Fabrication Of Mixed Matrix Membranes By Incorporation Of Exfoliated CTF Nanosheets And SSZ-13 Zeolite In Pebax For CO₂/CH₄ Separation

Carbon dioxide is a common component present in raw natural gas streams and biogas.Apart from being a greenhouse gas,its presence reduces the calorific value of CH₄,causes corrosion in transmission pipelines and increases the volume of gas stream.Therefore,CO₂ separation from CH₄ is an important industrial unit operation which needs to be made economical and energy efficient.CO₂/CH₄ separation using membrane technology is a promising alternative to the conventional,energy intensive techniques.It offers benefits like energy efficiency and eco-friendliness.But,it requires the fabrication of economical,defect free membranes that could meet the flux and selectivity requirements at industrial level.Utilization of mixed matrixed membranes(MMMs)is a good choice to meet this goal as it can overcome the drawbacks associated with using pure polymeric membranes.This study aims to fabricate MMMs by incorporating SSZ-13 zeolite and exfoliated covalent triazine framework(CTF)nanosheets separately into Pebax 1657 to achieve a better CO₂/CH₄ separation performance.SSZ-13 is physically blended with Pebax-1657 at loadings of 1-7wt%of polymer.SSZ-13 is a commercial zeolite with an 8-ring window structure.Its pore size of 0.38 nm lies in the range of kinetic diameter of CH₄(0.33 nm)and CO₂(0.38 nm).Incorporation of SSZ-13 has created selective pathways in polymer chains of Pebax-1657 at the cost of reduction of CO₂ permeability.At a filler loading of 5wt%,CO₂/CH₄ selectivity of 21.78has been observed as compared to 13.03 for pristine Pebax membrane.But the CO₂permeability has dropped to 66.2 Barrer,following the trade-off mechanism.5wt%loaded MMM also exhibits a better thermal stability.Exfoliated CTF nanosheets prepared from CTF-1 are highly porous frameworks and contain–NH₂ polar groups which are known to show affinity towards CO₂and also exhibit better dispersibility in water.A uniform dispersion of CTF nanosheets in Pebax-1657 has thus shown a significant improvement in the gas separation performance of MMM at 2wt%loading.In comparison with pristine Pebax membrane,the CO₂permeability is unaffected while the selectivity of MMMs has increased to 21.