Mild ultraviolet detemplation of SAPO-34 zeolite membranes toward pore structure control and highly selective gas separation

Abstract

SAPO-34 zeolite membranes were activated by ultraviolet (UV) radiation at low temperatures to reduce grain boundary defects. The successful detemplation of SAPO-34 zeolite powders using UV radiation was confirmed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and nitrogen adsorption-desorption. The irradiance exerted a significant impact on the quality of UV-detemplated SAPO-34 membranes. Under optimal UV detemplation conditions, SAPO-34 membranes showed a moderate H2 permeance of ∼10−7 mol Pa−1 m−2 s−1, with a H2/i-C4H10 permselectivity over 75 under room temperature. The membranes showed an exceptionally low CO2 permeance in comparison with N2 and CH4 despite the smaller molecular size of CO2, resulting in an unprecedentedly high H2/CO2 permselectivity over 50, which was ascribed mainly to the intense interaction between the CO2 molecules and confined organic structure directing agent (OSDA) residue in membrane channels. The temperature dependence of singe-gas permeance through SAPO-34 zeolite membranes showed that gases, including He, H2, CO2, CH4, C2H6, C3H8, and i-C4H10, markedly increased as the temperature increased, indicating an activated diffusion mechanism. The activation energies for H2 permeation through the SAPO-34 membranes were 17–23 kJ mol−1, which were reasonable based on the correlation between the activation energy for H2 permeation and the average pore size for reported membranes by assuming minimal grain boundary defects in the UV-detemplated SAPO-34 membranes.