Facile synthesis of highly permeable CAU-1 tubular membranes for separation of CO2/N2 mixtures

•A tubular CAU-1 membrane was fabricated by in-situ solvothermal growth.•The CAU-1 membrane exhibited a high CO2 permeance and selectivity for CO2/N2 mixtures.•Solvent ratio and reactant content largely affected performance of CAU-1 membranes.

Facile synthesis of a thin tubular CAU-1 membrane was carried by simple in-situ solvothermal growth method through the use of the asymmetric α-Al2O3 tube support with the same metal centre as the CAU-1 framework. The solvent ratio, reactant concentration and support property were found significant for the formation of a dense and continuous pure CAU-1 membrane with highly permeable and selective CO2 towards N2 and CH4. A high CO2 permeance of 0.80×10−6 mol m−2 s−1 Pa−1 with separation factor of 14.8 was achieved for the M3 for 1:1 CO2/N2 binary mixtures at room temperature. Both the increase of ethanol in the solvent mixture and reactant concentration were favourable for the formation of a dense and well intergrown pure CAU-1 membrane while their excessive increase led to impure NH2-MIL-53 formation. The composition and pore size of the support contributed to high permeance and selectivity of CAU-1 membrane for CO2/N2 separation.