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Octane and p-xylene are common components in crude gasoline, so their separation process is very important in petroleum industry. The azeotrope and near azeotrope are often separated by extractive distillation in industry, which can realize the recovery and utilization of resources. In this work, the vapor-liquid equilibrium experiment was used to obtain the vapor-liquid equilibrium properties of the difficult separation system, and on this basis, the solvent extraction mechanism was studied. The mechanism of solvent separation plays a guiding role in selecting suitable solvents for industrial separation. The interaction energy, bond length and charge density distribution of p-xylene with solvent are calculated by quantum chemistry method. The quantum chemistry calculation results and experiment results showed that N-Formylmorpholine is the best solvent among the alternative solvents in the work. This work provides an effective and complete solvent screening process from phase equilibrium experiments to quantum chemical calculation. An extractive distillation simulation process with N-Formylmorpholine as solvent is designed to separate octane and p-xylene. In addition, the feasibility and effectiveness of the intensified vapor recompression assisted extraction distillation are also discussed. In the extractive distillation process, the vapor recompression-assisted extraction distillation process is globally optimal. Compared with basic process, the total annual cost can be reduced by 43.2 %. This study provides theoretical guidance for extractive distillation separation technology and solvent selection.

A combination of molecular modelling and experiments was conducted to study the separation of acrylic acid and propionic acid through extractive distillation with polar aprotic entrainers. It was found that acrylic acid and propionic acid can be efficiently separated through extractive distillation with a polar aprotic entrainer, resulting in the entrainment of acrylic acid and making propionic acid the most volatile compound. Vapour-liquid equilibrium experiments were conducted with 25 wt% acrylic acid, 25 wt% propionic, and 50% wt% entrainer. Dimethyl sulfoxide (DMSO) was found to induce the highest relative volatility of 1.56 at 25 mbar, which agrees well with the predicted value of 1.66 using the simulation software COSMO-RS. The difference in pKa (ΔpKa = 0.63) between acrylic acid and propionic acid is the main cause for the enhanced relative volatility. The corresponding difference in hydrogen bonding strength was calculated using COSMO-RS to result in ΔE = 1.8 kJ/mol at 25 °C between acrylic acid and propionic acid with the total mixture. When dodecane was selected as an entrainer, acrylic acid became the most volatile compound instead of propionic acid. This is explained by the fact that propionic acid has two extra hydrogen atoms available to have a Van der Waals interaction with the carbon atoms of dodecane. The difference in total Van der Waals interaction between the two carboxylic acids in the mixture with dodecane is 1.34 kJ/mol at 25 °C. This difference results in a relative volatility of 0.91, which is too small to be exploited in a distillation process, and it was concluded that for this mixture, DMSO was the best entrainer in the study.

Background After ammoniation of propacetamol hydrochloride, the liquor contains an azeotropic mixture of acetone and diethylamine. The mixture must be separated to reuse the solvent and the raw material. However, the separation of acetone and diethylamine is difficult because the boiling point difference is only 0.6°C. Methods In this study, the mechanism of separating azeotropes was studied by quantum chemical calculations of the σ-profiles, interaction energy and molecular conformation. The vapor-liquid equilibrium data were supplemented by experimental analysis of the vapor-liquid equilibrium for cyclohexanol and diethylamine. The relative volatility of the light and heavy components of the azeotrope was investigated after adding the solvent. Sequential iteration method was used to optimize the extractive distillation process. The parameters in process such as the feeding position, number of stages and the amount of solvent are optimized, and the minimum total annual cost is obtained. Significant findings The results showed that the two-column feed preheating extractive distillation process was the lowest. The results showed that the two-column feed preheating extractive distillation process afforded the lowest total annual cost. Thermodynamic and environmental analyses showed that the two-column feed preheating extractive distillation process afforded good energy-saving, with minimal environmental impact. This study is significant for implementing the extractive distillation process for azeotrope separation and the sustainable development of acetone and diethylamine products.

To develop efficient ionic liquid (IL)-based separation processes like extractive distillation, the knowledge of IL-involved vapor–liquid equilibria (VLE) is necessary. Since experimental measureme...

In this work, a novel sequential approach for optimal conceptual design of extractive distillation columns for the separation of ternary azeotropic mixtures was developed. This approach is based on...

Ionic liquids (ILs) have been demonstrated as promising alternatives to conventional entrainers in separation of azeotropic mixtures mostly investigating phase equilibrium and process design scenarios. However, proper selection of ILs for a specific task always remains challenging. Hence a simulation tool, i.e. conductor like screening model for real solvents (COSMO-RS) was applied to address this challenge. Furthermore, screened ILs were simulated as entrainers for ethanol water separation by extractive distillation. The current study also aims to demonstrate a systematic approach to retrofit existing processes, by employing ILs as green entrainers. Screening of twenty-five (25) ILs was carried out using COSMO-RS to select suitable ILs as green entrainers based on activity coefficient, capacity and selectivity. Results illustrated that tetramethylammonium chloride ([TMAm][Cl]) due to its strong hydrogen bonding ability was found to be the best ILs entrainer. Moreover, in order to reduce the operating costs without compromising desired product purity (ethanol purity ≥99.5% in top product), the selected ILs (8 kg/h) in a mixture with ethylene glycol (72 kg/h) were simulated using Aspen plus v.11. The simulation results revealed that by combining tetramethylammonium chloride (2 kg/h) with ethylene glycol (78 kg/h) reduced 7.26 tons of CO2 emissions/year through heat integration by saving 1.49*108 kJ/year energy besides minimizing operating costs. In conclusion, the systematic selection of ILs as green entrainers in combination with ethylene glycol and then the appropriate simulation of the whole system will ultimately reduce the cost of the separation process and reduce the emission of greenhouse gases as well utilization of toxic conventional entrainers.

Background: Economically recovering valuable cyclohexane and sec-butyl alcohol from wastewater is an important industrial problem worthy of research and investigation. The available separation flowsheet in open literature was a heat pump assisted four-column scheme combining heterogeneous azeotropic and extractive distillation. However, the above design achieves significant energy saving at the cost of huge capital investment and increased operational complexity involved in the compression system. The purpose of this paper is to develop an improved configuration for separating the ternary system without using the expensive compression system, and it can also significantly improve the economics. Methods: The core design concept of our proposed three separation flowsheets is to fully utilize the advantage of the heterogeneity of the ternary system by introducing the fresh feed into a decanter for natural liquid-liquid splitting and innovatively applying a direct-contact heat exchanger to preheat the fresh feed. Besides, the technologies of dividing-wall column, side-stream extractive distillation and heat integration are also integrated to the heterogeneous azeotropic and extractive distillation for further energy saving. Significant findings: In comparison with the existing design, our final proposed heat-integrated heterogeneous distillation process with two dividing-wall columns can significantly save energy consumption 24.5%, total annual cost 43.6% and CO2 emission 13.2%.

Acetone and n-heptane are common solvents in the pharmaceutical industry and they have been found in wastewater. Under atmospheric conditions, the mixture of these compounds creates a minimum-boiling azeotrope. The extractive distillation process with a high boiling solvent is commonly utilized to separate the azeotropes in the industry to minimize waste, reuse resources, achieve clean production, and preserve the environment. In this work, extractive distillation was applied to separate the binary azeotropic system of acetone and n-heptane in wastewater using butyl propionate as a solvent. The characteristics of the process are designed and simulated via Aspen Plus. The simulation results showed that to get a distillate containing at least 99.5 mass% acetone, a solvent-to-feed ratio of 1.4, a reflux ratio of 1.5, a number of stages of 30, a feed stage of 26, a solvent stage of 10, and a solvent temperature of 298.15 K were required. The optimum operating parameters of the process were also obtained using the NLP optimization method, with the minimum total annual cost as the objective function. While the process was operating in optimal mode, CO2 emissions were calculated to be 0.0780 kg CO2/kg feed.

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.

A comparative analysis of energy consumption for extractive distillation flowsheets was carried out. This was done by the example of methanol - ethanol - acetonitrile - mixture. These solvents are used in pharmaceutical industries. The basic system methanol - ethanol - acetonitrile - water contains four binary and one ternary minimum-boiling azeotropes. Pressure change has almost no effect on the location of separatric surfaces. Therefore, extractive distillation should be used to separate solvents mixtures of any composition. Industrial entrainers dimethyl sulfoxide and glycerol are considered as selective agents. The effect of entrainer on vapor-liquid equilibrium at 30 and 101.32 kPa was evaluated by the relative volatility of the components forming azeotropes and the selectivity of the agents. The simulation was carried out on the Aspen Plus V.10.0 program environment. Two extractive distillation flosheets for the methanol - ethanol - acetonitrile - water separation are investigated. Both schemes include a two-column complex for the extractive distillation of the base mixture: in the first column, organic solvents are separated from water, and in the second column, the agent is regenerated. For subsequent separation of acetonitrile, extractive distillation with dimethyl sulfoxide or glycerol is also used. But separation of methanol-ethanol - entrainert zeotropic mixtures differs in the order of separation of components in schemes I and II. In scheme I, regeneration of the agent and further separation of the alcohol mixture is provided, in scheme II, methanol is first isolated, and then ethanol is separated from the agent. The optimized results for both schemes at columns pressures 30 and 101.32 kPa are performed. Different sets of selective agents introduced into extractive distillation columns are considered. The concept of an effective set of entrainers is introduced. The evaluation of the design alternatives need the assessment of energy demands. Total energy consumption for separation (reboiler duty) for the scheme II at 35-38% higher than values for scheme I. On the criterion of the minimum total energy consumption for the separation the scheme I was recommended: pressure columns 30 kPa, effective set of entrainers: glycerol for dehydration of the base mixture and dimethyl sulfoxide for acetonitrile isolation.

This article investigates the performances of different extractive distillation processes intensified with dividing-wall column for separating benzene-isopropanol-water ternary mixtures. All the processes with ethylene glycol as solvent are optimized with the minimal total annual cost (TAC) as target. In order to get the global optimal solution intelligently, an improved simulated annealing algorithm is adopted, which is programmed in MATLAB and linked to Aspen Plus. The results show that the extractive dividing wall column-solvent (EDWC-S) process consisting of an extractive dividing wall column and a solvent recovery column is the best scheme. It can reduce the TAC by 28.65% and CO2 emissions by 32.84% compared to the conventional triple-column extractive distillation process.

In this work, we firstly report on the rigorous design, optimization, and carbon emission analysis of the processes separating acrylonitrile (AN), acetonitrile (AC), and water. Two bi-sectional processes, which integrate heterogeneous extractive distillation with hybrid extraction-distillation (the HHED process), and that with pressure swing distillation (the HPSD process), are proposed. Compared with the existing configuration, operation using 30% less entrainer amount is found feasible for both processes, leading to 9.8% energy saving. Also, the optimized HHED process saves 4.8% total annual cost (TAC) and 5.8% carbon emission from the optimized HPSD process. Besides, implementing a vapor recompression cycle on the optimized HHED process reduces 31.1% CO2 emission but increases 6.6% of TAC. On the other hand, the heat-integrated HPSD process with an economizer design does not outperform the non-integrated HHED process. Finally, separation using heterogeneous azeotropic distillation or hybrid extraction-distillation process in single is conceptually rejected. Through this work, the industrial guidance could be provided.

To obtain the production of propylene oxide (PO) with high purity, a coupled azeotropic and extractive separation process is proposed to remove the impurities such as aldehyde, methanol, methyl for...

As there is an azeotropic point between methanol and ethyl formate, they cannot be completely separated by ordinary distillation. In this paper, extractive distillation was applied and dimethyl sul...

Stochastic optimization is inefficient, although it shows robustness against local optimum and can guarantee high-quality solutions. Parallel computation can be a promising way to improve the efficiency of stochastic optimization. However, the common environments do not support calling multiple simulators through the win32com interface, which hinders parallel computation. As a countermeasure, this study proposes a population-distributed differential evolution (DDE) framework, which combines multiple optimizers through the shared message passing medium. The framework distributes the population into groups (subpopulations) on different threads by a pool model, which can make full use of a multi-core CPU and significantly accelerate the computation. Moreover, we considered both the synchronously and asynchronously distributed differential evolution. Three case studies (benzene/toluene/xylene conventional distillation, acetone/methanol/water extractive distillation, and heat pump assisted dividing-wall column separating benzene/toluene/xylene) are optimized to show the superior performance of the DDEs. The parallel framework can reduce the computing time by ∼70% on a 4-core CPU, which is a significant improvement. DDEs cause some parallel efficiency loss, which is 5–10% and 10–20% for ADDE and SDDE, respectively. Further, based on time consumption analysis, we explain the reasons for the efficiency loss.

Extractive distillation (ED) can be used to separate mixtures with low relative volatilities that are even close to unity. It is widely adopted for the separation of aromatics and nonaromatics in t...

Orange processing generates a high amount of waste rich in natural compounds that can be used to obtain added-value products or as raw material in biorefineries. Limonene (terpene) and linalool (ox...

The paper is devoted to the development of diethyl ether + hexane + ethyl acetate + ethanol mixture (solvents of the dihydroquercetine production) separation flowsheets based on the analysis of the structure of the phase diagram. The phase equilibrium of the quaternary system was studied using mathematical modeling in the AspenPlus. The parameters of Non Random Two Liquid model allow reproducing vapor-liquid equilibrium data and azeotropes characteristics with a relative error not exceeding 5%. It was shown that the system was characterized by the presence of three binary azeotropes and the phase diagram was divided into three distillation regions. Based on a literature analysis N-methyl-2-pyrrolidone was selected as a solvent for the extractive distillation. The selectivity of the separating agent was calculated and it was shown that N-methyl-2-pyrrolidone influenced the relative volatility of components to varying degrees. Two flowsheets containing a diethyl ether separation column and two extractive distillation complexes were proposed. The flowsheets differ in the sequence of separation of the components: hexane, ethyl acetate and ethanol. The distillation process was simulated and the operating column parameters (number of stages, feed stage, reflux ratio, solvent to feed volume ratio) were determined. Selected parameters meet the minimum energy consumption. An energy-efficient separation variant was chosen.

The performance and effectiveness of the conventional and heat-integrated side-stream extractive distillation arrangements are explored with the simultaneous consideration of the steady-state economics, thermodynamics and dynamic controllability aspects of the process. The overall performance of simple stream-to-stream heat-integrated F-S-E configuration (serially preheating column inlet feeds by solvent stream) is superior to others because of the least total annual cost (TAC), CO2 emissions and highest second-law efficiency among these side-stream cases. It can further reduce 8.16% in TAC compared to the conventional extractive distillation configuration. Exergy and entropy generation analyses are employed in these heat-integrated side-stream extractive distillation arrangements to thorough evaluate the energy degeneration in each component. Furthermore, dynamic control analyses for conventional and heat-integrated side-stream extractive distillation processes are also explored. Two novel compromised tactics are proposed to make the economically optimal heat-integrated arrangement more stable at rejecting large feed disturbances according to the physical implemented issues of economizers. Both effective and robust dual-product quality controls are provided for tackling the large (20%) throughput and feed composition perturbations. Furthermore, a new developed control scheme with parallel arrangement works better than that with series exchangers’ arrangement by comprehensively weighing results of steady-state economic design and dynamic controllability.

Methanol and methylal form a minimum boiling point azeotrope and cannot be separated by conventional distillation. In this paper, the azeotrope was separated by extractive distillation with cyclohe...

Ternary extractive distillation (TED) is an effective and sustainable separation process for treating pharmaceutical wastewater containing ethyl acetate/isopropanol/water, corresponding to three bi...

Ethyl propionate is usually produced from esterification of propionic acid and ethanol in the industry. However, the purification of ethyl propionate remains a challenge because the unreacted ethan...

Ionic liquids (ILs) have shown remarkable potential for applications in separation, such as extractive distillation and liquid–liquid extraction. Crucial to these applications is the estimation of ...

The mixture of water, methanol, and ethanol is frequently produced in the pharmaceutical industry. To separate the mixture by extractive distillation, the selection of entrainer is a crucial step. ...

The extractive distillation of an isobutanol–isobutyl acetate mixture using dimethylformamide has been considered. Schemes that use vapor recompression heat pumps and partially thermally coupled distillation systems both without and with a heat pump are considered in comparison with the conventional schemes. It is shown that the use of heat pumps in the process under investigation allows for a considerable reduction in the energy consumption and total annual costs.

There are quite a few papers already published in open literature addressing the overall control strategy of minimum-boiling extractive distillation system. Although the two-column extractive disti...

n-Propanol, as an important chemical raw material, is used as a solvent and intermediate in chemical industrial production and drug synthesis. In chemical production, alcohol and water easily form ...

There are very few papers in the open literature studying the design of extractive distillation system for separating maximum-boiling mixtures. Using the knowledge of the curvature of the distillat...

In this work, an extractive distillation configuration for dehydration of nitric acid is proposed with sulfuric acid as a solvent. Thermodynamic modeling of the vapor–liquid equilibrium of binary a...

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 ...

Despite generating enormous interest, the full landscape of process intensification and multiobjective optimization (MOO) remains unexplored in the area of batch extractive distillation (BED). This...

The selective properties of individual and binary agents are compared according to data obtained by gas–liquid chromatography (GLC). The agents for the extractive distillation of 12 homogeneous binary systems of various types, composed of substances of a diverse chemical nature, are recommended.

The possibility of the formation of practically nonvolatile molecular complexes between the components of mixture and the separating agent of various compositions has been shown using the benzene–heptane–N-methylpyrrolidone system as an example. When modeling the vapor–liquid phase equilibrium, as a rule, the real structure of the solution is not taken into account, assuming the monomolecular structure of the substances contained in the solution. This significantly affects the real values ​​of coefficients of relative volatility, leading to the appearance of concentration inversion. The values ​​of fractions of substances in a monomolecular form are experimentally determined.

The formation of heterogeneous ternary azeotropes poses a serious challenge to the recovery of diisopropyl ether (DIPE) and isopropyl alcohol (IPA) from the industrial effluent. To reduce the energ...

Extractive distillation is a common method to separate the mixture, which has the low relative volatility. Many solvents were screened to separate the mixture based on the experiment. Because the n...

Extractive distillation using tricyanomethanide-based ionic liquids (ILs) has been shown to be a promising and feasible process for effectively separate aromatics from pyrolysis gasolines. The high performance of these mass agents has been reported by evaluating simple synthetic n-heptane/toluene binary mixtures, on a wide temperature and solvent to feed (S/F) ratio ranges. However, industrial streams are much more complex with the presence of other aromatic and aliphatic compounds, like benzene, xylenes, and shorter and longer linear alkanes, creating further difficulties to the separation and thus must be studied. This work covers the phase equilibrium characterization of {n-hexane + benzene + IL} and {n-octane + p-xylene + IL} ternary systems with two tricyanomethanide-based ILs, namely 1-ethyl-3-methylimidazolium tricyanomethanide ([C2C1im][TCM]) and 1-butyl-4-methylpyridinium tricyanomethanide ([4-C4C1py][TCM]), addressing also the phase characterization of the corresponding {hydrocarbon + IL} binary...

The separation of close-boiling and azeotropic components by extractive distillation (ED) is a costly process. Because ED columns usually have relatively large top/bottom temperature difference, traditional energy-saving measures like heat integration/heat pump, are limited in reusing the system inherent waste heat. However, this opens an otherwise door for organic Rankine cycle (ORC), capable of converting waste heat into power regardless of the large temperature span. Consequently, several integrated ED-ORC systems with or without economizer(s) are therefore proposed, aiming at recovering both latent and sensible waste heat. An azeotropic n-heptane/isobutanol separation is used to illustrate the performance of these integrated systems. R227EA is selected as the ORC working fluid from 11 chlorine free candidates for the highest thermal efficiency of 8.23%. Compared to the basic case, the optimum integrated system without economizer only reduces TAC by 3.01%. While reusing the system inherent waste heat by adding economizer(s) can dramatically enhance the energy efficiency, leading to TAC saving up to 30.30%. The TAC reduction is attributed to dramatic hot utility consumption saving (∼ 45%). Sharing close technical parameters, the ED process will benefit more when retrofitted into the integrated systems under minimized column modifications.

A novel process for ethanol dehydration using extractive distillation in a modified divided-wall column has been proposed and its control studied. A single vessel is used to perform the tasks of pre-concentrating the dilute feed, producing high-purity water and ethanol products and recovering the ethylene glycol solvent. Feed is introduced on one side of the wall that receives no liquid from the rectifying section. Water is removed from bottom of this side that has an intermediate reboiler, which is heated by compressed overhead vapor. Ethanol is the distillate product and solvent comes out the bottom of the column to be fed near the top of the column. A complex control structure has been proposed that appears to lack robustness since it can only handle slow ramp disturbances. This paper demonstrates that a more simple control structure can provide effective regulatory control for large step changes in throughput and feed composition.

The application of ionic liquids in separating complex ternary azeotropic system via extractive distillation (ED) is investigated. Five configurations using 1-butyl-3-methylimidazolium dicyanamide ...

Deep eutectic solvents (DESs) as novel entrainers can be used for the separation of azeotropic mixture, and have received much attention in recent years. However, the researches about DESs mainly focus on vapor–liquid equilibrium (VLE) and extractive distillation experiment. In this work, an overall extractive distillation process for ethanol dehydration using ChCl/Urea (1:2) as entrainer is investigated. The physical properties of the DES are defined by correlating the experimental data. Three thermodynamic methods are employed to describe the phase behavior of ethanol–water–ChCl/Urea (1:2) system. COSMO-based theory is adopted to explain the differences in separation performance among ChCl/Urea (1:2), glycerol and [EMIM][BF4]. The design parameters of extractive distillation process are optimized by multi-objective generic algorithm (MOGA) with minimum total annual cost (TAC), minimum CO2 emissions E C O 2 and maximum efficiency indicator of extractive section (EExt) as objective functions. In addition, the control structure of extractive process is studied by Aspen Dynamics, and the proposed control structure could resist fresh feed flow rate and composition disturbances. The results show that ChCl/Urea (1:2) exhibits better separation performance in ethanol dehydration compared with glycerol and [EMIM][BF4]. Both COSMOSAC model relying on molecular information and NRTL model based on experimental data can well describe the vapor–liquid behavior containing ChCl/Urea (1:2). Entrainer purity plays an important role in extractive distillation process, and a proper concentration rather than nearly pure entrainer should arouse our attention in extractive distillation process. DESs as promising novel entrainers can be used in extractive distillation industrial for separating azeotrope.

Extractive distillation is an effective method for separating azeotropic or close boiling point mixtures by adding a third component. Various technologies for performing the extractive distillation process have been explored to protect the environment and save resources. This paper focuses on the improvement of these advanced technologies in recent years. Extractive distillation is retrieved and analyzed from the view of phase equilibrium, selection of solvent in extractive distillation, process design, energy conservation, and dynamic control. The quantitative structure–property relationship used in extractive distillation is discussed, and the future development of extractive distillation is proposed to determine how the solvent affects the relative volatility of the separated mixture. In the steady state design, the relationship between the curvature of the residue curve and parameters of the optimal steady state is also highlighted as another field worthy of further study to simplify the distillation process.

An organic salt choline chloride (ChCl) was introduced in ethylene glycol (EG) for improving the entrainer performance for ethanol dehydration by extractive distillation. The mixed solvent EG + ChC...

Thiophene (T) is one of the main sulfur-containing impurities in crude benzene produced by coke production. One effective way to remove the majority of thiophene from crude benzene is extractive distillation (ED) with dimethylformamide (DMF), which has been reported to increase the relative volatility of the benzene–thiophene (B–T) pair from 1.13 to 1.46–1.5 or 1.8–2.18. The aim of this work is to investigate the possibility of increasing the benzene yield from the initial fraction and reducing the ED heat demand of the separation of the B–T mixture with DMF as an entrainer by using an extractive distillation system with partially thermally coupled distillation columns (PTCED). To achieve this goal, both a conventional extractive distillation (CED) and a PTCED system were optimized. The total energy consumption in the column reboilers was selected as the optimization criterion. The same yield of benzene was achieved in the PTCED system at a lower column reboiler heat demand. As the benzene yield was increased, the energy savings of PTCEDS over CED increased. In addition, the production of the thiophene fraction required a significantly smaller reflux ratio in the side section of the PTCED system (1.0–2.28) than in the recovery column of the CED system (7.17–73.13).

Extractive distillation (ED) is one of the most promising approaches for the separation of the azeotropic or close-boiling mixtures in the chemical industry. The purpose of this paper is to provide a broad overview of the recent development of key aspects in the ED process involving conceptual design, solvent selection, and separation strategies. To obtain the minimum entrainer feed flow rate and reflux ratio for the ED process, the conceptual design of azeotropic mixture separation based on a topological analysis via thermodynamic feasibility insights involving residue curve maps, univolatility lines, and unidistribution curves is presented. The method is applicable to arbitrary multicomponent mixtures and allows direct screening of design alternatives. The determination of a suitable solvent is one of the key steps to ensure an effective and economical ED process. Candidate entrainers can be obtained from heuristics or literature studies while computer aided molecular design (CAMD) has superiority in efficiency and reliability. To achieve optimized extractive distillation systems, a brief review of evaluation method for both entrainer design and selection through CAMD is presented. Extractive distillation can be operated either in continuous extractive distillation (CED) or batch extractive distillation (BED), and both modes have been well-studied depending on the advantages in flexibility and low capital costs. To improve the energy efficiency, several configurations and technological alternatives can be used for both CED and BED depending on strategies and main azeotropic feeds. The challenge and chance of the further ED development involving screening the best potential solvents and exploring the energy-intensive separation strategies are discussed aiming at promoting the industrial application of this environmentally friendly separation technique.

Reactive distillation (RD) process is an innovative hybrid process combining reaction with distillation, which has recently come into sharp focus as a successful case of process intensification. Considered as the most representative case of process intensification, it has been applied for many productions, especially for production of ester compounds. However, such problems existing in the RD system for ester productions are still hard to solve, as the removal of the water which comes from the esterification, and the separation of the azeotropes of ester–alcohol (–water). Many methods have been studying on the process to solve the problems resulting in further intensification and energy saving. In this paper, azeotropic–reactive distillation or entrainer enhanced reactive distillation (ERD) process, reactive extractive distillation (RED) process, the method of co-production in RD process, pressure-swing reactive distillation (PSRD) process, reactive distillation–pervaporation coupled process (RD–PV), are introduced to solve the problems above, so the product(s) can be separated efficiently and the chemical equilibrium can be shifted. Dividing-wall column (DWC) structure and novel methods of loading catalyst are also introduced as the measures to intensify the process and save energy.

The dehydration of isopropanol (B) from a mixture containing methyl ethyl ketone (A) and toluene (E) as pollutants by batch heteroazeotropic distillation (BHAD) is studied by dynamic simulation. The water (C) content of the feed is much lower than that of the BC azeotrope. Isopropanol can be obtained by conventional batch distillation under high reflux ratio and considerable loss. Toluene is a potential entrainer forming a ternary heteroazeotrope BCE. Dehydration is feasible by Mode II, Strategy A of BHAD, by which the whole amount of E-rich phase is refluxed, that of E-lean phase is withdrawn as distillate. Since the production is very slow due to the high (E-rich/E-lean) phase ratio, different operational strategies are studied in order to make the production faster without significant decrease in isopropanol recovery. These include taking a homogeneous fore-cut to remove methyl ethyl ketone, and Strategy B of Mode II, where one part of the E-rich phase is also withdrawn as distillate. A novel operational policy is proposed, as well, that is a combination of Strategies A and B. The application of cyclohexane (D) as entrainer and batch extractive distillation with dimethyl sulfoxide (F) are also studied.