Physical Absorption Of CO2 in Protic and Aprotic Ionic Liquids: An Interaction Perspective

Lignin-based porous carbon adsorbents for CO2 capture

A major driver of global climate change is the rising concentration of atmospheric CO2, the mitigation of which requires the development of efficient and sustainable carbon capture technologies. Solid porous adsorbents have emerged as promising alternatives to liquid amine counterparts due to their potential to reduce regeneration costs. Among them, porous carbons stand out for their high surface area, tailorable pore structure, and exceptional thermal and mechanical properties, making them highly robust and efficient in cycling operations. Moreover, porous carbons can be synthesized from readily available organic (waste) streams, reducing costs and promoting circularity. Lignin, a renewable and abundant by-product of the forest products industry and emerging biorefineries, is a complex organic polymer with a high carbon content, making it a suitable precursor for carbon-based adsorbents. This review explores lignin's sources, structure, and thermal properties, as well as traditional and emerging methods for producing lignin-based porous adsorbents. We examine the physicochemical properties, CO2 adsorption mechanisms, and performance of lignin-derived materials. Additionally, the review highlights recent advances in lignin valorization and provides critical insights into optimizing the design of lignin-based adsorbents to enhance CO2 capture efficiency. Finally, it addresses the prospects and challenges in the field, emphasizing the significant role that lignin-derived materials could play in advancing sustainable carbon capture technologies and mitigating climate change.

Does the active hydrogen atom in the hydantoin anion affect the physical properties, CO2 capture and conversion of ionic liquids?

Compared to the effect of the active hydrogen atom in the cation in protic ionic liquids (ILs) on their properties and applications, there are very few reports on the role of the active hydrogen atom in the anion. In order to better understand the role of the active hydrogen atom in the anion, the physical properties, CO2 capture and conversion of three hydantoin-based anion-functionalized ILs ([P4442][Hy], [P4442]2[Hy], and [HDBU][Hy]) have been investigated via experiments, spectroscopy, and DFT calculations in this work. The results show that the active hydrogen atom in the anion can form anionic hydrogen bonding networks, which significantly increase the melting point and viscosity and decrease the basicity of the IL, thereby weakening its ability to capture and convert CO2. Interestingly, [P4442][Hy] undergoes a solid/liquid two-phase transition during CO2 absorption/desorption due to the formation of quasi-intramolecular hydrogen bonding between the active hydrogen atom and the O- atom of the absorbed CO2, suggesting that the presence of the active hydrogen atom gives [P4442][Hy] the potential to be an excellent molecular switch. As there is no active hydrogen atom in the anion of [P4442]2[Hy], it shows excellent CO2 capture and conversion performance through the double-site interaction. [HDBU][Hy] shows the weakest catalytic CO2 conversion due to the presence of active hydrogen atoms on both its anion and cation. Therefore, the active hydrogen atom in the anion may play a more important role in the properties and potential applications of ILs than the active hydrogen atom in the cation.

Thermodynamics of Tri- and Tetraepoxyimidazolium NTf2 Amine Polyaddition: A Theoretical Perspective

The thermodynamics of newly designed tri- and tetraepoxyimidazolium NTf2 monomers reacting with several diamines used as curing agents to form epoxy/amine thermosets was studied. The ability of each epoxy/amine combination to induce cross-linking both through the substitution of multiple epoxy groups and through multiple additions to a single amine was investigated. Through an increased understanding of the thermodynamics of epoxy-amine polymerization in complex polyepoxy-ILs, it is possible to more thoroughly understand the factors affecting the reactivity in these complex systems. These calculations showed that while each possible epoxy-amine combination was exergonic to both forms of cross-linking, the degree to which both amines-induced cross-linking and epoxy-induced cross-linking was favored varied between epoxy-amine combinations. Thermodynamic results obtained using density functional theory were experimentally validated through differential scanning calorimetry results, wherein similar trends were noted between theory and experiment. Among the trends noted in amines-epoxy combinations tested, tetraepoxyimidazolium NTf2/PACM (i.e., a cycloaliphatic diamine) was found to be a prime candidate for amine cross-linking, with the addition of a second epoxy to a single amine group being notably the most negative of all epoxy-amine combinations at -77.6 kJ mol-1. While in the case of epoxy cross-linking, the aliphatic polyetheramine denoted Jeffamine-D230-containing systems were found to be the most exergonic, with additions of primary amines to triepoxyimidazolium and tetraepoxyimidazolium NTf2 averaging -86.9 kJ mol-1. Interaction energy analysis indicated that the aromatic amine named sulfanilamide is the most favorable to engage in reactions due to having the most negative interaction energies with already highly substituted epoxy monomers. These results can be used to adjust the cross-linking possibilities of tri- and tetraepoxyimidazolium NTf2/amine polymerization and give insight into the predominant cross-linking reactions in these unique systems.

Molecular simulation of osmometry in aqueous solutions of the BMIMCl ionic liquid: a potential route to force field parameterization of liquid mixtures

Despite widespread development and use of ionic liquids (ILs) in both academic and industrial research, computational force fields (FFs) for most of those are not available for a precise description of inter-species interactions in aqueous environments. In the scope of this study, by means of molecular simulations, the osmotic coefficient of an aqueous solution of an IL is calculated and used as a basis to reparameterize popular IL-FFs existing in the literature. We first calculate the osmotic coefficients (at 298.15 K and 1 atm pressure) of aqueous solutions of 1-butyl-3-methylimidazolium chloride (BMIMCl), a generic IL, popularly used in biomass processing and the subsequent conversion to value-added intermediates. The performance of two popular atomic, nonpolarizable FFs developed for BMIMCl, one by Lopes, Pádua, and coworkers (FF-LP) and the other by Sambasivarao, Acevedo, and coworkers (FF-SA), when mixed with the SPC/E water model, is tested with respect to their ability to reproduce the experimental osmotic coefficient data. Interestingly, the osmotic coefficient is found to be increasing with a gradual increase in IL molality within the concentration range of our investigation, which is contrary to the experimental trend reported in the literature for the same IL-water mixture. Henceforth, necessary corrections to the nonbonded ion-ion and ion-water interactions are made to match the experimental osmotic coefficient. To further assess the reliability of the new FF, we extensively explore the thermodynamic (density, isothermal compressibility, and thermal expansion coefficient), dynamic (diffusivity and viscosity), and association/dissociation properties (rationalized with the help of radial distribution functions) with both the original and reparameterized FF for a wider range of concentrations up to a molality of 18.50 mol kg-1. The calculated quantities are compared against experimental data wherever available. The modified FF parameters exhibit significant improvements in terms of its ability to match experimental solution properties, such as density, viscosity, association/dissociation, etc. We report that excessive dissociation of BMIMCl in water is responsible for the shortcomings observed in the original FFs and improved prediction of physicochemical properties could be achieved using the modified FFs.

Amine-functionalized ionic liquids for CO2 capture

In petroleum industry, the release of more and more carbon dioxide (CO₂) brings greenhouse effect and even results in climate change, leading CO₂ capture to become an urgent issue. To design ideal and effective absorbent, interaction mechanism for CO₂ capture was systematically investigated in a series of imidazolium-based ionic liquids (ILs). The potential effects of alkyl side chain, electron-philic halogen (F, Cl, Br) atom(s), electron-denoting groups OH and NH₂ (bound on cation or/and anion), and water solvent were disclosed on CO₂ capture using CAM-B3LYP functional with SMD-GIL solvation model, and the most potential green effective absorbent was predicted. This work provides an explicit idea and theoretical basis about the design of desired IL for CO₂ capture. Graphical abstract In present work, no/halogen/amino/hydroxy-functionalized imidazolium tetrafluoroborate ILs were studied for CO₂ absorption at the CAM-B3LYP/6-311++G** level of theory by SMD-GIL solvation model. NH₂ is more potent group in absorbing CO₂ than halogen and OH, and its number is proportional to the adsorption capacity of IL. A potentially high-capacity CO₂ absorbent with four NH₂ groups was predicted. In addition, the mixture of water could further enhance such chemical absorption by lowering the activation energy barriers and viscosity of IL.

The CO2 Absorption in Flue Gas Using Mixed Ionic Liquids

Because of the appealing properties, ionic liquids (ILs) are believed to be promising alternatives for the CO₂ absorption in the flue gas. Several ILs, such as [NH₂emim][BF₄], [C₄mim][OAc], and [NH₂emim[OAc], have been used to capture CO₂ of the simulated flue gas in this work. The structural changes of the ILs before and after absorption were also investigated by quantum chemical methods, FTIR, and NMR technologies. However, the experimental results and theoretical calculation showed that the flue gas component SO₂ would significantly weaken the CO₂ absorption performance of the ILs. SO₂ was more likely to react with the active sites of the ILs than CO₂. To improve the absorption capacity, the ionic liquid (IL) mixture [C₄mim][OAc]/ [NH₂emim][BF₄] were employed for the CO₂ absorption of the flue gas. It is found that the CO₂ absorption capacity would be increased by about 25%, even in the presence of SO₂. The calculation results suggested that CO₂ could not compete with SO₂ for reacting with the IL during the absorption process. Nevertheless, SO₂ might be first captured by the [NH₂emim][BF₄] of the IL mixture, and then the [C₄mim][OAc] ionic liquid could absorb more CO₂ without the interference of SO₂.

Solubility predictions through LSBoost for supercritical carbon dioxide in ionic liquids

The LSBoost model is developed to predict the solubility of supercritical carbon dioxide in 24 ionic liquids by using critical properties and biphasic system parameters as descriptors. The model is highly accurate and stable.

Greener synthesis of dimethyl carbonate from carbon dioxide and methanol using a tunable ionic liquid catalyst

Several types of ionic liquids (ILs) performance towards dimethyl carbonate (DMC) synthesis using cheap reactant (methanol) and waste CO2 which is abundantly available in the environment are discussed. We synthesized ILs with cheap raw materials such as ethylene glycol. The main aim of this study is to synthesize efficient catalysts for the production of profitable fuel additives. ILs show high thermal stability, less viscosity, and low vapor pressure. In addition, some ILs have high CO2 absorption capacity due to moderate acid-base properties. These ILs reversibly capture more CO2 which is more efficient towards mass transport of methanol at optimum reaction conditions which enhance the DMC yield. This catalytic system is easily reusable for several reactions without decreased performance under the same reaction conditions. These reaction conditions had an effect on the synthesis of DMC. Temperature, pressure, IL loading, and IL/DMAP ratio were fine tuned. We propose a mechanism which the reaction may follow. The synthesized ILs required moderate reaction conditions and reduce waste gases (CO2) from the environments as they have high CO2 absorption capacity compared to the metal oxide catalyst. Therefore, this catalytic system helps and gives new direction to synthesize new catalyst for other application.

CO2 Absorption by DBU-Based Protic Ionic Liquids: Basicity of Anion Dictates the Absorption Capacity and Mechanism

PILs are promising solvent systems for CO₂ absorption and transformations. Although previously tremendous work has been paid to synthesize functionalized PILs to achieve a high-performance absorption, the underlying mechanisms are far less investigated and still not clear. In this work, a series of DBU-based PILs, i.e., [DBUH][X], with anions of various basicities were synthesized. The basicities of the anions were accurately measured in [DBUH][OTf] or extrapolated from the known linear correlations. The apparent kinetics as well as the capacities for CO₂ absorption in these PILs were studied systematically. The results show that the absorption rate and capacity in [DBUH][X] are in proportional to the basicity of PIL, i.e., a more basic PIL leads to a faster absorption rate and a higher absorption capacity. In addition, the spectroscopic evidences and correlation analysis indicate that the capacity and mechanism of CO₂ absorption in [DBUH][X] are essentially dictated by the basicities of anions of these PILs.

Simultaneous CO2 and SO2 capture by using ionic liquids: a theoretical approach

Density functional theory (DFT) methods were used to analyze the mechanism of interaction between acidic gases and ionic liquids based on the 1-ethyl-3-methylimidazolium cation coupled with five different anions.

Preparation and Characterization of Facilitated Transport Membranes Composed of Chitosan-Styrene and Chitosan-Acrylonitrile Copolymers Modified by Methylimidazolium Based Ionic Liquids for CO₂ Separation from CH₄ and N₂

CO₂ separation was found to be facilitated by transport membranes based on novel chitosan (CS)-poly(styrene) (PS) and chitosan (CS)-poly(acrylonitrile) (PAN) copolymer matrices doped with methylimidazolium based ionic liquids: [bmim][BF₄], [bmim][PF₆], and [bmim][Tf₂N] (IL). CS plays the role of biodegradable film former and selectivity promoter. Copolymers were prepared implementing the latest achievements in radical copolymerization with chosen monomers, which enabled the achievement of outstanding mechanical strength values for the CS-based membranes (75-104 MPa for CS-PAN and 69-75 MPa for CS-PS). Ionic liquid (IL) doping affected the surface and mechanical properties of the membranes as well as the gas separation properties. The highest CO₂ permeability 400 Barrers belongs to CS-b-PS/[bmim][BF₄]. The highest selectivity α (CO₂/N₂) = 15.5 was achieved for CS-b-PAN/[bmim][BF₄]. The operational temperature of the membranes is under 220 °C.

Mechanisms of low temperature capture and regeneration of CO2 using diamino protic ionic liquids

Carbon dioxide chemical absorption and regeneration was investigated in two protic ionic liquids using novel calorimetric techniques.

Molecular mechanism of CO2 absorption in phosphonium amino acid ionic liquid

The time-scale and site preferential interaction of CO₂ absorption in tetra-butylphosphonium lysinate amino acid ionic liquid is examined using molecular dynamics simulations.

Efficient fixation and conversion of CO2 into dimethyl carbonate catalyzed by an imidazolium containing tri-cationic ionic liquid/super base system

The synthesis route used to prepare dimethyl carbonate from CO₂ and methanol is a most attractive route from a green chemistry point of view.