Tailoring the thermal, mechanical, and gas transport properties of cellulose acetate membranes with ionic liquids for efficient propene/propane separation

Abstract

In light of the importance of designing less energy-intensive and cleaner technologies for olefin purification, the current work aims to systematically enhance the separation of a challenging pair of olefin/paraffin gases, namely propene/propane. To achieve this goal, various blended membranes are fabricated by mixing cellulose acetate (CA), a carbohydrate-based biopolymer, with three different aprotic ionic liquids (ILs) including [BMIM]⁺[BF₄]^-, [BMIM]⁺[OTf]^-, and [BMIM]⁺[Tf₂N]^-, which are used as additives, with a plasticizer effect, at concentrations in the range of 10–30%. Extensive physicochemical characterization of these membranes by DSC and TGA (thermal properties), Tensile tests (mechanical properties), X-ray diffraction and SEM (structural properties) show that ILs are well-dispersed within the polymeric matrix owing to the interactions between the ILs and CA functional groups. The incorporation of ILs leads to enhanced gas transport properties of the blended membranes compared to the neat one, generally improving their permeability. In particular, the blended membrane, incorporated with 30 % of [BMIM]⁺[Tf₂N]^-, increased the C₃H₆ permeability by 35 times and the C₃H₆/C₃H₈ selectivity by nearly two times compared to the neat CA membrane. These results suggest that ionic liquid-doped cellulose acetate membranes are potential candidates for efficiently separating the propene/propane gas pair.