First-principles-guided design of ionic liquids for CO(2) capture

The identification of sorbents that combine selectively and reversibly with CO(2) is essential for efficient and economical abatement of ever-increasing CO(2) emissions. Room temperature ionic liquids (ILs) are a promising class of potential absorbents, especially when modified to chemically combine with CO(2). In this perspective we describe the evolution of IL-based CO(2) capture chemistries over the last ten years and in particular the important role that first principles simulations have played in helping guide those developments. Current anion-functionalized ILs achieve high CO(2) capture efficiencies tailorable to a wide range of separation conditions and avoid the viscosity problems that plagued the earliest amine-functionalized, CO(2)-reactive ILs. Further progress is needed to develop ILs able to meet all the requirements of a CO(2) separation system, and simulations will play a central role in those developments.     

Properties of alkylbenzimidazoles for CO2 and SO2 capture and comparisons to ionic liquids

To date, few reports have been concerned with the physical properties of the liquid phases of imidazoles and benzimidazoles-potential starting materials for a great number of ionic liquids. Prior research has indicated that alkylimidazole solvents exhibit different, and potentially advantageous physical properties, when compared to corresponding imidazolium-based ionic liquids. Given that even the most fundamental physical properties of alkylimidazole solvents have only recently been reported, there is still a lack of data for other relevant imidazole derivatives, including benzimidazoles. In this work, we have synthesized a series of eight 1-n-alkylbenzimidazoles, with chain lengths ranging from ethyl to dodecyl, all of which exist as neat liquids at ambient temperature. Their densities and viscosities have been determined as functions of both temperature and molecular weight. Alkylbenzimidazoles have been found to exhibit viscosities that are more similar to imidazolium-based ILs than alkylimidazoles, owed to a large contribution to viscosity from the presence of a fused ring system. Solubilities of CO2 and SO2, two species of concern in the emission of coal-fired power generation, were determined for selected alkylbenzimidazoles to understand what effects a fused ring system might have on gas solubility. For both gases, alkylbenzimidazoles were determined to experience physical, non-chemically reactive, interactions. The solubility of CO2 in alkylbenzimidazoles is 10%-30% less than observed for corresponding ILs and alkylimidazoles. 1-butylbenzimidazole was found to readily absorb at least 0.333 gram SO2 per gram at low pressure and ambient temperature, which could be readily desorbed under an N2 flush, a behavior more similar to imidazolium-based ILs than alkylimidazoles. Thus, we find that as solvents for gas separations, benzimidazoles share characteristics with both ILs and alkylimidazoles.     

CO2 capture and electrochemical conversion

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Highly efficient CO2 capture by tunable alkanolamine-based ionic liquids with multidentate cation coordination

A series of novel alkanolamine-based ionic liquids show a highly efficient and excellent reversible capture of CO(2) through multidentate cation coordination between alkanolamine and Li(+) ion in a quasi-aza-crown ether fashion.     

CO2 capture by hydrocarbon surfactant liquids

Here we found that CO(2) has high solubility in low-cost hydrocarbon surfactant liquids.     

Polyoxometalate-based ionic liquids-promoted CO2 conversion

Polyoxometalates (POMs) are a class of molecular metal oxides, showing numerous applications in various chemical processes due to their unique acid/base and redox features. By adjusting the tunable molecular structures of the anions and counter cations, plenty of POM-based ionic liquids (POM-based ILs) have been fabricated to be used in various fields, such as catalysis, structural chemistry and material science. As a class of excellent catalysts, POM-based ILs have shown advantages in the emerging field of CO₂ utilization such as CO₂ capture, cycloaddition of CO₂ to epoxides, and reduction of CO₂, owing to the efficient activation of CO₂ by POM anions. This review summarizes recent advances in the catalysis of POM-based ILs, and particularly highlights the areas that are related to CO₂ conversion.     

An interesting theoretical insight into CO2 capture of phosphonium-based ionic liquids with aprotic heterocyclic anions

Structural Chemistry - In this investigation, a systematic understanding of the nature of molecular interactions between aprotic heterocyclic anions (AHAs) and typically phosphonium-based cation...     

The polymeric ionic liquids/mesoporous alumina composites: Synthesis,characterization and CO2 capture performance test

The CO₂ capture materials and technology have received much attention in recent years due to the environmental deterioration caused by the greenhouse gas emissions. Several imidazolium polymeric ionic liquids (PILs) were synthesized and immobilized on mesoporous γ-Al₂O₃ (MA) using ultrasonic immersion method. The prepared adsorbents were characterized by FT-IR, ¹H NMR, EA, TGA, SEM, XRD, BET and TEM, indicating the successful synthesis of the desired PILs/MA. The CO₂ adsorption capacity was investigated under different loading ratios, temperatures, pressures and CO₂ flow rates, whose optimal adsorption conditions were 1/1, 313 K, 5 bar and 10 mL/min, respectively. Moreover, the adsorption curves for P[VCIm]Cl/MA were coincident with pseudo-second order model, and the CO₂ adsorption kinetics model was calculated and obtained. Compared with P[VRIm]Cl and P[VEIm]Cl, P[VCIm]Cl/MA demonstrated an outstanding adsorption amount of 0.562 mmol/g under the suitable conditions, and its regeneration efficiency could achieve 94.8% after 5 times cycle.     

Polystyrene-bound diethanolamine based ionic liquids for chemical fixation of CO2

Polystyrene-bound diethanolamine based ionic liquids (PS-DHEEAB and PS-THEAB) were synthesized and applied for the chemical fixation of CO₂ into cyclic carbonates without any additional co-catalyst and solvent. The effect of the catalysts with different number of hydroxyl group in the cation of the IL on the reaction was systematically investigated. Highest activity and selectivity were achieved in the presence of polystyrene supported diethanolamine ethyl bromide (PS-DHEEAB) in comparison with other catalysts employed. The catalyst was tough in stability and also found to be extended to a variety of terminal epoxides and aziridines. The relationship between high catalytic reactivity and the –OH functional groups was proposed.     

Capsules with polyurea shells and ionic liquid cores for CO2 capture

Many ionic liquids (ILs) have good solubilities of CO₂ but the high viscosity of ILs makes them cumbersome and kinetically limits gas uptake. Encapsulation of ILs is an effective approach to overcoming these limitations. In capsules with a core of IL, the chemical composition of the shell impacts performance. Here, we report the preparation of capsules with a core of the IL [Bmim][PF₆] and polymer composite shell, then evaluate how the identity of the polymer impacts CO₂ uptake. IL-in-oil Pickering emulsions stabilized by nanosheets are used, with capsules formed by interfacial polymerization between different diamines and diisocyanates (e.g., shells are polyurea and nanosheets). The capsules contain 60–80 wt% IL and the composition was verified using Fourier transform infrared spectroscopy. Optical microscopy, scanning electron microscopy, and particle sizing data showed spherical, discrete capsules with 50–125 μm in diameter. All capsules are stable up to 250°C. Brunauer–Emmett–Teller analysis of CO₂ gas uptake data showed that different polymer compositions led to different CO₂ uptake properties, with capacity ranging from 0.065 to 0.025 moles of CO₂/kg sorbent at 760 torr and 20°C. This work demonstrates that the polymer identity of the shell impacts gas uptake properties and supports that shell composition can tailor performance.     

A novel ionic liquids-based scrubbing process for efficient CO2 capture

A novel alkanolamine-based ionic liquid, N-methyl-diethanolammonium tetrafluoroborate ([MDEA][BF₄]), was synthesized in our laboratory. The ionic liquid-based composite solution consisting of N-methyl-diethanolamine (MDEA), [MDEA][BF₄], piperazine (PZ) and H₂O was investigated for CO₂ capture. The optimal performance for CO₂ capture was found at 45 °C, 1.50 MPa, probably due to a synergistic action of the reaction and the transport. No apparent corrosion was found on stainless and carbon steel with the above composite solution. This finding is very significant to the promotion of its engineering application.     

CO2 hydrogenation in ionic liquids: Recent update

The suppression of CO₂ emission is an important global issue. Therefore, CO₂ hydrogenation is a hopeful method for capturing and recycling of CO₂. Ionic liquids have been known to have a high affinity with CO₂, indicative of the expectation for the enhancement of CO₂ hydrogenation in case used as reaction medium. In this article, progress of this area in 2018–2021 is mainly reviewed, namely, formic acid, hydrocarbons, methanol formation, hydroformylation, enzymatic methanol formation, and electro-reduction of CO₂ (CO₂RR). Various products are obtained with coupling of catalysts and ILs with changing properties. It is convincing that promising methodologies are growing for the sustainable society.     

新型肼桥联共价三嗪聚合物在二氧化碳捕集和催化转化方面的应用（英文）

二氧化碳的捕集和催化转化是近年来二氧化碳利用方面的研究热点.其原因,一方面二氧化碳是储量丰富、廉价易得的可再生碳资源,另一方面它又是带来环境问题的温室气体.以金属有机框架、沸石和多孔聚合物材料为代表的同时具有规则孔道和活性催化位点的双功能材料为实践这一新概念创造了条件.但是,金属有机框架和沸石的应用面临由其自身结构所带来的热稳定性和/或水稳定性较低等问题.多孔聚合物材料则由于其高稳定性、低密度以及非金属等优点,逐渐成为该领域的研究重点.然而,当前关于利用多孔聚合物类材料作为有机催化剂以实现二氧化碳固定的报道,其反应过程一般需要较高温度、有机溶剂和/或过渡金属催化组分,仍有较大改进余地.本文设计合成了新型肼桥联共价三嗪聚合物(HB-CTP),意图在利用其富氮三嗪结构单元促进二氧化碳捕集的同时,以大量肼官能团通过氢键作用活化环氧化物,进而将二氧化碳在无溶剂和非金属的温和条件下催化固定为环状碳酸酯.HB-CTP材料的合成方法简便易行,由2,4,6-三肼基-1,3,5-三嗪与三聚氯氰发生的亲核取代反应制得.采用多种表征手段分析了该类新材料的结构和形态:红外光谱表明三聚氯氰的C–Cl键在聚合过程中反应完全,其位于850 cm.1处的吸收信号彻底消失;固体核磁谱图仅在168.1 ppm处显示三嗪环的单峰信号,表明了该材料结构的完整性;X射线粉末衍射测试并未发现特征峰,表明HB-CTP呈无定形态;透射电镜和扫描电镜的观测结果则进一步证实了该材料的团聚形态;最后,热重分析显示HB-CTP具有良好的热稳定性,250 ℃以上才开始分解.然后,通过氮气吸附测定了HB-CTP比表面积(51.2 m~2/g)和总孔容(0.28 cm3/g),其吸附等温线呈Ⅱ型,表明材料结构以大孔为主,通过层间吸附.随后的二氧化碳吸附测试发现,HB-CTP在0°C、0.1 MPa条件下显示出较高的二氧化碳捕集容量(8.2 wt%),并且经过连续吸附脱附循环五次,仍能保持较好的二氧化碳捕集能力.在HB-CTP材料良好的二氧化碳捕集容量基础上,本文考察了其催化活性,发现带有多种取代基的环氧化物均能在无溶剂、非金属的温和条件下,以较高的收率被转化为环状碳酸酯类产物;并且底物结构中的卤素、羟基、炔基、烯丙基和苄基等官能团均未发生副反应,显示出良好的底物适用范围.此外,HB-CTP材料可通过简单的离心操作实现分离回收,且经连续使用五次,其催化活性也没有明显降低.综上所述,该类新型肼桥联共价三嗪聚合物不仅能够高效捕集二氧化碳,而且还可以将其在温和条件下催化转化为环状碳酸酯类产物,具有一定理论研究意义和实际应用价值     

Tuning the physicochemical properties of diverse phenolic ionic liquids for equimolar CO2 capture by the substituent on the anion

Phenolic ionic liquids for the efficient and reversible capture of CO(2) were designed and prepared from phosphonium hydroxide and substituted phenols. The electron-withdrawing or electron-donating ability, position, and number of the substituents on the anion of these ionic liquids were correlated with the physicochemical properties of the ionic liquids. The results show that the stability, viscosity, and CO(2)-capturing ability of these ionic liquids were significantly affected by the substituents. Furthermore, the relationship between the decomposition temperature, the CO(2)-absorption capacity, and the basicity of these ionic liquids was quantitatively correlated and further rationalized by theoretical calculation. Indeed, these ionic liquids showed good stability, high absorption capacity, and low absorption enthalpy for CO(2) capture. This method, which tunes the physicochemical properties by making use of substituent effects in the anion of the ionic liquid, is important for the design of highly efficient and reversible methods for CO(2)-capture. This CO(2) capture process using diverse phenolic ionic liquids is a promising potential method for CO(2) absorption with both high absorption capacity and good reversibility.     

Next steps for solvent-based CO2 capture; integration of capture,conversion, and mineralisation

In this perspective, we detail how solvent-based carbon capture integrated with conversion can be an important element in a net-zero emission economy. Carbon capture and utilization (CCU) is a promising approach for at-scale production of green CO₂-derived fuels, chemicals and materials. The challenge is that CO₂-derived materials and products have yet to reach market competitiveness because costs are significantly higher than those from conventional means. We present here the key to making CO₂-derived products more efficiently and cheaper, integration of solvent-based CO₂ capture and conversion. We present the fundamentals and benefits of integration within a changing energy landscape (i.e., CO₂ from point source emissions transitioning to CO₂ from the atmosphere), and how integration could lead to lower costs and higher efficiency, but more importantly how CO₂ altered in solution can offer new reactive pathways to produce products that cannot be made today. We discuss how solvents are the key to integration, and how solvents can adapt to differing needs for capture, conversion and mineralisation in the near, intermediate and long term. We close with a brief outlook of this emerging field of study, and identify critical needs to achieve success, including establishing a green-premium for fuels, chemicals, and materials produced in this manner.

In this perspective, we detail how solvent-based carbon capture integrated with conversion can be an important element in a net-zero emission economy.     

CO(2) capture by a task-specific ionic liquid

Reaction of 1-butyl imidazole with 3-bromopropylamine hydrobromide, followed by workup and anion exchange, yields a new room temperature ionic liquid incorporating a cation with an appended amine group. The new ionic liquid reacts reversibly with CO2, reversibly sequestering the gas as a carbamate salt. The new ionic liquid, which can be repeatedly recycled in this role, is comparable in efficiency for CO2 capture to commercial amine sequestering reagents, and yet is nonvolatile and does not require water to function.     

Difference for SO2 and CO2 in TGML ionic liquids: a theoretical investigation

Quantum chemical calculations (QM) have been used to investigate the interaction between sulfur dioxide (SO(2)) or carbon dioxide (CO(2)) molecules and ions of 1,1,3,3-tetramethylguanidium (TMG) lactate (LAC) (TMGL) ionic liquid. The QM results give us a deeper understanding of the factors that govern the high solubility of SO(2) in TMGL and the difference in the solubility of SO(2) and CO(2) in TMGL. The predicted geometries and binding energies imply a strong organization of SO(2) about the TMGL components, especially the LAC anion; but indicate a relatively weak organization of CO(2). Both the SO(2) and CO(2) molecules can interact with the TMG cations forming a N-H...O interaction; however, the binding energies demonstrate that the interaction with CO(2) is weaker than that with SO(2). The theoretical results indicate that the oxygen atoms of the LAC anion are the main active sites for the absorption of SO(2). Strong SO interactions are found for both the SO(2)-LAC and SO(2)-TMGL complexes.     

Metal-organic framework supported ionic liquid membranes for CO2 capture: anion effects

IRMOF-1 supported ionic liquid (IL) membranes are investigated for CO(2) capture by atomistic simulation. The ILs consist of identical cation 1-n-butyl-3-methylimidazolium [BMIM](+), but four different anions, namely hexafluorophosphate [PF(6)](-), tetrafluoroborate [BF(4)](-), bis(trifluoromethylsulfonyl)imide [Tf(2)N](-), and thiocyanate [SCN](-). As compared with the cation, the anion has a stronger interaction with IRMOF-1 and a more ordered structure in IRMOF-1. The small anions [PF(6)](-), [BF(4)](-), and [SCN](-) prefer to locate near to the metal-cluster, particularly the quasi-spherical [PF(6)](-) and [BF(4)](-). In contrast, the bulky and chain-like [BMIM](+) and [Tf(2)N](-) reside near the phenyl ring. Among the four anions, [Tf(2)N](-) has the weakest interaction with IRMOF-1 and thus the strongest interaction with [BMIM](+). With increasing the weight ratio of IL to IRMOF-1 (W(IL/IRMOF-1)), the selectivity of CO(2)/N(2) at infinite dilution is enhanced. At a given W(IL/IRMOF-1), the selectivity increases as [Tf(2)N](-) < [PF(6)](-) < [BF(4)](-) < [SCN](-). This hierarchy is predicted by the COSMO-RS method, and largely follows the order of binding energy between CO(2) and anion estimated by ab initio calculation. In the [BMIM][SCN]/IRMOF-1 membrane with W(IL/IRMOF-1) = 1, [SCN](-) is identified to be the most favorable site for CO(2) adsorption. [BMIM][SCN]/IRMOF-1 outperforms polymer membranes and polymer-supported ILs in CO(2) permeability, and its performance surpasses Robeson's upper bound. This simulation study reveals that the anion has strong effects on the microscopic properties of ILs and suggests that MOF-supported ILs are potentially intriguing for CO(2) capture.