Enhanced CO₂ Absorption in Organic Solutions of Biobased Ionic Liquids

Abstract

and in the field of biomass conversion. Future applications for CO 2 separation technologies are presumed to be within the so-called carbon capture and utilization (CCU) route. [6][7][8] The idea is to exploit CO 2 as a raw material for further chemical or industrial use and, thus, to valorize it by recycling. In the long term, CCU aims the development of a circular economy concept with neutral carbon emissions.Absorption is one of the main techniques used for CO 2 capture, [9] it relies on either chemical or physical interactions between the solvent and the solute CO 2 . In physical absorption, intermolecular forces, such as Coulomb, Van-der-Waals or other dispersion forces dominate the solute-solvent interactions. In chemical absorption, CO 2 chemically reacts with the solvent molecules and forms covalent bonds. Due to their stoichiometric reaction with CO 2 , their CO 2 absorption capacity is very high even at low CO 2 partial pressures. Chemical absorption is particularly appropriate if CO 2 is to be recovered from flue gas streams with relatively low concentrations. The major advantages of chemical absorption processes are the high selectivity for CO 2 and the high achievable gas product purity.The most commonly used chemical absorbents are amines (15-60 wt%) in aqueous solutions (i.e., typical loading of 0.5 mol CO 2 /mol amine for monoethanolamine, MEA). Amines have some drawbacks like a high corrosion rate at high concentrations, the outlet purified gas contains a high-water amount, the energy demand for their regeneration is high and they suffer from high evaporation losses. [10] Indeed, the reverse chemical reaction requires considerable activation energy that is commonly supplied by increasing the temperature of the absorbent. When a volatile absorbent is used, it must be either condensed from the purified gas stream or replenished with the consequent rise of operative costs. Therefore, improvement of the absorption medium, e.g., decreasing the volatility without losing the high loading of the absorbent phase is the primary research interest in physical and chemical absorption technologies.Since the 1990s, low-melting salts have gained increasing interest for application as alternative absorbents in a wide field of chemical processes. For salts with melting points below 100 °C, the term ionic liquid (IL) has been coined. As ILs are built up from an organic cation and an inorganic or organic anion, there is a vast variety of possible structures. Over the last years, a plethora of ILs and their mixtures have been Solutions of biobased ionic liquids (ILs) for recovering CO 2 from industrial flue gas are investigated. Four CO 2 task-specific choline-based amino acids ([Cho][AA]): Alanine, Glycine, and, for the first time, Proline and Serine are tested. The drawbacks related to the high viscosity of these ILs are limited by applying dimethyl sulfoxide (DMSO) as a solvent, which is chosen because it is a polar aprotic liquid with a low toxicity, low vapor pressure, and relatively low price. The choline-based...

Cholinium amino acid-based ionic liquids

“…Attempts at using co-solvents have been made in order to reduce the viscosities of ChAAILs. Davarpanah et al ( 2020 ) have attempted dissolution of the IL into another solvent with high boiling point such as DMSO, but the dilution of the absorbent material led to a reduced absorption capacity (with 12.5 wt% IL in DMSO, only 0.3 mol CO 2 /mol IL of CO 2 ).…”

State of the art of ionic liquid‐modified adsorbents forCO2capture and separation

“…13 Ionic liquids (ILs) as novel absorbents are widely used for CO 2 capture owing to their extremely low vapor pressure and tunable structures. 14 Since the pioneer design of [C 4 mim][PF 6 ] at 25 C and pressure up to 40 MPa for dissolving CO 2 by Blanchard et al, 15 many efforts were devoted to developing a great number of ILs including conventional ILs with physisorption 15,16 and functionalized ILs with chemisorption [17][18][19] for CO 2 capture in succession. Due to the weak physical dissolution of CO 2 in conventional ILs, the CO 2 absorption performance cannot surpass those of amine solvents.…”

“…Due to the weak physical dissolution of CO 2 in conventional ILs, the CO 2 absorption performance cannot surpass those of amine solvents. Thereafter, functionalized ILs with chemical interaction sites, such as carboxylbased ILs, 20 amino-based ILs, 18,[21][22][23][24] amino acid (AA)-based ILs, 14,17,22,25,26 and so on 27,28 were developed to enhance CO 2 absorption performance. 14,18,29 The first amino-functionalized IL was synthesized by Bates et al, 30 namely [NH 2 p-bim][BF 4 ] with a high capacity of nearly 0.50 molCO 2 /molIL under 0.1 MPa.…”

“…Thereafter, functionalized ILs with chemical interaction sites, such as carboxylbased ILs, 20 amino-based ILs, 18,[21][22][23][24] amino acid (AA)-based ILs, 14,17,22,25,26 and so on 27,28 were developed to enhance CO 2 absorption performance. 14,18,29 The first amino-functionalized IL was synthesized by Bates et al, 30 namely [NH 2 p-bim][BF 4 ] with a high capacity of nearly 0.50 molCO 2 /molIL under 0.1 MPa. Subsequently, more promising stoichiometry than one CO 2 to two amines is realized by tethering the amine to anions comparing with ILs with aminofunctionalized cations.…”

“…37 It was found that many anion-functionalized ILs, especially AA-functionalized ILs, have quite high viscosity lead to low mass transfer efficiency and slow CO 2 absorption rate, and the viscosity will further increase exponentially after absorbing CO 2 due to the chemical reaction, which becomes one of the main snags hindering their industrial applications. 14,17,19,[38][39][40] Considering high CO 2 separation performance and high viscosities of ILs especially during CO 2 absorption, combining ILs with porous materials by physical or chemical methods to prepare ILmodified adsorbents is an effective way, 41 which not only improves…”