离子液体中电化学还原CO2研究评述与展望

近百年来,伴随着矿石燃料的大量消耗,CO₂的排放量剧增,引发了全球性的生态环境和社会问题。CO₂同时也是廉价且可再生的碳资源,可作为生产醇、醚、酸、酯等重要化工品的原料。在众多吸引力十足的CO₂利用路线中,作为清洁、可控的反应过程,电化学还原固定CO₂技术在温和条件下生产化学品方面具有独特的优势。离子液体以其特有的性质被广泛用于电化学还原CO₂过程,本文对目前国内外离子液体介质中电化学还原CO₂的研究现状进行了综述,介绍了离子液体介质中电化学还原CO₂的主要反应及基本原理;针对离子液体对CO₂高效活化和转化等关键科学问题进行深入探讨,提出新型功能化离子液体的应用将成为CO₂电化学还原领域的发展方向和热点。     

碱性离子液体-NaOH/MEA混合体系的CO2吸收性能

为了改善有机醇胺与无机碱液对生物质燃气中CO2的吸收性能,制备了具有代表性的4种功能化离子液体:[TMG]+ [C3H4N2]-、[TMG]+[TFEA]-、[MEA]+[BF4]-、[MEA]+[CHOO]-,并按一定的比例分别与NaOH溶液和乙醇胺(MEA)溶液复配组成新型CO2吸收剂,以研究其对CO2的吸收特性.实验结果显示,MEA-[TMG]+[C3H4N2]-、MEA-[MEA]+[CHOO]-和NaOH-[MEA]+[CHOO]-对CO2的吸收去除率高于单纯的MEA和NaOH溶液,而MEA-[TMG]+[TFEA]-、MEA-[MEA]+[BF4]-和NaOH-[MEA]+[BF4]-对CO2的去除率则低于单纯碱液吸收剂.同时发现,当离子液体[MEA]+[CHOO]-与MEA的混合比例为2∶3时,混合溶剂对CO2的吸收效果比MEA溶液的显著提高,生物质燃气中CO2去除率从91.3％增加至95.7％.     

Enhanced gravimetric CO2 capacity and viscosity for ionic liquids with cyanopyrrolide anion

Ionic Liquids (ILs) are considered as alternative solvents for the separation of CO₂ from flue gas due mainly to their CO₂ affinity and thermal stability. The cation architecture in a matrix of ammonium and mostly phosphonium‐based ILs with 2‐cyanopyrrolide as the anion to evaluate its impact on gravimetric CO₂ absorption capacity, viscosity, and thermal stability and the three fundamental properties vital for application realization are systematically investigated. Among the investigated ILs, [P2,2,2,8][2‐CNpyr] demonstrated the lowest viscosity, 95 cP at 40°C, and highest CO₂ uptake, 114 mg CO₂ per g IL at 40°C. Combined effects of asymmetry and the optimized chain lengths also resulted in improved thermal stability for [P2,2,2,8][2‐CNpyr], with a mass loss rate of 1.35 × 10^?6 g h^?1 (0.0067 mass % h^?1) at 80°C. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2280–2285, 2015     

Design and construction of an equipment for the determination of solubility of gases in liquids

This article presents the design and construction of a new isochoric saturation apparatus for the determination of gas solubility in liquids based on the gas drop pressure method. The major improvement of this design is the separation between the solubility and the gas cells. With this separation, the change of pressure and temperature inside the system is minimum when the gas gets in contact with the liquid and it allows degassing the liquid in an easy way. The performance of the equipment was evaluated measuring the solubility of argon and nitrogen in pure water at 283.15, 288.15, 293.15, and 298.15 K. The gas solubility was calculated according to the Henry's law. The results obtained and the comparison with literature values show that the equipment provides an accurate and precise method for determination of gas solubility in water. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3105–3109, 2017     

Screening ionic liquids as candidates for separation of acid gases: Solubility of hydrogen sulfide,methane, and ethane

The solubility of the major constituents of natural gas in ionic liquids (ILs) can be used to identify their potential for acid gas removal from a producing gas stream. We have developed models for the solubility of H₂S, CH₄, and C₂H₆ in ILs at typical conditions encountered in natural gas treatment. In this work, a conductor‐like screening model for realistic solvation was used to predict the activity coefficients for solutes in ILs and a cubic EOS was used for vapor‐phase corrections from ideality. Empirical correlations were developed to extrapolate solubilities where experimental data are not available at desired conditions; targeted in this study at 298.15 K and 2000 kPa. Over 400 possible ILs were ranked based on the higher selectivity of absorption of CO₂ and H₂S over CH₄ and C₂H₆. The best 15% (58) of promising ILs for sour gas treatment predominantly contain the anions BF₄, NO₃, and CH₃SO₄ and the cations N₄₁₁₁, pmg, and tmg. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2993–3005, 2013     

Solubility of propane in N-formyl morpholine

N-formyl morpholine (NFM) is a solvent that has been used to separate acid gases from gas streams. An advantage of NFM is the high solubility of acid gases compared with the low solubility of light hydrocarbons. The solubility of the light hydrocarbons in NFM is important, as the hydrocarbons constitute a loss to the process, and result in hydrocarbon emissions to the atmosphere. However, there are only a few experimental data sets dealing with the solubility of hydrocarbons in NFM. To provide data to be used in the design of plants in the natural gas processing industry, the solubility of propane (C₃H₈) in NFM was measured at 298.15, 313.15, and 343.15 K at pressures up to 20.15 MPa. The Peng-Robinson equation of state was employed to correlate the experimental data and to obtain binary interaction parameters. The binary interaction parameters were used to obtain the parameters of the Krichevsky-Ilinskaya equation and Henry's law constants for propane were calculated. Henry's law constants for propane were compared with those of hydrogen sulphide, carbon dioxide, methane, and ethane in NFM.     

Promoted adsorption of CO2 on amine‐impregnated adsorbents by functionalized ionic liquids

Amine‐impregnated adsorbents are promising alternatives to aqueous amines for CO₂ capture. However, the diffusion‐controlled CO₂ adsorption process is a significant issue associated with them, resulting in the insufficient utilization of amine groups. Herein, we propose the use of functionalized ionic liquids 1‐ethyl‐3‐methylimidazolium acetate ([emim][Ac]) with chemical reactivity to CO₂ and low viscosity as the additive to amine‐impregnated adsorbents. The key is that [emim][Ac] does not show drastic increase in viscosity after reacting with CO₂. Taking the polyethyleneimine (PEI)‐impregnated SBA‐15 as a model system, it is found that the CO₂ capacities of PEI/SBA‐15 composites are improved by 86%, and the active site efficiencies are improved by 270%, after the addition of [emim][Ac]. The addition of [emim][Ac] to PEI/SBA‐15 composites also helps improve the CO₂ adsorption rate and recycling stability of composites. Therefore, [emim][Ac] offers the opportunity to fabricate amine‐impregnated adsorbents with simultaneously improved CO₂ capacities, adsorption kinetics, and recycling stability. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3671–3680, 2018     

聚离子液体二氧化碳分离膜材料的研究进展

近年来,全球二氧化碳排放超过370亿吨/年,对气候和自然环境造成严重影响,亟需发展碳捕集、利用与封存技术。气体膜分离是一种条件温和、操作简单的无相变分离技术,随着高渗透性、高选择性膜材料的不断涌现,逐渐成为全球碳捕集技术的主要发展方向。聚离子液体膜材料中含有大量高度亲和二氧化碳的功能基团,有望实现超高渗透选择性,被誉为下一代气体分离膜材料。综述了聚离子液体膜材料的研究进展,以渗透机制为主线重点介绍了面向碳捕集的阳离子型聚离子液体膜材料(主链型和支链型)的设计合成,包括阳离子和阴离子基团的选择,合成途径的选择,以及聚离子液体膜的结构设计优化。讨论了聚离子液体作为二氧化碳分离膜材料的优势和面临的挑战。     

Solubility of N2O and CO2 in n-Dodecane

The solubility of CO₂ and N₂O in a physical solvent, n-dodecane [C.A. Registry N° 124–18–5], has been measured at 40, 80 and 120°C at pressures up to 9.6 MPa. The experimental results were correlated by the Peng-Robinson (1976) equation of state, and the interaction parameters, the Henry's constants and the N₂O analogy parameters were obtained.     

Efficient capture of CO2 from flue gas at high temperature by tunable polyamine-based hybrid ionic liquids

For an ideal absorbent for CO₂ capture from flue gas, there are some key features including easy preparation, high stability, low absorption enthalpy, high capacity at high temperature and excellent reversibility. Herein, several polyamine-functionalized ionic liquids (ILs) were easily prepared from cheap polyamines and lithium salts, which exhibited significantly improved stability due to the presence of multisite coordinating interactions. The viscosity was reduced by introducing polyalcohol-based ILs, leading to polyamine-based hybrid ILs. Interestingly, these polyamine-based hybrid ILs exhibited high CO₂ capacity (4.09 mmol/g, 0.1 bar) at high temperature (80°C) and excellent reversibility in the presence of H₂O and O₂, which is superior to many other good absorbents. Moreover, these ILs also showed good performance for CO₂ capture from stimulated air (2.10 mmol/g, 380 ppm). We believe that this method with easy preparation, low cost, high efficiency and excellent reversibility has a great potential in the industrial capture of CO₂ from flue gas.     

Solubility of CO2 in Methanol, 1-Octyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide, and Their Mixtures

Solubility data of carbon dioxide (CO₂) (1) in methanol (2), 1-octyl-3-methylimidazolium bis(trifluoro- methylsulfonyl)imide ([omim]⁺[Tf₂N]^-) (3), and their mixtures (w₃ 0.2, 0.5, and 0.8) at temperatures 313.2 and 333.2 K and pressures up to 7.0 MPa were measured by a high-pressure view-cell technique. The solubility of CO₂ in methanol (w₃=0), [omim]⁺[Tf₂N]^- (w₃=1.0) and their mixtures follows the order of (w₃=0)<(w₃=0.2)< (w₃=0.5)<(w₃=0.8)<(w₃=1.0) at the same temperature and pressure, while the magnitude of Henry's constants follows the reverse order at a given temperature, which is consistent with the COSMO-RS (conductor-like screening for real solvents) calculation. The solubility data of CO₂ in methanol and [omim]⁺[Tf₂N]^- are correlated with the Peng-Robinson equation of state, and the solubility of CO₂ in the mixtures of methanol and [omim]⁺[Tf₂N]^- can be well predicted based on the mole fraction average of methanol and [omim]⁺[Tf₂N]^- over the solubility of CO₂ in pure methanol and [omim]⁺[Tf₂N]^-. The mixtures of methanol and [omim]⁺[Tf2N]^- may be used as physical solvents for capturing CO₂ with high partial pressures since they combine the advantages of organic solvents and ionic liquids.     

Mass‐transfer rate enhancement for CO2 separation by ionic liquids: Theoretical study on the mechanism

To promote the development of ionic liquid (IL) immobilized sorbents and supported IL membranes (SILMs) for CO₂ separation, the kinetics of CO₂ absorption/desorption in IL immobilized sorbents was studied using a novel method based on nonequilibrium thermodynamics. It shows that the apparent chemical‐potential‐based mass‐transfer coefficients of CO₂ were in three regions with three‐order difference in magnitude for the IL‐film thicknesses in microscale, 100 nm‐scale, and 10 nm‐scale. Using a diffusion‐reaction theory, it is found that by tailoring the IL‐film thickness from microscale to nanoscale, the process was altered from diffusion‐control to reaction‐control, revealing the inherent mechanism for the dramatic rate enhancement. The extension to SILMs shows that the significant improvement of CO₂ flux can be obtained theoretically for the membranes with nanoscale IL‐films, which makes it feasible to implement CO₂ separation by ILs with low investment cost. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4437–4444, 2015     

Designing amino-based ionic liquids for improved carbon capture: One amine binds two CO2

Generally, amine group captures CO₂ according to 2:1 or 1:1 stoichiometry. Here, we report a kind of improved carbon capture using amino-functionalized ionic liquids (ILs) through 1:2 stoichiometry. A serial of amino-functionalized ILs various with basicity and steric hindrance of anion were designed, prepared, and applied in CO₂ capture. Through a combination of absorption experiment, quantum chemical calculation, spectroscopic investigation and calorimetric method, the results indicated that one amine group could bind two CO₂ through proton transfer (PT) process and intramolecular hydrogen bond formation, which leading to enhanced capacity that breaks through equimolar. The basicity and steric hindrance of anion play a significant role in promoting amine group to capture two CO₂. [P₆₆₆₁₄]₂[Asp] with dual anion was further designed and synthesized to promote PT process, which showed high capacity of 1.96 mol/mol IL at 30°C and 1 atm as well as excellent reversibility. © 2018 American Institute of Chemical Engineers AIChE J, 65: 230–238, 2019     

Hydrophobic protic ionic liquids tethered with tertiary amine group for highly efficient and selective absorption of H2S from CO2

Developing absorbents with both high absorption capacity of H₂S and large selectivity of H₂S/CO₂ is very important for natural gas sweetening process. To this end, a class of novel hydrophobic protic ionic liquids (ILs) containing free tertiary amine group as functional site for the absorption of H₂S were designed in this work. They were facilely synthesized through a simple neutralization‐metathesis methodology by utilizing diamine compounds and bis(trifluoromethylsulfonyl)imide as the building blocks for cation and anion, respectively. Impressively, the solubility of H₂S can reach 0.546 mol mol^?1 (1 bar) and 0.225 mol mol^?1 (0.1 bar), and the selectivity of H₂S/CO₂ can reach 37.2 (H₂S solubility at 1 bar vs. CO₂ solubility at 1 bar) and 15.4 (H₂S solubility at 0.1 bar vs. CO₂ solubility at 1 bar) in the hydrophobic protic ILs at 298.2 K. Comparing the hydrophobic protic ILs with other absorbents justifies their superior performance in the selective absorption of H₂S from CO₂. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4480–4490, 2016     

固定分离CO2离子液体的合成进展

因具有性质稳定、无挥发、CO2溶解能力强、产物易于分离、循环使用性高等特点,离子液体可望替代传统有机吸收剂用于气相CO2的固定分离.在简述其应用概况的基础上,主要综述了近期国内外此类离子液体(主要分为常规型和功能型两种)的合成方法的研究进展,并对功能型离子液体和相关材料的绿色合成方向进行了展望.     

负载型离子液体吸附分离CO2的研究现状及展望

人口增长与全球工业化的加速发展促使化石能源需求量逐年递增,由此导致大气中二氧化碳（CO₂）含量快速上升并引发了全球系列气候问题,“碳达峰·碳中和”背景下的CO₂减排刻不容缓。传统工业捕集CO₂方法由于能耗高、选择性较差、溶剂损耗大等问题限制了其大规模推广应用,离子液体因其极低挥发性、强的气体亲和性、可调的结构性质等特点在CO₂捕集分离领域逐渐显示出独特优势,但离子液体特别是功能化后通常黏度较高或室温呈固态,导致气液传质效果差或无法直接应用于吸收分离过程。负载型离子液体兼具离子液体和多孔材料的共同优势,不仅能提升选择性分离效果,有效避免离子液体直接吸收造成的高黏度,还可拓展离子液体应用范围,具有广阔的发展前景。重点总结了近些年物理和化学负载型离子液体在CO₂吸附分离方面的研究现状和进展,并对负载型离子液体捕集分离CO₂研究的发展趋势进行了展望。     

Protic ionic liquids for the selective absorption of H2S from CO2: Thermodynamic analysis

The solubilities of H₂S and CO₂ in four protic ionic liquids (PILs)—methyldiethanolammonium acetate, methyldiethanolammonium formate, dimethylethanolammonium acetate, and dimethylethanolammonium formate were determined at 303.2–333.2 K and 0–1.2 bar. It is shown PILs have higher absorption capacity for H₂S than normal ionic liquids (ILs) and the Henry's law constants of H₂S in PILs (3.5–11.5 bar at 303.2 K) are much lower than those in normal ILs. In contrast, the solubility of CO₂ in PILs is found to be a magnitude lower than that of H₂S, implying these PILs have both higher absorption capacity for H₂S and higher ideal selectivity of H₂S/CO₂ (8.9–19.5 at 303.2 K) in comparison with normal ILs. The behavior of H₂S and CO₂ absorption in PILs is further demonstrated based on thermodynamic analysis. The results illustrate that PILs are a kind of promising absorbents for the selective separation of H₂S/CO₂ and believed to have potential use in gas sweetening. © 2014 American Institute of Chemical Engineers AIChE J 60: 4232–4240, 2014     

离子液体吸收CO2的研究进展

CO2的捕集、分离与利用已成为人类共同关心的重要课题。工业上,通常使用传统的有机胺水溶液或热钾碱溶液等脱除CO2。有机胺具有蒸气压,易产生挥发性有机物(VOCs)对环境造成污染;热钾碱溶液等脱除CO2需要较高操作温度因而能耗较高,生产过程经济性有待改善。离子液体具有几乎无蒸气压、热稳定性、结构可设计性等独特优点,在CO2分离领域的巨大应用潜力已成共识。本文结合课题组近期的研究工作,就国内外离子液体吸收CO2的主要研究成果进行综述。