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.