Thermoresponsive CO2 absorbent for various CO2 concentrations: tuning the pKa of ammonium ions for effective carbon capture

• Published in: Polymer journal 2021-01, Vol.53 (1), p.157-167
• Main Authors: Honda, Ryutaro, Hamasaki, Akira, Miura, Yoshiko, Hoshino, Yu
• Format: Article
• Language: English
• Subjects: 639/301/923/1027; 639/638/440; 704/172/169; Absorbents; Biomaterials; Bioorganic Chemistry; Carbon; Carbon dioxide; Carbon sequestration; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Desorption; Gas mixtures; Heating; Hydrogels; Low concentrations; Low temperature; Microgels; Original Article; Polymer Sciences; Recycling; Separation; Space stations; Surfaces and Interfaces; Thin Films
• ISSN: 0032-3896; 1349-0540
• DOI: 10.1038/s41428-020-00407-5

Amine absorbents that efficiently absorb and desorb CO 2 in response to small temperature changes are desired for CO 2 separation from concentrated and dilute gases. Thermoresponsive hydrogel films consisting of amine-containing microgel particles (GPs), which capture CO 2 at a low temperature (30 °C) and desorb it upon mild heating (75 °C), are attractive for capturing CO 2 from postcombustion gases containing 10% CO 2 (10 kPa). However, little information has been reported about thermoresponsive GPs for CO 2 separation from gas mixtures with low concentrations of CO 2 . Herein, we describe the effect of the p K a of ammonium ions in GPs on the amount of CO 2 desorption upon heating at 75 °C, which was investigated at various CO 2 concentrations. The efficiency of CO 2 desorption (mol-desorbed CO 2 /mol-amine) depends on the p K a and p K a shift ( Δ p K a ) of the ammonium ions in the range of 30‒75 °C. Computational predictions also indicated that the p K a values and Δ p K a are both important for reversible CO 2 absorption. A guideline for designing thermoresponsive amine absorbents for various applications including direct air capture and carbon recycling in closed spaces, such as space stations and submarines, is provided. Amine-containing microgel particles (GPs), which capture CO 2 at a low temperature and desorb it upon a mild heating, are attractive materials for capturing CO 2 . In this paper, the effect of p K a of ammonium ions in the GPs on the amount of CO 2 desorption upon heating was investigated at various CO 2 concentrations by experiments and thermodynamic predictions. A guideline for designing thermoresponsive amine absorbents for various applications including direct air capture and carbon recycling in closed spaces, such as space stations and submarines, is provided.