Chemical vapor deposition (CVD) with methyldiethoxysilane (MDES) for MFI zeolitic pore size reduction is an effective way to improve the H 2/CO2 separation factor of zeolite membranes. However, only good membranes with few intercrystalline defects are able to show considerable improvement in H2/CO2 separation factor through CVD modification. It is unreliable to evaluate the membrane quality on the basis of the H2/SF6 or N2/SF6 ideal separation factor because the SF6 adsorption-induced crystal swelling causes shrinkage of the intercrystalline defects in the MFI zeolite membranes. In this study, the quality of MFI zeolite membranes was evaluated on the basis of their performance in separating equimolar H2/CO 2 mixture gas at room temperature. High-quality membranes are more selective to CO2 molecules rather than H2 at room temperature due to the adsorption of CO2 into the zeolitic pores and blocking of the pore channels for H2 diffusion. The effectiveness of the quality evaluation method was confirmed by on-stream CVD modification of MFI zeolite membranes with different initial H2/CO2 separation factors/ideal separation factors at room temperature. Experimental results showed that only those membranes with low H2/CO2 separation factor at room temperature (good membranes) showed improvement in H2/CO2 separation factor through CVD modification. For the CVD modified zeolite membrane with good initial quality, the permeance of H2 is lower than that of He with an activated diffusion behavior for small gas molecules in the modified zeolitic pores.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering