Next Generation Ionic Liquid based Membranes for Dehydration of Bioethanol

Abstract

As the world looks for practical alternatives to fossil fuels, biofuels created from renewable energies have emerged as a promising solution. Bioethanol, in particular, has become the leading biofuel for transportation. But producing bioethanol can be challenging, especially when it comes to removing excess water. This study aims to explore a cutting-edge method for eliminating water from bioethanol: using solid dense membranes in a process called pervaporation. The use of Ionic liquid based membranes is particularly attractive because they can separate azeotropic mixtures with a high rate of molecular diffusion, low energy consumption, and no phase change or chemical reactions. To evaluate the performance of these membranes, we used Polydimethyl siloxane (PDMS) based membranes as a benchmark and studied the use of ionic liquids (ILs) as a way to improve ethanol selectivity. We synthesized three specific ILs, Tributyl methyl Phosphonium Bis [(trifluoromethyl) sulfonyl] imide, trihexyl tetradecyl phosphonium bis 2,4,4 trimethyl pentyl phosphinate and Tetrabutyl phosphonium bis [(trifluoromethyl) sulfonyl] imide and tested them in custom-built pervaporation se-up. We used various characterization methods like FTIR, BET, XRD, SEM and TEM to evaluate their performance in removing water from bioethanol. The study demonstrated that employing supported ionic liquid membranes (SLMs) effectively enhanced the dehydration process of bioethanol. The introduction of IL-modified PDMS membranes resulted in notable advancements in both ethanol selectivity and water removal efficiency compared to unmodified PDMS membranes. Furthermore, the stability of the SLMs was found to be satisfactory, and the study also explored methods to further enhance their stability. These findings strongly indicate that integrating SLMs in pervaporation holds great promise as an efficient and sustainable approach for eliminating water from bioethanol, consequent ly enhancing biofuel production. This research focused on the integration of membrane properties and ionic liquids for the dehydration of bioethanol. Specifically, ionic liquid-based membranes were synthesized by incorporating three different ionic liquids: tetradecyl trihexyl phosphonium bis(2,4,4-trimethylpentyl phosphinate)[TDTHP][Phosph],phosphonium bis(2,4,4 tributyl methyl phosphonium bis(trifluoromethyl sulfonyl) imide [TBMP][NTf2 - ], and tetrabutyl phosphonium bis (trifluoromethyl sulfonyl) imide [TBP] [NTf2 -] into a polymeric material i.e PDMS, which was then coated on PES. Characterization was conducted on the synthesized ionic liquids using FTIR analysis, which confirmed the successful synthesis by identifying the presence of Phosphinate, Phosphonium, and Sulfonyl (SO2) groups. The hydrophobicity of the membranes was evaluated using contact angle measurements, which showed excellent hydrophobic properties for all the membranes. Sorption analysis and degree of swelling tests demonstrated the compatibility of permeate towards the IL-based membranes at ambient room temperature. Subsequently, the performance of membranes has been assessed by help of pervaporation setup developed in-house. Among the tested membranes, the Tributyl methyl Phosphonium bis (trifluoromethyl sulfonyl)imide [TBMP][NTf2 -] based membrane demonstrated the highest separation factor of 16% accompanied by suitable flux of 4.19 kg/m2.hr. These findings highlight the potential of ionic liquid-based membranes, particularly the Tributyl methyl Phosphonium bis (trifluoromethyl sulfonyl) imide [TBMP] [NTf2 -] membrane, for the dehydration of bioethanol. The integration of membrane properties and ionic liquids offers promising prospects for the development of efficient bioethanol dehydration processes.