Thermodynamic regulation of carbon dioxide capture by functionalized ionic liquids

Carbon dioxide capture has attracted worldwide attention because CO2 emissions cause global warming and exacerbate climate change. Ionic liquids (ILs) have good application prospects in carbon capture due to their excellent properties, which provide a new chance to develop efficient and reversible carbon capture systems. This paper reviews the recent progress in CO2 chemical absorption by ILs, such as N-site, O-site, C-site, and multi-site functionalized ILs. The application of thermodynamic regulation methods in CO2 capture is discussed in detail. Among them, the methods of enthalpy regulation are mainly introduced, for which different regulatory targets are proposed for single sites and multiple sites. Furthermore, the strategies of achieving entropy compensation through the design of spatial configurations are discussed. Particular attention is paid to the application of thermodynamic regulation in direct air capture (DAC) due to its great significance. The methods to improve the absorption kinetics are also outlined. Finally, the future development of carbon capture by functionalized ILs is proposed.

Robust Method for Property Prediction via Artificial Neural Networks: Incorporating Key Structural Features for Carbon Dioxide-Ionic Liquid Mixtures

This study addresses a critical gap in the existing literature on carbon dioxide and ionic liquid (IL) mixtures, where fragmented and incomplete data, particularly for flow properties, hinder practical applications. Therefore, this work aimed to establish a robust and efficient method for predicting the density of the CO2-IL mixtures across diverse operating conditions and IL families using novel validation techniques. Both linear and symbolic regression models provided relevant insights but failed to accurately capture the IL-CO2 interactions in a mixture that determine the molar volume of CO2 at infinite dilution when solubilized by a given IL. Therefore, more mathematically flexible artificial neural networks (ANN) were trained based on three different sets of features: (1) IL critical properties, (2) IL structural descriptors, and (3) a selective combination of (1) and (2). While all models showed relative deviations consistently below 3% for the testing data, combining critical and structural data significantly improved accuracy (R2 = 0.986, testing data set). A postprocessing outlier-handling method enhanced model performance, removing a minimal fraction (below 0.2%) of unphysical data points. Furthermore, molecular dynamics simulations validated the robust generalization of all ANN models, with the combined model exhibiting remarkable accuracy over operating conditions outside the training ranges for ILs in the training set and even for ILs that are not included in this data set. This computational approach provides a significantly faster and broader alternative to other thermodynamical tools, establishing a solid method for future machine learning (ML)-based property prediction augmented by external validation from cross-comparison tests and statistical thermodynamics models.

Oxometallate-Based Ionic Liquid Catalyzed CO2-Promoted Hydration of Propargylic Alcohols for α-Hydroxy Ketones Synthesis

α-Hydroxy ketones are a crucial class of organic compounds prevalent in natural products and pharmaceutical molecules. The CO2-promoted hydration of propargylic alcohols is an efficient method for the synthesis of α-hydroxy ketones. Herein, an ionic liquid (IL) was designed to catalyze this reaction individually under atmospheric CO2 pressure, volatile organic solvents, and additives. This IL, constructed from the molybdate anion, can be recycled from industrial (NH4)2MoO4 production wastewater, demonstrating its high tolerance to catalytic environments and significant potential for practical applications. To our knowledge, this is the first instance of an oxometallate-based IL catalyst being utilized for the CO2-promoted hydration of propargylic alcohols. Further mechanistic studies revealed the bifunctionality of this IL in activating both CO2 and substrates.

Multiscale modeling of CO2 capture in dicationic ionic liquids: Evaluating the influence of hydroxyl groups using DFT-IR, COSMO-RS, and MD simulation methods

This work employs a combination of density functional theory-infrared (IR), conductor-like screening model for real solvents (COSMO-RS), and molecular dynamic (MD) methods to investigate the impact of hydroxyl functional groups on CO2 capture within dicationic ionic liquids (DILs). The COSMO-RS reveals that hydroxyl groups in DILs reduce the macroscopic solubility of CO2 but improve the selectivity of CO2 over CO, H2, and CH4 gases. Quantum methods in the gas phase and MD simulations in the liquid phase were conducted to delve deeper into the underlying mechanisms. The IR spectrum analysis confirms red shifts in CO2's asymmetric stretching mode and blue shifts in the CR-HR bond of the dication, indicating CO2-DIL interactions and the weakening of the anion-cation interactions caused by the presence of CO2. The results show that the positioning of anions around hydroxyl groups and HR atoms in rings inhibits the proximity of CO2 molecules, causing the hydrogen atoms within methylene groups to accumulate CO2. van der Waals forces were found to dominate the interaction between ions and CO2. The addition of hydroxyl groups strengthens the electrostatic interactions and hydrogen bonds between dications and anions. The stronger interaction energy between ions in [C5(mim)2-(C2)2(OH)2][NTf2]2 limits the displacement of CO2 molecules within this DIL compared to [C5(mim)2-(C4)2][NTf2]2. Compared to [C5(mim)2-(C4)2][NTf2]2, [C5(mim)2-(C2)2(OH)2][NTf2]2 exhibits stronger ion-ion interactions, higher density, and reduced free volume, resulting in a reduction in CO2 capture. These results provide significant insights into the intermolecular interactions and vibrational properties of CO2 in DIL complexes, emphasizing their significance in developing efficient and sustainable strategies for CO2 capture.

Viscosity of Ionic Liquids: Theories and Models

Ionic liquids (ILs) offer a wide range of promising applications due to their unique and designable properties compared to conventional solvents. Further development and application of ILs require correlating/predicting their pressure-viscosity-temperature behavior. In this review, we firstly introduce methods for calculation of thermodynamic inputs of viscosity models. Next, we introduce theories, theoretical and semi-empirical models coupling various theories with EoSs or activity coefficient models, and empirical and phenomenological models for viscosity of pure ILs and IL-related mixtures. Our modelling description is followed immediately by model application and performance. Then, we propose simple predictive equations for viscosity of IL-related mixtures and systematically compare performances of the above-mentioned theories and models. In concluding remarks, we recommend robust predictive models for viscosity at atmospheric pressure as well as proper and consistent theories and models for P-η-T behavior. The work that still remains to be done to obtain the desired theories and models for viscosity of ILs and IL-related mixtures is also presented. The present review is structured from pure ILs to IL-related mixtures and aims to summarize and quantitatively discuss the recent advances in theoretical and empirical modelling of viscosity of ILs and IL-related mixtures.

Innovative Strategy for Truly Reversible Capture of Polluting Gases-Application to Carbon Dioxide

This paper consists of a deep analysis and data comparison of the main strategies undertaken for achieving truly reversible capture of carbon dioxide involving optimized gas uptakes while affording weakest retention strength. So far, most strategies failed because the estimated amount of CO2 produced by equivalent energy was higher than that captured. A more viable and sustainable approach in the present context of a persistent fossil fuel-dependent economy should be based on a judicious compromise between effective CO2 capture with lowest energy for adsorbent regeneration. The most relevant example is that of so-called promising technologies based on amino adsorbents which unavoidably require thermal regeneration. In contrast, OH-functionalized adsorbents barely reach satisfactory CO2 uptakes but act as breathing surfaces affording easy gas release even under ambient conditions or in CO2-free atmospheres. Between these two opposite approaches, there should exist smart approaches to tailor CO2 retention strength even at the expense of the gas uptake. Among these, incorporation of zero-valent metal and/or OH-enriched amines or amine-enriched polyol species are probably the most promising. The main findings provided by the literature are herein deeply and systematically analysed for highlighting the main criteria that allow for designing ideal CO2 adsorbent properties.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Evaluation of a Phosphinate Functionalized Ionic Liquid for the Separation of Nb and Ta from Nitric Acid Feed Conditions

A 'green' single-step separation process, involving a phosphonium phosphinate functionalized ionic liquid (FIL) in C8mim·NTf2, has been developed for highly encouraging improvements in the mutual separation of Nb and Ta with a maximum separation factor of ∼48 at 2 M nitric acid. The separation factor in C4mim·NTf2 was found to be somewhat lower compared to that seen in C8mim·NTf2. In C8mim·NTf2, the extraction proceeded via the neutral NbOF3(R4P+)(R2POO-) and TaOF3(R4P+)(R2POO-) species predominated by a 'solvation' mechanism at 2 M HNO3, where both the cationic and anionic parts of the FIL took part in the metal ion extraction. However, in the case of C4mim·NTf2, the extraction proceeded via a cation exchange mechanism involving the mono-positive species viz. [NbO(R2POO-)2]+IL, [TaO(R2POO-)2]+IL. Only the phosphinate group of the FIL was directly involved in the binding to the metal ion. The charge neutrality was maintained by the exchange of the C4mim+ ion from the ionic liquid phase to the aqueous phase. The processes were spontaneous, exothermic involving outer sphere complexation. The radiolytic stabilities of the C8mim·NTf2-based solvent systems were poorer than those of the solvents based on C4mim·NTf2. Aqueous solutions of EDTA-guanidine carbonate or DTPA-guanidine carbonate showed promising back extraction ability though three contacts of these organic phases were required for more than 99.99% stripping of the metal ion. The reusability of these solvent systems was evaluated. After four consecutive cycles, a maximum of only 8% reduction in the extraction efficiency of Ta was noticed, while for Nb it was less than 4% for Nb.

Functionalized Ionic Liquids for CO2 Capture under Ambient Pressure

Ionic liquids (ILs) have been widely explored as alternative solvents for carbon dioxide (CO2) capture and utilization. However, most of these processes are under pressures significantly higher than atmospheric level, which not only levies additional equipment and operation costs, but also makes the large-scale CO2 capture and conversion less practical. In this study, we rationally designed glycol ether-functionalized imidazolium, phosphonium and ammonium ILs containing acetate (OAc-) or Tf2N- anions, and found these task-specific ILs could solubilize up to 0.55 mol CO2 per mole of IL (or 5.9 wt% CO2) at room temperature and atmospheric pressure. Although acetate anions enabled a better capture of CO2, Tf2N- anions are more compatible with alcohol dehydrogenase (ADH), which is a key enzyme involved in the cascade enzymatic conversion of CO2 to methanol. Our promising results indicate the possibility of CO2 capture under ambient pressure and its enzymatic conversion to valuable commodity.

A state-of-the-art review on capture and separation of hazardous hydrogen sulfide (H2S): Recent advances, challenges and outlook

Hydrogen sulfide (H₂S) is a flammable, corrosive and lethal gas even at low concentrations (ppm levels). Hence, the capture and removal of H₂S from various emitting sources (such as oil and gas processing facilities, natural emissions, sewage treatment plants, landfills and other industrial plants) is necessary to prevent and mitigate its adverse effects on human (causing respiratory failure and asphyxiation), environment (creating highly flammable and explosive environment), and facilities (resulting in corrosion of industrial equipment and pipelines). In this review, the state-of-the-art technologies for H₂S capture and removal are reviewed and discussed. In particular, the recent technologies for H₂S removal such as membrane, adsorption, absorption and membrane contactor are extensively reviewed. To date, adsorption using metal oxide-based sorbents is by far the most established technology in commercial scale for the fine removal of H₂S, while solvent absorption is also industrially matured for bulk removal of CO₂ and H₂S simultaneously. In addition, the strengths, limitations, technological gaps and way forward for each technology are also outlined. Furthermore, the comparison of established carbon capture technologies in simultaneous and selective removal of H₂S-CO₂ is also comprehensively discussed and presented. It was found that the existing carbon capture technologies are not adequate for the selective removal of H₂S from CO₂ due to their similar characteristics, and thus extensive research is still needed in this area.

Effectiveness of ionic liquid-supported membranes for carbon dioxide capture: a review

The world's population explosion creates a need for natural resources for energy, which will become a significant contributor to global climate change. As we all know, carbon dioxide (CO₂) is one of the most critical elements of the global greenhouse gas effect. CO₂ capture and storage innovations have piqued researchers' attention in recent decades. Compared to other methods, membrane separation has some positive performance in CO₂ capture. CO₂ capture with membrane separation using enhanced ionic liquids (ILs) is described in this review. ILs have made an appearance in CO₂ capture work as the potential additive, and companies and academics have been interested in CO₂ separation for the past two decades. This article comprehensively analyzes the current modern approach in ILs and IL-based membranes for gas separation processes. Based on the latest literature and performance data, this work provides a complete compressive examination of types of ILs and IL-supported membrane performances. ILs for CO₂ capture were also explored, and IL-based membranes for different ILs were also studied. This study emphasizes the supremacy of novel ILs for CO₂ capture in membrane separation.

Ammonium-, phosphonium- and sulfonium-based 2-cyanopyrrolidine ionic liquids for carbon dioxide fixation

The development of carbon dioxide (CO₂) scavengers is an acute problem nowadays because of the global warming problem. Many groups around the globe intensively develop new greenhouse gas scavengers. Room-temperature ionic liquids (RTILs) are seen as a proper starting point to synthesize more environmentally friendly and high-performance sorbents. Aprotic heterocyclic anions (AHA) represent excellent agents for carbon capture and storage technologies. In the present work, we investigate RTILs in which both the weakly coordinating cation and AHA bind CO₂. The ammonium-, phosphonium-, and sulfonium-based 2-cyanopyrrolidines were investigated using the state-of-the-art method to describe the thermochemistry of the CO₂ fixation reactions. The infrared spectra and electronic and structural properties were simulated at the hybrid density functional level of theory to characterize the reactants and products of the chemisorption reactions. We conclude that the proposed CO₂ capturing mechanism is thermodynamically allowed and discuss the difference between different families of RTILs. Quite unusually, the intramolecular electrostatic attraction plays an essential role in stabilizing the zwitterionic products of the CO₂ chemisorption. The difference in chemisorption performance between the families of RTILs is linked to sterical hindrances and nucleophilicities of the α- and β-carbon atoms of the aprotic cations. Our results rationalize previous experimental CO₂ sorption measurements (Brennecke et al., 2021).

Binary mixtures containing imidazolium ionic liquids: properties measurement

Densities and transport properties (dynamic viscosity) of pure imidazolium ionic liquids 1-butyl-3-methylimidazolium acetate and 1-butyl-3-methylimidazolium dicyanamide and their binary mixtures with water and ethanol were measured within the temperature range of 293.15—333.15 K. Obtained experimental data were used to calculate excess molar volume and viscosity deviation. For the chosen binary mixtures, variations of excess molar volume, partial molar volumes of mixture components and of the viscosity deviation with the binary mixture composition were correlated using the Redlich-Kister equation. In addition, variation of viscosity with the binary mixture composition and temperature was fitted using the Jouyban-Acree model.

Experimental investigation of density, viscosity, and surface tension of aqueous tetrabutylammonium-based ionic liquids

The physical properties such as density, dynamic viscosity, and surface tension of aqueous tetrabutylammonium-based ionic liquids were measured experimentally by varying temperature (283.4 to 333.4 K) and concentration of ILs (10-50 wt%) at an interval of 10 K and 10 wt% respectively. In this study, the aqueous tetrabutylammonium-based ionic liquids namely tetrabutylammonium acetate [TBA][OAC], tetrabutylammonium bromide [TBA][Br], and tetrabutylammonium hydroxide [TBA][OH] was used to investigate the influence of temperature and concentration of ILs on the physical properties data was examined. It is observed that both density and surface tension increase with increasing concentration of [TBA][Br], whereas the opposite trend is observed for [TBA][OAC] and [TBA][OH] respectively. This is due to stronger molecular interaction between [TBA][Br] and water compared to other ILs. The dynamic viscosity of all aqueous ILs increases with increasing IL concentration. The measured physical properties of ILs decrease as temperature increases. Furthermore, the experimental data is correlated and compared with that of the calculated model; the agreement was satisfactory. Graphical abstract.

A QSPR model for estimating Henry's law constant of H2S in ionic liquids by ELM algorithm

Ionic liquids (ILs) as green solvents have been studied in the application of gas sweetening. However, it is a huge challenge to obtain all the experimental values because of the high costs and generated chemical wastes. This study pioneered a quantitative structure-property relationship (QSPR) model for estimating Henry's law constant (HLC) of H₂S in ILs. A dataset consisting of the HLC data of H₂S for 22 ILs within a wide range of temperature (298.15-363.15 K) were collected from published reports. The electrostatic potential surface area (S_EP) and molecular volume of these ILs were calculated and used as input descriptors together with temperature. The extreme learning machine (ELM) algorithm was employed for nonlinear modelling. Results showed that the determination coefficient (R²) of the training set, test set and total set were 0.9996, 0.9989,0.9994, respectively, while the average absolute relative deviation (AARD%) of them were 1.3383, 2,4820 and 1.5820, respectively. The statistical parameters for the measurement of the model exhibited the great reliability, stability, and predictive power of the ELM model. The Applicability Domain (AD) of the ELM model is also investigated. It proves that the majority of ILs in the training and test sets are located in the model's AD and verifies the reliability of the model. The proposed model is potentially applicable to guide the application of ILs for gas sweetening.

Acidic Gases Solubility in Bis(2-Ethylhexyl) Sulfosuccinate Based Ionic Liquids Using the Predictive Thermodynamic Model

To properly design ionic liquids (ILs) adopted for gases separation uses, a knowledge of ILs thermodynamic properties as well their solubilities with the gases is essential. In the present article, solubilities of CO₂ and H₂S in bis(2-Ethylhexyl)sulfosuccinate based ILs were predicted using the conductor like screening model for real solvents COSMO-RS. According to COSMO-RS calculations, the influence of the cation change was extensively analyzed. The obtained data are used for the prediction of adequate solvent candidates. Moreover, to understand the intrinsic behavior of gases solubility the free volume of the chosen ILs and their molecular interactions with respectively CO₂ and H₂S were computed. The results suggest that hydrogen bonding interactions in ILs and between ILs and the gases have a pivotal influence on the solubility.

Choline-Based Ionic Liquids-Incorporated IRMOF-1 for H2S/CH4 Capture: Insight from Molecular Dynamics Simulation

The removal of H2S and CH4 from natural gas is crucial as H2S causes environmental contamination, corrodes the gas stream pipelines, and decreases the feedstock for industrial productions. Many scientific researches have shown that the metal-organic framework (MOF)/ionic liquids (ILs) have great potential as alternative adsorbents to capture H2S. In this work, molecular dynamics (MD) simulation was carried out to determine the stability of ILs/IRMOF-1 as well as to study the solubility of H2S and CH4 gases in this ILs/IRMOF-1 hybrid material. Three choline-based ILs were incorporated into IRMOF-1 with different ratios of 0.4, 0.8, and 1.2% w/w, respectively, in which the most stable choline-based ILs/IRMOF-1 composite was analysed for H2S/CH4 solubility selectivity. Among the three choline-based ILs/IRMOF-1, [Chl] [SCN]/IRMOF-1 shows the most stable incorporation. However, the increment of ILs loaded in the IRMOF-1 significantly reduced the stability of the hybrid due to the crowding effect. Solvation free energy was then computed to determine the solubility of H2S and CH4 in the [Chl] [SCN]/IRMOF-1. H2S showed higher solubility compared to CH4, where its solubility declined with the increase of choline-based IL loading.

Is basicity the sole criterion for attaining high carbon dioxide capture in deep-eutectic solvents?

A critical analysis of the role of Hammett basicity (H_-) and aqueous basicity (pK_a) in CO₂ uptake in deep-eutectic solvents (DESs) suggests that neither H_- nor pK_a correlates with the CO₂ w/w% capacity in the studied DESs. Instead, strong "synergistic interactions" between donor and acceptor moieties satisfactorily relate to the w/w% of CO₂ in DESs.

Rigorous Connectionist Models to Predict Carbon Dioxide Solubility in Various Ionic Liquids

Estimating the solubility of carbon dioxide in ionic liquids, using reliable models, is of paramount importance from both environmental and economic points of view. In this regard, the current research aims at evaluating the performance of two data-driven techniques, namely multilayer perceptron (MLP) and gene expression programming (GEP), for predicting the solubility of carbon dioxide (CO2) in ionic liquids (ILs) as the function of pressure, temperature, and four thermodynamical parameters of the ionic liquid. To develop the above techniques, 744 experimental data points derived from the literature including 13 ILs were used (80% of the points for training and 20% for validation). Two backpropagation-based methods, namely Levenberg–Marquardt (LM) and Bayesian Regularization (BR), were applied to optimize the MLP algorithm. Various statistical and graphical assessments were applied to check the credibility of the developed techniques. The results were then compared with those calculated using Peng–Robinson (PR) or Soave–Redlich–Kwong (SRK) equations of state (EoS). The highest coefficient of determination (R2 = 0.9965) and the lowest root mean square error (RMSE = 0.0116) were recorded for the MLP-LMA model on the full dataset (with a negligible difference to the MLP-BR model). The comparison of results from this model with the vastly applied thermodynamic equation of state models revealed slightly better performance, but the EoS approaches also performed well with R2 from 0.984 up to 0.996. Lastly, the newly established correlation based on the GEP model exhibited very satisfactory results with overall values of R2 = 0.9896 and RMSE = 0.0201.

Theoretical Study of CO2 Absorption into Novel Reactive 1DMA2P Solvent in Split-flow Absorber-stripper Unit: Mass Transfer Performance and Kinetic Analysis

In the present study, the mass transfer performance of CO2 absorption into 1-dimethylamino-2-propanol (1DMA2P) as a novel amino alcohol solvent has been theoretically investigated in a split-flow absorber-stripper unit. The mass transfer performance has been presented in terms of CO2 absorption flux and overall mass transfer coefficient (KGav) by simultaneous considering of chemical reactions and mass transfer phenomenon. The developed comprehensive mathematical model has been validated based on related experimental data in literature. The impact of main operation parameters including liquid feed temperature, amine concentration, liquid velocity and CO2 loading were evaluated. The presented results indicated that increasing the liquid feed temperature, amine concentration and liquid flow rate improves the overall mass transfer coefficient. Also, the CO2 absorption performance of conventional and alternative amines such as monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), methyldiethanolamine (MDEA), piperazine (PZ), 4-(diethylamino)-2-butanol (DEAB) and 1DMA2P have been investigated and compared in order to provide guidelines about effective screening of solvents. The modeling results indicated that the KGav for CO2 absorption into different solution can be ranked as follows: PZ>MEA>DEA>DEAB>1DMA2P>MDEA>TEA.

Acidic Gases Separation from Gas Mixtures on the Supported Ionic Liquid Membranes Providing the Facilitated and Solution-Diffusion Transport Mechanisms

Nowadays, the imidazolium-based ionic liquids containing acetate counter-ions are attracting much attention as both highly selective absorbents of the acidic gases and CO₂ carriers in the supported ionic liquid membranes. In this regard, the investigation of the gas transport properties of such membranes may be appropriate for better understanding of various factors affecting the separation performance and the selection of the optimal operating conditions. In this work, we have tested CH₄, CO₂ and H₂S permeability across the supported ionic liquid membranes impregnated by 1-butyl-3-methylimidazolium acetate (bmim[OAc]) with the following determination of the ideal selectivity in order to compare the facilitated transport membrane performance with the supported ionic liquid membrane (SILM) that provides solution-diffusion mechanism, namely, containing 1-butyl-3-methylimidazolium tetrafluoroborate (bmim[BF₄]). Both SILMs have showed modest individual gases permeability and ideal selectivity of CO₂/CH₄ and H₂S/CH₄ separation that achieves values up to 15 and 32, respectively. The effect of the feed gas mixture composition on the permeability of acidic gases and permeselectivity of the gas pair was investigated. It turned out that the permeation behavior for the bmim[OAc]-based SILM toward the binary CO₂/CH₄, H₂S/CH₄ and ternary CO₂/H₂S/CH₄ mixtures was featured with high acidic gases selectivity due to the relatively low methane penetration through the liquid phase saturated by acidic gases.

Improving Physical Adsorption of CO2 by Ionic Liquids‐Loaded Mesoporous Silica

CO2 sorption capacities of the neat and silica‐supported 1‐butyl‐3‐methylimidazolium‐based ionic liquids (ILs) were measured under atmospheric pressure. The silica‐supported ILs were synthesized by the impregnation‐vaporization method and charactrized by N2 adsorption/desorption and thermogravimeteric analysis (TGA). Evaluation of the effects of influential factors on sorption capacity demonstrated that by increase of the temperature, flow rate, and the weight percentage of ILs in sorbents, the sorption capacity decreases. Among the sorbents, [Bmim][TfO] and SiO2‐[Bmim][BF4](50) had the highest capacity. By increasing the IL portion in SiO2‐[Bmim][BF4], the selectivity for CO2 to CH4 could be improved. The CO2‐rich sorbents could be easily recycled.

Critical review of existing nanomaterial adsorbents to capture carbon dioxide and methane

Innovative gas capture technologies with the objective to mitigate CO₂ and CH₄ emissions are discussed in this review. Emphasis is given on the use of nanoparticles (NP) as sorbents of CO₂ and CH₄, which are the two most important global warming gases. The existing NP sorption processes must overcome certain challenges before their implementation to the industrial scale. These are: i) the utilization of the concentrated gas stream generated by the capture and gas purification technologies, ii) the reduction of the effects of impurities on the operating system, iii) the scale up of the relevant materials, and iv) the retrofitting of technologies in existing facilities. Thus, an innovative design of adsorbents could possibly address those issues. Biogas purification and CH₄ storage would become a new motivation for the development of new sorbent materials, such as nanomaterials. This review discusses the current state of the art on the use of novel nanomaterials as adsorbents for CO₂ and CH₄. The review shows that materials based on porous supports that are modified with amine or metals are currently providing the most promising results. The Fe₃O₄-graphene and the MOF-117 based NPs show the greatest CO₂ sorption capacities, due to their high thermal stability and high porosity. Conclusively, one of the main challenges would be to decrease the cost of capture and to scale-up the technologies to minimize large-scale power plant CO₂ emissions.

Carbon Dioxide Capture with Ionic Liquids and Deep Eutectic Solvents: A New Generation of Sorbents

High cost and high energy penalty for CO₂ uptake from flue gases are important obstacles in large-scale industrial applications, and developing efficient technology for CO₂ capture from technical and economic points is crucial. Ionic liquids (ILs) show the potential for CO₂ separation owing to their inherent advantages, and have been proposed as alternatives to overcome the drawbacks of conventional sorbents. Chemical modification of ILs to improve their performance in CO₂ absorption has received more attention. Deep eutectic solvents (DESs) as a new generation of ILs are considered as more economical alternatives to cope with the deficiencies of high cost and high viscosity of conventional ILs. This Review discusses the potential of functionalized ILs and DESs as CO₂ sorbents. Incorporation of CO₂ -philic functional groups, such as amine, in cation and/or anion moiety of ILs can promot their absorption capacity. In general, the functionalization of the anion part of ILs is more effective than the cation part. DESs represent favorable solvent properties and are capable of capturing CO₂ , but the research work is scarce and undeveloped compared to the studies conducted on ILs. It is possible to develop novel DESs with promising absorption capacity. However, more investigation needs to be carried out on the mechanism of CO₂ sorption of DESs to clarify how these novel sorbents can be adjusted and fine-tuned to be best tailored as optimized media for CO₂ capture.

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.

A Comparative Study of the CO2 Absorption in Some Solvent-Free Alkanolamines and in Aqueous Monoethanolamine (MEA)

The neat secondary amines 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(isopropylamino)ethanol, 2-(benzylamino)ethanol and 2-(butylamino)ethanol react with CO2 at 50-60 °C and room pressure yielding liquid carbonated species without their dilution with any additional solvent. These single-component absorbents have the theoretical CO2 capture capacity of 0.50 (mol CO2/mol amine) due to the formation of the corresponding amine carbamates and protonated amines that were identified by the (13)C NMR analysis. These single-component absorbents were used for CO2 capture (15% and 40% v/v in air) in two series of different procedures: (1) batch experiments aimed at investigating the efficiency and the rate of CO2 capture; (2) continuous cycles of absorption-desorption carried out in packed columns with absorption temperatures brought at 50-60 °C and desorption temperatures at 100-120 °C at room pressure. A number of different amines and experimental setups gave CO2 capture efficiency greater than 90%. For comparison purposes, 30 wt % aqueous MEA was used for CO2 capture under the same operational conditions described for the solvent-free amines. The potential advantages of solvent-free alkanolamines over aqueous MEA in the CO2 capture process were discussed.