Isopropanol accelerated crystallization of AlPO-18 membranes for CO2/CH4 and N2/CH4 separations

The aluminophosphate (AlPO-n) materials are the potential candidates for the gas separations. And the characters of zeolite crystals on membrane commonly affected its separation properties. In this work, a co-solvent strategy was used to tune the crystal growth behaviors on the synthesis of AlPO-18 membrane. Isopropanol (IPA), served as the organic co-solvent, was adopted to prepare the AlPO-18 membrane. The effects of the IPA/DIPEA ratio and the synthesis time on the AlPO-18 membranes preparation were investigated. The crystallization of AlPO-18 membrane was accelerated when adding the extra isopropanol into the initial synthetic gel. A similar acceleration effect also occurred with the addition of methanol or ethanol into the initial gel. Under the same reaction condition, the morphology of the AlPO-18 crystals on membranes tends to develop from flake-like to bulk-like after the addition of the extra IPA, the size of AlPO-18 crystals increased with the increase of IPA/DIPEA molar ratio. Compared with the case of water as sole solvent, the synthetic time for the AlPO-18 membrane with good gas permeation properties was reduced to 12 h, where less template N-Ethyldiisopropylamine (DIPEA) was used. The optimized AlPO-18 membrane exhibited a CO2 and N2 permeance of (9.1, 0.79) × 10−7 mol/(m2∙s∙Pa) with the CO2/CH4 (50/50) and N2/CH4 (50/50) mixture selectivity of 91 and 5.0 at 298 K, 0.2 MPa. Those results may provide a strategy to prepare the AlPO-18 molecular sieve with reduced synthesis times.