Design and screening of ionic liquids for C2H2/C2H4 separation by COSMO‐RS and experiments

Ionic liquids (ILs) have been proposed as promising solvents for separating C₂H₂ and C₂H₄, but screening an industrially attractive IL with high capacity from numerous available ILs remains challenging. In this work, a rapid screening method based on COSMO‐RS was developed. We also present an efficient strategy to improve the C₂H₂ capacity in ILs together with adequate C₂H₂/C₂H₄ selectivity with the aid of COSMO‐RS. The essence of this strategy is to increase molecular free volume of ILs and simultaneously enhance hydrogen‐bond basicity of anions by introducing flexible and highly asymmetric structures, which is validated by a new class of tetraalkylphosphonium ILs featuring long‐chain carboxylate anions. At 298.1 K and 1 bar, the solubility of C₂H₂ in ILs reaches 0.476 mol/mol IL, very high for a physical absorption, with a selectivity of up to 21.4. The separation performance of tetraalkylphosphonium ILs to the mixture of C₂H₂/C₂H₄ was also evaluated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2016–2027, 2015     

Gas solubility in long‐chain imidazolium‐based ionic liquids

The gas solubility in 1‐dodecyl‐3‐methylimidazolium [C₁₂MIM] based ionic liquids (ILs) was measured at temperatures (333.2, 353.2, and 373.2) K and pressures up to 60 bar for the first time. The popular UNIFAC‐Lei model was successfully extended to long‐chain imidazolium‐based IL and gas (CO₂, CO, and H₂) systems. The free volume theory was used to explain the gas solubility and selectivity in imidazolium‐based ILs by calculating the fractional free volume and free volume by the COSMO‐RS model. Furthermore, the excess enthalpy of gas‐IL system was concerned to provide new insights into temperature dependency of gas (CO₂, CO, and H₂) solubility in ILs. The experimental data, calculation, and theoretical analysis presented in this work are important in gas separations with ILs or supported ionic liquid membranes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1792–1798, 2017     

Aromatic sulfur‐nitrogen extraction using ionic liquids: Experiments and predictions using an a priori model

The tie‐line composition of three quaternary system namely 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][OAc]) ([EMIM][OAc]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium ethylsulphate ([EMIM][EtSO₄]) (1) + thiophene (2) + pyridine (3) + toluene (4), 1‐ethyl‐3‐methylimidazolium methylsulphonate ([EMIM][MeSO₃]) (1) + thiophene (2) + pyridine (3) + toluene (4) were experimentally determined at 298.15 K. The measured tie‐line data were successfully correlated with the nonrandom two liquid and UNIversal QUAsiChemical model prediction which gave less than 1% root mean square deviation (RMSD). [EMIM][MeSO₃] looks to be a promising solvent for the simultaneous separation having distribution ratios less than unity for both thiophene and pyridine. The quantum chemical‐based conductor like screening model for real solvent (COSMO‐RS) model was then used to predict the tie‐line composition of quaternary systems. COSMO‐RS gave the RMSD for the studied systems to be 8.41, 8.74, and 6.53% for the ionic liquids, respectively. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4806–4815, 2013     

Ionic liquids for absorption and separation of gases: An extensive database and a systematic screening method

Ionic liquids (ILs) have attracted considerable attention in both the academic and industrial communities for absorbing and separating gases. However, a data‐rich and well‐structured systematic database has not yet been established, and screening for highly efficient ILs meeting various requirements remains a challenging task. In this study, an extensive database of estimated Henry's law constants of twelve gases in more than ten thousand ILs at 313.15 K is established using the COSMO‐RS method. Based on the database, a new systematic and efficient screening method for IL selection for the absorption and separation of gases subject to important target properties is proposed. Application of the database and the screening method is highlighted through case studies involving two important gases separation problems (CO₂ from CH₄ and C₂H₂ from C₂H₄). The results demonstrate the effectiveness of using the screening method together with the database to explore and screen novel ILs meeting specific requirements for the absorption and separation of gases. © 2017 American Institute of Chemical Engineers AIChE J, 63: 1353–1367, 2017     

Quantum chemical studies on the simultaneous interaction of thiophene and pyridine with ionic liquid

The simultaneous interaction of thiophene and pyridine with different ionic liquids:1‐butyl‐1‐methylpyrrolidinium tetrafluoroborate([BPYRO][BF₄]),1‐butyl‐1‐methylpyrrolidinium hexafluoro‐phosphate ([BPYRO][PF₆]), 1‐butyl‐4‐methylpyridinium tetrafluoroborate ([BPY][BF₄]), 1‐butyl‐4‐methylpyridinium hexafluorophosphate ([BPY][PF₆]) and 1‐benzyl‐3‐methylimidazolium tetrafluoroborate ([BeMIM][BF₄]) were investigated using quantum chemical calculations. A three‐tier approach comprising of partial charges, interaction energies and sigma profile generation using conductor‐like screening model for real solvents (COSMO‐RS) was chosen to study the systems. A quantitative attempt based on the CH‐π interaction in ionic liquid; thiophene–pyridine complexes gave the interaction energies of ILs in the order: [BPY][BF₄] > [BPYRO][PF₆] > [BeMIM][BF₄] > [BPY][PF₆] > [BPYRO][BF₄]. An inverse relation was observed between the activity coefficient at infinite dilution predicted via COSMO‐RS–based model and interaction energies. The dominance of CH‐π interaction was evident from the sigma profiles of ionic liquid together with thiophene and pyridine. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

A molecular design method based on the COSMO‐SAC model for solvent selection in ionic liquid extractive distillation

In this study, a molecular design method was used to select solvents for extractive distillation. A COSMO‐SAC model was used to screen for prospective solvents from a wide variety of ionic liquids for extractive distillation. Based on the COSMO‐SAC model, the σ‐profile database of ILs was established. Selectivity and solubility were used as the indexes for solvent screening. According to the molecular design method, three suitable extractive distillation solvents were determined for acetonitrile‐water and ethanol‐cyclohexane systems. Vapor ‐ liquid equilibrium experiment were used to test chosen ILs. This study showed that the experimental and design results were consistent with each other. Therefore, this method is effective and applicable to pick ILs solvents for extractive distillation, and the results could provide a theoretical foundation for industrial production. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2853–2869, 2016     

Modelling carbon dioxide solubility in ionic liquids

Solubility information for CO₂ in different ionic liquids, ILs, in part can potentially be used to select a specific IL for the separation of CO₂ from hydrocarbon fluids. Unfortunately, not all CO₂–IL systems have been experimentally described at similar temperatures and pressures; therefore, a direct comparison of performance by process simulation is not always possible. In the extreme cases, the design of a CO₂ separation process may require predicting the CO₂–IL equilibria for which there are no available solubility data. To address the need for this information, a semi‐empirical correlation was developed to estimate the dissolution of CO₂ in CO₂–IL solvent systems. The theoretical COSMO–RS calculation method was used to calculate the chemical potential of CO₂ in a wide variety of ILs and the Soave–Redlich–Kwong equation was used to calculate the fugacity coefficient of the CO₂ vapour phase. The model was correlated with available literature data, yielding an average error of AAR = 23% and small bias. © 2012 Canadian Society for Chemical Engineering     

Characterization of ionic liquid‐based biocatalytic two‐phase reaction system for production of biodiesel

The property of a variety of ionic liquids (ILs) as reaction media was evaluated for the production of biodiesel by enzymatic methanolysis of rapeseed oil. The IL Ammoeng 102, containing tetraaminum cation with C₁₈ acyl and oligoethyleneglycol units, was found to be capable of forming oil/IL biphasic reaction system by mixing with substrates, which is highly effective for the production of biodiesel with more than 98% biodiesel yield and nearly 100% conversion of oil. Conductor‐like screening model for real solvent (COSMO‐RS) in silico prediction of substrate solubility and simulation of partition coefficient change vs. reaction evolution indicated that the amphiphilic property of Ammoeng 102 might be responsible for creating efficient interaction of immiscible substrates; while big difference of partition coefficients of generated biodiesel and glycerol between the two phases suggests a large chemical potential to move reaction equilibrium for maximum oil conversion and yield of target biodiesel. The reaction behavior and specificity of oil/IL biphasic system for enzymatic production of biodiesel were theoretically delineated through COSMO‐RS computation with experimental validation. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Characterization of Absorption Performance for Gaseous Acetone with Ionic Liquid Solutions

New absorbents composed of diethylene glycol monobutyl ether (DGBE), paraffin oil, and ionic liquids (ILs) were prepared for the removal of gaseous acetone. Three ILs, namely, [bmim][PF₆], [bmim][BF₄], and [bmim][Ac], were used to regulate the absorption performance. Different paraffin oil mass fractions and IL mass fractions were applied to determine the right formula with suitable physical properties and absorption performance. The Henry coefficients of acetone in the absorbents were measured to evaluate the influence of absorbent composition on the absorption capacity. The removal performances of these absorbents were investigated in a bubbling bottle to evaluate the combined impact of Henry coefficient and physical properties.     

Prediction of Equilibrium Partitioning of Nonpolar Organic Solutes in Water‐ Surfactant Systems by UNIFAC and COSMO‐RS Models

In the present study the potential of two thermodynamic‐based models (the group‐contribution UNIFAC model and the a priori predictive COSMO‐RS model) to predict solute partitioning in aqueous surfactant solutions is evaluated. In order to take into account the small size of micelles, the UNIFAC model was extended by the interfacial contribution based on the Gibbs‐Thompson equation. The applicability of the approach was successfully proved for the partitioning of nonpolar solutes (toluene, p‐xylene) in aqueous solutions of nonionic surfactants. The original COSMO‐RS model underestimates the concentration of the solute in the aqueous phase in the case of micellar systems since it does not account for the small size of micelles. At the same time, this model gives quantitative results for the octanol/water partition coefficients of both solutes under study leading to the conclusion that the affinity of both solutes to a certain solvent is well described. Thus, extending the COSMO‐RS by the interfacial term seems to be promising.     

Chelation-activated multiple-site reversible chemical absorption of ammonia in ionic liquids

Developing new and facile strategies for multiple-site reversible chemical absorption of pollutant gases is of wide interests in chemical engineering research. Herein, a series of lithium (Li)-triethylene glycol (TEG)–chelated ionic liquids (ILs) with crown-ether-like cation and different anions were designed. The Li-TEG–chelated ILs were prepared in quantitative yields by simply mixing equimolar TEG and Li salts. It is found that the chelation of TEG with Li⁺ activates the hydroxyl sites in TEG for strong interaction with ammonia (NH₃). Thus, the hydroxyl sites chelated with Li⁺, as well as the chelation-unsaturated Li⁺, provide the multiple sites for chemical absorption of NH₃ in Li-TEG–chelated ILs. Moreover, the absorption of NH₃ in Li-TEG–chelated ILs is totally reversible, with the NH₃ solubilities remaining unchanged after eight times of recycling. The results obtained herein can provide useful guidance for the construction of gas absorbents with high capacity and excellent reversibility.     

Gas drying with ionic liquids

The gas drying technology with ionic liquids (ILs) was systematically studied ranging from the molecular level to industrial scale. The COSMO‐RS model was first used to screen the suitable IL and provide theoretical insights at the molecular level. Toward CO₂ gas dehydration, we measured the CO₂ solubility in single [EMIM][Tf₂N] and in the [EMIM][Tf₂N] + H₂O mixture, as well as the vapor‐liquid equilibrium (VLE) of [EMIM][Tf₂N] + H₂O system, to justify the applicability of UNIFAC model. Based on the thermodynamic study, the rigorous equilibrium (EQ) stage mathematical model was established for process simulation. The gas drying experiment with IL was also performed and the water content in gas product can be reduced to 375 ppm. It was confirmed that a less flow rate of absorbent, a higher CO₂ recovery ratio and a much lower energy consumption can be achieved with IL than with the conventional triethylene glycol (TEG). © 2017 American Institute of Chemical Engineers AIChE J, 64: 606–619, 2018     

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     

1H nuclear magnetic resonance study of polyurethane prepolymers from toluene diisocyanate and polypropylene glycol

Polyurethane prepolymers prepared from toluene 2,4‐diisocyanate, toluene 2,6‐diisocyanate, and polypropylene glycol with a ratio between the isocyanate and hydroxyl groups equal to 2 were analyzed by ¹H nuclear magnetic resonance (NMR) spectroscopy in acetone‐d₆. Different temperatures and concentrations were used. Toluene 2,4‐dimethylurethane and toluene 2,6‐dimethylurethane were synthesized and used as model compounds to assign prepolymers signals. Measurements of spin–lattice relaxation time T₁ by “inversion recovery” experiments were carried out on toluene 2,4‐diisocyanate, toluene 2,6‐diisocyanate, toluene 2,4‐dimethylurethane, toluene 2,6‐dimethylurethane, and polyurethane prepolymers. Differences in T₁ times were used to interpret prepolymers spectra, by means of the strong observed effect on protons due to the presence of adjacent isocyanate groups. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 347–357, 2003     

Effect of Electrolytes on Octanol‐Water Partition Coefficients: Calculations with COSMO‐RS

In this work, the possibility of the a priori predictive model COSMO‐RS to describe partitioning of pharmaceutically active compounds in the octanol‐water system (P_OW) in the presence of electrolytes is investigated. It is shown that the calculated values of P_OW depend on the pH and the ionic strength of the solution for both dissociated and non‐dissociated solutes. Whereas the partitioning of the non‐dissociated form in the presence of salts or buffers can be explicitly described by COSMO‐RS, the partitioning of the ionized pharmaceuticals is taken into account by their dissociation constants. Overall, reasonable agreement with experimental values is achieved. Principally, these types of calculations can be extended to other two‐phase systems used for extraction and formulations of pharmaceuticals and further organic solutes.     

Development of ethanolamine‐based ionic liquid membranes for efficient CO2/CH4 separation

This study is focused on the development of ionic liquids (ILs) based polymeric membranes for the separation of carbon dioxide (CO₂) from methane (CH₄). The advantage of ILs in selective CO₂ absorption is that it enhances the CO₂ selective separation for the ionic liquid membranes (ILMs). ILMs are developed and characterized with two different ILs using the solution‐casting method. Three different blend compositions of ILs and polysulfone (PSF) are selected for each ILMs 10, 20, and 30 wt %. Effect of the different types of ILs such as triethanolamine formate (TEAF) and triethanolamine acetate (TEAA) are investigated on PSF‐based ILMs. Field emission scanning electron microscopy analysis of the membranes showed reasonable homogeneity between the ILs and PSF. Thermogravimetric analysis showed that by increasing the ILs loading thermal stability of the membranes improved. Mechanical analysis on developed membranes showed that ILs phase reduced the amount of plastic flow of the PSF phase and therefore, fracture takes place at gradually lower strains with increasing ILs content. Gas permeation evaluation was carried out on the developed membranes for CO₂/CH₄ separation between 2 bar to 10 bar feed pressure. Results showed that CO₂ permeance increases with the addition of ILs 10–30 wt % in ILMs. With 20–30 wt % TEAF‐ILMs and TEAA‐ILMs, the highest selectivity of a CO₂/CH₄ 53.96 ± 0.3, 37.64 ± 0.2 and CO₂ permeance 69.5 ± 0.6, 55.21 ± 0.3 is observed for treated membrane at 2–10 bar. The selectivity using mixed gas test at various CO₂/CH₄ compositions shows consistent results with the ideal gas selectivity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45395.     

An ionic liquid proposed as solvent in aromatic hydrocarbon separation by liquid extraction

Liquid–liquid extraction is the most common method for extraction of aromatics from their mixtures with aliphatic hydrocarbons. An ionic liquid (IL) 1‐butyl‐1‐methylpyrrolidinium bis (trifluoromethylsulfonyl) imide [BMpyr][NTf₂] was tested as solvent for this separation. The liquid–liquid equilibria (LLE) of the ternary mixtures heptane + benzene, or toluene, or ethylbenzene + [BMpyr][NTf₂] were carried out at 298.15 K. The solvent ability of the IL was evaluated in terms of solute distribution ratio and selectivity. The results were compared with those previously reported for the extraction of aromatics from its mixtures with heptane by using ILs. The conventional process using sulfolane as solvent was discussed. The experimental LLE data were correlated by non‐random two liquid equation. A proposal of extraction process with this IL as solvent is simulated by conventional software and the results are shown. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Predicting Solubility of Military,Homemade, and Green Explosives in Pure and Saline Water using COSMO‐RS

The conductor‐like screening model for real solvents (COSMO‐RS) has previously been shown to give accurate aqueous solubilities for a range of organic compounds using only quantum chemical simulation data. Application of this method for solid organic explosives, however, faces two difficulties; it requires correction for the free energy of fusion (a generally unknown quantity for these compounds) and it shows considerable error for common explosive classes such as nitramines. Herein we introduce a correction factor for COSMO‐RS that is applicable to a wide range of explosives, and requires no data beyond a quantum chemistry calculation. This modification allows COSMO‐RS to be used as a predictive tool for new proposed explosives or for systems lacking experimental data. We use this method to predict the temperature‐dependent solubility of solid explosives in pure and saline water to an average accuracy of approximately 0.25 log units at ambient temperature. Setschenow (salting‐out) coefficients predicted by this method show considerable improvement over previous COSMO‐RS results, but are still slightly overestimated compared to the limited experimental data available. We apply this method to a range of military, homemade, and “green” explosives that lack experimental seawater solubility data, an important property for environmental fate and transport modeling.     

基于COSMO-SAC模型的分子筛选方法用于咪唑类离子液体吸收甲苯蒸气

采用基于COSMO-SAC模型的分子筛选方法,对作为甲苯蒸气吸收剂的咪唑类离子液体进行了筛选。建立了100种常见的N,N'-二烷基咪唑阳离子与阴离子构成的咪唑类离子液体的s-谱图,在此基础上计算了303.15 K下离子液体对甲苯的吸收势,并以此为热力学评价标准对吸收剂进行筛选。选取6种离子液体进行甲苯蒸气的吸收实验,通过其饱和吸收量验证此方法的可行性。研究表明,实验和分子筛选结果相吻合。利用Gaussian 09软件进行微观结构分析,计算了离子液体阳离子与甲苯的相互作用能。对进气浓度和进气速度等动力学因素的影响进行探究,在条件为303.15 K、进气浓度为10000 mg·m^-3、进气速度为0.05 m³·h^-1情况下,离子液体对甲苯的初始吸收率高达96.2%。此外,实验验证了离子液体随着重复利用次数的增加,其吸收效果基本不变。