Hollow SAPO-34 incorporated mixed matrix membranes with the improved solubility selectivity and permeability for N2/CH4 separation

Abstract

Hollow SAPO-34 with an average particle size of ca.370 nm was synthesized by selective etching its precursor under the controlled alkaline condition. Subsequently, freestanding mixed matrix membranes were synthesized by UV-induced in-situ polymerization of the mixture of hollow SAPO-34, the fluorinated monomer, and the trifunctional cross-linker. The structure and the physical characteristic of hollow SAPO-34 and membranes were characterized by scan electron microscope, wide-angle X-ray diffraction, etc. The effect of the hollow SAPO-34 loading amount on the gas permeation-separation performance of mixed matrix membranes was investigated. The results showed that hollowing out SAPO-34 improved the N2/CH4 sorption selectivity and converted the crystals from preferential adsorption of N2 to preferential adsorption of CH4, the incorporation of hollow SAPO-34 into membranes increased the N2/CH4 solubility selectivity and the permeability. The optimal membrane exhibited a 39-fold increase in N2 permeability from 6.9 × 10−13 to 2.7 × 10−11 cm3(STP)cm·cm−2·s−1·Pa−1 at 0.2 MPa and 35 °C without the loss of N2/CH4 permselectivity, which exceeded the 2008 Robeson upper bound.