Entrainer For Extractive Distillation Research Articles

ETHYL ALCOHOL - WATER SEPARATION BY EXTRACTIVE DISTILLATION: SIMULATION USING ASPEN PLUS™ AND EXPERIMENTAL VALIDATION

Dilute ethyl alcohol (ethanol, EtOH) is produced using fermentation (< 20 mass%), but it needs to be further purified because it contains large water content. EtOH forms an azeotrope with water and to separate this azeotrope, advanced separation processes like pressure swing distillation (PSD), azeotropic distillation (AD), and extractive distillation (ED) are employed. In this work, ethylene glycol (EG) was used as an entrainer in extractive distillation. Vapour liquid equilibrium (VLE) data was used to validate the chosen rigorous thermodynamic model. To find a workable range of operating parameters, sensitivity analysis was performed to find out the number of stages (N), feed stage (NF), distillate rate (DR), and reflux ratio (RR). Simulation shows that use of accurate operating parameters and correct entrainer can help to obtain almost pure EtOH (99.89 mole %, 99.92 mass %). In order to validate the theoretical findings from the simulation, experimental investigations in the form of batch and semi - batch distillation runs were conducted. It was seen from these runs that it is indeed possible to obtain EtOH with high purity. It was also verified that EG can be separated and recycled back with high purity with a very high recovery.

The molecular nature of the eliminating azeotropy of dimethyl carbonate–ethanol system by ionic liquid entrainer

Ionic liquids (ILs) have unique physicochemical features, such as insignificant vapour pressure, which make ILs excellent entrainers in extractive distillation to separate the azeotrope. For better utilization of the IL entrainer in extractive distillation, the microstructure properties of dimethyl carbonate (DMC)–ethanol azeotrope mixtures, before and after the separation breaking of the azeotrope by IL, were studied by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations with focus on the vibrational region of the ethanol hydroxyl group. Excess spectroscopy followed by two-dimensional correlation spectroscopy (2D-COS) was performed on the original IR spectra to extract the microstructural features of different mixtures step by step. Different sizes of ethanol self-aggregations, DMC–ethanol interaction complex and different IL–ethanol interaction complexes were identified in different mixtures. Specifically, the DMC–ethanol interaction complex existed in both the DMC–ethanol and IL–DMC–ethanol systems at lower IL concentrations (x(IL) < 0.125) while broken out by IL at higher IL concentrations (x(IL) > 0.125). The intrinsic cause of the azeotrope breaking by the 1-hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide ([HMIM][Tf2N]) entrainer was revealed to be the disappearance of the DMC–ethanol interaction complex by the IL at higher IL concentrations. The hydrogen-bonds between DMC/IL and ethanol were also identified and confirmed in the DMC–ethanol and different IL–ethanol interaction complexes. Both the oxygen atom and the hydrogen atom in the hydroxyl group of ethanol participated in the hydrogen-bond, which confirmed the sensitivity of the hydroxyl group vibrational region. The hydrogen-bonds are weak strength, closed shells and electrostatic dominant interactions.

Separation of Azeotropic Refrigerant Mixtures Using Ionic Liquids

Refrigeration and air-conditioning systems are widespread throughout modern society, from the refrigerated cold chain that provides fresh foods and storage of medicines to the air conditioning of homes and buildings. Refrigeration is viewed as one of the most transformative engineering achievements of the 20th century and the demand for cooling will continue to increase as economic conditions improve and the climate continues to warm; however, refrigerants do come with an environmental cost.In 1987, the Montreal Protocol phased out chlorofluorocarbon (CFC) refrigerants because of their high ozone depletion potential (ODP). The replacements, typically mixtures of hydrofluorocarbons (HFCs), are safe for the Earth's ozone layer, but most have high global warming potentials (GWPs). HFCs account for 7.8% of total global greenhouse gas emissions, with 63% of that from “indirect” emissions (i.e., energy for running the system). As a result, 197 countries signed the Kigali agreement in 2016 to phase out high-GWP HFCs, with the goal of reducing emissions by 80% in the next 20 years. Millions of metric tons (mts) of high-GWP refrigerants will need to be reclaimed, but there are no good methods for separating and recycling the individual components, given that many are azeotropic mixtures.Currently, there is no means of separating azeotropic HFC mixtures, and the refrigerants will ultimately have to be incinerated. The commercial HFC mixture R-410A containing 50 wt.% HFC-32 (GWP = 675) and 50 wt.% HFC-125 (GWP = 3500) is a prime example. The HFC-32 can be reused when separated in new low-GWP products such as R-454B (69 wt% HFC-32 and 31 wt% HFO-1234yf) with a 75% lower GWP than R-410A.Ionic liquids are being developed that can separate azeotropic HFC mixtures based on differences in solubility and used as entrainers in extractive distillation. This presentation will provide experimental data on the solubility of HFCs in ionic liquids that have been measured using gravimetric microbalances and modeling using the Peng-Robinson equation of state. ASPEN Plus simulations will show how a pilot process has been designed that can continuously separate azeotropic refrigerant mixtures such as R-410A.

Ionic liquids as entrainer in extractive distillation for effectively separating 1-propanol–water azeotropic mixture

Economically separating 1-propanol (NPA) from water is an emergent issue for producing pharmaceutical intermediates such as n-propyl acetate, n-propylamine and so on. In this work, fourionic liquids (ILs) 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), 1,3-dimethylimidazolium methylsulfate ([MMIM][MS]), 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]) were introduced as potential entrainers for separating NPA–water azeotropic mixture. The results show that [MMIM][MS] is the most suitable entrainer compared with other ILs from the analysis of vapor–liquid equilibrium and relative volatilities. The extractive distillation process with the entrainer regeneration system of flash tank and stripper was employed and optimized by the two-step optimization method. The results show that total annual cost and energy consumption per product flow rate were reduced by 39.79% and 60.47% compared with literature. In addition, the efficiency indicator of extractive section, efficiency indicator of per tray in extractive section, carbon dioxide emissions were also selected as the evaluation index for selection of operating parameters and calculated for different cases. The CO2 emissions of the optimal design can be reduced by 60.98% from environmental aspect.

N-octylpyridinium bromide applied to purification of benzene by extractive distillation: Thermodynamic properties for intuitive evaluation of entrainer

The N-octylpyridinium bromide ([Opy]Br) ionic liquid was subjected to thermodynamic properties studies, including those of activity coefficients at infinite dilution (γ12∞) and Flory–Huggins interaction parameters (χ12∞), to evaluate the interaction and solubility of [Opy]Br and solvents. [Opy]Br showed different separation potentials for three inseparable systems (benzene/ethanol, benzene/isopropanol, and benzene/thiophene), but no phase separation was observed when it was used as an entrainer for extractive distillation. Through the analysis of relative volatility curve, [Opy]Br can effectively separate benzene from benzene/ethanol and benzene/isopropanol azeotropic mixture, but it had no evident enhancement effect on benzene/thiophene. The results of separation performance were consistent with the analysis of selectivity (Sij∞) and capability (kj∞). Furthermore, an extractive distillation process was designed with Aspen Plus software to evaluate the competitiveness of [Opy]Br entrainer in the separation of benzene/ethanol. The results showed that [Opy]Br can be fully recycled without loss, which is more in line with the concept of green development than organic solvent entrainers.

Separation of ethanol – water mixture by extractive distillation using pyridinium-based ionic liquid 1-ethyl-3-methylpyridinium ethylsulfate

Ionic liquids (ILs) have received considerable attention for their use in chemical industry and are considered to be an alternative to conventional entrainers in extractive distillation, because of their ability to selectively separate azeotropic or close boiling mixtures. In this work, an extractive distillation process was investigated, comparing the pyridinium-based (IL) “1-ethyl-3-methylpyridinium ethylsulfate” [EMPy][ESO4] with the ethylene glycol (EG) organic solvent for the ethanol/water separation. This (IL) was proposed because of its high selectivity compared to conventional (EG). The electrolyte non-random-two-liquid (eNRTL) activity coefficient model was used to calculate the vapor-liquid equilibrium (VLE) of the ethanol-water mixture in the presence of the solvent. Indeed, the VLE behavior of ethanol-water in the presence of [EMPy][ESO4] showed that the (IL) enhances the relative volatility of ethanol and allows to eliminate the azeotrope at smaller solvent concentration, comparing to (EG). The best operating conditions of the extractive distillation process were determined for three cases of ethanol composition in feed mixture to obtain ethanol with higher purity (i.e. 99.9 mol.%). Besides, it has been found that the [EMPy][ESO4] (IL) is more efficient than EG for the separation of ethanol-water azeotropic system even at low concentrations; it is less energy consuming and more economical compared to the conventional solvent.

Design Optimization of Deep Eutectic Solvent Composition and Separation Performance of Cyclohexane and Benzene Mixtures with Extractive Distillation

Deep eutectic solvents (DESs) have properties that make them suitable candidates to be used as entrainers for extractive distillation. In the previous work, it was proven that DES(1:2) (tetrabutylammonium bromide: levulinic acid, 1:2, molar ratio) can break the cyclohexane-benzene azeotrope. In the present work, the HBA and HBD ratio and molar concentration of DES were optimized to obtain a better constitute and condition of DES to be utilized in cyclohexane and benzene extractive distillation. The physical properties and structure of the prepared DESs were characterized. Vapor–liquid equilibrium data of the ternary system (benzene + cyclohexane + DESs) were also measured at atmospheric pressure. All experimental equilibrium data were correlated with Wilson, nonrandom two-liquid (NRTL), and universal quasichemical (UNIQUAC) activity coefficient models, from which the coefficient of determination (R2) of the three pseudo-ternary systems fitting was calculated. From the obtained results, the best HBA and HBD ratio in the DESs is elucidated as 1:2, the best molar concentration of DES is 0.1, and the NRTL model predicts the experimental data more accurately than the Wilson and UNIQUAC models. From the derived mechanism, the formation of stronger hydrogen bond and π–π bond interactions between DES and benzene is obtained when HBA and HBD ratio in DES is 1:2. In other conditions, the azeotrope cannot be broken, or the efficiency is low. The present work provides an environmentally friendly method to separate aromatic/aliphatic mixtures and act as a guide for further study of DESs in extractive distillation.

Investigation of multi-objective optimization for integrating design and control of ionic liquid-based extractive distillation

Extractive distillation is widely accepted and commercialized for separating azeotrope mixtures, but using traditional organic solvents leads to intrinsic obstacles such as the high energy requirement and solvent-related environmental problems. Benefiting from the development of green solvents, using ionic liquids instead of traditional solvents as entrainers for extractive distillation has attracted wide attention. This paper presents a multi-objective optimization strategy to integrate the design and control of the ionic liquid-based extractive distillation processes. In the optimization processes, the condition number (CN) and total annual cost (TAC) are minimized as the objective functions to evaluate the control properties and design of three different separation systems. The optimization results are shown by the Pareto front, which is based on trade-offs between controllability and economics. The environmental impact is evaluated by the environmental impact potential of energy for each system in a posterior stage during the optimization processes. Designs with minimum TAC (PT), trade-off designs between TAC and CN (PO) and designs with minimum CN (PC) on Pareto front are optimized and compared. The results show that the increase of reflux ratio can improve the control properties for the ionic liquid-based extractive distillation processes. Furthermore, the dynamic simulation of PT and PO are carried out to compare their dynamic responses based on the same dynamic control structure, and PO shows better performance in the aspects which include maximum deviation and residual error of dynamic response.

Natural Deep Eutectic Solvent-Mediated Extractive Distillation for Separation of Acetonitrile + Water Azeotropic Mixture

Natural deep eutectic solvents (NADESs) are designer green solvents which share many properties with ionic liquids. The uncommon intermolecular adjustment in a NADES matrix shows exceptional solubilizing and stabilizing properties. These properties make them suitable to be used as an entrainer for extractive distillation. The present work investigates the synthesis of choline chloride-based NADES and its viability as an entrainer for separation of acetonitrile (ACN) + water mixture by extractive distillation. A NADES was prepared by employing two natural and biodegradable compounds, dl-malic acid and choline chloride in a 1:1 molar ratio (MC1:1). The vapor–liquid equilibria at isobaric condition were measured for pseudo-binary mixtures (water + MC1:1 and ACN + MC1:1) using an improved Othmer recirculation still at 101.3 kPa. Other than these, the vapor–liquid equilibrium data for ACN + water + MC1:1 pseudo-ternary mixture were also measured at different NADES concentrations. From the results, MC1:1 could ...

Bio-based solvents as entrainers for extractive distillation in aromatic/aliphatic and olefin/paraffin separation

A series of bio-based solvents were studied for application as entrainers in extractive distillation with Cyrene™, and compared to sulfolane, 30% energy saving was found for methylcyclohexene distillation from toluene.

Effect of ionic liquids as entrainers on the dynamic behavior of ethanol-water extractive columns

Ionic liquids (ILs) have been recently considered as potential entrainers for extractive distillation. The use of ILs may affect the vapor-liquid properties to aid the separation of azeotropic mixtures. In particular, their effectiveness has been observed for ethanol dehydration, showing promising perspectives for their industrial implementation. However, there is still a lack of information about the effect of ILs on the system controllability. The objective of this work is to explore the dynamic implications of the use of two types of ionic liquids on the ethanol dehydration process. An equimolar feed mixture of ethanol and water was considered, and different IL concentrations were tested. The results show that changing the IL concentration affect the degree of stabilization of the product stream, even when smooth dynamic responses were in many cases observed.

Determination of an optimum entrainer for extractive distillation based on an isovolatility curve at different pressures

The selection of a proper entrainer is a key factor affecting the feasibility of extractive distillation. Presently, we simply compare the relative volatility based on the same pressure to select the entrainer. In this work, we found that the separation effect on entrainers was impacted by pressure to a different extent. Two binary azeotropic systems, ethanol-benzene and ethanol-ethyl acetate, were used to demonstrate the entrainer selection based on an isovolatility curve at different pressures. The results indicated that ethanol-benzene with 1,2-propanediolas an entrainer can save 7.42% of the total annual cost compared to ethanol-benzene with p-xylene as an entrainer at atmospheric conditions, but after the pressure was considered, the ethanol-benzene-p-xylene system can save a 9.17% total annual cost compared to the ethanol-benzene-1,2-propanediol system. The relationship between pressure and total annual cost was nonlinear, and there was a minimum total annual cost at the corresponding pressure. Similar to the ethanol-benzene system, the above situation also existed in the ethanol-ethyl acetate system. The change in the isovolatility curve with the change in pressure shows different trends, and the change in pressure results in a change in the selection of the entrainer. The results provide more insight for the choice of an entrainer in extractive distillation.

Low transition temperature mixtures (LTTMs) as novel entrainers in extractive distillation

Low transition temperature mixtures (LTTMs) are evaluated as potential entrainers for extractive distillation for the first time. The selected LTTMs were lactic acid–choline chloride 2:1 (LC 2:1), malic acid–choline chloride 1:1 (MC 1:1), glycolic acid–choline chloride 3:1 (GC 3:1) and glycolic acid–choline chloride 1:1 (GC 1:1). Vapour–liquid equilibrium (VLE) data for the pseudo-binary mixtures of water–LTTM and ethanol–LTTM were measured and fitted with the NRLT model to calculate the interaction parameters. These parameters were used to predict the pseudo-ternary VLE data using the same model. The prediction was compared with new experimental data for the water–ethanol–LTTM system and the prediction was found to be adequate. It was found that the ethanol–water azeotrope can be broken by MC 1:1, GC 1:1 and GC 3:1 and it can be moved to the pure ethanol side with LC 2:1.

Extractive distillation with the mixture of ionic liquid and solid inorganic salt as entrainers

The use of the mixture of ionic liquid (IL) and solid inorganic salt in place of the single IL as entrainers for extractive distillation, which integrates the advantages of a liquid solvent, that is, IL (easy operation and nonvolatility) and a solid salt (high separation ability) has been proposed in this work. The vapor–liquid equilibrium experiments indicated that the combination of [EMIM]+[Ac]− and KAc is the most promising for the separation of ethanol and water among all of the entrainers investigated. Based on the thermodynamic study, the conceptual process design was developed to evaluate the competitiveness of the suggested entrainers for the separation of ethanol and water. It was determined that the overall heat duty on reboilers in the extractive distillation process using the new mixed entrainers decreases 19.04% compared with the benchmark entrainer [EMIM]+[Ac]−. Moreover, the density functional theory and COSMO‐RS model were used to achieve theoretical insights at the molecular level. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2994–3004, 2014

Dehydration of Bioethanol by Hybrid Process Liquid–Liquid Extraction/Extractive Distillation

Bioethanol is among the most promising of biofuels because it has an energy content similar to gasoline while generating lower pollutant emissions than gasoline. But, in order to be used as an automotive fuel mixed with gasoline, ethanol must have less than 0.5 wt % of water. To achieve required ethanol purity, in light of the fact that the ethanol–water mixture forms an azeotrope, unconventional separation techniques such as extractive distillation or azeotropic distillation are necessary. However, the purification of ethanol using conventional distillation followed by extractive distillation has the disadvantage of high cost of services. Thus, this study proposes alternative hybrid systems using liquid–liquid extraction and extractive distillation. The use of n-dodecane as entrainer for liquid–liquid extraction and glycerol as entrainer for extractive distillation has been considered. The proposed systems are analyzed and a comparison is done on their performance in terms of energy and total annual cost...

Computer-aided biocompatible solvent design for an integrated extractive fermentation–separation process

Computer-aided process/solvent design is introduced to find a feasible biocompatible solvent for an extractive fermentation and separation process. The designed biocompatible solvent serves as both the extractant for extractive fermentation and the entrainer for extractive distillation, to yield water-free ethanol. Several goals, such as maximizing production rate and extraction efficiency, and limiting solvent utilization, are simultaneously considered in the optimal solvent design problem. Thus, the design was formulated as a mixed-integer nonlinear optimization problem. A two-phase computational scheme was introduced to solve the problem. The mixed-integer hybrid differential evolution (MIHDE) algorithm was first applied to solve the problem in order to obtain a feasible solution. The feasible solution was then served as an initial starting point for the mixed-integer sequential quadratic programming (MISQP) solver to numerically confirm that the optimal design was achieved. We have compared the crisp and fuzzy approaches to the design problem. The fuzzy goal attainment approach is able to address goal trade-offs and yield an overall satisfactory grade for the problem.

Ionic Liquids for Chloromethane/Isobutane Distillative Separation: Express Screening

AbstractThe present study centres on room‐temperature ionic liquids (ILs) as entrainers in extractive distillation of chloromethane/isobutane mixtures. The binary system, chloromethane/isobutene, is an azeotropic system. In this study, IL entrainers are shown to be able to break the azeotrope and, thus, assure the separation in the whole range of chloromethane/isobutane ratios. ILs formed from different cations and anions are considered and their influence on chloromethane/isobutane separation is explored. Among the ILs studied, those containing the trifluoromethanesulfonate ([CF3SO3]–) or tricyanomethanide ([C(CN)3]–) anion are demonstrated to exhibit an enhanced potential for chloromethane/isobutane separation compared to the corresponding ILs based on the bis(trifluoromethylsulfonyl)imide ([Tf2N]–) anion. Moreover, the ILs enclosing these anions are cheaper than those with the [Tf2N]– anion. Thus, the separation ability, solubility of chloromethane/isobutane mixtures, and costs of IL entrainers can be adjusted by the right choice of cations and anions.

(Vapour + liquid) equilibria of ternary systems with ionic liquids using headspace gas chromatography

(Vapour + liquid) equilibrium (VLE) data for the ternary systems (hexane + benzene), (hexane + cyclohexane), (benzene + cyclohexane), and (ethanol + water) with an ionic liquid as entrainer for extractive distillation were measured by headspace gas chromatography. As ionic liquids, 1-hexyl-3-methyl-imidazolium bis (trifluoromethyl-sulfonyl) imide [HMIM][BTI], 1-octyl-3-methyl-imidazolium bis (trifluoromethyl-sulfonyl) imide [OMIM][BTI], 1-octyl-3-methyl-imidazolium trifluoro-methanesulfonate [OMIM][OTF], and 1-butyl-3-methyl-imidazolium trifluoro-methanesulfonate [BMIM][OTF] were used. The experimental data show that the ionic liquids investigated have a great influence on the separation factors of the systems (hexane + benzene), (hexane + cyclohexane), and (benzene + cyclohexane). The experimental data were compared with the predicted results using mod. UNIFAC (Do). The predicted results are in good agreement with the experimental data.

Multi-scale simulation of the 1,3-butadiene extraction separation process with an ionic liquid additive

A multi-scale simulation method is proposed to enable screening of ionic liquids (ILs) as entrainers in extractive distillation. The 1,3-butadiene production process with acetonitrile (ACN) was chosen as a research case to validate the feasibility of the methodology. Ab initio calculations were first carried out to further understand the influence of ionic liquids on the selectivity of ACN and the solubility of C4 fractions in [CnMIM][PF6](n = 2–8), [C2MIM][X] (X = BF4−, Cl−, PF6−, Br−), by investigating the microstructure and intermolecular interaction in the mixture of C4 fractions and several selected ionic liquids. It was found that the selectivity of the ionic liquid is determined by both its polarity and hydrogen-bonding ability. Based on the analysis, a suitable ionic liquid was chosen. With the ab initio calculation, a priori prediction of thermophysical data of the IL-containing system was performed with COSMO-RS. The calculation revealed that the selectivity of the extractive solvent was increased by an average of 3.64% after adding [C2MIM][PF6]. With above calculations, an improved ACN extraction distillation process using ILs as an entrainer was proposed, and a configuration for the new process was constructed. Based on the established thermodynamic models which have considered the properties from the molecular structure of ILs, process simulation was performed to obtain the process parameters which are important for the new process design. The simulation results indicated that the temperatures at the bottom of the extractive distillation column with the ionic liquid as an additive are lowered by an average of 3.1 °C, which is significant for inhibition of polymerization. We show that the ACN consumption using this process can be lowered by 24%, and the energy consumption can likewise be lowered by 6.62%.

Ionic Liquids as Entrainers in Extractive Distillation: Isobaric Vapor−Liquid Equilibria for Acetone + Methanol + 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate

Isobaric vapor−liquid equilibria for the binary systems acetone + methanol, acetone + 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][triflate]), and methanol + [emim][triflate] as well as the vapor−liquid equilibrium for the acetone + methanol + [emim][triflate] ternary system have been obtained at 100 kPa using a recirculating still. The addition of the ionic liquid to the solvent mixture produced an important salting-out effect, and the azeotrope tended to disappear for small contents of ionic liquid. The experimental binary data sets were independently fitted with the electrolyte NRTL model, and the parameters of Mock's model were estimated for each binary system. These parameters were used to predict the ternary vapor−liquid equilibrium which agreed very well with the experimental one.