Enhancement of the H2-permselectivity of a silica-zirconia composite membrane enabled by ligand-ceramic to carbon-ceramic transformation

This work reports the preparation of a carbonized SiO 2 –ZrO 2 composite membrane with enhanced H 2 permselectivity via a sol-gel process. The sol-gel synthesis of the precursor SiO 2 –ZrO 2 -acetylacetonate composite was optimized by studying the effect that the water/alkoxide molar ratio exerted on the final properties of carbon-SiO 2 -ZrO 2 . Characterization by thermogravimetry, XRD, and N 2 adsorption revealed that utilizing a water/alkoxide molar ratio of 60 was optimal for the retention of carbon and for promoting the qualities of amorphousness and microporosity. Furthermore, using a Si/Zr ratio of 9/1 in a carbon-SiO 2 -ZrO 2 membrane resulted in a high level of H 2 permselectivity. This membrane showed H 2 permeance of 16 x 10 −7 mol m −2 s −1 Pa −1 and H 2 /N 2 and H 2 /CH 4 ideal selectivities of 75 and 148, respectively. More importantly, the H 2 permselectivity of the carbon-SiO 2 -ZrO 2 membrane exceeded that of a similarly pore-distributed unmodified SiO 2 –ZrO 2 membrane with an H 2 permeance of 3 x 10 −7 mol m −2 s −1 Pa −1 . This enhanced H 2 permselectivity was attributed to the increase in pore volume contributed by ultra-micropore-bearing carbon nanoparticles. • SiO 2 –ZrO 2 -acetylacetone was transformed into a carbon-SiO 2 -ZrO 2 by pyrolysis. • Hydrolysis water molar ratio optimized to be 60 gave the adequate carbon-SiO 2 -ZrO 2 . • Difference of microstructure at different Si/Zr ratios achieved upon carbonization. • Carbon-SiO 2 -ZrO 2 composite-derived membrane showed improved H 2 permselectivity.