HOF-21 nanofillers incorporated mixed matrix membranes for high-performance N2/CH4 separation

N2/CH4 separation membranes based on N2 preferential permeation can effectively reduce the recompression cost of CH4 gas and show promising application prospects in the field of natural gas purification. However, the performance of N2/CH4 separation membranes still needs to be improved. Here, we report a kind of mixed matrix membranes (MMMs) for N2/CH4 separation via using HOF-21 as nanofiller and 6FDA-DAM polyimide as polymer matrix. In this work, the effects of HOF-21 loading, feed side pressure and temperature based on membrane performance were explored, and finally performance variation of the MMMs with operation time was tested. The incorporated HOF-21 nanoparticles with the most probable pore size of about 3.6 Å can significantly increase the diffusion rate of smaller N2 molecules and enhance the N2/CH4 diffusivity selectivity of the membrane. In addition, compared with polyimide, HOF-21 exhibits almost the same dynamic adsorption of N2 and CH4, which can weaken the solubility of CH4 and enhance the N2/CH4 solubility selectivity of the membrane. When feed gas pressure was 0.2 MPa, the optimum membrane performance was achieved at the HOF-21 loading of 7 wt%, with N2 permeance of 5.13 GPU and N2/CH4 (50/50, vol%) selectivity of 20.52 at 298.15 K. Compared with N2 permeation and N2/CH4 selectivity of the 6FDA-DAM/PAN membrane, the MMMs increased by 67% and 54%, respectively, possessing potential applications in the field of N2 removal in CH4 purification.