Surface modification of silica membranes in a tubular-type module

Microporous silica membranes were prepared on a γ-alumina coated α-alumina tube using a sol–gel technique. Methacryloxypropyltrimethoxysilane (MOTMS), a template for controlling the pore structure, was added to the ethanol solution of tetraethylorthosilicate (TEOS) and was used in the formation of the silica sol. The ethanol solution of TEOS was used to impregnate the prepared silica membrane, followed by calcinating without hydrolysis for surface modification. The unmodified silica membrane in a permeation cell showed molecular-sieve properties at permeation temperatures in the range of 100–400 °C. Permeances to H2 through the unmodified silica membrane were 2.1×10−7 mol m−2 s−1 Pa−1 and the H2/N2 ideal separation factor was 18 at 100 °C. Similar permeation properties were observed for the tubular-type module assembled with 10 pieces of silica membranes, indicating that no large pinholes were present and no gas leakage occurred. As the result of the surface modification processes, the permeance to n-C4H10 was significantly reduced, resulting in an increase in the separation factor of H2/n-C4H10.