Large and Highly Selective and Permeable CHA Zeolite Membranes

Abstract

Large (100 cm2 membrane area) tubular chabazite (CHA) zeolite membranes (450 nm thick) were experimentally evaluated for the separation of CO2/CH4 in an industrial laboratory. An industrially relevant feed flow rate of 250 Ndm3/min was used. The feed pressure and temperature were varied in the ranges of 5–18 bar and 292–318 K, respectively. For a CO2/CH4 feed with a molar ratio of 1:1, the experimental CO2/CH4 selectivity was high at 205, and the CO2 permeance arrived at 52 × 10–7 mol/(m2·s·Pa) at 5 bar and 292 K. As far as we know, there is no report in the literature on large CHA membranes with such high permeability and selectivity. A high CO2/CH4 selectivity was also observed for a 1:4 CO2/CH4 feed. However, as indicated by mathematical modeling, concentration polarization was still an issue for membrane performance, especially at high operating pressures, even though the flow rate of the feed was relatively high. Without concentration polarization, the theoretical CO2/CH4 selectivity was 41% higher than the experimental value for a 1:1 CO2/CH4 feed at 18 bar. The corresponding CO2 permeance without concentration polarization was 23% higher than the experimentally observed value, reaching 34 × 10–7 mol/(m2·s·Pa). CHA membrane processes for the removal of CO2 from CH4 were designed, and the electricity consumption and module cost of the process were also estimated. All of the results in this study indicate a great potential of the large CHA membranes for biogas and natural gas upgrading; however, concentration polarization should be minimized in industrial processes