Microstructural control of a SSZ-13 zeolite film via rapid thermal processing
A SSZ-13 zeolite (CHA type zeolite having a pore size of 0.37 × 0.42 nm2) can separate CO2 (0.33 nm) from larger molecules (N2 (0.364 nm) or CH4 (0.38 nm)) because of the molecular size differences. However, methods to control the non-zeolitic defects of SSZ-13 membranes are lacking. Here, we demonstrate that rapid thermal processing (RTP) of as-synthesized SSZ-13 films tunes their microstructural defect properties and increases their CO2 separation ability. The maximum CO2/N2 separation factor (SF) at 30 °C increased from ~2.9 to ~4.8 due to RTP because the defective region was reduced. Furthermore, the addition of water vapor (the third main component of coal-fired power plant flue gas) to the feed markedly improved the CO2/N2 SF of the RTP-treated SSZ-13 membrane; from ~4.3 at 50 °C (a representative flue gas stream temperature) under dry conditions to ~10.1 under wet conditions (vs. ~1.6 across the conventionally calcined counterpart). Furthermore, the less-defective RTP-treated SSZ-13 membranes achieved a CO2/CH4 SF as high as ~43.7 under wet conditions at 50 °C. Fluorescence confocal optical microscopy analyses complemented with the permeation modeling revealed that the reduced defect size after RTP (~2.2 nm against ~3.9 nm for the conventionally calcined counterpart) improved the CO2 permselectivity, even though the defect porosities were low (~0.1%).