Ionic Liquid Mixtures for Direct Air Capture: High CO2 Permeation Driven by Superior CO2 Absorption with Lower Absolute Enthalpy

Yuki Kohno; Mitsuhiro Kanakubo; Masao Iwaya; Yo Yamato; Takashi Makino

doi:10.1021/acsomega.2c04756

Ionic Liquid Mixtures for Direct Air Capture: High CO₂ Permeation Driven by Superior CO₂ Absorption with Lower Absolute Enthalpy

ACS Omega. 2022 Nov 11;7(46):42155-42162. doi: 10.1021/acsomega.2c04756. eCollection 2022 Nov 22.

Authors

Yuki Kohno¹, Mitsuhiro Kanakubo¹, Masao Iwaya², Yo Yamato², Takashi Makino¹

Affiliations

¹ National Institute of Advanced Industrial Science and Technology (AIST), 4-2-1 Nigatake, Miyagino-Ku, Sendai983-8551, Japan.
² Daicel Corporation, Business Development Center, Innovation and Business Development Headquarters, 2-18-1 Konan, Minato-ku, Tokyo108-0075, Japan.

Abstract

This paper reports a series of liquid materials suitable for use as high-performance separation membranes in direct air capture. Upon mixing two ionic liquids (ILs), namely N-(2-aminoethyl)ethanolamine-based IL ([AEEA][X]) and 1-ethyl-3-methylimidazolium acetate ([emim][AcO]), the resulting mixtures with a specific range of their composition showed higher CO₂ absorption rates, larger CO₂ solubilities, and lower absolute enthalpies of CO₂ absorption compared to those of single ILs. NMR spectroscopy of the IL mixture after exposure to ¹³CO₂ allowed elucidation of the chemisorbed species, wherein [AEEA][X] reacts with CO₂ to form CO₂-[AEEA]⁺ complexes stabilized by hydrogen bonding with acetate anions. Supported IL membranes composed of [AEEA][X]/[emim][AcO] mixtures were then fabricated, and the membrane with a suitable mixing ratio showed a CO₂ permeability of 25,983 Barrer and a CO₂/N₂ selectivity of 10,059 at 313.2 K and an applied CO₂ partial pressure of 40 Pa without water vapor. These values are higher than those reported for known facilitated transport membranes.