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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.

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.

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.

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.

The separation of dimethyl carbonate (DMC)/methanol/water azeotropic mixtures has been a hot topic in the study of DMC synthesis process. In this work, the efficient organic solvent methyl salicylate, ionic liquids (ILs) 1‐butyl‐3‐methylimidazolium chloride ([BMIM][Cl]), or 1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) was employed to break azeotropic mixtures. Interaction mechanisms between DMC/methanol/water and entrainers were revealed by sigma-profile. Energy and economic comparison of two alternative separation sequences including pre-separation integration with extractive-heterogeneous distillation and direct extractive distillation processes were investigated. The average relative deviations (ARD) were used to check the reliability of the NRTL model. The effect of high viscosity fluid on the mass transfer was analyzed from the perspective of the overall efficiency of column. For [BMIM][Cl], the separation mechanism is the formation of H-bond between [BMIM][Cl] and methanol/water. Direct extractive distillation process is superior to pre-separation integration with extractive-heterogeneous distillation process in terms of steam consumption, capital cost, mass transfer efficiency and total annual cost (TAC), and [BMIM][Cl]-based direct extractive distillation process is the best. This work provides a green and efficient separation route for replacing organic solvent-based process.

Separation of a ternary mixture containing methanol/toluene/water is a tough task because toluene forms azeotropes with both methanol and water. A recent paper proposed using N-methyl-2-pyrrolidone as heavy entrainer and included a two-column extractive distillation system plus a decanter for the separation of this ternary mixture. In this paper, an energy-efficient simpler process composed of an extraction column and a regular distillation column is investigated in order to achieve the same separation task. Water is used as the solvent to extract methanol from toluene in the extraction column. Toluene is obtained as raffinate while extract phase containing water and methanol is sent to a distillation column for the purification of these two components. Because water itself is a component in the separation mixture, there is no need to introduce any foreign component into the system and hence avoid the possibility of contaminating the products. To compare the optimal result of this design flowsheet with the recently published separation method, our proposed design provides 56.3% savings in total annual cost and 57.1% savings in annual operating cost. Furthermore, a control structure with adjustable solvent flowrate is devised for our proposed process based on the results of open-loop and closed-loop sensitivity tests. Closed-loop dynamic responses show that all products can be maintained at high purity despite large throughput and feed composition disturbances.

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

Ionic liquids (ILs) are potential neoteric solvents to design new advanced separation processes. Among several separation cases studied so far, the good performance of ILs regarding the dearomatization of liquid fuels, i.e. pyrolysis and reformer gasolines, has received especially attention. Indeed, a wide number of works has been done to characterize the phase equilibria for {aliphatic + aromatic + ILs} systems as well as the IL thermophysical properties, concluding in the development of a liquid-liquid extraction process. However, this technology seems not to be enough to fulfill current aromatic commercial standards nor potential incoming restrictions for aromatic content in liquid fuels as a result of its low separation effectiveness for extreme aliphatic and aromatic purification. Extractive distillation with ILs stands as a new process configuration to overcome these limitations by enhancing the aliphatic/aromatic relative volatilities. In this work, an IL experimental screening in the n-heptane/toluene separation was done to further develop this new IL-based technology. Nine ILs were tested as mass agents in a wide range of conditions, i.e. solvent to feed (S/F) ratios from 1 to 10 and temperatures from 323.2 to 403.2 K. The required vapor-liquid-liquid equilibria (VLLE) data were obtained by an experimental procedure based on headspace gas chromatography (HS-GC) developed in the framework of this work. Although all pre-selected ILs have shown good performance, tricyanomethanide-based ILs have been the most promising mass agents.

Ionic liquids (ILs) are highly attractive entrainers for separating close-boiling alkane-cycloalkane mixtures in extractive distillation processes while studies on this particular topic are still scarce. This work employs computer-aided molecular design (CAMD) and process simulation to identify suitable ILs for the extractive distillation of n-hexane-methylcyclopentane, a representative alkane-cycloalkane mixture. A large number of experimental data on the infinite dilution activity coefficient of methylcyclopentane and vapor-liquid equilibria of relevant systems are collected from literature to validate the reliability of the employed UNIFAC-IL model, which is the basis of CAMD and process simulation. Combining the UNIFAC-IL model and two group contribution models of IL physical properties, a mixed integer nonlinear programming (MINLP) problem is then formulated for the CAMD of ILs. The top IL candidates pre-identified from MINLP-CAMD are further introduced into Aspen Plus for process simulation and evaluation. By comparing their process performances with the benchmark solvent N-methyl-2-pyrrolidinone, 1-nonyl-imidazolium thiocyanate ([C9Im][SCN]) is consequently identified as the optimal entrainer.

Separations account for approximately 50% of all manufacturing costs, making the selection of the proper technology, and a potential affinity separation agent (ASA) of essential importance for process design. This selection is not straightforward. In this paper, aspects of fluid separation technologies, including shortcut calculations to estimate heat duties, are reviewed and applied to create insights in ab initio fluid separation process selection without extensive process simulations. It was found that composition and state of the feed can have major impacts on the minimal required heat duty, as well as the desired product purity. Distillation of dilute feeds is intrinsically hindered by a low internal efficiency and solvent based separations should be considered. Furthermore, the minimal heat duty for liquid-liquid extraction (LLX) with high boiling solvents is primarily feed composition dependent, while for low boiling solvents the solvent to feed ratio is important. This is also the case for the minimal duty for extractive distillation (ED) with light solvents, whereas the minimal duty of ED using high boiling solvents is independent of the composition, and generally higher than the minimal LLX duty. ED can be operated with only two columns, whereas LLX generally requires at least three, leading to higher capital costs. The feed composition dependence of the LLX minimal heat duty can result in a feed compositional break-even point when comparing LLX with ED. Using these theoretical insights in fluid separations, a series of industrial cases was reviewed and critical aspects in technology selection, and solvent selection and design such as selectivity and capacity are discussed. The results confirm the applicability of the minimal heat duty approach as a quick prediction tool for opportunities of solvent based technologies, as well as the need for including other considerations such as the number of required columns (capital costs) and the possibility to recover sensible heat.

Herein, the development of a basic extractive distillation process for the separation of an ester/alcohol/water system, e.g., N-propyl acetate (PAC)/isopropanol (IPA)/H2O, is reported. To reduce the energy consumption of the process, mechanical vapor recompression technology was added to the basic extractive distillation process, and the heat exchange network was redesigned to further develop an enhanced distillation process. A hybrid pervaporation-distillation process was also developed to improve the high energy consumption of the solvent recovery tower used in the traditional extractive distillation process. Compared with the basic process, the total annual cost of the enhanced distillation process is 36.03% lower; thus, it is more economical. The global warming potential and acid potential of the hybrid pervaporation-distillation process are 500 kg CO2-ep and 0.75 kg SO2-ep, respectively, which indicates an improved environmental performance compared with that achieved by the traditional process. Although the economic advantage of the hybrid process compared with the enhanced distillation process is not clear when taking into account the high equipment cost, the hybrid process exhibits clear environmental performance advantages.

This study is focused on the separation for the ternary mixture of isopropanol/tetrahydrofuran/water with extractive distillation method, including indirect extractive distillation and direct extractive distillation. Dimethyl sulfoxide is selected to be the optimal solvent in the separation process through COSMO-SAC model and relative volatility. The vapor recompressed heat pump technology and heat integration are introduced for further energy saving. The energetic, economic, environment and exergy evaluation are utilized to estimate the performance of the proposed processes. The direct extractive distillation tends to be better than indirect extractive distillation. The double-heat pump assisted direct extractive distillation with heat integration shows the best performance in energy conservation and reducing cost, which achieve a reduction on energy consumption and total cost by 64.97% and 34.26% respectively compared to the direct extractive distillation process.

In the process of synthesis or application of alcohols, water always presents the coexistence relationships with alcohols. The subsequent separation of homogenous mixtures composed of one or more alcohols and water to treat wastewater is needed. In this work, ionic liquids (ILs) single column extractive distillation (SCED) integration with heat pump distillation (HPD) process for recovery of ethanol and isopropyl alcohol (IPA) from wastewater was proposed. The thermodynamic vapor–liquid equilibrium (VLE) was applied to analyze the separation sequences and the abilities for the mixtures using ILs or organic solvent as entrainer. The ILs 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) was selected as the optimal entrainer considering the viscosity and the selectivity of ethanol to water, and the mechanisms on enhancing VLE was explained via the sigma-profiles. Two alternative separation sequences with two alternative entrainers involving SCED with ethylene glycol (EG), SCED with EG integration with HPD, SCED with [EMIM][DCA] integration with HPD, and double-column extractive distillation (DCED) with EG processes were investigated. This work aimed to compare ILs and organic solvent processes by considering energy and economic aspects. Compared with EG-SCED, EG-SCED-HPD and EG-DCED process, the energy cost of ILs-SCED-HPD can reduce by 57.7%, 28.6%, and 28.3%, respectively. Economic analysis indicted that the total annual cost (TAC) of ILs process was similar with EG process with increase of price of CO2 emission. ILs-SCED-HPD was confirmed as the promising process both in energy and economic perspectives for recovery of ethanol and IPA from wastewater.

Octafluoropropane (C3F8), hexafluoropropylene (C3F6), and octafluorocyclobutane (c-C4F8) are being widely used as etching/cleaning gases in microelectronic or semiconductor manufacturing process. These high-purity perfluorocarbons (PFCs) are becoming increasingly important as modern industry develops. In this work, a thermally coupled extractive distillation (TCED) process for separating the mixture of C3F6/C3F8/c-C4F8 is proposed and compared to the traditional extractive distillation (ED) process. Two kinds of entrainers, toluene and N, N-dimethylformamide (DMF), are selected. These processes are optimized by minimizing the total annual cost (TAC) and restricting the product purity and recovery. The results show that toluene is more suitable to be used as the entrainer for thermally coupled improvement than DMF, and the TAC of the TCED is 5.9 % smaller than that of the ED process.

Separation of ternary mixture is a challenging task if multiple azeotropes exist among the components, and special distillation techniques should be adopted. For water-containing ternary mixtures with multiple azeotropes, a dehydrating agent, ethylene oxide (EO), can be used to consume water with the production of ethylene glycol (EG) as the product, which can be utilized as entrainer for separating the remaining two components. In this work, systematic thermodynamic analysis was conducted to screen for the feasible ternary systems. After conducting suggested analysis without needing of rigorous process simulation, tert-butyl alcohol (TBA)/ethanol (EtOH)/water, tetrahydrofuran (THF)/EtOH/water and acetonitrile (ACN)/isopropyl alcohol (IPA)/water mixtures were chosen to be suitable for this application. Within the scope of using dehydrating agent, a process configuration of triple column reactive-extractive distillation (TCRED) is developed for three different ternary systems. Subsequently, an intensified process configuration - double column reactive-extractive distillation (DCRED), which combines both functions of reactive distillation and extractive distillation in a single unit, is constructed to significantly reduce capital cost and energy consumption. With the application of further energy-saving schemes in the systems, total annual cost and total operating cost of the final proposed design flowsheets can be considerably saved compared to respective separation systems recently published in open literature.

Methyl tert-butyl ether as an excellent gasoline additive has been widely used. There are a lot of mixtures of Methyl tert-butyl ether and methanol in the process of Methyl tert-butyl ether production. In this work, the interaction between different ionic liquids and methyl tert butyl ether / methanol was studied by the combination of quantum chemistry and molecular dynamics. In addition, there is little difference between the experimental data and the MD simulation results, indicating that the extraction performance can be predicted by MD simulation even without the phase equilibrium data. The interaction energy, radial and spatial distribution functions, and self-diffusion coefficients are calculated based on the molecular dynamics simulation results. It is proved that anions play a key role in the extraction process. The process of synthesis of methyl tert-butyl ether with ionic liquid extraction as separation unit was studied and the optimum process parameters were determined. Methyl tert-butyl ether with mole fraction greater than 99.9% could be obtained by ionic liquid extraction, and the use of Ionic liquids liquid-liquid extraction can save 26.77% of total annual cost than extractive distillation using conventional solvents. It plays a guiding role in the selection of green solvent ionic liquids extractant and the energy saving of liquid-liquid extraction.

N-heptane and ethyl acetate are important solvents for chemical intermediates such as hexanitrohexaazaisowurtzitane. Based on molecular dynamics simulation, the interaction between mixed extractant and azeotrope was discussed through microscopic mechanism, and the optimal mixing ratio was determined. Based on the process, the influence of different ratio on the separation effect was further verified. It is found that the increase of the proportion of organic solvents can effectively promote the interaction between ionic liquids and esters. In addition, the separation processes of common distillation, extractive dividing wall column distillation and vapor recompression assisted extractive distillation were studied. Based on the sequential iterative algorithm, the process was optimized with the minimum annual total cost as the objective function, and the economy of vapor recompression assisted extractive distillation with mixed entrainers was the best. Compared with traditional organic solvent extractive distillation, the annual total cost can be reduced by 10.81%. According to the optimization results, the economic performance of carbon dioxide, nitrogen oxides and sulfur dioxide emissions was calculated. Through calculation, the technology of vapor recompression assisted extractive distillation with mixed entrainer is significantly better than other processes, and the gas emission can be reduced by 21.03%. In conclusion, the use of mixed entrainer in extractive distillation process can greatly improve the energy-saving effect than a single entrainer. This provides some guidance for industrial separation of other azeotropes.

Large amount of high purity acetonitrile and isopropanol are required as the raw material to meet the growth requirements of rapidly the chemical industries development. The high demands for acetonitrile and isopropanol have created the need for an efficient sustainable process to reduce the energy consumption which satisfies the environment regulations. Thus, a sustainable process of reactive coupling extractive distillation to separate acetonitrile/isopropanol/water ternary mixture is proposed. The intensified processes of heat-integrated combination intermediate reboiler are explored to further reducing energy consumption. The comparisons from the views of 4E which contains energy, exergy, economic and environment are conducted to assessment proposed processes benefits. The advanced intensification process of reactive extractive distillation (RED-HI-IR) has the best energy saving potential and economic benefits which achieves the reductions on energy, total annual cost and gas emissions of approximately 54.16%, 39.02% and 54.16% respectively, and the total exergy efficiency is up to 97.52%. Thus, heat-integrated and intermediate reboiler technology used of distillation is of significance for the sustainable chemical process development.

The existence of heterogeneous azeotrope of toluene-water and homogenous azeotrope of toluene-methanol makes it difficult to separate the toluene-methanol-water mixture. Two methods of three column extractive distillation and two column extractive distillation using decanter were explored to separate the ternary azeotrope. Diethylene glycol and N-methyl-2-pyrrolidone were used as heavy solvent in the two processes, respectively. The UNIQUAC physical model was used in both simulations. Based on the minimum total annual cost, variables of the two processes were optimized and the results indicated the two column extractive distillation using decanter can save 51.4% of total annual cost than three column extractive distillation. The dynamics of two column extractive distillation using decanter was studied due to its superiority of economics. Several common control schemes were used to investigate the controllability of two column extractive distillation using decanter and all schemes showed poor controllability on feed composition disturbances. An improved control structure was designed to achieve better control of the process. In the improved control scheme, the temperature controller of column C1 was replaced by a proportional controller, and a certain amount of solvent flow rate was increased. The integral squared error was calculated to compare the dynamic performances of the improved control structure with different solvent flow rate, and a suitable amount of solvent was found in view of the controllability and economy.

Several new extractive distillation configurations using green and highly selective ionic liquid (IL) as extractant are proposed as an alternative to the conventional extractive distillation (CED) and conventional extractive dividing wall column (CEDWC) configuration to separate methyl alcohol (MeOH)-methyl ethyl ketone (MEK)-tert butyl alcohol (TBA) azeotropic mixture, including direct and indirect extractive distillation (direct-ED, indirect-ED), azeotropic extractive distillation (AED), and extractive dividing wall column (EDWC). These schemes are optimized with the objective of total annual costs (TAC) by simulated annealing based optimization method. Among these schemes, EDWC is undoubtedly the best due to the benefits of IL and dividing wall column. As compared with the CED process, it can reduce TAC by 22.19%, total capital cost by 31.47%, total operating cost by 8.35%, CO2 emission by 7.7%. In addition, the computation shows that the used optimization method is very practical for the optimal design of complex distillation systems with the advantages of direct, efficient, robust and global optimal.

The preparation of dimethyl carbonate by transesterification of ethylene carbonate and methanol has an important application in industry. The preparation of dimethyl carbonate by reactive distillation and the efficient separation of dimethyl carbonate and methanol are the inevitable requirements of the sustainable development of extractive distillation. Based on the quantum chemistry calculation and molecular dynamics calculation analysis, a better extractant (2-Furaldehyde) was selected. The simulated extractive distillation was designed to separate dimethyl carbonate methanol. The σ - profile was drawn by using COSMO-SAC model, and three different separation processes of dimethyl carbonate production were compared and optimized. Taking TAC as the objective function, the separation process of reactive dividing-wall extractive distillation can reduce about 21% and carbon dioxide emission by about 10% compared with the common reactive distillation process, which has obvious economic advantages and environmental performance. Through the economic and environmental optimization analysis of the production and separation process of dimethyl carbonate, it provides a certain guiding significance for the actual production of dimethyl carbonate and the separation of dimethyl carbonate methanol.

A mixture of ethyl acetate and ethanol is difficult to separate because of a minimum-boiling homogeneous azeotrope. The characteristics of the ethyl acetate/ethanol system are analyzed. The energy-saving potential of a three-column extractive distillation process to separate the system is explored. The effects of the distillate composition of pre-concentrator, the temperature of solvent feed and operating pressures are studied. Energy-saving processes including heat pump distillation, heat integration and partial condensation are proposed. A novel way of partial condensation is proposed and compared with the conventional way. An innovative method of vapor–liquid coupling between the per-concentrator and the extractive column is then proposed. It is more economical and energy-efficient than the above processes. Besides, based on the vapor–liquid coupling process, two further improvements are proposed through heat integration and through compressors. All processes are optimized using the sequential iterative optimization procedure with the minimum total annual cost as the target. Compared with the conventional process operated at 101.3 kPa, the two improved processes can reduce total annual cost by more than 52%, reduce energy consumption by more than 60%, and reduce CO2 emissions by more than 61%.

The energy analysis and optimization of process system aiming to solve the problems of high consumption, low efficiency and unreasonable use of energy in the process of energy utilization has been widely researched and developed in recent decades. In this work, advanced exergy analysis was carried out for the triple-column extractive distillation (TCED) process separating ternary azeotropic mixture of ACN/EtOH/H2O. The total exergy destruction is 1097.69 KW. The avoidable exergy destruction, is 29.20%, mainly caused by the cooler and three condensers. Based on the thermodynamic analysis results, a superstructure TCED with four-parallel evaporator organic Rankine cycles (FPE-ORC) system is proposed, four working fluids were selected. An improved genetic algorithm is used to obtain the optimal operating parameters of the ORC system by using the exergy efficiency and annual net profit (ANP) of the ORC as two conflict objective functions. Compare with existing process, the FPE-ORC system with working fluid R600 provides the highest exergy efficiency of 12.27%, with working fluid R600a leads to the best economic benefit of 6.43 E + 4 dollar/year.

The acetone/methanol/butanone/tert-butanol system is a quaternary organic compound with multi-azeotropes and often appears in the chemical and petrochemical industries. In view of achieving its energy efficient separation, this article establishes seven alternative thermally coupled extractive distillation configurations by introducing one or more liquid side-streams into one regular four-column configuration with chlorobenzene as an entrainer. Furthermore, the intensified configurations having multiple side-streams, multiple recycling-streams, and multiple solvent recovery sections features are optimized by a simulated annealing based systematic optimization method with the minimum total annual cost (TAC) as the target. Finally, a comprehensive assessment is made among all the configurations in terms of several metrics such as TAC, energy-saving, exergy loss and CO2 emissions. The results demonstrate that these intensified configurations can respectively reduce 5.32–14.38% energy consumption, 3.91–10.11% TAC and 5.65–18.05% CO2 emissions as compared with the regular configuration. One of double-side-stream configurations is the optimal option while the only triple-side-stream configuration is the suboptimal one. Besides, the proposed optimization method for side-stream extractive distillation configurations shows high computational efficiency and good applicability and flexibility.

The selection of feasible solvent is of great significance for separating azeotropes via extractive distillation since various solvents can cause different product orders, flowsheet structures, and eco-efficiencies of extractive distillation processes. Limited efforts are focused on the effect of various solvents on the separation of ternary mixtures embedding two azeotropes, especially for the design of the extractive dividing-wall column separation configurations. To fill the research gap, the separation of azeotropic mixtures embedding two azeotropes is investigated using extractive distillation method with various solvents through taking the methyl acetate/ethyl acetate/methanol mixture as an example. First, the theoretical thermodynamic feasibility of four solvents including ethylene glycol, dimethyl sulfoxide, chlorobenzene, and aniline is explored. The individual light-heavy component orders are determined through the thermodynamic insights including the construction of the pseudo binary vapor–liquid phase equilibrium diagrams and overall phase diagrams with residue curves and iso-volatility curves after adding solvents, while are further verified using σ-profiles from microscopic mechanism. Second, the conceptual design of the extractive distillation flowsheets including conventional extractive distillation and extractive dividing-wall column separation configurations with individual solvents is performed. The effects of various solvents on the flowsheet structures and product orders are analyzed. Afterwards, the extractive distillation flowsheets are simulated and optimized economically to minimize the total annual costs through the genetic algorithm, except for the solvent ethylene glycol due to the unfeasibility of realistic simulation. The eco-efficiency analysis is performed via quantifying the Eco-Indicator 99 and thermodynamic performances as well as economic costs. The results indicate that the extractive distillation processes with dimethyl sulfoxide or chlorobenzene as solvent can show a certain degree of advantage compared with that using aniline as solvent in terms of eco-efficiency. The optimal separation configuration is the extractive dividing-wall column containing two dividing-walls with CB as solvent, and its Eco-efficiency Comparison Index increased to 80.54% compared to the worst scheme that is the extractive dividing-wall column containing one dividing-wall with AN as solvent.

To further reduce the energy consumption, investment and operating costs of the extractive distillation (ED) process, this study focuses on the process intensification by the combination of ionic liquids-based mixed entrainers and dividing wall column (DWC) for methanol/ethanol/water separation process. Based on the process simulation results, energy efficiency, economic and environmental impact assessments were carried out and compared with the benchmarked ED process using ethylene glycol as entrainer. The ternary ED process using the ionic liquids-based mixed entrainer can reduce the total annual cost (TAC) by about 5.98% and the energy consumption by 2.93%. The TAC and energy consumption for the proposed ternary ED process with DWC using the ionic liquids-based mixed entrainer can be reduced by 7.81% and 4.52%, respectively. The novel ED process shows the high energy efficiency, low economy cost and low CO2 emissions with a great industrial application prospect when compared to the benchmarked process.

This paper provides process design and simulation methodology for the separation of ethyl acetate and ethanol by extractive distillation using ionic liquids (ILs) as solvents and obtains the design parameters of extractive distillation process with solvent recovery system on the basis of a suitable IL solvent. The feasibility of IL-extractive distillation was examined via process simulation for the separation of ethyl acetate and ethanol in Aspen Plus. Four ILs [EMIM][MeSO 3 ], [EMIM][MeSO 4 ], [BMIM][CF 3 SO 3 ] and [EMIM][BF 4 ] were created in Aspen Plus database with several thermodynamic and physical property parameters to allow the process to be simulated via the UNIFAC-Lei thermodynamic method. The results show that the separation process containing the hybrid regeneration system of flash tank and stripper with [EMIM][MeSO 3 ] as a suitable solvent is the best option in extractive distillation for the separation of ethyl acetate and ethanol compared with other ILs from the analysis of relative volatilities. The separation process was optimized by sensitivity analysis and the optimal design parameters were verified by economic evaluation based on the total annual cost (TAC).

1,3-butadiene is an essential platform chemical for producing rubberlike polymers, which is extracted from C4 hydrocarbons that are produced through steam cracking. The current state-of-the-art technology is the BASF process that uses thermally coupled extractive distillation (ED) followed by two distillation columns. However, the process requires high temperature heat input, thus high cost hot utility and reduces the possibility for process heat integration. To solve these issues, this study proposes novel enhancements: the ED part is modified with intermediate heating and the classic columns are replaced with a heat pump assisted dividing wall column (DWC). Rigorous simulations were carried out in Aspen Plus for a typical ED process. The intermediate reboiler system is designed to maximize the possible process heat recovery. The results show that the heat pump assisted DWC is able to reduce the energy intensity of the classic distillation section of the BASF process by 54.8% and reduces the total annual costs by 29.9%. Additionally, the intermediate reboiler reduces the energy intensity of the ED section by 8.3% while also reducing the CAPEX of the system due to the need for a smaller recycle compressor. In combination, these modifications are able to achieve up to a 21% reduction in the energy intensity of the overall process, with a payback time of 1 year.

With the improvement of people's living standards, higher requirements are put forward for food safety, variety and quality. Edible oil is essential in people's life, but the production and processing process will produce a lot of waste, it is necessary to develop efficient and energy-saving treatment technology. Taking the wastewater containing ternary azeotropic system of cyclohexane-isopropanol-water produced in rapeseed oil production as an example, cyclohexane and isopropanol were separated and recovered by extractive distillation. Through the analysis of relative volatility, density functional theory and molecular mechanism, the suitable extractants of DMSO and EG were selected from the perspective of action mechanism. Aiming at the lowest economic cost, optimize the parameters of the process with single solvent and the mixed solvents by sequential iterative method, and further to determine the optimal process parameters and the optimal ratio of mixed extractant. In addition, the effects of single extractant and mixed extractant on the azeotropic system of extractive distillation were compared in terms of thermodynamic efficiency and environmental impact. The results shown that, compared with the single extractant, the extractive distillation process using the mixed extractant can save 30.71% and 16.71%, the thermodynamic efficiency was increased by 24.13% and 16.72%, GWP was reduced by 19.32% and 3.77%, AP was decreased by 19.26% and 3.43%. Combined with thermal integration technology, the economic cost was further reduced by 28.12%, the thermodynamic efficiency was increased by 10.49%, GWP and AP were reduced by 51.72% and 51.78% respectively on the basis of the optimal extractive distillation process with mixed extractants. The results shown that cyclohexane and isopropanol can be effectively recovered from the wastewater produced in rapeseed oil production by using mixed extractant and heat integrated energy-saving technology in extractive distillation process, which is of great significance for food safety, resource saving and environmental protection, and has guiding significance for the separation of other similar azeotropes.

A conventional triple-column extractive distillation is researched for the separation of acetonitrile/isopropanol/water mixture with ethylene glycol (EG) as entrainer. In this article, the pressure-relative volatility curve is investigated to find the suitable pressure of column. To achieve the further energy saving, three heat-integrated schemes and two heat-integrated combined with intermediate reboilers schemes are researched based on the conventional extractive distillation. Both two heat integration with intermediate reboilers schemes shown the better performance than other schemes since the further analysis of the energy, exergy, economic and environment (4E) were investigated. For the most energy saving design, PHI-IHI2, it has 48.50% energy-saving, 70.73% exergy efficiency enhanced, 36.24% reduction in total annual cost (TAC) and 48.55% reduction in gas emissions with the comparison of the conventional extractive distillation (CED) process. The result shows the extractive distillation combined with heat-integrated and intermediate reboilers presented great energy-efficient, economy saving and environment friendly for separating acetonitrile/isopropanol/water mixture.

This work deals with the formulation of a mixed-integer nonlinear multi-objective optimization (MOO) problem having five objectives to optimize the design of a conventional batch extractive distillation (BED). Of them, three primary objectives are to minimize total annual cost (TAC) and CO2 emissions while maximizing the total annual production of the desired component, and the two secondary objectives are total annual solvent (entrainer) recovery and total annual production of the undesired component. The MOO problem with five objectives is solved using the elitist non-dominant sorting genetic algorithm (NSGA-II) to obtain Pareto-optimal solutions. Two strategies, both using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) along with entropy weights, are examined for selecting one of the Pareto-optimal solutions. The selected optimal solutions by these strategies are analyzed in terms of performance indicators such as TAC savings, CO2 emissions reduction, amount of product per dollar, etc. Separation of isopropanol and water with ethylene glycol as the homogeneous entrainer is used to illustrate the above procedure for BED optimization. In the next phase, the retrofit of the optimal conventional BED using vapor recompression is studied. Here, a novel limited vapor recompressed BED (L-VRBED) is proposed and compared with the traditional vapor-recompressed BED (T-VRBED) using several performance indicators. The results show that retrofitting CBED to L-VRBED is justifiable for reducing CO2 emissions by 45% despite a 2.5% increase in TAC.

Distillation is one of the most studied processes in the control literature because of its importance as a separation process. However, little attention has been paid to the dynamics and control of the simultaneous changes in the feed and product specifications. In this study, it is proposed an intelligent control system based on artificial neural network for the extractive process to obtain anhydrous ethanol using ethylene glycol as a solvent. The study considered the changes in the azeotropic feed and the specification of anhydrous ethanol simultaneously, taking both the extractive and recovery columns into account, and keeping the process operating at minimum energy consumption condition. The performance of the intelligent control system was evaluated using Aspen Plus Dynamics™, and the results showed that it is is able to efficiently determine the new setpoints of controllers when facing changes in anhydrous ethanol specification and/or disturbances in the azeotrope feed. The new steady-state is reached in a short time interval (2–4 h, depending on the disturbance type). Based on the integral squared error, integral absolute error, and steady-state error, the results showed that the intelligent control system presented superior performance when compared to conventional control systems. The implementation of the developed control is simple and the existing control structure remains unchanged.

Complex multi-azeotrope and multi-boundary lead to immense challenges of solvent selection for the separation of the ternary multi-azeotrope system. In principle, integrating reactive distillation (RD) with extractive distillation (ED) is fundamental to achieve higher energy efficiencies and to reduce process expenses and environmental impacts. However, these hybrid distillation processes that can overcome the challenges have not been fully investigated. To this end, this article developed and compared the energy-saving reactive-extractive hybrid distillation processes for purification and recovery of the high-value ethyl acetate and EtOH from the wastewater containing multi-azeotrope. The proposed hybrid distillation processes include triple-column reactive-ED (TCRED), double-column reactive-ED (DCRED). In the hybrid processes, ethylene glycol (EG) and dimethyl sulfoxide (DMSO) are adopted as solvents in the ED, while ethylene oxide is introduced as reactant to perform the hydration reaction in the RD process. These separation schemes are optimized with the objective of the minimum total annual costs (TAC) via genetic algorithm procedure to obtain the optimal design parameters. Subsequently, environmental assessment indicator (CO2 emissions) is also calculated to perform the comprehensive analysis for the presented separation processes. The results demonstrate that the hybrid distillation processes coupled with RD can significantly reduce process costs as well as CO2 emissions compared to the conventional TCED process, especially for the DCRED process. The DCRED scheme with EG as solvent has the lowest TAC and CO2 emissions, with a reduction of 43.29%/35.10% TAC and 38.06%/24.73% CO2 emissions compared with the TCRED configurations with EG or DMSO as solvents, respectively. The major contributions of this work are to facilitate the future development for conceptual design of the hybrid distillation processes containing RD.

The non-sharp side-stream extractive distillation (SSED) differs from the sharp one in that it partially, instead of entirely, collects intermediate components through the side stream. Compared to the sharp one, the non-sharp SSED is preferred in some extractive distillation (ED) systems with high boiling-point solvents. However, the number of candidate configurations increases sharply when a design considers both the sharp and non-sharp SSEDs. Correspondingly, it results in a challenge to optimization, particularly in systems with multiple side-stream options. In this study, we propose an adaptive superstructure-differential evolution (DE) method which optimizes the sequences and parameters simultaneously. As a case study, the industrial benzene/cyclohexane/cyclohexene separation is optimized, which has two extractive distillation columns and 30 feasible configurations with different SSED options. Compared to the conventional superstructure-DE approach, the improved method, which selects the feasible flowsheet instead of predetermining a random one, performs better in the optimization. The less computational cost and better solutions demonstrate its superiority. Moreover, the optimized 3-column and 4-column SSED configurations apply non-sharp side-stream options, which proves that the non-sharp SSED options are more competitive for this ternary system. In summary, this study highlights the significance to consider both the sharp and non-sharp SSED configurations and provides a systematic approach to find high-quality configurations from an increased number of candidates.

The recovery of ethyl acetate and isopropanol from ampicillin sodium wastewater is an important task. The existence of azeotropes system makes it difficult to achieve high purity separation by conventional distillation. In this work, the extractive distillation of ethyl acetate/isopropanol/water by efficient separation method was explored. Based on the COSMO-SAC model, the infinite dilution activity coefficients of the components were calculated, and the potential extractant was further determined. Taking the minimum TAC as the objective function, a sequential iterative method was used to optimize the process. Furthermore, steam recompression and pervaporation technologies were used to reduce the process energy consumption. The economic and environmental performance of several processes was calculated to assess their feasibility. It is conclusion that compare with basic process, the steam recompression process performs well in both economy and environment. While the pervaporation-distillation hybrid process obtained a better environmental performance but showed poor economic performance due to huge equipment costs, which requires a corresponding tradeoff based on the actual industry.

Selection of the operating pressure of a distillation column is one of the most important design decisions. Pressure has a major impact on phase equilibrium in terms of relative volatilities, column temperatures and the existence of azeotropes, which affect energy requirements, utility costs and process configurations. Since many separations are favored by low temperatures, pressures in most columns are established by the desire to use inexpensive cooling water as the heat sink in the condenser. For components with low vapor pressures, this criterion results in pressures below atmospheric. However, there appears to be some hesitancy to use vacuum distillation columns, particularly in azeotropic separations. Numerous papers simply fix the pressure arbitrarily at 1 atm despite the fact that lower pressure could be achieved and still use cooling water. This paper illustrates the significant economic advantages, both in capital investment and utility costs, of using vacuum distillation in some systems. The numerical example is taken from a recent paper in which an extractive distillation system to separate n -heptane from isobutanol is designed with column pressures fixed at 1 atm. Our results show that vacuum operation can reduce total annual cost by 27%, despite an 8% increase in capital investment, because of a 37% decrease in reboiler steam costs.

In a recent publication, a triple-column side-stream extractive distillation system was proposed for the separation of benzene/isopropanol/water ternary mixture using ethylene glycol as a heavy entrainer. However, the above design needs to introduce a foreign component into the separation task. In this paper, the newly proposed design principle is to make use of large liquid–liquid envelope together with pressure-sensitive distillation boundary of this ternary system for the development of an energy-efficient design consisting of a decanter and three columns operating at different pressures. In order to give reliable simulation results, a new set of UNIQUAC model parameters for this ternary system is obtained in this paper by regression from liquid-liquid and vapor–liquid equilibria data in open literatures. Simulation investigations reveal that significant savings of 63.4% in the total operating cost and 51.0% in the total annual cost can be realized by our proposed heat-integrated design flowsheet. Furthermore, overall control strategy of the proposed design has also been developed using closed-loop and open-loop sensitivity analyses for the determinations of crucial tray-temperature control points and also to make decision on holding which flow ratio(s) in the flowsheet to be fixed. Dynamic simulations demonstrate that the proposed overall control strategy is capable of holding three products at high-purity despite feed flow rate and feed composition disturbances. No online composition analyzer is required in the proposed control strategy.

In the production of isobutyl alcohol by hydroxyl synthesis process, a large number of industrial effluent rich in isobutyl alcohol and ethanol would be produced, and the direct discharge could cause double harm to resources and environment. Therefore, it has important economic and environmental value to develop efficient and energy-saving separation methods to realize the recovery of high value-added chemicals. Based on the conventional four column extractive distillation scheme (CED), this paper developed a more energy-saving extractive-azeotropic distillation alternative (EAD), which reduced energy consumption and TAC by 16.14% and 22.25%. Then, the steam recompression and variable pressure heat exchange were introduced to complete the heat integration strengthening design (HI1-EAD, HI2-EAD), which saves 54.32% and 54.36% energy consumption respectively. In order to further improve the energy efficiency, the dividing wall column distillation strengthening configuration (EADWC) was embedded into the EAD scheme. Compared with the CED scheme, TAC of the EADWC scheme and its heat integration configuration (HI-EADWC) decreased by 23.21% and 36.90%, respectively. However, the high bottom temperature of the main column leads to a significant increase in the duty and equipment investment, which makes the HI-EADWC scheme not show enough attraction. Through comprehensive evaluation, the HI2-EAD alternative presents more application potential.

Deterpenation of an essential oil improves its stability and quality, thus increasing its market value. In this work, different unit operations to carry out the deterpenation of citrus essential oil were evaluated by simulation. The selected processes were: liquid-liquid extraction using the ionic liquid 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) as solvent, vacuum distillation, and extractive distillation using [C2mim][OAc] as entrainer. A pressure of 5 kPa was selected for distillation processes in order to maintain the organoleptic properties of the essential oil. To that aim, isobaric vapor-liquid equilibria were determined at that pressure for limonene + linalool and linalool + [C2mim][OAc] binary, and limonene + linalool + [C2mim][OAc] ternary, systems. NRTL adequately correlated experimental data and the obtained parameters were used for simulations. Liquid-liquid extraction was shown to be unsuccessful in providing a significant deterpenation. Distillation allowed the recovery of all the fed linalool (100 kg/h) almost pure, but very demanding conditions were required: a reflux ratio and number of plates of 3 and 45, respectively. The use of [C2mim][OAc] as entrainer increases the relative volatility of limonene and linalool, and greatly facilitates their separation by reducing the reflux ratio and number of plates required to 1 and 20 respectively, and also diminishes the energy requirements. The vacuum level of the flash unit used to recover the entrainer drastically affects the essential oil production rate.