Propylene/propane Permeation Properties of Metal-doped Organosilica Membranes with Controlled Network Sizes and Adsorptive Properties

摘要

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 H-2/CH4, H-2/C3H6, H-2/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 (H-2/N-2, H-2/CH4) increased largely because of enhanced molecular sieving separation by densified networks. Ag-BTESM membranes showed negative values for activation energy (similar to-10 kJ mol(-1)) for C3H6 permeation, which were a much smaller values than those for BTESM (similar to-7 kJ mol(-1)) and Al-BTESM (similar to-3 kJ moll) membranes. BTESM, Al-, and Ag-BTESM membranes showed values for alpha(mix) (binary separation) that were higher than those for ash, (single permeation) at 50 degrees C. For example, Ag-BTESM (Si/Ag = 9/1) membrane showed higher C3H6/C3H8 selectivity (= 32.5) by binary separation than selectivity (similar to 19) by single permeation at 50 degrees C, but the selectivity by binary separation was approximately the same, irrespective of a different pressure ratio (feed pressure/permeate pressure).