CO2/离子液体混合物相平衡的研究进展

离子液体对二氧化碳有良好的溶解性能,可以实现二氧化碳的固定与转化。超临界二氧化碳可以从离子液体/有机物体系中选择性萃取有机物,避免相间的交叉污染,实现离子液体的回收。从CO2在离子液体中的溶解度实验测定方法、CO2/离子液体二元体系高压相平衡测定、SC-CO2/离子液体/有机物的三元体系相平衡研究以及模型预测四个方面介绍了CO2/离子液体体系相平衡研究的最近进展,分析了这一研究领域的发展方向。     

Synthesizing cyclic carbonates from olefin oxides and carbon dioxide. I: Catalysis with ionic liquids

A review of catalytic systems based on ionic liquids used for promoting reactions between olefin oxides and carbon dioxide is presented. It is shown that ionic liquids based on imidazoles, pyridines, quaternary ammonium salts, and other compounds exhibit high activity in these processes and can serve as alternatives to conventional catalysts of cyclocarboxylation of olefin oxides under certain conditions. Specific features of the reactions between oxiranes and carbon dioxide in the presence of ionic liquids are considered, including reactions with the use of promoting additions based on metal salts. Mechanisms of the catalytic action of ionic liquids in syntheses of cyclocarbonates are described. Other works are critically analyzed to develop new lines in the catalysis of cyclocarboxylations of olefin oxides with ionic liquids.     

Binary mixtures of HMIMPF6 ionic liquid and n-butyl acetate cosolvent in the extraction of acetone from aqueous solutions

A remarkable disadvantage of pure ionic liquids, to be used as a solvent in different processes, is their high viscosity and density. Here, n-butyl acetate was used as a cosolvent in the liquid–liquid system of {water?+?acetone?+?1-hexyl-3-methylimidazolium hexafluorophosphate (HMIMPF₆) ionic liquid}. Mixtures of the ionic liquid and the cosolvent were used as the organic phase to extract acetone from aqueous phase. A drastic decrease in viscosity and a significant decrease in density of the ionic liquid were achieved in the presence of cosolvent. Accordingly, the liquid–liquid equilibrium of different provided systems was studied under temperature of 298.2?K and atmospheric pressure of 81.5?kPa. Binary phase regions and corresponding tie-lines and binodal curves were obtained for ternary and quaternary systems. Results show the extension of the binodal solubility region as well as enhancements up to 41.8% in the acetone separation factor. The tie-line data consistency was confirmed by the Othmer–Tobias and the Hand equations. Moreover, the nonrandom two-liquid model of activity coefficient was applied satisfactorily to reproduce the equilibrium data with a root-mean-square deviation of only 1.95%.     

离子液体中二氧化碳的溶解度研究进展

室温离子液体具有独特的气体选择溶解性,在二氧化碳(CO2)的捕集和分离中有很好的应用前景。综述了近年来CO2在不同离子液体中的溶解度研究进展,比较了CO2在常规离子液体和功能型离子液体中的不同溶解机制,分析、归纳了向离子液体中引入不同官能团对CO2溶解性能的影响规律,指出了离子液体捕集CO2的未来研究方向。     

Diffusion coefficients and phase equilibria of carbon dioxide–ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) system

This article presents the mutual diffusion coefficients of a carbon dioxide–ionic liquid, [bmim][PF₆], system at temperatures of 313.15 and 323.15 K and pressures of 5 and 8 MPa. In order to estimate the diffusion coefficients, we have carried out experiments to find time-dependent carbon dioxide solubilities in the ionic liquid and then fit a transport model to the data. In a system containing high pressure carbon dioxide and ionic liquid, carbon dioxide dissolves in the liquid until its equilibrium mole fraction is reached. During this process, the position of the liquid–vapour interface and the density of the liquid phase change. To account for the variation in liquid density, an equation fit to the experimental density data is included in the transport model. To track the moving interface, the volume-of-fluid method is used. The diffusivities at dilute concentration and at thermodynamic phase equilibrium are determined and compared with the literature values and those obtained from correlations.     

The effect of [bmim][Br] on the solubility of carbon dioxide and methane in glycols at pressures up to 14 MPa and temperatures ranging from 303 to 423 K

Solubility data of methane in ethylene glycol and 1-4 butylene glycol and carbon dioxide in ethylene glycol and 1-2 propylene glycol in the presence of the ionic liquid 1-butyl-3-methylimidazolium bromide have been measured in the temperature range (303–423) K at pressures up to 14 MPa. Henry's law constant of each solute in the studied solvent at saturation pressure is given. The experiments were performed in an autoclave type phase equilibrium apparatus using the total pressure method. For mixtures containing carbon dioxide and ethylene glycol no influence was observed. For mixtures containing carbon dioxide and 1-2 propylene glycol it was observed salting-out effect at 303.2 K and 323.2 K and salting-in effect at the remaining temperatures. For mixtures containing methane and ethylene glycol or 1-4 butylene glycol salting-in effect was observed.     

Phase behavior of mixtures of ionic liquids and organic solvents

A corresponding-states form of the generalized van der Waals equation, previously developed for mixtures of an ionic liquid and a supercritical solute, is here extended to mixtures including an ionic liquid and a solvent (water or organic). Group contributions to characteristic parameters are implemented, leading to an entirely predictive method for densities of mixed compressed ionic liquids. Quantitative agreement with experimental data is obtained over wide ranges of conditions. Previously, the method has been applied to solubilities of sparingly soluble gases in ionic liquids and in organic solvents. Here we show results for heavier and more-than-sparingly solutes such as carbon dioxide and propane in ionic liquids.     

Biocatalytic ester synthesis in ionic liquid media

Ionic liquids have shown potential as green reaction media compared with organic solvents, mainly due to their lack of vapour pressure. In non‐aqueous enzymology, ionic liquids are opening up new fields. The advantages of using ionic liquids over the use of organic solvents as reaction medium for biocatalysis include enhancement of enzyme activity, stability and selectivity. In this work, the enzymatic synthesis of esters in ionic liquids has been extensively reviewed. Numerous examples of the application of ionic liquids as reaction medium for the enzymatic production of esters have been included. The effect of the nature of the ionic liquid on activity, selectivity and stability of enzymes which catalyze esters synthesis has been carefully analysed. Innovative reaction methodologies for the biosynthesis of esters, including ionic liquid/supercritical carbon dioxide biphasic systems and the integrated reaction/separation processes using supported liquid membranes based on ionic liquids have been revised. Copyright © 2010 Society of Chemical Industry     

Cycloaddition of carbon dioxide to butyl glycidyl ether using imidazolium salt ionic liquid as a catalyst

The catalytic performance of imidazolium salt ionic liquids in the cycloaddition of carbon dioxide to butyl glycidyl ether (BGE) was investigated. The catalytic activity was tested with different imidazolium salt ionic liquids at 60–140 °C under 0.62–2.17 MPa of CO₂ pressure. The imidazolium salt ionic liquid with the cation of bulkier alkyl chain length and with more nucleophilic anion showed higher conversion of BGE. High carbon dioxide pressure and high reaction temperature up to 140 °C was favorable for the high reactivity of the catalyst. The presence of zinc bromide co-catalyst enhanced the reactivity of the imidazolium salt ionic liquid. Kinetic studies with a semi-batch reactor revealed that the reaction could be considered as first order with respect to the concentration of BGE, and the activation energy was estimated as 22.6 and 22.8 kJ/mol for 1-ethyl-3-methylimidazolium chloride (EMImCl) and 1-butyl-3-methylimidazolium chloride (BMImCl), respectively.     

Lewis Basic Ionic Liquids‐Catalyzed Conversion of Carbon Dioxide to Cyclic Carbonates

A series of easily prepared Lewis basic ionic liquids were developed for cyclic carbonate synthesis from epoxide and carbon dioxide at low pressure without utilization of any organic solvents or additives. Notably, quantitative yields together with excellent selectivity were attained when 1,8‐diazabicyclo[5.4.0]undec‐7‐enium chloride ([HDBU]Cl) was used as a catalyst. Furthermore, the catalyst could be recycled over five times without appreciable loss of catalytic activity. The effects of the catalyst structure and various reaction parameters on the catalytic performance were investigated in detail. This protocol was found to be applicable to a variety of epoxides producing the corresponding cyclic carbonates in high yields and selectivity. Therefore, this solvent‐free process thus represents an environmentally friendly example for the catalytic conversion of carbon dioxide into value‐added chemicals by employing Lewis basic ionic liquids as catalyst. A possible catalytic cycle for the hydrogen bond‐assisted ring‐opening of epoxide and activation of carbon dioxide induced by the nucleophilic tertiary nitrogen of the ionic liquid was also proposed.     

Solubility of carbon dioxide in ammonium-based ionic liquids: Butyltrimethylammonium bis(trifluoromethylsulfonyl)imide and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide

Solubility results of carbon dioxide (CO₂) in two ammonium-based ionic liquids, butyltrimethylammonium bis(trifluoromethylsulfonyl)imide ([N4,1,1,1][Tf₂N]) and methyltrioctylammonium bis(trifluoromethylsulfonyl)imide ([N1,8,8,8][Tf₂N]), are presented at pressures up to approximately 45 MPa and temperatures ranging from 303.15 K to 343.15 K. The solubility was determined by measuring bubble point pressures of mixtures of CO₂ and ionic liquid using a high-pressure equilibrium apparatus equipped with a variable-volume view cell. Sharp increase of equilibrium pressure was observed at high CO₂ compositions. The CO₂ solubility in ionic liquids increased with the increase of the total length of alkyl chains attached to the ammonium cation of the ionic liquids. The experimental data for the CO₂+ionic liquid systems were correlated using the Peng-Robinson equation of state.     

Solubility of supercritical gases in organic liquids

Chrastil (1982) [6] demonstrated that the solubility of a substance in a supercritical fluid (SCF) can be correlated with the density of the pure supercritical gas. Therefore, Chrastil's equation permits calculation of the supercritical phase composition of binary SCF + substance mixture based on the knowledge of the supercritical gas density and avoiding the use of equation of state based models.In this work, it is demonstrated that the supercritical fluid density also defines the liquid phase composition of binary systems; a density-dependent relationship is presented to calculate the solubility of supercritical gases in organic liquids. The isothermal solubility of several gases commonly employed in supercritical processing, such as carbon dioxide, methane, and ethane, in different organic liquids, including alkanes, alkenes, alcohols, acids, ketones, esters, terpenes and aromatic compounds, was successfully correlated as a function solely of the pure supercritical fluid density. As an application, pressure vs. composition phase diagrams of binary SCF + substance mixtures were obtained circumventing the use of equation of state models.     

Theoretical pressure dependency of carbon dioxide solubility under hydrate–liquid water equilibrium

The effect of pressure on carbon dioxide solubility in water is significantly smaller than that of temperature under hydrate–liquid water (H–L_w) equilibrium. As a result, experimental values of carbon dioxide solubility in the water rich liquid phase under H–L_w equilibrium are often inconclusive and in some cases contradictory. This work proposes a theoretical derivation, based on fundamental thermodynamics, of the gas hydrate former solubility dependency on pressure for any binary system under two‐phase equilibrium. The obtained expression is applied to the carbon dioxide–water system under both hydrate–liquid water and vapour–liquid water equilibrium. It is shown that the solubility of carbon dioxide in the water rich liquid phase increases with increasing pressure under H–L_w equilibrium. The predicted trend is then compared to the limited experimental data available in the literature.     

Purification of flue gas by ionic liquids: Carbon monoxide capture in [bmim][Tf2N]

Knowledge of the solubility of carbon monoxide in ionic liquids is important for investigating the potential use of ionic liquids in reactions and gas separations. There is very limited information available on the capacity of ionic liquids to capture CO. The solubility of CO in 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was investigated experimentally up to temperatures and pressures of 460 K and 10 MPa, respectively. The solubility was shown to be only slightly temperature‐dependent, and the P–T diagram for a constant composition mixture is concave‐downward with a peak in pressure. By comparing the single‐gas solubility results of CO with various other gases in the same ionic liquid, it seems that ionic liquids can potentially be used as gas‐separating media. However, although the single‐gas solubilities vary considerably among some gases, further studies on mixed (multicomponent) gases should be carried out as the presence of other components can influence the solubility of each gas component. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3886–3891, 2013     

Phase behavior measurement for the ethylene glycol dimethacrylate in supercritical carbon dioxide at temperatures between (313.2 and 393.2) K and pressures from (5.8 to 22) MPa

High pressure experimental data are presented on the phase equilibrium of ethylene glycol dimethacrylate in supercritical carbon dioxide. Pressure-composition (P-x) isotherms were measured in static method at five temperatures of (313.2, 333.2, 353.2, 373.2 and 393.2) K and at pressures up to 22.0MPa. This (carbon dioxide+ethylene glycol dimethacrylate) system has continuous critical mixture curves that exhibit maximums in pressure at temperatures between the critical temperatures of carbon dioxide and ethylene glycol dimethacrylate. At a fixed pressure, the solubility of ethylene glycol dimethacrylate for the (carbon dioxide+ethylene glycol dimethacrylate) system increases with increasing temperature. The (carbon dioxide+ethylene glycol dimethacrylate) system exhibits type-I phase behavior. The experimental result for the (carbon dioxide+ethylene glycol dimethacrylate) system is correlated with Peng-Robinson equation of state using mixing rule including two adjustable parameters. The critical property of ethylene glycol dimethacrylate is predicted with Joback and Lee-Kesler method.     

High-pressure phase behavior of carbon dioxide in ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

Phase equilibrium data of carbon dioxide in the ionic liquid 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]) are presented at high pressures up to about 30 MPa and at temperatures between 298.15 K and 343.15 K. The solubilities at a given temperature were determined by measuring the bubble point pressure of the ionic liquid solution with carbon dioxide dissolved using the high-pressure equilibrium apparatus equipped with a variable-volume view cell. Solubility results are reported for carbon dioxide concentrations ranging from 0.21 up to 0.80 mole fraction. Carbon dioxide gave very high solubilities in the ionic liquid at lower pressures, while the equilibrium pressure increased very steeply at higher concentrations of carbon dioxide. The solubility of carbon dioxide in the ionic liquid decreased with an increase in temperature.     

Thermodynamic analysis of absorption refrigeration cycles using ionic liquid + supercritical CO2 pairs

Absorption refrigerators are alternative systems to conventional compression cycles in which the energy necessary for the refrigeration is provided by heating instead of mechanical power. Commercial absorption refrigerators use two absorbent/refrigerant pairs: NH₃-H₂O and H₂O-LiBr. These systems have some limitations due to the difficulty of separating absorbent and refrigerant, the narrow refrigeration temperature range, or the possibility of corrosion and salt deposition. The application of ionic liquids as absorbents with supercritical carbon dioxide as refrigerant can solve some of these problems because separation of ionic liquid from CO₂ is easy due to the negligible vapor pressure of ionic liquids. In this work, suitable ionic liquids-CO₂ pairs have been selected considering their phase equilibrium properties, calculated with the Group-Contribution equation of state developed by Skjold-Jørgensen. The energetic efficiency of the process with ionic liquids has been estimated by calculation of the Coefficient of Performance (COP) of the process. It has been found that the process with ionic liquids has a lower COP than conventional NH₃-H₂O systems due to the necessity of operating with a higher solution flowrate. Nevertheless, near-optimum performance is obtained in a wide range of process conditions.     

High pressure solubility of CO2 in non-fluorinated phosphonium-based ionic liquids

High pressure solubility of carbon dioxide in three phosphonium-based ionic liquids has been measured experimentally. A synthetic method was used to measure vapor–liquid, vapor–liquid–liquid and liquid–liquid equilibria of carbon dioxide in the ionic liquids trihexyltetradecylphosphonium bromide [thtdp][Br], trihexyltetradecylphosphonium dicyanamide [thtdp][dca] and trihexyltetradecylphosphonium bis(2,4,4-trime-thylpentyl)phosphinate [thtdp][phos] for a temperature range of 271–363 K and up to 90 MPa. Furthermore, the densities and viscosities of these ILs have been measured in a temperature range of 293–363 K. The solubility of carbon dioxide in these ILs is (on mole fraction basis) significantly larger than most of the commonly used fluorinated imidazolium ionic liquids. The latter statement, however, does not hold for the [Br] and [dca] based IL if the solubility is compared on molality (mole/mass solvent) basis, where the solubility differences among physical ILs tends to vanish indicating a strong molecular weight effect. The solubility of carbon dioxide in [thtdp][phos], both on mole fraction and molality basis, is among the highest compared to all the other physical ILs reported so far in the literature. The Peng–Robinson equation of state in combination with Wong–Sandler mixing rules incorporating the NRTL Gibbs excess energy model was applied to represent the experimental data with acceptable accuracy.     

Solubility of CO2, CH4, C2H6, C2H4, O2, and N2 in 1-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide: comparison to other ionic liquids

The solubilities of gases in ionic liquids are important in evaluating ionic liquids as solvents for reactions involving permanent gases, as gas storage media, and as solvents for gas separations. Gas solubilities are also important in developing methods to separate solutes from ionic liquid solutions. Here we describe our measurements of the solubilities of CO2, CH4, C2H 6, C2H 4, O2, and N2 in 1-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide and compare these results to our previous investigations. In addition, focus is placed on efforts to tailor ionic liquids to enhance the solubilities of some gases, with particular emphasis on carbon dioxide.     

离子液体在有机合成和分析化学中的应用研究进展

离子液体目前已在有机合成化学、电化学、分析化学等领域得到广泛的应用。主要介绍离子液体在有机合成化学和分析化学领域的最新研究进展。