CO2 Capture in Biocompatible Amino Acid Ionic Liquids: Exploring the Reaction Mechanisms for Bimolecular Absorption Processes

Adsorption of Choline Phenylalanilate on Polyaromatic Hydrocarbon-Shaped Graphene and Reaction Mechanism with CO2: A Computational Study

The interaction of ionic liquids (ILs) with carbon materials is of fundamental importance in several areas of materials science, physics, and chemistry. Their adsorption on pristine and N-doped graphene surfaces is discussed here on the basis of results of density functional theory calculations. The nature of adsorption was investigated for an amino acid (AA)-based IL consisting of the choline cation [Ch] and the l-phenylalanilate anion [Phe] that interacts with a sheet of N-doped graphene. The interaction mechanism, binding energy, electron density, and non-covalent interaction analysis were evaluated by considering the cation, anion, and ion pair adsorbed on graphene separately. The distribution of cations and anions in the liquid bulk and on the graphene surface was then analyzed by molecular dynamics simulations. Since AA-based ILs are efficient absorbents for capture of CO2 due to the pronounced affinity of carbon dioxide to react with amino groups, we investigated the capacity of [Ch][Phe] to react with CO2 under various conditions. We considered the multistep mechanism of the reaction of [Phe] with CO2 first for the anion in the liquid bulk and then for the [Phe] anion adsorbed on the graphene surface. The initial step, the formation of the zwitterionic addition product, is followed by its structural rearrangement through intramolecular proton transfer and conformational isomerization processes to form carboxylic acid derivatives. The entire mechanism was evaluated for the [Phe] anion before and after adsorption on graphene to investigate how interactions with surfaces of carbon materials can affect the CO2 capture capacity of an AA-based IL such as [Ch][Phe].

Ionic Liquids Hybridization for Carbon Dioxide Capture: A Review

CO2 absorption has been driven by the need for efficient and environmentally sustainable CO2 capture technologies. The development in the synthesis of ionic liquids (ILs) has attracted immense attention due to the possibility of obtaining compounds with designated properties. This allows ILs to be used in various applications including, but not limited to, biomass pretreatment, catalysis, additive in lubricants and dye-sensitive solar cell (DSSC). The utilization of ILs to capture carbon dioxide (CO2) is one of the most well-known processes in an effort to improve the quality of natural gas and to reduce the green gases emission. One of the key advantages of ILs relies on their low vapor pressure and high thermal stability properties. Unlike any other traditional solvents, ILs exhibit high solubility and selectivity towards CO2. Frequently studied ILs for CO2 absorption include imidazolium-based ILs such as [HMIM][Tf2N] and [BMIM][OAc], as well as ILs containing amine groups such as [Cho][Gly] and [C1ImPA][Gly]. Though ILs are being considered as alternative solvents for CO2 capture, their full potential is limited by their main drawback, namely, high viscosity. Therefore, the hybridization of ILs has been introduced as a means of optimizing the performance of ILs, given their promising potential in capturing CO2. The resulting hybrid materials are expected to exhibit various ranges of chemical and physical characteristics. This review presents the works on the hybridization of ILs with numerous materials including activated carbon (AC), cellulose, metal-organic framework (MOF) and commercial amines. The primary focus of this review is to present the latest innovative solutions aimed at tackling the challenges associated with IL viscosity and to explore the influences of ILs hybridization toward CO2 capture. In addition, the development and performance of ILs for CO2 capture were explored and discussed. Lastly, the challenges in ILs hybridization were also being addressed.

Reaction Mechanism of CO2 with Choline-Amino Acid Ionic Liquids: A Computational Study

Carbon capture and sequestration are the major applied techniques for mitigating CO2 emission. The marked affinity of carbon dioxide to react with amino groups is well known, and the amine scrubbing process is the most widespread technology. Among various compounds and solutions containing amine groups, in biodegradability and biocompatibility perspectives, amino acid ionic liquids (AAILs) are a very promising class of materials having good CO2 absorption capacity. The reaction of amines with CO2 follows a multi-step mechanism where the initial pathway is the formation of the C-N bond between the NH2 group and CO2. The added product has a zwitterionic character and can rearrange to give a carbamic derivative. These steps of the mechanism have been investigated in the present study by quantum mechanical methods by considering three ILs where amino acid anions are coupled with choline cations. Glycinate, L-phenylalanilate and L-prolinate anions have been compared with the aim of examining if different local structural properties of the amine group can affect some fundamental steps of the CO2 absorption mechanism. All reaction pathways have been studied by DFT methods considering, first, isolated anions in a vacuum as well as in a liquid continuum environment. Subsequently, the role of specific interactions of the anion with a choline cation has been investigated, analyzing the mechanism of the amine-CO2 reaction, including different coupling anion-cation structures. The overall reaction is exothermic for the three anions in all models adopted; however, the presence of the solvent, described by a continuum medium as well as by models, including specific cation- -anion interactions, modifies the values of the reaction energies of each step. In particular, both reaction steps, the addition of CO2 to form the zwitterionic complex and its subsequent rearrangement, are affected by the presence of the solvent. The reaction enthalpies for the three systems are indeed found comparable in the models, including solvent effects.

A Computational Analysis of the Reaction of SO2 with Amino Acid Anions: Implications for Its Chemisorption in Biobased Ionic Liquids

We report a series of calculations to elucidate one possible mechanism of SO₂ chemisorption in amino acid-based ionic liquids. Such systems have been successfully exploited as CO₂ absorbents and, since SO₂ is also a by-product of fossil fuels’ combustion, their ability in capturing SO₂ has been assessed by recent experiments. This work is exclusively focused on evaluating the efficiency of the chemical trapping of SO₂ by analyzing its reaction with the amino group of the amino acid. We have found that, overall, SO₂ is less reactive than CO₂, and that the specific amino acid side chain (either acid or basic) does not play a relevant role. We noticed that bimolecular absorption processes are quite unlikely to take place, a notable difference with CO₂. The barriers along the reaction paths are found to be non-negligible, around 7–11 kcal/mol, and the thermodynamic of the reaction appears, from our models, unfavorable.