A carbon-silica-zirconia ceramic membrane with CO2 flow-switching behaviour promising versatile high-temperature H2/CO2 separation

Many researchers regard silica, silica-based and zeolite membranes as the agents that will accomplish H-2 separation. These membranes are expected to be productive in various mixture systems and under very high temperatures. This work reports the successful fabrication of a composite carbon-SiO2-ZrO2 ceramic membrane with a unique pressure-induced switching of CO2 flows that allows versatile H-2/CO2 separation at elevated temperatures. TG-MS, DTG-TGA, FT-IR, CP-MAS-C-13-NMR, and TEM provide corroborative evidence of the carbonization of starting material SiO2-ZrO2-acetylacetonate into C-SiO2-ZrO2. The resultant C-SiO2-ZrO2 displayed significant hysteresis in the CO2 adsorption isotherm at a temperature well above the critical temperature of CO2 (31 degrees C), which indicates structural conformation. Furthermore, single-gas permeation measurements showing upstream pressures of 200 and 500 kPa reveal different permeation values for CO2 at 300 degrees C. In separating a H-2/CO2 mixture at 50 and 300 degrees C under upstream pressures of 200 and 500 kPa, respectively, the flow of H-2 permeance reduces as the concentration of CO2 increases in the feed side at 50 degrees C (1.14 x 10(-8) down to 3.9 x 10(-9) mol m(-2) s(-1) Pa-1 at 200 kPa). The pressure-induced surface flow of CO2 at 300 degrees C and 500 kPa, however, reduces the hindrance to H-2 flow and results in H-2/CO2 selectivity of similar to 20-30 for all CO2 concentrations, which is on a par with molecular sieving membranes. This novel C-SiO2-ZrO2 material shows promise for many interesting applications.