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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.

Two energy efficient extractive distillation processes are proposed to separate acetonitrile/1,4-dioxane/water mixture in this study. The COSMO-SAC model is chosen to screen suitable entrainer and dimethyl sulfoxide is selected. Process intensification technologies of heat pumps and heat integration are utilized in the processes for energy conservation. Several evaluation methods containing energy, economic, environmental and exergetic analysis are introduced to evaluate the performance of different processes. The most energy-saving and environmental friendly process is heat pump assisted direct extractive distillation that achieves an energy reduction by 53.58% and a carbon dioxide emission reduction by 53.56% compared to the indirect scheme, while the direct scheme assisted with heat integration performs best that achieves a reduction by 40.38% on total annual cost.

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.

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%.

Recently, a new industrial relevant wastewater (water/Cyclohexane/sec-butyl alcohol) separation process with vapor recompression and thermal coupling was proposed as the conventional homogeneous extractive distillation. This highly integrated and interactive multivariable process presents great challenges to the dynamic controllability and process safety analysis. In this paper, based on the concept of “simultaneous design”, the newly proposed process is systematically investigated from the perspective of process improvement, plantwide control and safety analysis. Firstly, for energy conservation and CO2 emission reduction, the new complex process is further improved by applying the features of heterogeneous distillation. And a modified heterogeneous distillation process with heat pump is proposed, which can save reboiler duty about 16.8 % and save compressor electricity up to 67.7 %, while the reduction of CO2 emissions is 23.5 %. Secondly, for the efficient heterogeneous distillation process, an effective and robust plantwide control strategy is developed and tested under large throughput and feed composition disturbances. Last, with the dynamic simulation assisted HAZOP, a quantitative safety analysis is conducted, which can help experts to consider the nature, scale and response time of hazards and identify the potential propagation of deviation between different units, and then propose more specific or accurate safety recommendations correspondingly.

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.

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.

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.

N-propanol and benzene are important chemical organic compounds, which widely exist in wastewater of chemical industry, medicine and other fields. Because they form azeotrope with water, extractive distillation was used to separate them. In order to increase the efficiency of energy utilization, vapor recompression technology was added on the basis of extractive distillation. On the basis of vapor recompression assisted extractive distillation, energy integration was carried out according to pinch technology, and the optimal energy utilization method was found. The exergy loss and gas emission of each process were studied and analyzed. The results show that the vapor recompression assisted distillation process with feed preheating can reduce the heat duty and gas emissions, and improve exergy efficiency and economic performance. Therefore, the vapor recompression assisted distillation process with feed preheating can effectively treat the wastewater containing benzene / n-propanol. It has the advantages of low cost, energy saving and environmental protection, which is of great significance to the development of environmental protection industry.

Cyclohexane and sec-butyl alcohol are widely used in the pharmaceutical and chemical industries. The separation of cyclohexane/sec-butyl alcohol/water azeotropic mixture is of great significance for mitigating environmental risk, recycling solvents, and maintaining developmental sustainability. Based on the COSMO-SAC model, the infinite dilution activity coefficients of the components were calculated, and the final solvent was further obtained by relative volatility and solvent power screening. Taking the total annual cost as the objective function, the extractive distillation process is optimized based on a sequential iterative optimization algorithm. To further reduce the process energy consumption, several energy-saving processes were explored. Energy-saving processes are compared in terms of total annual cost, CO2 emissions, and thermodynamic efficiency. It was found that the total annual cost and thermodynamic efficiency of the processes show an increasing trend, while CO2 emissions show a decreasing trend. The results of stage-exergy indicate that the processes with heat pump are relatively small. The heat pump combined with the thermal coupling extractive distillation process exhibits better thermoeconomic and environmental performance. It provides theoretical guidance for improving the separation and recovery of value organics and energy-saving optimization of processes, which conforms to the theme of sustainable and environmental development.

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.

Ethyl acetate is a vital chemical raw material and is usually produced by esterification in industry. But this reaction can produce multiazeotrope mixtures of ethyl acetate/ethanol/water. In this work, triple column pressure-swing distillation process with and without heat integration and hybrid processes combining extractive distillation and pervaporation are proposed to separate a mixture of ethyl acetate/ethanol/water. Furthermore, the three processes are comprehensively compared with the triple-column extractive distillation process. Based on minimization of the total annual cost, the parameters of the all processes are optimized. The triple-column extractive distillation process has the greatest economic advantage. Additionally, the performances of the all processes in environmental protection and energy efficiency are evaluated. The energy efficiency of the combined extractive distillation and pervaporation unit process is relatively low, but its environmental impact is the lowest among the four processes.

In this study, a few extractive distillation processes with ethylene glycol as solvent are proposed to separate high-purity ethanol and tert-butanol from industrial effluents, including direct ED, indirect ED and heat pump assisted indirect ED. All these processes are optimized with targeting minimum annual total costs by a sequential iteration algorithm. After that, a head-to-head comparison is completed regarding distributions of cost, energy and CO2 emission. The results showed that the direct ED is the most economical process reducing minimum annual total costs by 30.15 % than the heat-pump assisted indirect ED, while the latter is the most energy-efficient process saving energy consumption and CO2 emissions by 14.78 % and 21.79 % than the direct ED.

The production of ethylbenzene from dry gas is a representative of an energy-intensive process in oil refineries, and the distillation process accounts for the major energy consumption and carbon emissions. Due to the increasing energy and environmental challenges, there is a strong demand for new technologies or intensified process designs that enable us to have energy-efficient and sustainable process operations. In this work, an ionic liquid (IL)-based energy-efficient extractive distillation (ED) process with low carbon emission is proposed for the distillation process of ethylbenzene production from dry gas. First, the structure of task-specific ILs is optimized through the computer-aided IL design (CAILD) method with a novel design objective. An ammonium-based IL ethylammonium trifluoromethanesulfonate ([C2H8N][TfO]), that has the best objective performance, is identified by solving a mixed-integer nonlinear programming (MINLP) problem. The energy, environmental (carbon emission), and economic performance of this [C2H8N][TfO]-based ED process in the ethylbenzene production is then thoroughly evaluated on the basis of optimized process operations in Aspen Plus. For demonstration purposes, a case study for the separation process of an industrial-scale ethylbenzene production in a Chinese refining industry is performed. When compared to the conventional process that is currently used in the petrochemical industry, our proposed [C2H8N][TfO]-based ED separation process has 40 % energy (hot utility) savings and a 11 % cost reduction. Notably, the IL-based ED separation process has 40 % lower carbon emissions versus the conventional process, indicating its great potential for sustainable operation in the production of ethylbenzene from dry gas.

The major intrinsic obstacle of extractive distillation (ED) is high energy consumption. Thus it is significant to reduce the energy consumption of ED processes as low as possible. In this work, using green solvent ILs which have high selectivity, process intensification and optimizing operation parameters are adopted in the ED of ethyl acetate-ethanol-water mixture. For high-selective entrainers, ionic liquid (IL) 1-butyl-3-methylimidazolium acetate ([bmim][OAc]) is used as the solvent for the ED process of ethyl acetate-ethanol-water, and the physical properties of [bmim][OAc] are accurately defined in Aspen Plus by correlating the experimental data. To optimize the distillation sequence for process intensification, thermally coupled ternary extractive distillation (TCTED) process is adopted for the separation of the ternary mixture. Moreover, multi-objective generic algorithm with total annual cost (TAC), CO2 emissions (ECO2) and thermodynamic efficiency (η) as objective functions is used to optimize the operation parameters in order to evaluate the economy, the energy efficiency and environmental impact of alternative ternary extractive distillation processes. The result shows that the TCTED process can result in the reduction of both TAC and ECO2. So, this study can provide a reference for the separation of ethyl acetate-ethanol-water mixture in industry.

The investigation of dynamic controllability for the double side-streams ternary extractive distillation (DSTED) is necessary due to its advantages in energy-efficient. However, the control strategy of the energy-saving DSTED scheme is unique and complex issues owing to the wobbly of side-stream flow rate. Herein, control strategy of the energy-saving DSTED scheme is explored for separating ternary azeotropic mixtures acetonitrile/methanol/benzene. Inspiring from the control strategy of the ordinary triple-column extractive distillation scheme, the fundamental control structure CS1 is firstly designed. The control scheme CS2 with feed/side-stream (F/SS) ratio and control structure CS3 with feedforward and F/SS are then investigated to achieve higher efficiency of process control. Finally, a robust control strategy CS4 with the ratio of reboiler duty and feed flow rate and without F/SS ratio is proposed to well maintain the product purities. Moreover, additional ±15% feed flow rate and composition disturbances are added in the CS4 to assess the stability and controllability of the energy-saving DSTED. Dynamic performances illustrate that the structure CS4 can handle as well as that of confronted ±10% disturbances when the large disturbances are occurred in the real chemical process.

The separation of ternary mixtures with homogeneous or heterogeneous multi-azeotropes has received increasing attention. In this work, a systematic design, optimization and control procedure is proposed for extractive distillation of heterogeneous mixtures with four azeotropes. Herein, the ternary system isopropyl alcohol/isopropyl acetate/water is taken as a case study. The suitable entrainer is first obtained through a proposed approach combining the vapor–liquid equilibrium (VLE) curves and infinite dilution activity coefficient ratios. Conceptual design of two alternative separation sequences involving double-column extractive distillation with a pre-concentrator (DEDP) and triple-column extractive distillation (TED) are then investigated based on thermodynamic insights. With the method of sequential iterative optimization and taking total annual cost (TAC) as the objective function, the two processes are optimized. The optimal results indicate that the DEDP process with dimethyl sulfoxide as entrainer can save 6.43% TAC than that of TED. Finally, a new control structure combining reflux flowrate-to-feed (R/F) and adjustable reboiler duty-to-feed (QR/F) with “HiLoSelect” strategy is proposed to better handle three product purities than that of the basic control structure while feed flowrate and composition disturbances are introduced in the studied DEDP process.

Ethyl acetate and ethanol are important organic solvents in fine chemical industry, which form with water ternary minimum-boiling azeotrope and three binary azeotropes, including heterogeneous-azeotrope. In this article, different distillations and pervaporation methods are studied to separate sharply the ternary mixture. In the case of separation of highly non-ideal mixtures the distillation based separation methods can be extraordinarily complex. The extractive heterogeneous-azeotropic distillation (EHAD) as new improvement can be a promising tool for splitting the ternary mixture. This process contains the preferences of heterogeneous-azeotropic- and extractive distillations in one unit without extra material addition. Four advanced separation methods are compared: Method I (pressure swing distillation (PSD) for ethyl acetate purification with extractive distillation (ED) for ethanol purification), Method II (PSD with distillation-hydrophilic pervaporation (D + HPV) for ethanol purification), Method III (EHAD + PSD with ED) and Method IV (EHAD + PSD with D + HPV). The different alternatives are rigorously modelled in ChemCAD simulator and optimized with the dynamic programming optimization method first in the literature. In the case of distillation operations, heat integration is also considered, the feed is preheated with its bottom stream. Such ternary pervaporation separation with new semi-empirical model has not been published in this professional flowsheet environment yet. The distillation and pervaporation models are experimentally verified. Separation factor values are compared to those of other published membranes in the recent literature and it is found that PERVAP™ 1510 has the highest separation factor value. It can be determined that every method is capable for the separation of ethyl acetate-ethanol-water ternary mixture. The methods are optimized by economic evaluation based on the total annual cost (TAC) and the EHAD + PSD with D + HPV is found the optimum, because it has the lowest heat duties.

This paper explores the dynamic control of thermally coupled ternary extractive distillation process containing two extractive columns with recycle splitting of mixed separating agent by taking the separation of tetrahydrofuran/ethanol/water as a demonstrating example. A series of control structures are devised and assessed by the large (20%) perturbations of throughput and feed composition, and the robust regulatory control is achieved since the purities of all three products are closely going back to their initial steady-state design specifications when facing the large (20%) feed flowrate and composition disturbances. Besides, the dynamic response performance for control strategy with product ethanol purity controlled by manipulating the reflux ratio is superior to that with manipulating solvent flowrate in terms of peak dynamic transients, settling time and steady-state offsets when facing the large (20%) throughput and feed composition disturbances for extractive rectifier column C2. The direct dynamic response performance comparisons for conventional and thermally coupled processes with mixed entrainer are also investigated and showed that there is no conflict (tradeoff) between the steady-state economics and dynamic controllability for this system.

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.

The existence of heterogeneous azeotrope of CO2–C2H6 makes it difficult to separate CO2 from the hydrocarbons in the associated gas by cryogenic extractive distillation process. A four-column extractive distillation system using natural gas liquid as heavy solvent is used to separate CO2–C2H6 azeotrope. Carbon dioxide, ethane, propane and butane are recovered from the top of the extractive distillation column, deethanizer, depropanizer and debutanizer respectively. The C3+ hydrocarbon mixture called natural gas liquid is recovered at the bottom of the debutanizer, one part of which is transported as NGL product and the other part is pumped back near the top of the extractive distillation column as solvent. The purpose of this paper is to develop an effective plant wide control structure for this four-column extractive distillation system. Fixed reflux ratio and reflux/feed ratio control structure are used to investigate the controllability of four-column extractive distillation. Results show that both control structures have successfully realize the dynamic simulation of the extractive distillation process. However, under the disturbance of feed flow rate and composition, the controllability of reflux/feed ratio control structure on purity of top distillation products is better than that of fixed reflux ratio control structure. The reflux/feed ratio controller of four columns can adjust the reflux ratio in real time according to the disturbance of feed flow and composition, which greatly improves the stability of the top distillation products purity.

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.

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.

The increasing concern about environmental issues and the requirement to reduce the negative influence of industrial processes has directed the attention of scientific community toward the development of new green solvents. Recently, Deep Eutectic Solvents (DESs), which are ILs analogues have appeared as a promising substitutes to conventional volatile organic solvents. Unlike ILs, DESs offer inexpensive and easy synthesis, less toxicity and good biodegradability. In this study, ammonium-based deep eutectic solvent was synthesized and its feasibility was assessed as extracting agent for acetonitrile dehydration using extractive distillation. Glycolic acid and tetramethylammonium chloride (TMAC) based DES was prepared in 3:1 M ratio (GTM3:1) due to its well-known advantages over ionic liquids or organic molecular solvents. Isobaric vapor–liquid equilibrium data for pseudo-binary mixtures (acetonitrile–GTM3:1 & water–GTM3:1) were determined at 101.32 kPa. The pseudo-ternary VLE data of acetonitrile–water–GTM3:1 were also determined by keeping the concentration of DES nearly constant (x3 = 0.05, 0.10, and 0.15). The experimental data for these systems, were fitted using nonrandom two-liquid (NRTL) model and good correlation between predicted values and experimental data were obtained. From the results, GTM3:1 was capable of improving the relative volatility of the studied azeotropic mixture and successfully eliminated the azeotrope. The recoverability of used GTM3:1 was also investigated and the chemical properties of recovered GTM3:1 were found stable.

In this work, we propose the development of a dividing wall column (DWC) for the separation of ternary azeotropic mixture using an entrainer. Traditionally, this type of complex ternary system is traditionally separated in a triple column extractive distillation (TCED), among which, the first column is served as an extractive distillation. For this, at first, the first two towers are proposed to transform into a single column with a dividing wall. The resulting scheme is called here as extractive single-partitioned dividing wall column (ESPDWC). Subsequently, further intensification is made by merging all three columns of TCED into a single unit with two dividing walls, from which, one can get three products and the entrainer simultaneously with reasonably high purity. This proposed configuration is named as extractive double-partitioned dividing wall column (EDPDWC). To make the proposed extractive DWCs more practical, the heat transfer through the internal dividing wall is taken into account. For the separation of a ternary azeotropic mixture (tetrahydrofuran-methanol-water) with the use of an entrainer (ethylene glycol), the performance improvement of the proposed DWCs is quantified over the conventional TCED in terms of energy and cost savings. It appears that the proposed double-partitioned extractive DWC secures a better performance than its single-partitioned counterpart for the sample multiple binary azeotropes case.

With the development and improvement of solvents (or entrainers), the extractive distillation process has been significantly enhanced, and the energy consumption of the separation process has been effectively reduced. In this work, the energy-efficient separation process for extractive distillation with deep eutectic solvent ChCl/Urea (1:2) is designed. The ethanol dehydration process is selected as a case study to evaluate the practical utility of this novel solvent in large-scale production. The multi-objective genetic algorithm is used to optimize the extractive distillation process, and the waste heat is recovered through the heat intensification strategy to achieve the optimal design. Five control schemes, which include proportional-integral (PI) and model predictive control strategies (MPC), are developed for the proposed separation process. According to the nonlinear relationship between manipulated variables and controlled variables, the improved control structures are designed to enhance the dynamic performance. Integral absolute error (IAE) and destroyed exergy are applied as evaluation criteria to test the controllability and energy efficiency of the system. The results show that both CS4 and MPC control schemes have good controllability, and the MPC control scheme displays better energy efficiency than the CS4 control scheme.

Design and control of an energy and cost efficient separation process is deduced amongst several evaluated separation alternatives for Dichloromethane-Methanol binary mixture. Separation process evaluation for this specific binary mixture has not received much attention in the open literature so far. In the present study, several other significant alternatives (Pressure swing distillation, Extractive distillation and Azeotropic distillation) for the separation of the mixture have been explored and compared with the single reported work published earlier wherein separation using pressure swing batch distillation method has been discussed. Steady state analysis reveals that out of these evaluated alternatives; Extractive distillation is the best method in terms of economics and energy efficiency. The TAC of the extractive distillation method (best amongst four alternatives studied including the published work of PSBD method) was found to be 27.62% less than that of the second best from the list, which is Pressure Swing Batch Distillation method (Heat integration variant). The saving by extractive distillation method will result in significant benefits based on the futuristic surge in compound annual growth rate in the production of Dichloromethane-Methanol. Further, a plantwide control structure is designed for the recommended extractive distillation flow sheet which is further evaluated for throughput and composition disturbances. The present study will be helpful in designing the real process plants for the separation of Dichloromethane-Methanol binary mixture.

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.

Ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][DCA]) and a mixture of ionic liquids [C2mim][DCA] + 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) were used as extractive distillation solvents to separate tert-Butyl alcohol (TBA) + water. The vapor-liquid equilibria for TBA + water + [C2mim][DCA] and TBA + water + [C2mim][DCA] + [C2mim][OAc] were measured at 101.3 kPa. The NRTL model was employed to correlate the vapor-liquid equilibrium data, and the binary interaction parameters were obtained. The experimental results show that both of the solvents can improve the relative volatility of TBA to water, and completely destroy the azeotropic point of TBA-water. There is no synergistic effects between [C2mim][DCA] and [C2mim][OAc], and the selectivity of [C2mim][OAc] is higher than that of [C2mim][DCA], but the viscosity of [C2mim][DCA] is lower.

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.

Dimethyl carbonate and ethanol can form an azeotrope with the minimum boiling point. To separate the azeotrope (dimethyl carbonate + ethanol) by extractive distillation, p-xylene, butyl propionate, and isobutyl acetate were chosen as entrainers, and the isobaric vapour-liquid equilibrium (VLE) data for the binary systems of (dimethyl carbonate + p-xylene), (dimethyl carbonate + butyl propionate), (dimethyl carbonate + isobutyl acetate) and (ethanol + isobutyl acetate) were measured at 101.3 kPa using a modified Rose type recirculating still. The thermodynamic consistency of the VLE experimental data for the four binary mixtures was tested by the Herington and van Ness methods. Furthermore, the measured VLE data were correlated by the NRTL, UNIQUAC and Wilson thermodynamic models and the binary interaction parameters of the three models were regressed. Based above, an extractive distillation process with the entrainer of p-xylene was proposed and simulated to separate the azeotrope (dimethyl carbonate + ethanol).

The production of bioethanol is growing, as it is been used as biofuel which is termed as a clean energy fuel. When ethanol is blended with gasoline, the octane number of the mixture increases and acts as an antiknock agent, besides releasing fewer pollutant emissions. To use as an automobile fuel when blended with gasoline, this ethanol should have less than 0.5 wt% of water. Therefore, ethanol has to be dehydrated; but it forms an azeotrope with water. In these scenarios, the implementation of conventional distillation technique is difficult and therefore unconventional techniques like extractive distillation have to be implemented. But this process leads to high operating costs, and hence researchers have investigated adsorption-based techniques. This methodology is not only very effective but also less expensive. The performance of the adsorption process depends on the type of adsorbent, its physical characteristics like particle and pore size, the phase in which it is carried and process parameters like temperature, initial concentration, and dosage. Thus, this paper presents a comprehensive review of the intrinsic characteristics of adsorbents, the effect of process parameters on adsorption efficiency and the influence of the phase of operation. Various types of isotherm and kinetic models utilized in the adsorption process are also presented in detail. Mathematical models describe the inherent mechanisms of the adsorption process; hence the governing equations like mass, energy and momentum balances for both liquid and gas phase are also reviewed.

Column pressure is one of the most important decision variables in the design and optimization of energy-efficient extractive distillation (ED) as it impacts on phase equilibrium, column temperature, and azeotropic concentration. However, many previous works fixed column pressure heuristically before optimization, resulting in divergence from the global optimum with variable column pressures. This ignorance gives this work the target to simultaneously optimize ED systems with fully considering the effect of column pressures. In detail, the task is carried out through combining the genetic algorithm programmed in MATLAB with Aspen Plus. Three binary systems are investigated to demonstrate the importance of pressure optimization – two sensitive (n-heptane/isobutanol and acetonitrile/water) and one insensitive (isopropanol/water) to pressure. Significant economic benefits are validated through optimizing pressure in the results for pressure sensitive systems, with the pressure insensitive system on the contrary. This suggests an optional pre-exclusion of pressure optimization, which requires to decipher the pressure sensitivity of the target system.

Ternary extractive distillation is a green and sustainable separation process for the treatment of pharmaceutical wastewater containing methanol/acetonitrile and acetonitrile/water azeotropes that achieves the recovery of the acetonitrile and methanol solvents. A novel sequential iterative optimization methodology is proposed and the isovolatility curves of systems at different pressures are analyzed in this work to investigate the effect of the operating pressure on the ternary extractive distillation process. Four optimization procedures with different conditions of pressure and limits for the use of cold utilities were carried out. The optimization results showed that the optimal pressures of the first column and the third column are related to the top vapor that can be condensed by chiller water and cooling water, respectively, and the pressure of the second column is related to the effect of preheating on the third column. The ternary extractive distillation process with optimal operating pressure shows 60.1% energy cost savings and 47.0% total annual cost savings compared with the optimal process operating at atmospheric pressure. The proposed optimization method has the advantages of automatic optimization with a smaller number of simulator runs, providing a new solution for the simulator-based process optimization. The investigation of the operating pressure effect provides additional insight for the design and optimization of ternary extractive distillation.

Ionic liquid (IL) was selected as extractive distillation entrainer to separate the binary mixture of methanol and methyl propionate with the lowest azotropic temperature. Experimental determination of isobaric vapor-liquid equilibrium for the system of methanol + methyl propionate + 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) was made at atmospheric pressure with an all-glass dynamic recirculating still. The results show that the addition of [BMIM][NTf2] can produce an obvious salting-out effect and well enhances the relative volatility of methanol to methyl propionate, and the azeotropy of the investigated binary system is ultimately eliminated by increasing the concentration of IL to a certain value in liquid phase. Additionally, the experimental data were well fitted with the NRTL model and the binary parameters were obtained.

Solvent selection is key in extractive distillation process development and solvent effects are often predicted based on the activity coefficients at infinite dilution. For close-boiling polar systems with strong or specific interacting species, standard simulation tools, e.g. using UNIFAC or COSMO-RS, often predict poor as the activity coefficients at infinite dilution not always reflect the selectivity in the process. For these systems, a heuristic solvent selection method in which molecular properties such as acidity, hydrogen bonding and polarity are applied is desired as first estimate in the solvent selection. To explore the key parameters for such a first selection, solvent effects on the relative volatility ( α ) were measured for three different industrially relevant polar mixtures, valeric acid – 2-methylbutyric acid, diethylmethylamine – diisopropylether, and 2-butanol – 2-butanone. For each of the cases the effect of potential solvents on α was measured in an ebulliometer. For the acids, the difference in p K a of 0.1 was too small to separate based on acidity with a moderately basic solvent. Stronger basic solvents resulted in thermal and chemical instability. Although the solvent methyl-2-methyl butyrate is not suitable as a solvent because of reactivity, this structurally similar solvent showed selectivity, indicating also in extractive distillation the like dissolves like phenomenon can be applied to induce selectivity. A larger difference in basicity of the mixture components (amine–ether mixture) and a difference in hydrogen bonding affinity between the mixture components (ketone–alcohol mixture) allowed for increasing α based on differences in acidity and hydrogen bonding, respectively.

A computer-aided ionic liquid design (CAILD) study is presented for the frequently encountered alkane/cycloalkane separations in petrochemical industry. Exhaustive experimental data are first collected to extend the UNIFAC-IL model for this system, where the proximity effect in alkanes and cycloalkanes is considered specifically by defining distinct groups. The thermodynamic performances of a large number of ILs for 4 different alkane/cycloalkane systems are then compared to select a representative example of such separations. By applying n-heptane/methylcyclohexane extractive distillation as a case study, the CAILD task is cast as a mixed-integer nonlinear programming (MINLP) problem based on the obtained task-specific UNIFAC-IL model and two semi-empirical models for IL physical properties. The top 5 IL candidates determined by solving the MINLP problem are subsequently introduced into Aspen Plus for process simulation and economic analysis, which finally identify 1-hexadecyl-methylpiperidinium tricyanomethane ([C16MPip][C(CN)3]) as the best entrainer for this separation. Keywords: CAILD, Alkane/cycloalkane extractive distillation, UNIFAC-IL, MINLP, Process performance and economics

For separation of the azeotrope isopropyl alcohol and diisopropyl ether by extractive distillation, 2-ethoxyethanol and butyl acetate were adopted as extractive solvents, and the vapour–liquid equilibrium data for the binary systems of isopropyl alcohol + 2-ethoxyethanol, isopropyl alcohol + butyl acetate, diisopropyl ether + 2-ethoxyethanol and diisopropyl ether + butyl acetate were measured at 101.3 kPa by a modified Rose type recirculating still. The Herington and van Ness consistency method were used to check the thermodynamic consistency of the VLE data. Meanwhile, the VLE data were correlated using the NRTL, UNIQUAC and Wilson models, and the binary interaction parameters of the three models were regressed. The correlation results indicate that the three models can correlate the experimental data with the root-mean-square deviation value of vapour phase mole faction less than 0.0062. Finally, an extractive distillation process for separating the azeotrope of isopropyl alcohol and diisopropyl ether is explored in this work.

A systematic strategy for the screening of organic solvents and ionic liquids as entrainers along with the design of the corresponding homogeneous extractive distillation processes has been developed. The proposed approach is illustrated by an example of the entrainer screening in the dehydration of tert-butanol. The toxicity and the physical properties of two types of entrainers (e.g., 19 organic solvents and 289 ionic liquids) are first considered. Then, the properties related to separation performance are further evaluated and three organic solvents and 11 ionic liquids are found to conform to the process feasible restrictions. In the third step, glycerol, triethylene glycol, 1-butyl-3-methylimidazolium thiocyanide [C4MIM][SCN], and 1-pentyl-3-methylimidazolium thiocyanide [C5MIM][SCN] are chosen as the representatives to perform thermodynamic topological analysis. Finally, the process design and optimization with four entrainers are performed using the minimization of total annualized cost as the objective function. And the process economic evaluation proves that the ability of glycerol in separating tert-butanol-water system is superior to those of 18 organic solvents candidates while that of [C4MIM][SCN] is the most advantageous entrainer among 289 ILs in terms of saving energy.

It is important to study the dynamic controllability for the side-stream extractive distillation due to its superiority of energy saving. Control structures of the side-stream extractive distillation process are special and complex due to the instability of side-stream flow rate. In this work, the dynamic control of the side-stream extractive distillation was explored for separating azeotropic mixture of acetone and methanol. The detailed control structures were used to investigate the control strategies of side-stream extractive distillation. During the whole design process, the control of flow rate on side stream is a key factor for achieving this process efficient control. A new control structure combining a component controller and a side-stream throughput valve was proposed to achieve good dynamic performance for the side-stream extractive distillation process when ±10% disturbances were introduced, but it is difficult to control the ±20% feed disturbances. In addition, the side-stream extractive distillation takes about a longer time to reach a steady state while maintaining the purity of products, compared with conventional process. Research on control performance is of great significance to the development of energy saving technology for side-stream extractive distillation.

One of the most critical challenges in the distillation process to reach a pure component is the azeotropic point. Usually, extractive distillation is used to purify the compounds around the azeotropic point. In this paper, a heat pump assisted extractive divided column (E-DWC) is proposed, designed and simulated to produce ultra-pure ethanol around its azeotropic point. The performance of this technique is compared with the conventional extractive distillation at the same operating conditions. The results show the proposed technique is more efficient than the conventional extractive distillation in the energy aspect. The cooling, heating and total required energies in heat pump assisted E-DWC are 19.24%, 38.61% and 18.77% less than extractive distillation, respectively. The sensitivity analysis shows that the heat pump assisted E-DWC process is more stable than extractive distillation and E-DWC processes. The economic performance also shows that the total annual cost will be reduced by 10.42% if heat pump assisted E-DWC is used.

In the present paper, an intensive analysis of simulation of conventional distillation and extractive distillation to separate a mixture of toluene and heptane (toluene-heptane azeotrope) has been performed. A literature review has been performed for both conventional and extractive distillation and also the advancements and new techniques developed to increase the efficiency of both processes. Aspen Hysys was used as the simulator of choice for simulating both conventional distillation and extractive distillation, whereas Aspen Plus was used to compute the VLE data for interaction of the three compounds with each other. Comparison of the energy consumed by both the processes to achieve the same separation efficiency was done. Cost analysis was performed by using aspen cost analyzer. Cost efficiency was used as the criteria to determine the best process. Extractive distillation was determined to be costing less than13⁄ times the price of conventional distillation process. Hence extractive distillation is clearly the more economical process.

1-propanol or 2-propanol and water form azeotropic mixtures with the minimum boiling point at constant pressure. The separation of these azeotropes is an important issue in the chemical industries. Their separation by simple distillation is basically impossible, and the extractive distillation consumes much more energy than liquid- liquid extraction. For a better understanding of extraction processes, liquid-liquid equilibrium data containing binodal data and tie-lines are essential. The aim of this work is investigating the choline ability for recovering 1-propanol and 2-propanol from water mixtures by liquid-liquid extraction method. In this respect, binodal data and tie-lines were experimentally measured for (1-propanol or 2-propanol + choline chloride + water) systems at T = (298.15, 308.15 and 318.15) K under atmospheric pressure (≈85 kPa). The phase-separation ability of these systems was discussed on the basis of the solubility of the constitutive alcohol. Moreover, the critical concentration of the choline, slope and tie-line length for these systems were determined and the obtained results were used to evaluate temperature influence on these parameters. Two empirical equations consist of the Merchuk equation and a logarithmic equation with the temperature dependency was utilized for representing the experimental binodals. Furthermore, the experimentally obtained compositions for tie-lines were correlated by Othmer-Tobias, Bancraft, Bachman, and Setschenow equations and non-random two-liquid models (e-or m-NRTL). Finally, the distribution coefficients and selectivity of the studied alcohols in this work were computed and compared with the same values reported for these alcohols in the literature using other ionic liquids. It was found that the choline has more ability for breaking of azeotropes formed between 1-propanol or 2-propanol and water.

Though p-xylene derived from naphtha reformate is in high demand as a raw material in the production of polyesters and polyethylene terephthalates, its separation from the FCC reformate is not easy due to close boiling points among the components in the reformate. When a proper solvent for the p-xylene separation is available, an extractive distillation can be applied in the separation. Currently the separation utilizes an adsorption process requiring a large amount of costly adsorbent and a desorption process followed by distillation. In the proposed extractive distillation here, p-dinitrobenzene has been utilized to improve the separation of p-xylene from its ethylbenzene mixture. The VLE data of the ternary mixture estimated with the UNIFAC were compared to those computed from molecular simulation to show their reliability. An extractive distillation and solvent recovery were applied to obtain 99.6% purity p-xylene with 99.1% recovery. The economics of the proposed process demonstrates its comparability to the existing Parex process.

As an excellent solvent, ionic liquids (ILs) have received much attention in the last two decades. One of the most important applications is to be used as an extractant for separation of azeotropic mixtures via extractive distillation (ED). In this work, 1-ethyl-3-methylimidazolium dicyanamide ([emim][N(CN)2]) is selected as the extractant to separate isopropanol (IPA)-water azeotrope based on two ED processes. Multi-objective genetic algorithm (MOGA) is used to determine the operating parameters for these ED processes. Total annual cost (TAC), efficiency indicator of extractive section (Eext), efficiency indicator of per tray in extractive section (eext) and energy consumption per product flow rate (GEC) are selected as objective functions in the ED process optimization, and the Pareto front provides a series of solutions satisfying the constraints with different operating parameters. The results show that TAC of the process 2 with two evaporators used in the phase of solvent recovery is 4.26% lower than that of process 1 with one evaporator. In addition, the thermodynamic efficiency (η) and CO2 emissions are calculated for different cases, and they provide the reference for the selection of operating parameters. On this basis, the control structures of ED processes are further studied, and the traditional two-point temperature control structure works pretty well for disturbances of both feed rate and feed composition.

Solvents are widely used in chemical industries, especially in various separation processes. As traditional trial-and-error solvent selection is time-consuming and expensive, model-based methods for solvent selection/design become important for efficient and sustainable chemical manufacturing. A lot of contributions have been made in this area in the past few decades. This article first reviews the prediction methods for solvent properties, including single molecular properties and mixture properties. Then, the solution strategies of solvent design problems are summarized, including generate-and-test, deterministic optimization, and stochastic optimization methods. Next, latest progresses of computer-aided solvent-process design in separation processes including liquid–liquid extraction, extractive distillation, gas absorption, and crystallization are reviewed. Finally, several remaining challenges and possible future directions for solvent design in separation processes are pointed out.