CO2 separation by supported liquid membranes synthesized with natural deep eutectic solvents.

Betaine-based natural deep eutectic solvents (NADESs), a new class of green solvents, were immobilized into a porous polyvinylidene fluoride (PVDF) support and evaluated for the separation of CO₂ from CO₂/N₂ and CO₂/CH₄ mixtures. Two types of NADESs were synthesized by mixing betaine (hydrogen bond acceptor-HBA) with malic acid and tartaric acid (hydrogen bond donors-HBD) respectively. FTIR and Raman spectroscopy were studied to confirm the synthesis and purity of the NADESs. The thermal strength of the NADESs was investigated using thermogravimetric analysis. The gas permeation results of the fabricated NADES-based-supported liquid membranes (NADES-SLMs) showed that the permeability of CO₂ increased from 25.55 to 29.33 Barrer on substitution of hydrogen bond donor from tartaric acid to malic acid. Similarly, the ideal CO₂/CH₄ selectivity varied from 51.1 to 56.4 as tartaric acid was replaced by malic acid as the HBD. The performance of NADES-SLMs was compared with the competing imidazolium-based-supported ionic liquid membranes, and proved NADES-SLMs as a promising alternative considering their green potential and comparable gas separation performance. The current effort for the exploitation of NADESs into PVDF membranes in this study is expected to open new routes for the efficient separation of CO₂ from the industrial gas mixture. [ABSTRACT FROM AUTHOR]