diffusion CVD (chemical vapor deposition) method. The deposition mechanism was investigated to improve hydrogen permeance through the silica membrane. Nitrogen was introduced into the outer side of the porous substrate and the diffusion of the nitrogen through the pores of the porous substrate during the silica deposition was measured with a quadrupole mass spectrometer. The deposition reaction was found to be a primary reaction and the rate determining step must be the decomposition of the alkoxide of the silica precursor. The influence of organic groups such as alkyl groups in the silica precursors on the decomposition rate was not significant. The organic groups at the deposited silica decomposed and the pore size became larger after vapor deposition. By increasing the pore size, the hydrogen permeance can be improved. The hydrogen and propane permeances through the deposited silica membrane were the similar between the single component permeation and the mixed gas permeation. The propane was separated by a molecular sieving mechanism, and the effect of the adsorption of propane to the membrane was negligible at high temperature permeation tests. This silica membrane was applied to the propane dehydrogenation reaction. Both the propane conversion and selectivity were improved by the hydrogen extraction through the membrane. However, the coke deposition on the catalyst and the cold spots in the reactor must be solved for the improvement of the reactor.
