Effects of synthesis conditions on MFI zeolite membrane quality and catalytic cracking deposition modification results

MFI zeolite membranes were synthesized by the templated in-situ synthesis method on α-alumina porous supports under various conditions and subsequently modified by catalytic cracking deposition (CCD) of methyldiethoxysilane (MDES) to improve high temperature H2/CO2 separation performance. The quality of the zeolite membranes was examined by helium permeation (before template removal) and room temperature H2/CO2 separation (after template removal). For membranes prepared through single hydrothermal synthesis, the helium permeance decreases and the room temperature H2/CO2 separation factor increases with increasing synthesis time (or membrane thickness). Helium flows through the defects of the as-prepared membranes before template removal decreases as membrane thickness increases, but the thicker membranes contain more defects formed during the template removal step. Twice-hydrothermal treatment with calcination in between is effective to improve the quality of MFI zeolite membranes. However, a minimal synthesis time for each hydrothermal cycle is needed to eliminate the intercrystalline defects. Catalytic cracking deposition of MDES improves the high temperature H2/CO2 separation performance of the MFI zeolite membranes and the extent of the improvements is directly correlated with the membrane synthesis conditions. After CCD modification, the H2/CO2 separation factor of the membrane synthesized twice with 4 h for each hydrothermal cycle was improved from 4.2 to 8.6 with around 40% reduction in H2 permeance.

An MFI zeolite membrane synthesized twice at 180 °C with 4 h for each hydrothermal synthesis cycle showed the best quality. The lower defect concentration in this membrane is due to the improved connectivity between zeolite crystals resulting from two hydrothermal treatments. After catalytic cracking deposition (CCD) modification with methyldiethoxysilane for zeolitic pore size reduction, the H2/CO2 separation factor of this membrane was improved from 4.2 to 8.6 at 450 °C.Figure optionsDownload as PowerPoint slideResearch highlights
► MFI zeolite membranes were in-situ synthesized at different conditions.
► Membrane becomes thicker as the single hydrothermal synthesis time increases.
► More defects are formed in the thicker membrane during the template removal step.
► Twice synthesis with calcination in between improves membrane quality.
► The H2/CO2 separation factor at 450 °C was improved to 8.6 after modification.