Direct Air Capture of CO₂ via Ionic Liquids Derived from “Waste” Amino Acids

Abstract

Direct capture of CO 2 from anthropogenic emissions is an imperative societal task as the concentration of global atmospheric CO 2 continues to increase drastically. The longterm goal of negative emission requires methods to remove carbon directly from the atmosphere, oceanwater, and nonpoint sources. Ionic liquids (ILs) have had a pivotal impact on finding and implementing innovative solutions that enable a more sustainable future. Here, we report the first example of an IL-enabled approach for direct CO 2 capture from the atmosphere on a laboratory scale. These de novo bioderived materials represent an ideal milieu for direct carbon capture applications because of their nonvolatility and a priori low toxicity. Easily prepared liquid salts based on a mixture of three common amino acids, valine, leucine, and isoleucine, were found to be effective sorbents for ready and reversible CO 2 sequestration from air despite its very low concentration. Collectively known as branched-chain amino acid, they are commonly derived from biowaste products, for example, feathers, fur, and even human hair. Therefore, the resultant ILs from the "waste" amino acids provide an exciting prospect in terms of CO 2 transformation and waste utilization. We provided valuable design insights for engineering structure−property relationships in amino acid-based ILs. The impact of moisture on the absorption characteristics and capacity was evaluated in ambient conditions. We postulate that the high capture efficiency and stability of these ILs make them superior to present amine-and alkali-assisted approaches for the direct air capture of CO 2 as a scalable process.

Materials for Direct Air Capture and Integrated CO2 Conversion: Advancement, Challenges, and Prospects

“…Their potential in DAC is based on their versatility to combine various cations and anions, which offers the possibility of fine-tuning the chemical and physical attributes of the absorbent. Furthermore, particularly given their low volatility, minimal corrosiveness, exceptional chemical and thermal stability, nonflammable nature, and reduced vapor pressure are key features for sustainable CO 2 capture process. , In addition, basic ILs can activate water molecules, forming a guest@host complex that can react with CO 2 to produce bicarbonate . This presents a significant advantage compared to other materials, as they can achieve a high sorption capacity even under humid conditions.…”

CO2 Capture with Capsules of Ionic Liquid/Amines

“…25−28 Such task-specific ionic liquids (TSILs) have demonstrated promising potential in DAC. 29,30 However, ILs suffer from high viscosity that impedes fast absorption rates of CO 2 and TSILs exhibit increase in viscosity upon CO 2 binding, limiting mass transport of CO 2 . 31 To overcome challenges associated with the viscosity and cost of TSILs, small molecule amines have been introduced to ILs for improved CO 2 absorption, providing both chemisorption pathways and low-volatility solvents for amines.…”

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

“…first reported a series of amino acid ILs (AAILs) with 20 natural amino acids as anions, which were prepared by neutralization between various onium hydroxides and amino acids. − In the context of green and sustainable chemistry, AAILs offer greener alternatives to existing CO 2 -chemsorptive materials because amino acids are readily available from renewable sources in large quantities. The solubility and reaction mechanism of CO 2 in the resulting AAILs have been widely investigated by several research groups. − In particular, AAILs with phosphonium cations and l -prolinate anion ([Pro] − ) show superior properties for CO 2 capture. Brennecke et al reported that a trihexyl­(tetradecyl)­phosphonium ([P 666,14 ] + )-type AAIL with [Pro] − as the anion can absorb CO 2 in a 1:1 stoichiometry of CO 2 /AAIL by stabilizing the carbamic acid moiety rather than through carbamate formation. , Matsuyama et al investigated various facilitated transport membranes using tetra- n -butylphosphonium ([P 4444 ] + )-based AAILs, and [P 4444 ]­[Pro] exhibited CO 2 permeability and CO 2 /N 2 selectivity considerably greater than the Robeson upper bounds under low CO 2 feed pressure conditions. , …”