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

Hiroi Sei; Yu Nagai Kanasaki; Kouki Oka; Norimitsu Tohnai; Yuki Kohno; Takashi Makino

doi:10.1021/acsomega.3c02116

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

ACS Omega. 2023 May 31;8(23):21154-21161. doi: 10.1021/acsomega.3c02116. eCollection 2023 Jun 13.

Authors

Hiroi Sei^{1

2}, Yu Nagai Kanasaki¹, Kouki Oka², Norimitsu Tohnai², Yuki Kohno¹, Takashi Makino¹

Affiliations

¹ National Institute of Advanced Industrial Science and Technology (AIST), 4-2-1, Nigatake, Miyagino-Ku, Sendai 983-8551, Japan.
² Department of Applied Chemistry and Center for Future Innovation (CFi), Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan.

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].