Tailoring CO2/CH4 Separation Efficiency with [THTDP][Cl]/Pebax-1657 Supported Ionic Liquid Membranes: Design, Characterization, and Theoretical Insights

The use of renewable resources to generate energy is growing, but regrettably, the large amount of CO₂ emissions it releases harms the environment. The main greenhouse gas, CO₂, is a major factor in global climate change, which eventually disrupts the delicate balance of ecosystems within the globe. Therefore, the development of effective and sustainable technology for CO₂ capture and storage is both urgent and compelling. Among many different approaches for CO₂ capture, membrane separation has shown to be one of the most promising, yielding excellent results in terms of effectiveness as well as affordability. Nonetheless, to enhance membrane performance more significantly in CO₂ separation, researchers have focused on ionic liquids, a family of organic salts recognized for their high thermal stability, low volatility, and tuneable characteristics. Because of this, ionic liquids have attracted a lot of attention from the academic and industrial sectors as possible additions to enhance membranes’ capacity for CO₂ separation. This study explores the potential of Tetrahexyl tetradecyl phosphonium chloride incorporated into Pebax-1657 to enhance CO₂/CH₄ separation performance. Ion gel membranes were synthesized with varying ionic liquid concentrations (5, 10, 20 wt%) and characterized for structural and morphological evaluations. Gas separation performance was assessed through permeation experiments, showing increased CO₂/CH₄ selectivity from 19.23 to 21.81 with higher IL concentrations, especially under high pressure. CO₂ permeability increased from 70.01 to 273.61 barrer with the addition of 20% [THTDP][Cl]. Density functional theory calculations provided theoretical insights into the interaction energies between ionic liquid and gas molecules, corroborating experimental findings. The study demonstrates the novelty of integrating phosphonium-based ionic liquid with Pebax-1657, significantly enhancing CO₂/CH₄ selectivity due to strong CO₂ interactions. This research offers a promising approach to developing advanced membranes for efficient and selective CO₂ capture, contributing to sustainable gas separation technologies.

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