Accelerated Oxidative Degradation of Phosphonium-Type Ionic Liquid with l-Prolinate Anion: Degradation Mechanism and CO₂ Separation Performance

Abstract

Amino acid ionic liquids (AAILs) are regarded as green alternatives to existing CO2-sorptive materials because amino acids are readily available from renewable sources in large quantities. For widespread applications of AAILs, including direct air capture, the relationship between the stability of AAILs, especially toward O2, and the CO2 separation performance is of particular importance. In the present study, the accelerated oxidative degradation of tetra-n-butylphosphonium l-prolinate ([P4444][Pro]), a model AAIL that has been widely investigated as a CO2-chemsorptive IL, is performed using a flow-type reactor system. Upon heating at 120–150 °C and O2 gas bubbling to [P4444][Pro], both the cationic and anionic parts undergo oxidative degradation. The kinetic evaluation of the oxidative degradation of [P4444][Pro] is performed by tracing the decrease in the [Pro]− concentration. Supported IL membranes composed of degraded [P4444][Pro] are fabricated, and the membranes retain CO2 permeability and CO2/N2 selectivity values in spite of the partial degradation of [P4444][Pro].

Progress in the applications of biocompatible ionic liquids: renewable commodity production, catalytic and pharmaceutical approaches – a review

“…38 The synthesis of amino acid-based ILs occurs by converting cationic moieties into hydroxides using ion exchange resin and neutralizing these hydroxides with amino acids as the anionic moiety of the IL. 58 Various IL-forming cations, such as choline, 59 phosphonium, 60 ammonium, 61 and imidazolium, 62 have been used in the synthesis of amino acid-containing ILs. A special highlight is ILs based on choline and amino acids, with applications in various fields, from computational chemistry to electrochemistry, biomass processing, CO 2 capture, and medicine.…”