Abstract
The separation of small molecule gases by membrane technologies can help performance enhancement and process intensification for emerging advanced fossil energy systems with CO2 capture capacity. This paper reports the demonstration of controlled modification of zeolitic channel size for the MFI-type zeolite membranes to enhance the separation of small molecule gases such as O2 and N2. Pure-silica MFI-type zeolite membranes were synthesized on porous α-alumina disc substrates with and without an aluminum-containing thin skin on the outer surface of zeolite membrane. The membranes were subsequently modified by on-stream catalytic cracking deposition (CCD) of molecular silica to reduce the effective openings of the zeolitic channels. Such a pore modification caused the transition of gas permeation from the N2-selective gaseous diffusion mechanism in the pristine membrane to the O2-selective activated diffusion mechanism in the modified membrane. The experimental results indicated that the pore modification could be effectively limited within the aluminum-containing surface of the MFI zeolite membrane to minimize the mass transport resistance for O2 permeation while maintaining its selectivity. The implications of pore modification on the size-exclusion-enabled gas selectivity were discussed based on the kinetic molecular theory. In light of the theoretical analysis, experimental investigation was performed to further enhance the membrane separation selectivity by chemical liquid deposition of silica into the undesirable intercrystalline spaces.
Highlights
The energy-efficient membrane gas separation technology can play significant roles in performance enhancement and process intensification for the advanced fossil energy systems withCO2 capture capacity
The chemical liquid liquid deposition deposition (CLD) modified zeolite membrane was again tested for separation of an O2/N2 equimolar mixture in a temperature range of 293–473 K and a feed pressure range of 1–6 bar
The CLD modified zeolite membrane was again tested for separation of an O2 /N2 equimolar mixture in a temperature range of 293–473 K and a feed pressure range of 1–6 bar
Summary
Zeolites with pore openings formed by 10-membered rings have effective dp of around 0.6 nm, which are much less resistive to small gas transport but become incapable of achieving size-selectivity or molecular sieving effect between the closely sized molecules like O2 , N2 , H2 and CO2. Such relatively large pore size allows for depositing molecular modifiers to the internal pore wall to fine tune the effective channel openings. The modified MFI-type zeolite membranes are examined by permeation for a number of small molecule gases including O2 and N2
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