Study of mixed matrix membranes with in situ synthesized zeolite imidazolate frameworks (ZIF-8, ZIF-67) in polyethersulfone polymer for CO2/CH4 separation

Abstract

Biogas, produced from anaerobic digestion, is a sustainable and renewable energy source. To upgrade biogas to Bio-CNG, CO₂ must be removed from the raw mixture. Membrane separation is an economical process for the removal of CO₂, and mixed matrix membranes (MMMs) are being explored for CO₂/CH₄ separation. MMMs are fabricated using techniques such as in situ techniques to overcome research gaps, such as in filler agglomeration and filler–polymer interfaces. In this work, MMMs were fabricated using the in situ growth of ZIF-8 and ZIF-67 in polyethersulfone (PES) and compared with traditional filler dispersion of ZIF-8 and ZIF-67. The fabricated MMMs were characterized and tested for gas permeation using a model biogas. Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FESEM) analysis were conducted to confirm in situ synthesis of ZIF-8 and ZIF-67. CO₂ permeability of in situ ZIF-8 and ZIF-67-based MMMs have enhanced to 84.5 Barrer and 78.8 Barrer, respectively, compared to pure PES membrane, which is around 25 Barrer. Similarly, ZIF-8 and ZIF-67-based traditional MMMs have shown an increase in the CO₂ permeability of 75.6 Barrer and 68 Barrer, respectively. Additionally, the selectivity for CO₂/CH₄ separation increased for some of the prepared MMMs, demonstrating the effectiveness of the in situ fabrication method.