Aluminophosphate-17 and silicoaluminophosphate-17 membranes for CO2 separations

Aluminophosphate (AlPO)-17 and silicoaluminophosphate (SAPO)-17, for the first time, were made into selective membranes for CO2separations. Pure and submicron SAPO-17 seeds were synthesized using nano zeolite T crystals as silica precursor. Membrane microstructure (thickness and crystal size) and separation performance were strongly affected by the support chemistry and seeds. The selective membranes were prepared by a single hydrothermal synthesis step using the low-cost symmetric macroporous ceramic tubes as substrates. Single-gas and CO2/CH4 mixed-gas permeations through SAPO-17 membranes were investigated as functions of pressure and temperature. Carbon dioxide permeance and CO2/CH4 selectivity were decreased with the increase of pressure and temperature. The best membrane showed the smaller-component permeances of 1.1×10−6 and 8.0×10−7 mol/(m2 s Pa), and mixture selectivities of 53 and 14 for equimolar CO2/CH4 and CO2/N2 mixtures, respectively, at 298 K and 0.2 MPa pressure drop.