Cellulose triacetate doped with ionic liquids for membrane gas separation

Cellulose triacetate (CTA) is a workhorse polymeric membrane material for industrial CO₂/CH₄ separation. This study investigates the doping of CTA with ionic liquids (ILs) to reduce the crystallinity of the CTA and enhance its affinity with CO₂, thus increasing CO₂ permeability and CO₂/light gas selectivity. CTA films doped with 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF₄]) and 1-ethyl-3-methylimidazolium dicyanamide ([emim][dca]) were prepared; and the effect of IL loading on properties of the CTA, such as crystallinity, density, degradation temperature, glass transition temperature, and gas transport properties, were determined. The IL doping reduces the glass transition temperature and degree of crystallinity of CTA, increasing gas diffusivity and permeability. The IL doping also increases CO₂/CH₄ solubility selectivity and CO₂/N₂ permeability selectivity, due to the affinity of these ILs with CO₂, compared to light gases such as CH₄ and N₂. This study demonstrates a promising route in manipulating the morphology and gas transport properties of semi-crystalline polymers by doping with ILs.