No abstract

The sol-gel method was applied to Al-doped bis (triethoxysilyl) methane (BTESM, Si-C-Si unit) membranes. High C 3 H 6 : C 3 H 8 permeance ratios of approximately 40 at 200 uC were achieved through the precise control of the silica network size via a spacer method using Si-C-Si units as well as the incorporation of Al in BTESM-derived networks.

Metal-doped organosilica membranes for C3H6/C3H8 separation were fabricated via a sol-gel method. Al and Ag was selected as a doping material in the fabrication of metal-doped bis (triethoxysilyl) methane (BTESM) membranes, and the effects that doping materials exerted on the organosilica network size and on the C3H6/C3H8 permeation properties were evaluated. Gas permeance ratios such as H2/CH4, H2/C3H6, H2/C3H8, and C3H6/C3H8 were approximately independent of Ag concentration, indicating that network size did not change when doped Ag existed as Ag ions in BTESM networks, as suggested by the X-ray absorption fine structure (XAFS) spectrum. On the other hand, when Al was doped into BTESM, each permeance decreased as Al concentration increased, and the selectivity (H2/N2, H2/CH4) increased largely because of enhanced molecular sieving separation by densified networks. Ag-BTESM membranes showed negative values for activation energy ( 10 kJ mol -1 ) for C3H6 permeation, which were a much smaller values than those for BTESM ( 7 kJ mol -1) and Al-BTESM ( 3 kJ mol -1 ) membranes. BTESM, Al-, and Ag-BTESM membranes showed values for αmix (binary separation) that were higher than those for αsin (single permeation) at 50 . For example, Ag-BTESM (Si/Ag 9/1) membrane showed higher C3H6/C3H8 selectivity ( 32.5) by binary separation than selectivity ( 19) by single permeation at 50 , but the selectivity by binary separation was approximately the same, irrespective of a different pressure ratio (feed pressure/permeate pressure).