High-vacuum-calcined multi-MOF mixed-matrix membrane for CH4/N2 separation

Methane/nitrogen (CH4/N2) separation remains a persistent challenge owing to the similar polarities, kinetic diameters, and boiling points of CH4 and N2. Herein, a novel method is proposed for enhancing the separation performance of CH4/N2 via vacuum resistance calcination, which uses surface-carbonized and hardened ZIF-8 (SCH-Z), MOF-74-Ni (SCH-M), and UiO-66-NH2 (SCH–U). The nanoparticles treated by vacuum resistance calcination remain the microporous characteristics of MOF, while introducing additional mesoporous structure and unsaturated metal sites. Such multistage pore structure and rich metal sites display a significant improvement in the CH4 adsorption over N2. In addition, the separation performance of multiple metal–organic frameworks (MOFs) mixed matrix membranes (MMMs) fabricated by homogeneously mixing the alkaline polymer polyvinylamine (PVAm) with SCH-M/SCH-Z and SCH-M/SCH–U was investigated, respectively. When the measured pressure was 0.1 MPa and the binary filler loading was 48 %, the PVAm/(SCH-M)0.7(SCH-Z)0.3/MPSf MMM exhibited outstanding CH4/N2 separation performance (CH4 permeance of 2888.48 GPU and selectivity of 4.38). Furthermore, when the loading of the binary filler was 45 %, the ideal CH4/N2 selectivity and CH4 permeance of PVAm/(SCH-M)0.67(SCH–U)0.33/MPSf MMM are 5.57 and 2263.94 GPU, respectively. This study provides a novel idea that introducing multi-MOF nanoparticles into MMMs for optimizing gas separation performance.