Investigation of cellulose acetate and ZIF-8 mixed matrix membrane for CO₂ separation from model biogas

The separation of CO2 from the biogas mixtures (CH4/CO2) is essential for biogas upgradation. However, polymer membranes used for CO2 separation exhibit low permeability. Mixed Matrix Membranes (MMMs) incorporating inorganic filler in the polymer enhance CO2 separation. In this work, bio-degradable cellulose acetate (CA) based MMMs with varying filler weight percentages (2-20 wt.%) of ZIF-8 were studied for the separation of CO2 from a model biogas (CH4/CO2) mixture. The MMMs were characterized by analysis of TGA and DSC for thermal stability and FTIR for alteration or formation of any new functional group. FESEM was done to evaluate the dispersion and interaction of ZIF-8 in the CA polymer matrix. Considering the economic aspect, the fabricated MMMs were tested for gas separation performance at reasonably lower feed pressure (1.5, 2 bar). MMM with 5 and 10 wt.% of ZIF-8/ CA MMMs showed the best performance with CO2 permeability of 9.65 Barrer and 9.5 Barrer, approximately two folds as compared to pure CA, and CO2/CH4 selectivity was 10.37 and 15.3. The experimental results were compared with the predicted gas permeation results determined using MMM transport predictive models, and found that the permeabilities were higher than the model predictions.