IL-based Solvents Research Articles

MODELING AND SIMULATION OF POST-COMBUSTION CO 2 CAPTURE PROCESS FOR 6.4 MWE BAGASSE FUELED POWER PLANT

The emission of carbon dioxide, a greenhouse gas, contributes to the phenomenon of climate change; the largest source of carbon dioxide emissions are fossil fuel power plants. Post-combustion carbon capture (PCC) technology, which is based on solvents, is currently the most advanced technology for reducing carbon dioxide emissions from power plants. The Post-combustion Process, which uses conventional solvents, has a number of disadvantages, including high energy consumption for regeneration, solvent losses, corrosion of equipment, thermal instability, and environmental impact. Ionic liquids (ILs) and IL-based solvents have produced a novel method of CO 2 capture that is highly efficient, economical, and environmentally friendly. A rate-based steady-state model of the PCC process using the ionic liquid 1-hexyl-3-methylimidazolium glycine ([Hmim] [Gly]) was investigated using Aspen Plus ®. In Aspen Plus ® Electrolyte NRTL method and RK equation of state are used to compute liquid and vapor properties. From the process analysis carried out, it was found that the height and diameter of the absorber packing, the liquid-to-gas ratio and the solvent and flue gas temperatures have a positive effect on the CO 2 capture efficiency. The result showed a maximum CO 2 capture efficiency of 92% at a packed height of 12m and diameter of 0.9m. The best capture efficiency of 98.82% was achieved at an L/G ratio of 4.0.the process simulation study examined five key parameters for ([Hmim] [Gly]) solvent which may reduce the energy and cost required for CO 2 capture. The results show that aqueous ([Hmim] [Gly]) is a promising absorbent for CO 2 capture. Offering a pathway towards more sustainable and efficient carbon capture technologies. This study contributes to the advancement of carbon capture technologies and underscores their significance in mitigating climate change impacts.

Cost and Heat Integration Analysis for CO2 Removal Using Imidazolium-Based Ionic Liquid-ASPEN PLUS Modelling Study

The recent advancement in efficient and recoverable CO2 capture solvents has been stimulated by the environmental harm resulting from the accumulation of greenhouse gases. Ionic liquids (ILs) and IL-based solvents have given rise to a novel method of CO2 collection that is highly efficient, economical, and environmentally benign. However, there is a lack of knowledge about the implementation of this process on a wider scale, and it has limitations, including high solvent costs. This simulated study shows that [EMIM][NTF2] can remove up to 99.4% of the CO2 from industrial waste effluents using three distinct compositions. Following an economic study using a 20-year plant life estimate, with a plant capacity of 4000 kg/h (206.165 kmol/h) for the raw mixed stream flow (inlet) and a maximum CO2 capacity of 38.1 kmol/h, it was determined that the process’s overall annualized cost was USD 2.1 million with operating expenses being USD 1.8 million. The Aspen Activated Energy Analysis’s recommendation of adding a heat exchanger, with a payback year of 0.0586 years, a 23.34 m2 area, and potential energy cost savings of USD 340,182/Year was also implemented successfully. These findings propose a conceptual framework for the development of novel ionic liquids for CO2 capture. It also demonstrates that sustainable [EMIM][Tf2N]-based absorption techniques for CO2 capture have the potential to be an industrial technology.

Tuning Functionalized Ionic Liquids for CO2 Capture.

The increasing concentration of CO2 in the atmosphere is related to global climate change. Carbon capture, utilization, and storage (CCUS) is an important technology to reduce CO2 emissions and to deal with global climate change. The development of new materials and technologies for efficient CO2 capture has received increasing attention among global researchers. Ionic liquids (ILs), especially functionalized ILs, with such unique properties as almost no vapor pressure, thermal- and chemical-stability, non-flammability, and tunable properties, have been used in CCUS with great interest. This paper focuses on the development of functionalized ILs for CO2 capture in the past decade (2012~2022). Functionalized ILs, or task-specific ILs, are ILs with active sites on cations or/and anions. The main contents include three parts: cation-functionalized ILs, anion-functionalized ILs, and cation-anion dual-functionalized ILs for CO2 capture. In addition, classification, structures, and synthesis of functionalized ILs are also summarized. Finally, future directions, concerns, and prospects for functionalized ILs in CCUS are discussed. This review is beneficial for researchers to obtain an overall understanding of CO2-philic ILs. This work will open a door to develop novel IL-based solvents and materials for the capture and separation of other gases, such as SO2, H2S, NOx, NH3, and so on.

Practical Online Monitoring of Ionic Liquid Fiber Welding Solvent.

Ionic liquids (ILs) are becoming important solvents in commerce, but monitoring their purity and performance in industrial applications presents new challenges. Fiber welding technology utilizes ILs to mold and shape natural fibers (cotton, hemp, flax, silk, and wool) into morphologies that are typically attained only using synthetic, petroleum-based non-biodegradable plastics. The result is an atom-efficient process that up-converts fibrous substrates to value-added products and materials. A key aspect of bringing this and other IL-enabled technologies to market relies on efficient monitoring and recycling of IL-based solvents. Implementing online IL quality monitoring enhances the unit economics of these processes. Here, we characterize and report conductivity measurements, refractometry, and ATR–FTIR spectroscopy techniques for online IL monitoring during an industrial fiber welding process. The online analysis enables more efficient recycling of the IL solvent, increasing the process efficiency and product quality.

Efficient and Reversible Chemisorption of Carbon Dioxide with Dianionic-Functionalized Ionic Liquid-Based Solvents

Developing carbon dioxide (CO2) capture technologies has caused worldwide interest because of the baneful influence of CO2 on climate change as a main greenhouse gas. Ionic liquids (ILs) are considered as potential absorbents for CO2 capture because of their unique properties compared with current amine-based solvents. In this work, new dianionic-functionalized IL-based solvents, bi­(1,8-diazabicyclo[5.4.0]­undec-7-ene) dimethylhydantoin/ethylene glycol ([(DBUH)2]­[Dhyd]/EG), were designed and prepared for efficient and reversible chemisorption of CO2. Among the absorbents, [(DBUH)2]­[Dhyd]/EG with a mass ratio of 5:5 exhibited not only a high CO2 absorption capacity of 0.11 g CO2/g absorbent at 20 °C and 0.10 MPa but also good recyclability. Spectroscopic characterizations and simulation calculations confirmed that the superior CO2 capacity may be attributed to the simultaneous reaction of CO2 with both the [Dhyd]2– anion and deprotonated EG. The excellent CO2 absorption and regeneration performance imply that [(DBUH)2]­[Dhyd]/EG solvents may have great industrial application potentials.

Reaction Mechanism and Free Energy Barriers for the Chemisorption of CO2 by Ionic Entities.

Ionic liquids, a class of alternative solvents, are known for their ability to capture carbon dioxide (CO2). The understanding of the role of the individual ionic entity of the ionic liquid (IL) and the involved mechanism is essential to design a better solvent for the capture process. In the present study, we employed density functional theory based electronic structure calculations and metadynamics method based first-principles molecular dynamics (FPMD) simulations to investigate the roles of the cation and anion of the IL by analyzing the energetics and free energy profile of the involved chemical reactions. The mechanism of chemisorption of CO2 by the aprotic N-heterocyclic and phenolate anions paired with tetrapropyl phosphonium cation [P3333] were studied to understand the reaction mechanism of the initial capture process. The process of uptaking of CO2 by the [P3333][1,2,4-Triz] was studied by the first-principles calculations. The transition states in the reaction pathways were computed by the synchronous transit-guided quasi-Newton method and confirmed by the intrinsic reaction coordinate calculations using first-principles simulations. The dynamics of the energetics of the chemisorption process were studied by constructing the free energy surface using metadynamics-based FPMD simulations. First, the nucleophilic center was generated at the α-carbon of the cation by transferring a proton to the anion with the formation of the phosphorus ylide. The formed cation ylide chemisorbs CO2 through the formation of a bond between the α-carbon of ylide and the carbon of CO2. The direct addition of CO2 to the anion of the ionic pair was studied as the second pathway. We find that the chemisorption of CO2 by the anion is more favorable than that by the cation. By comparing the chemisorption of CO2 by the ions, we observe that the deprotonation of the alkyl chain is the more deciding factor, which depends on the basicity of anion and the length of the alkyl chain. We computed the free energy landscapes for the ionic pairs by varying another four anions like cyclohexanolate, 2,4,6-trifluorophenolate, imidazolate, and benzotriazolide paired with tetrapropyl phosphonium cation. The effect of the alkyl chain on the proton transfer was studied by tetrabutyl and tetrapentyl phosphonium cations paired with 1,2,4-triazolide anion. The carbonated product, formed from the anion, is thermodynamically controlled, while the carboxylated product (formed from cation) is kinetically controlled. We hope that our findings will enhance the knowledge of the selectivity of ionic entities for designing IL-based solvents for the capture process of CO2.

Non-covalent interactions in bmimCl/co-solvent mixtures: A FTIR spectroscopy and computational study

Ionic liquids such as 1-butyl-3-methylimidazolium chloride (bmimCl) are efficient solvents for cellulose, but high viscosity of the resulting solutions hampers further cellulose shaping and derivatization. To solve this problem, mixtures of ILs with various organic co-solvents are often employed in place of neat ILs. So far, the intermolecular interactions in such mixtures are poorly understood, which hinders further development of this class of cellulose solvents. In this work, we utilized infrared spectroscopy (IR) and quantum chemical model calculations to study the intermolecular interactions in differently concentrated mixtures of bmimCl with two typical co-solvents, dimethyl sulfoxide (DMSO) and N,N-dimethylacetamide (DMAc). First, we refined the assignment of the relevant characteristic bands in the IR spectra of the individual mixture components. This then helped us to reveal that bmim+-DMSO and bmim+-DMAc associates, stabilized by hydrogen bonds between the imidazolium ring CH groups and oxygens of DMSO or DMAc, are formed in the studied mixtures. Importantly, only a relatively small fraction of co-solvent molecules (up to ca. 20 mol% for DMSO and ca. 45 mol% for DMAc) are involved in the associate formation, leaving a large proportion of bmimCl molecules non-solvated. While the maximum co-solvent concentration at which direct cellulose dissolution can be achieved is considerably different for DMSO and DMAc, the corresponding molar ratio of bmimCl to interacting co-solvent molecules was the same for both the studied systems (about 2.5:1). We propose that this ratio might be related to the critical size of bmimCl clusters necessary for achieving cellulose dissolution. Furthermore, increasing the temperature from 25 to 80 °C resulted in a significantly decreased fraction of interacting solvent molecules for bmimCl/DMSO but not for bmimCl/DMAc. This indicates that the comparatively lower tendency of DMSO to form associates with bmimCl is due to the lower strength of the underlying hydrogen bond. The results of this study illustrate how intermolecular interactions influence the macroscopic performance of different IL-based solvent systems.

Ionic-Liquid-Based CO2 Capture Systems: Structure, Interaction and Process.

The inherent structure tunability, good affinity with CO2, and nonvolatility of ionic liquids (ILs) drive their exploration and exploitation in CO2 separation field, and has attracted remarkable interest from both industries and academia. The aim of this Review is to give a detailed overview on the recent advances on IL-based materials, including pure ILs, IL-based solvents, and IL-based membranes for CO2 capture and separation from the viewpoint of molecule to engineering. The effects of anions, cations and functional groups on CO2 solubility and selectivity of ILs, as well as the studies on degradability of ILs are reviewed, and the recent developments on functionalized ILs, IL-based solvents, and IL-based membranes are also discussed. CO2 separation mechanism with IL-based solvents and IL-based membranes are explained by combining molecular simulation and experimental characterization. Taking into consideration of the applications and industrialization, the recent achievements and developments on the transport properties of IL fluids and the process design of IL-based processes are highlighted. Finally, the future research challenges and perspectives of the commercialization of CO2 capture and separation with IL-based materials are posed.

Pretreatment of Lignocellulosic Biomass with Ionic Liquids and Ionic Liquid-Based Solvent Systems.

Pretreatment is very important for the efficient production of value-added products from lignocellulosic biomass. However, traditional pretreatment methods have several disadvantages, including low efficiency and high pollution. This article gives an overview on the applications of ionic liquids (ILs) and IL-based solvent systems in the pretreatment of lignocellulosic biomass. It is divided into three parts: the first deals with the dissolution of biomass in ILs and IL-based solvent systems; the second focuses on the fractionation of biomass using ILs and IL-based solvent systems as solvents; the third emphasizes the enzymatic saccharification of biomass after pretreatment with ILs and IL-based solvent systems.

Microviscosity Offered by Ionic Liquids and Ionic Liquid-Glycol Mixtures Is Probe Dependent.

Interactions present within the solubilizing media constituted of ionic liquids (ILs) govern the outcomes of chemical processes carried out within such media by controlling the behavior of solutes dissolved therein. Fluidity afforded by IL-based media, in this context, not only reveals interactions present within the system, but it also helps decide whether the system is suitable for an application. The response of spectroscopic microviscosity probes dissolved in IL and IL-based solvents, in this regard, reveals information on both solute-solvent and solvent-solvent interactions present within the system. Interactions present within the cybotactic region of a microviscosity probe strongly depend on the functionalities present on the probe. Five different fluorescence probes representing three different classes of microviscosity reporting systems based on intramolecular excimer formation, steady-state fluorescence anisotropy, and fluorescence intensity are used to explore fluidity afforded by 11 ILs and their equimolar mixtures with tetraethylene glycol (TEG), a solvent having the ability to readily hydrogen bond, under ambient conditions. ILs are categorized into four sets: first having the same cation and different anions to assess the role of the anion, second having the same anion and different cations to assess the role of the cation, and the last two having C2-H substituted imidazolium cations with different anions to reveal the role of C2-H, if any, in H-bonding interactions involving ILs. The responses of all of the microviscosity probes within ILs and (IL + TEG) equimolar mixtures are compared with the bulk dynamic viscosities of the corresponding systems. The overall investigation reveals the lack of a trend between the probe responses representing microviscosity and the dynamic viscosities of IL and (IL + TEG) mixtures. The cybotactic region viscosity of the (IL + TEG) equimolar mixture depends on the identity of the probe; it may be higher than, lower than, or in between the microviscosities reported in both neat IL and neat TEG. Evidence of the role of C2-H on the imidazolium cation in intraspecies (within IL) or interspecies (between IL and TEG) H-bonding was not found.

Designing ionic liquid solvents for carbon capture using property-based visual approach

Recently, ionic liquids (ILs) have been introduced as potential carbon dioxide (CO2)-capturing solvents, as a substitute to conventional amine-based solvents. Conventional amine-based solvents that are used for CO2 capture show some drawbacks, such as high solvent loss, high regeneration energy requirement, and solvent degradation. These shortcomings can be potentially overcome if IL-based solvents are considered. ILs have negligible vapour pressure, high thermal stability, and wide range of thermophysical properties. Nonetheless, using experimentation to identify suitable ILs as CO2-capturing solvents is a tedious and costly task, as there are more than a million possible combinations of cations and anions that make up the ILs. Computer-aided tools have been previously developed for targeted IL design, which often involve non-linear programming. However, non-linear programming sometimes fails to converge, due to enlarged search space for optimal solution and its complex formulations. In this paper, the authors present a simple yet systematic visual approach to design IL solvents for carbon capture. Property integration framework is employed in this approach to systematically design IL, where the design problem can be mapped from the property domain into a cluster domain through clustering technique. The advantage of the visual approach is the ability to enumerate novel IL candidates. Group contribution (GC) method is included in the framework to estimate the properties of designed ILs. By combining property integration framework and GC method, the proposed approach is able to provide a property-based platform to visualise the performance of designed ILs on a ternary diagram. A case study is presented to illustrate the validity of the proposed approach.

Selective recovery of aliphatics from aromatics in the presence of the {[4empy][Tf2N] + [emim][DCA]} ionic liquid mixture

Lately, the use of binary mixtures of ionic liquids (ILs) has been revealed as an interesting election in order to find alternative solvents in the liquid–liquid extraction of aromatics from aliphatics. Specifically, the {[4empy][Tf2N]+[emim][DCA]} mixture has exhibited both aromatic selectivity and distribution ratios higher than sulfolane in the BTEX separation from several gasolines and naphthas. Moreover, its density and viscosity are comparable with those showed by sulfolane, and its thermal stability is also quite high. However, the absence of (vapor+liquid) equilibria (VLE) studies concerning aliphatics/aromatics mixtures in ILs has not led to propose a recovery section to selectively separate aliphatics, aromatics, and the IL-based solvent. For that reason, the aim of this work is to study the VLE of several {aliphatic+aromatic} systems in the presence of {[4empy][Tf2N]+[emim][DCA]} mixture over the whole composition range of the IL mixture and also at several temperatures. The results showed high aliphatic relative volatility from all aromatics, fact that would facilitate the selective separation of aliphatics, BTEX, and ILs. On the other hand, the Yalkowsky–Roseman log-linear model was successfully apply to predict the phase behavior of {aliphatic+aromatic+[4empy][Tf2N]+[emim][DCA]} systems.

Dearomatization of pyrolysis gasolines from mild and severe cracking by liquid–liquid extraction using a binary mixture of [4empy][Tf2N] and [emim][DCA] ionic liquids

In Europe and Japan, benzene, toluene, and xylenes (BTX) are usually obtained by liquid–liquid extraction from pyrolysis gasolines using organic solvents such as sulfolane. In the last few years, ionic liquids (ILs) have been studied as potential substitutes of conventional solvents in the extraction of BTX from alkanes. In this paper, we have studied the dearomatization of pyrolysis gasolines obtained by mild and severe cracking using the binary IL mixture composed of the 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) and the 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) and also employing sulfolane to compare the performance of both extraction solvents. To choose the most appropriate conditions of temperature and solvent to feed ratio to perform the extraction of BTX from pyrolysis gasolines, several extractive properties have been estimated from the experimental results employing the IL mixture and sulfolane. Simulations of countercurrent extraction columns in the dearomatization of both pyrolysis gasolines have also been made using the Kremser equation. The dearomatization of pyrolysis gasolines by the {[4empy][Tf2N]+[emim][DCA]} IL mixture would require a higher number of equilibrium stages in the extractor than that employing sulfolane. By contrast, the purity of extracted aromatics would be substantially greater using the IL-based solvent, simplifying the subsequent purification of the BTX.

Ionic Liquid-Facilitated Preparation of Lignocellulosic Composites

Lignocellulosic composites (LCs) were prepared by partially dissolving cotton along with steam exploded Aspen wood and burlap fabric reinforcements utilizing an ionic liquid (IL) solvent. Two methods of preparation were employed. In the first method, a controlled amount of IL was added to preassembled dry matrix of cotton and Aspen wood with a burlap weave reinforcement. In the second method, IL solvent, cotton, and Aspen wood were mixed to produce a thick paste matrix that was subsequently pressed into the burlap weave reinforcement. The IL-based solvent was removed via water soaking, and the flexural and tensile properties of the LCs were examined. In this study, the matrix paste method produced a superior LC. Variables such as processing time (IL interaction time) and fabric weaves were found to influence the mechanical properties of the LCs. Although significant process optimization can still be realized, the mechanical properties of several of the LCs fabricated in this study were comparable to injection molded test specimens of neat high density polyethylene or neat polypropylene.

Vapor–liquid equilibria of {n-heptane + toluene + [emim][DCA]} system by headspace gas chromatography

The potential use of ionic liquids (ILs) in the extraction of aromatics from aromatic/aliphatic mixtures has been widely evaluated in the last decade. In addition to the good results obtained in the extraction step, the non-volatile character of ILs could simplify the aromatic recovery unit. However, the scarce vapor–liquid equilibria (VLE) data for {aliphatic+aromatic+IL} systems demand additional experimental VLE data for such systems to correctly define the aromatic recovery from the extract stream. Only then, it will be possible to assess as a whole if the application of ILs as replacement to conventional organic solvents could represent a real improvement of the present aromatic extraction industrial methods. Thus, the aim of this work has been to measure the VLE for the {n-heptane+toluene+1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA])} system. This mixture includes one of the most promising IL-based solvents reported previously for aromatic extraction. Static headspace gas chromatography (HS-GC) was employed to measure isothermal VLE at 323.2K, 343.2K, and 363.2K over the whole range of compositions within the rich-IL miscibility region. Also, the correlation of the VLE data to non-random two liquids (NRTL) thermodynamic model was successfully done. A high increase in the n-heptane relative volatility from toluene was achieved under the presence of [emim][DCA].

Mixing and decomposition behavior of {[4bmpy][Tf2N] + [emim][EtSO4]} and {[4bmpy][Tf2N] + [emim][TFES]} ionic liquid mixtures

Mixing ionic liquids (ILs) has been revealed as a useful way to finely tune the properties of IL-based solvents. The scarce available studies on IL mixtures have shown a quasi-ideal behavior of their physical properties. In this work, we have performed a thermophysical characterization of two binary IL mixtures, namely {4-methyl-N-butylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N])+1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4])} and {[4bmpy][Tf2N]+1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate [emim][TFES]}. Both binary IL mixtures have been recently proposed as promising solvents in the (liquid+liquid) extraction of aromatic hydrocarbons from mixtures with alkanes. Densities, viscosities, refractive indices, thermal stability, and specific heats of the {[4bmpy][Tf2N]+[emim][EtSO4]} and {[4bmpy][Tf2N]+[emim][TFES]} IL mixtures have been measured as a function of both temperature and composition. Dynamic viscosities, refractive indices, and thermal stability of the {[4bmpy][Tf2N]+[emim][EtSO4]} mixture have exhibited strong deviations from the ideality, in contrast with the quasi-ideal properties of the {[4bmpy][Tf2N]+[emim][TFES]} mixture and the behavior of the imidazolium and pyridinium-based IL mixtures studied hitherto. The reliability of predictive methods of the thermophysical properties of the mixtures has also been evaluated.

Thermal stability and specific heats of {[bpy][BF4] + [bpy][Tf2N]} and {[bpy][BF4] + [4bmpy][Tf2N]} mixed ionic liquid solvents

In the last years, mixing ionic liquids (ILs) is a common trend looking for IL-based solvents with high extractive properties in the liquid–liquid extraction of aromatics from alkanes. The aim of mixing ILs is to find intermediate extractive properties between ILs which showed good selectivity and those with high aromatic capacity of extraction. In addition to this, there are several thermophysical properties that are of interest to evaluate an IL-based solvent. Therefore, many studies have been carried out focusing on the knowledge of density, viscosity, or surface tension behavior of IL mixture, proposing several mixing rules that could correctly predict these magnitudes from pure IL data in most of the mixtures studied. However, only a few measurements of thermal stabilities and specific heats for IL binary mixtures have been recently realized. The present study was aimed to evaluate the thermal stability of {[bpy][BF4] + [bpy][Tf2N]} and {[bpy][BF4] + [4bmpy][Tf2N]} IL mixtures by thermogravimetric analysis. Also specific heats of the IL mixtures were determined using differential scanning calorimetry.

Liquid–Liquid Extraction of BTEX from Reformer Gasoline Using Binary Mixtures of [4empy][Tf2N] and [emim][DCA] Ionic Liquids

Reformer gasoline is the main source for benzene, toluene, ethylbenzene, and xylenes (BTEX). Nowadays, the separation of BTEX is performed by liquid–liquid extraction using organic solvents such as sulfolane. Ionic liquids (ILs) have been recently proposed as potential replacements of sulfolane in the separation of aromatics from alkanes, being the binary IL mixture formed by the 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) and the 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) one of the most promising IL-based solvents. In this work, we have studied the liquid–liquid extraction of BTEX from a reformer gasoline model using the {[4empy][Tf2N] + [emim][DCA]} IL mixture with a [4empy][Tf2N] mole fraction of 0.3 and sulfolane as solvents at temperatures between 303.2 and 323.2 K. The effects of temperature and solvent to feed ratio on the extractive properties have been studied to select the most appropriate conditions to extract BTEX using the IL mixture. From the expe...

Liquid–liquid extraction of toluene from n-heptane by {[emim][TCM] + [emim][DCA]} binary ionic liquid mixtures

Ionic liquids (ILs) have been widely researched to replace organic solvents in the liquid–liquid extraction of aromatics from their mixtures with aliphatic hydrocarbons. However, the ILs studied so far have exhibited high dynamic viscosities and most of them have not shown better extractive properties than those of conventional solvents. Recently, the 1-ethyl-3-methylimidazolium tricyanomethanide ([emim][TCM]) and the 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) ILs have been proposed as aromatic extraction solvents. Both ILs have shown high toluene distribution ratios and toluene/n-heptane selectivities, dynamic viscosities comparable to the sulfolane value, and adequate thermal stabilities. In this paper, we have mixed [emim][TCM] and [emim][DCA]} ILs to obtain an IL-based solvent with intermediate extractive and physical properties between the values of pure ILs. The liquid–liquid equilibrium (LLE) of the n-heptane+toluene+{[emim][TCM]+[emim][DCA]} pseudoternary system at 313.2K and atmospheric pressure has been measured. LLE data have been validated using the Othmer–Tobias correlation and fitted to the NRTL model. Densities and viscosities of the mixed ILs have also been determined as a function of temperature, and the reliability of several predictive models of these physical properties has been studied. The {[emim][TCM]+[emim][DCA]} IL mixture with [emim][TCM] mole fraction of 0.8 has shown suitable physical properties and extractive properties higher than the sulfolane values. Therefore, this IL-based solvent could be considered as a potential substitute of conventional solvents used in the extraction of aromatics.

Separation of toluene from n-heptane, 2,3-dimethylpentane, and cyclohexane using binary mixtures of [4empy][Tf2N] and [emim][DCA] ionic liquids as extraction solvents

The use of ionic liquids (ILs) in the separation of aromatic hydrocarbons from alkanes could decrease the environmental impact of the aromatic extraction units, reducing the number of steps and simplifying the solvent recovery. Mixing ILs has been also revealed as a useful tool to tune the extractive and physical properties of IL-based solvents. In this work, the suitability of binary mixtures of 1-ethyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4empy][Tf2N]) and 1-ethyl-3-methylimidazolium dicyanamide ([emim][DCA]) ILs as aromatic extraction solvent has been evaluated. For this purpose, we have studied the liquid–liquid extraction of toluene from a straight-chain alkane (n-heptane), a branched-chain alkane (2,3-dimethylpentane), and a cycloalkane (cyclohexane) at 313.2K, using {[4empy][Tf2N]+[emim][DCA]} mixed IL solvents. A physical characterization of the IL mixtures has also been performed by measuring their densities and dynamic viscosities as a function of temperature. Extractive and physical properties of the mixed IL solvents have been intermediate between the values of pure ILs. A {[4empy][Tf2N]+[emim][DCA]} mixture with a 0.3mole fraction of [4empy][Tf2N] has shown extractive properties better than those of sulfolane for the extraction of toluene from alkanes and adequate densities and viscosities. Finally, a log-linear mixing rule has successfully estimated the extractive properties of the mixed ILs, and the use of predictive models of densities and viscosities of binary IL mixtures has also been studied.