Preparation and performance of a novel mixed-matrix membrane supported on porous substrate for CH4/N2 separation

Coalbed methane enrichment is crucial for improving energy efficiency and reducing greenhouse gas emissions. Membrane separation technology shows significant potential for efficient CH4/N-2 separation, making membrane material design a key research focus. Metal-organic framework-based mixed-matrix membranes have attracted much attention due to its good comprehensive performances and superior development potential. However, the balance between gas permeability and selectivity in membranes still needs further improvement. In this study, a novel supported mixed-matrix membrane with Ni-MOF-74 as the functional fillers and SBS polymer as the matrix material was fabricated by a simple dip-coating method, in which Al2O3 porous tube was used as the substrate. This strategy can significantly enhance CH4 permeability while maintaining or improving CH4/N-2 permeation selectivity. Results show that porous substrate exhibits good compatibility with the polymer-filler composite separation layer. The ratio of SBS polymer to Ni-MOF-74 particles has a significant impact on the comprehensive performances of the membrane. The as-fabricated SBS/Ni-MOF-74 membrane with 10% Ni-MOF-74 loading displays superior morphology and excellent CH4 permeation performance. Pure CH4 and N2 permeation tests indicate that the optimized membrane exhibits a high CH4 permeability of 66.4 Barrer, which is about 1.5 times higher than that of pure SBS membrane. It has an ideal CH4/N-2 selectivity of 3.5, greatly exceeding the 1.6 selectivity of SBS membrane. This improvement can be attributed to the differences in diffusion and solubility coefficients of CH4 and N-2 in the membrane. Moreover, this membrane exhibits relatively stable gas permeability and selectivity under different pressure differentials. Therefore, the membrane developed in this study exhibits excellent mechanical and gas permeation properties, showing potential applications in methane enrichment.