Chemical vapor deposition on chabazite (CHA) zeolite membranes for effective post-combustion CO₂ capture

Chabazite (CHA) zeolites with a pore size of 0.37 × 0.42 nm² are expected to separate CO₂ (0.33 nm) from larger N₂ (0.364 nm) in postcombustion flue gases by recognizing their minute size differences. Furthermore, the hydrophobic siliceous constituent in CHA membranes can allow for maintaining the CO₂/N₂ separation performance in the presence of H₂O in contrast with the CO₂ affinity-based membranes. In an attempt to increase the molecular sieving ability, the pore mouth size of all silica CHA (Si-CHA) particles was reduced via the chemical vapor deposition (CVD) of a silica precursor (tetraethyl orthosilicate). Accordingly, an increase of the CVD treatment duration decreased the penetration rate of CO₂ into the CVD-treated Si-CHA particles. Furthermore, the CVD process was applied to siliceous CHA membranes in order to improve their CO₂/N₂ separation performance. Compared to the intact CHA membranes, the CO₂/N₂ maximum separation factor (max SF) for CVD-treated CHA membranes was increased by ∼2 fold under dry conditions. More desirably, the CO₂/N₂ max SF was increased by ∼3 fold under wet conditions at ∼50 °C, a representative temperature of the flue gas stream. In fact, the presence of H₂O in the feed disfavored the permeation of N₂ more than that of CO₂ through CVD-modified CHA membranes and thus, contributed to the increased CO₂/N₂ separation factor.