A systematic review on CO2 capture with ionic liquids: Current status and future prospects

Global warming triggered by greenhouse gas (GHG) emissions, particularly carbon dioxide (CO2), significantly influences climate change and has become a common environmental issue recently. The current amine-based technologies (ABTs) for CO2 capture (CAPCO2) have high energy demand, low absorption, and desorption rates, and are less environmentally sustainable due to high emissions of volatile solvents. Therefore, the development of environmentally friendly CAPCO2 materials and/or processes is a growing area of research. The utilization of ionic liquids (ILs) for CAPCO2 has recently attracted attention. The unique characteristics of ILs, such as their low vapor pressure and high affinity for CAPCO2 as well as their low volatility make them a viable substitute for the existing processes. This work provides a comprehensive overview of the accomplishments and challenges during the use of ILs for CAPCO2. The Review also outlines the mechanisms of the CAPCO2 with ILs at the molecular level, the properties of ILs, characterization of the CO2/IL systems, and the effect of operating conditions on CO2 uptake (UPCO2) capacity by ILs. It also emphasizes the impact of cations, anions, and functional groups on the solubility of CO2 ((SCO2)) in ILs as well as the biodegradability and toxicity of ILs. Additionally, recent advances in IL membrane technology for the CAPCO2 processes are considered. Lastly, the contribution of molecular simulations to create and assess ILs was reviewed. Protic and aprotic ILs properties have shown outstanding efficiency of UPCO2. The interactions between the anionic part of IL and CO2 enhance the UPCO2 and outperform the efficiency of traditional organic solvents. Functionalized ionic liquids (FUNILs) with tuned functional groups, supported ionic liquids membranes (SILMs) as well as reversible ionic liquids (RILs) have improved the efficiency of ILs as a promising CO2 capturing process from industrial streams even under low CO2 partial pressure. The relative importance of the chemical breakdown of the IL constituents (cation–anion interfacial structuring) during the CAPCO2 process at different operating temperatures is unclear, and more research in this area is required to better inform the design of new ILs. This review provides a proper/systematic guideline to help ILs manufacturers and engineers design high-capacity ILs for appropriate CAPCO2.

Despite significant advancements in this area, techniques for collecting commercialised CO2 relying on absorption processes still have significant limits. The main barriers to CO2 capture include high capital costs, lower absorption, and desorption rates, evaporation of solvents and usage of corrosive solvents. Ionic liquids (ILs) and CO2 capture have received a lot of interest recently. Different amines are currently used as solvents, however, ILs are a viable option due to their unique features, such as their affinity to collect CO2 molecules and their minimal vapour pressure. Since greenhouse gas emissions, particularly those of carbon dioxide have a significant impact on global warming, and this subject is generating increased public concern. The carbon capture, use, and sequestration technique appears to be effective in lowering carbon dioxide concentrations in the atmosphere. An overview of previous engineering and research work on many topics, previous engineering and research work on many topics, CO2 capture techniques is provided in this study.

Ionic liquids (ILs) have been used for carbon dioxide (CO2) capture, however, which have never been used as catalysts to accelerate CO2 capture. The record is broken by a uniquely designed IL, [EMmim][NTf2]. The IL can universally catalyze both CO2 sorption and desorption of all the chemisorption‐based technologies. As demonstrated in monoethanolamine (MEA) based CO2 capture, even with the addition of only 2000 ppm IL catalyst, the rate of CO2 desorption—the key to reducing the overall CO2 capture energy consumption or breaking the bottleneck of the state‐of‐the‐art technologies and Paris Agreement implementation—can be increased by 791% at 85 °C, which makes use of low‐temperature waste heat and avoids secondary pollution during CO2 capture feasible. Furthermore, the catalytic CO2 capture mechanism is experimentally and theoretically revealed.

The industrial revolution during the twentieth century has caused a drastic increase in global warming. Carbon dioxide (CO2) gas is the main constituent of anthropogenic greenhouse gases (GHGs) which cause global warming. The concentration of CO2 in the atmosphere has reached 414.83 ppm. This high CO2 level in the atmosphere has far-ranging effects on health and the environment. CO2 traps heat and hence causes climate change. Respiratory diseases are also caused by a high level of CO2. Various approaches are under consideration to control the emission of CO2 into the atmosphere. Conventional methods for CO2 capture include physical adsorption, absorption, cryogenic distillation, and membrane gas separation. Novel material has been explored for carbon capture and storage (CCS). Ionic liquids (ILs) and metal-organic frameworks (MOFs) are some of these materials. ILs represent a class of materials consisting entirely of ions and are at a liquid state below 100 °C. ILs emerged as exciting materials for CO2 capture and conversion to valuable products because of their non-volatile nature, structure-tunability, and high CO2 adsorption capacity. Similarly, MOFs have gained tremendous attention from researchers in the field of CCS. MOFs are compounds having metal ions or clusters connected through organic ligands to form one-, two-, or three-dimensional structures. MOFs are porous materials with ultra-high porosity, low mass to volume ratio, high surface area, high thermal and chemical stability, and adjustable functionalities. This chapter starts with a brief introduction of existing carbon capture technologies and is followed by an introduction to ILs, their CO2 solubility, and selectivity. The transport properties of ILs and mixed solvents used for CO2 capture have also been discussed. Furthermore, a brief history of MOFs and criteria for MOFs selection for environmental applications have been described as well. MOFs’ adsorption capacity and selectivity for CO2, and their physical, thermal, and chemical stability have also been presented. The applications of MOFs for wastewater treatment and CO2 capture have also been discussed.KeywordsGlobal warmingGreenhouse gases (GHGs)Carbon-dioxide capture and storage (CCS)Ionic Liquids (ILs)Metal-organic frameworks (MOFs)

Screening of conventional ionic liquids for carbon dioxide capture and separation

In this work, an efficient strategy for improving CO2 capture based on anion-functionalized ionic liquids (ILs) by reducing cation-anion interactions in ILs was reported. The influence of the cationic species on CO2 absorption was investigated using 2-hydroxyl pyridium anions ([2-Op]) as a probe. CO2 capture experiments indicated that the CO2 absorption capacity in [2-Op] anion-based ILs varied from 0.94 to 1.69 mol CO2 per mol IL at 30 °C and 1 atm. Spectroscopic analysis and quantum chemical calculations suggested that the increase of the CO2 absorption capacity may be ascribed to the reduction of the strength of cation-anion interactions in ILs, and stronger cation-anion interactions would make one CO2 site in the [2-Op] anion inactive. Furthermore, the effect of the cation unit on the anion was evidenced by FT-IR spectra, implying that strong interactions between ions may lead to the decrease of the IR absorption wavenumber of hydroxy pyridium and work against CO2 capture. Following this strategy, it was finally found that [Ph-C8eim][2-Op] (Ph-C8eim = 1-N-ethyl-3-N-octyl-2-phenylimidazolium) with weaker cation-anion interactions exhibited a significant increase in the CO2 uptake capacity, and extremely high capacities of 1.69 and 1.83 mol CO2 per mol IL could be achieved at 30 and 20 °C, respectively. The study presented here would be helpful for further designing novel and effective ILs for advancing CO2 capturing performance.

Ionic liquids (ILs) have shown great potential in CO₂ capture from the exhaust of fossil fuels burning due to their unique structures and properties. Since the flue gas often contains a small amount of water, understanding the effect of water is critical for the direct capture of postcombustion CO₂ by ionic liquids. In recent years, the effect of water in CO₂ capture by ILs has been studied in some details, but little is known of the new species produced after humid CO₂ capture and thus for the system composition as well as the contribution of each absorption site of ILs to the capture capacity of CO₂. In this work, a simple amino acid ionic liquid, 1-ethyl-3-methylimidazolium glycinate ([C₂mim][Gly]), has been prepared and used to absorb humid CO₂ at 25 °C, and a quantitative approach is established to estimate the absorption capacity of CO₂ by different absorption sites. It is found that the absorption capacity of CO₂ is as high as 0.91 mol CO₂ per mol IL in the wet environment, which is nearly double that of dry CO₂ by neat IL. Quantitative investigations by multiple spectral techniques and quantum chemical calculations indicate that the inhalation of H₂O results in the production of [HCO₃]⁻ in the system and activation of the C2 site of the imidazolium cation. It is this activated site that reacts with CO₂ to form imidazolium-2-carboxylate (NHC-CO₂) and significantly improves the absorption capacity of CO₂. This is remarkably different from the absorption of dry CO₂, in which anions of the IL are predominant for the absorption of CO₂.

Assessment of carbon dioxide solubility in ionic liquid/toluene/water systems by extended PR and PC-SAFT EOSs: Carbon capture implication

Thermodynamic and kinetic evaluation of ionic liquids + tetraglyme mixtures on CO2 capture

Properties of ionic liquids and ionic liquid mixtures.

Process Based Screening Method and Systems Analysis for Pre-Combustion Carbon Capture Using Ionic Liquids

Mechanism study on CO2 capture by [TETAH][HCOO]-PEG200 mixed system

Mechanism study on CO2 capture by ionic liquids made from TFA blended with MEA and MDEA

The CO2 level is increasing continuously in the atmosphere and causing environmental problems. Among the several methods which have been studied to mitigate the CO2 amount in the atmosphere, CO2 electroreduction (CO2ER) has attracted much attention. However, CO2 electroreduction is not efficient due to poor selectivity, high overpotential requirement and the presence of the parasitic hydrogen evolution reaction (HER). As a method to address these challenges, using ionic liquids (ILs) has been recently proposed due to their unique properties such as high CO2 absorption capacity. ILs can enhance CO2ER by making a complex with CO2 and stabilizing the intermediates on the surface. The properties of ILs are affected by several factors such as the nature of anion, cation, and functional groups. In this study, we have investigated the effect of anion in diluted IL/water mixtures on the product selectivity and activity of the copper catalysts.CO2ER was performed on electropolished Cu foils in electrolytes containing 0.1 M KHCO3 and 10 mM of an IL. A range of ILs with same cation (1-butyl-3-methylimidazolium ([BMIM]+)) and different anions (bis(trifluoromethylsulfonyl)imide ([NTF2]-), triflate ([OTF]-), dicyanamide ([DCA]-), acetate ([Ac]-), and chloride ([Cl]-)) were used. These ILs were chosen to cover different size, hydrophilicity and CO2 absorption ability. The catalytic activity was significantly impacted by adding ILs to the electrolyte. The cyclic voltammograms (CVs) in CO2-saturated electrolytes showed that by adding ILs (except for [BMIM][DCA]) to the buffer electrolyte, the onset potential shifted toward positive potentialswhich indicates the enhanced activity in the presence of ILs. Moreover, electrochemical impedance spectroscopy (EIS) showed that all ILs (except for [BMIM][DCA]) had alower charge transfer resistance compared to IL-free electrolyte at -0.92 V. Results also showed that ILs significantly affected the product selectivity. Faradaic efficiency (FE%) toward formate for all ILs increased (except for [BMIM][DCA]) compared to IL-free electrolyte. [BMIM][NTF2] showed the maximum FE% for formate (39%) at -0.92 V. This observation can be attributed to its high CO2 absorption capacity and high hydrophobicity which could attract more CO2 molecules to the surface. The results showed that adding ILs decreased the FE% toward the C2 products compared to IL-free electrolyte likely due to the presence of adsorbed [BMIM]+ cations on the surface which prevent CO2 molecules approach to each other and do dimerization. [BMIM][Ac] had the maximum FE% for CO (a 211% increase in FECO% compared to IL-free electrolyte at -1.02V) and C2 products (a 27% increase in FEC2% compared to IL-free electrolyte at -1.12V) compared to other ILs studied. It has been reported that [BMIM][Ac] can chemically react with CO2, where other ILs in this study were expected to have physical interaction with CO2. A completely different behavior was observed for [BMIM][DCA] in our study. [BMIM][DCA] had a very high activity and low charge transfer resistance in both N2- and CO2-saturate electrolytes. However, this activity was due to the enhanced HER not CO2ER. [BMIM][DCA] had the highest FE% for hydrogen and the lowest FEs for hydrocarbons.This is likely attributed to the high hydrophilicity and low CO2 absorption capacity of [BMIM][DCA] which can cause more water molecules to be attracted to the surface and enhance HER. X-ray photoelectron spectroscopy (XPS) for the Cu electrodes after CO2ER showed that ILs had a strong interaction with the electrode surface. This study showed how anions of imidazolium-based ILs affect the selectivity and activity in CO2 electroreduction.

Limits to Paris compatibility of CO2 capture and utilization