Side-stream Extractive Distillation Research Articles

Novel energy-efficient design of side-stream extractive distillation process with intermediate reboiler for separating multi-azeotropic mixture based on multi-objective optimization

Side-stream extractive distillation is extensively employed to separate azeotropic mixtures since its energy-efficient benefits. Nevertheless, its economic effect is not always obvious due to the introduction of expensive high-pressure steam. In this article, a conventional triple-column extractive distillation process is firstly researched for separating n-hexane/ethyl acetate/acetonitrile mixture. To effectively decrease the requirement for high-pressure steam and achieve a reduction in economic costs of side-stream extractive distillation, three innovative side-stream extractive distillation processes with intermediate reboiler are proposed. A multi-objective genetic method is applied to optimize the four processes with total annual cost (TAC) and entropy production as two objective functions. Additionally, due to the presence of intermediate reboiler, heat integration design is implemented to the three side-stream extractive distillation processes with intermediate reboiler. Compared to the triple-column extractive distillation process, the heat integration of the three side-stream extractive distillation processes with intermediate reboiler exhibit better performance considering economy, energy-efficient, and entropy production. It indicates that the heat integration of the double side-stream extractive distillation process with intermediate reboiler can reduce 20.10% of TAC, 29.65% of energy consumption, and 35.63% of entropy production, respectively.

Investigation of side-stream extractive distillation for separating multi-azeotropes mixture based on multi-objective optimization

In this study, a conventional triple-column extractive distillation process and three side-stream extractive distillation processes are investigated for separating a ternary mixture of n-hexane/ethyl acetate/acetonitrile. A multi-objective genetic optimization method is applied to optimize the four processes with the minimum total annual cost (TAC) and entropy production as two objective functions. The results indicate that the three side-stream extractive distillation processes can effectively reduce the remixing phenomenon, achieving a reduction in energy consumption. In addition, the three side-stream extractive distillation processes exhibit better economic advantages and significantly decrease entropy production compared to the conventional triple-column extractive distillation process. Among the processes, the single side-stream extractive distillation process presents the optimal performance considering economy, energy-efficient and entropy production. Specifically, it can reduce 6.17% of TAC, 7.85% of energy consumption and 15.54% of entropy production in comparison to the conventional triple-column extractive distillation process, respectively.

Applicability exploration and sustainable assessment of heat integration and vapor recompression heat pump to side-stream extractive distillation processes for separating ternary azeotropic system

The side-stream extractive distillation (SSED) process is attracting extensive attention due to its high energy efficiency for separating ternary azeotropic mixture. However, the correlation between the bottom temperature level of distillation columns depending on the flowrates and compositions of side streams and the introduction of heat integration (HI) and vapor recompression heat pump (VRHP) technology is ignored. In the work, a range of initialization extractive distillation processes including one conventional extractive distillation (CED) process and five SSED processes considering different flowrates, compositions, and feed locations of side streams are proposed for separating acetonitrile/isopropanol/water ternary azeotropic system. The optimization results with the minimum the total annual costs (TAC) as the optimization objective show that not all SSED schemes are superior to the CED separation process, and the SSED separation schemes can achieve up to a 2.72 % reduction in the TAC. Following that, the HI and VRHP assisted extractive distillation schemes are proposed based on the temperature levels between the top and bottom of different distillation columns and compressor restraints for the initialization extractive distillation schemes mentioned after optimization. Moreover, sustainable evaluations covering economy, energy consumption, environment, and energy utilization are implemented for the extractive distillation schemes proposed. The evaluation results indicate that the CED-HI scheme overcomes all SSED-HI and SSED-VRHP schemes in terms of economic costs, but the optimal SSED-HI processes can reduce 8.77 % of energy consumption and 4.73 % of CO2 emissions, while the energy utilization raised from 1.70 % to 1.78 % compared to the CED-HI process.

Energy-saving exploration of separation for EG/1,2-BDO binary azeotrope based on energy, environmental and economic analysis

In the synthesis of ethylene glycol (EG) from syngas, the inevitable by-product, 1,2-butanediol (1,2-BDO), is generated. Additionally, EG and 1,2-BDO form minimum boiling homoazeotrope, which is a challenge for conventional distillation method. To address this, four processes, extractive distillation process (EDP), extractive distillation with heat integration process (HI-EDP), side-stream extractive distillation process (SSEDP), and extractive dividing wall column process (EDWCP), are used for the separation of EG/1,2-BDO binary system. Firstly, a combination of VLE analysis and COSMO-SAC model analysis was employed to select appropriate entrainers (eugenol). Subsequently, interaction region indicator (IRI) was utilized to reveal the extractive distillation mechanism at the molecular level, demonstrating the feasibility of eugenol as an entrainer for separating EG/1,2-BDO mixture. Next, simulations of the EDP, HI-EDP, SSEDP, and EDWCP processes were conducted through Aspen Plus V11. The optimal process parameters for each flowsheet were determined by the minimum Total Annual Cost (TAC). Furthermore, the process performance was evaluated from economic, energy, and environmental aspects. The EDWCP process demonstrates superior performance compared to the EDP process, with reductions of 16.79% in TAC, 17.6% in TOC, and 14.8% in TCC. Additionally, emissions of acidic gases of decreased by 19.78%, while thermal efficiency improved by 32.91%. EDWCP process represent enormous potential in the field of energy efficiency, economy and environment.

Optimal design and multicriteria comparison of extractive distillation processes for separating of a quaternary low-boiling solvent mixture

This article mainly explores the eco-efficient separation of a complex quaternary azeotropic mixture of methanol, n-hexane, ethyl acetate and ethanol from a pharmaceutical enterprise via extractive distillation. To this end, aniline (AN) and ethylene glycol (EG) are selected as two alternative entrainers based on the relative volatility curve. Two conventional processes with AN and EG (AN-CED and EG-CED) are proposed and optimized with total annual costs (TAC) as a goal by simulated annealing algorithm. To improve energetic and economic performance, two optimal strengthening processes, that is, low-pressure side-stream extractive distillation process with AN (AN-SSED) and dividing-wall extractive distillation process with EG (EG-EDWC) are also developed for the first time. Finally, the four processes are compared in terms of economics, CO2 emissions and inherent safety. The results show that the AN-SSED process is recommended due to the best economic, environmental and inherent safety properties, as reflected by the lowest TAC, CO2 emission and process route index (PRI). It can reduce TAC by 9.38%, CO2 emission by 26.34% and PRI by 38.02% relative to the EG-EDWC process. Remarkably, the EG-EDWC process can reduce TAC by 11.12% than AN-CED process and 6.9% than the EG-CED process, but it is inferior to the two conventional processes in terms of CO2 emissions and inherent safety.

An environmentally benign, energy intensified single-column side stream extractive distillation (SC-SSED) process for Acetone/n-heptane separation

The single-column, side-stream extractive distillation (SSED) process has been proposed as a simple, novel, and energy-saving configuration for separating azeotropic mixtures, using an intermediate-boiling entrainer. However, within limited progress in separating the mixture of acetone (ACE) and n-heptane (HEP) through such processes, benzene (BEN), a human carcinogen, was frequently used as an entrainer. In view of this, our study aims to propose an environmentally benign SSED process to separate the same mixture. In the proposed process, 1-chlorobutane (CHL) is used as an entrainer. With thorough analysis, the economic performance of this process was found to outperform the other process using heavy entrainers (i.e. p-xylene and butyl propionate), while being economically comparable to the process using BEN as an entrainer. In addition, limited improvement is achieved by employing the SSED configuration for heavy entrainer-based processes, since a higher-grade steam is required at the reboiler of the extractive distillation column. Subsequently, a suitable control strategy with two temperature loops and three measurements (i.e. a side-stream temperature control loop, and a temperature difference control loop in the extractive section of the SSED column) was established. It can satisfactorily reject the specified feed disturbances (i.e. ±20% change in flowrate and composition). Compared to all other existing studies, the currently proposed control structure does not require any composition loop and, at the same time, is able to handle disturbances to a greater extent.

Analyzing the sustainability of intensified side‐stream extractive distillation for binary azeotropic separation: a comparative study

AbstractBACKGROUNDThe sustainability performance of extractive distillation (ED) that collectively considers energy efficiency, process safety, economic profitability, process control, and environmental emission has not been widely reported. Motivated by this lack of research, we analyzed and compared the sustainability performance of the intensified side‐stream ED (SSED) with that of the conventional extractive distillation (CED) for the separation of binary azeotropic mixtures. Two different design approaches were analyzed; the first approach involves designing the intensified SSED by preserving the original CED column configuration, while the second approach involves optimizing the original column configuration to become a new intensified SSED configuration.RESULTSWe found that preserving the original configuration usually provides energy‐savings, but this advantage is not guaranteed unless the process is optimized. Generally, the reduction in energy consumption improves economic and environmental performance. However, the optimized design has a higher risk index because it is usually larger in size, for the sake of lowering the energy consumption. In addition, the optimized design usually has a higher condition number, which signifies that a more complex control structure is required.CONCLUSIONAltogether, designing the intensified process via process optimization does not always guarantee significant improvement in all sustainability indicators. © 2023 Society of Chemical Industry (SCI).

Effect of entrainers with different boiling point sequences on the design and performance for side-stream extractive distillation processes

BackgroundAn azeotropic mixture of acetone and n-heptane is commonly found in many pharmaceutical wastewaters. In this work, the separation of acetone / n-heptane was studied using intermediate- and high-boiling-point entrainers (benzene and p-xylene, respectively). MethodsTo maximize the economic benefits and mitigate the economic and environmental impact of the separation process, traditional extractive distillation and side-stream extractive distillation processes were developed for different entrainers. The sequential iteration method was employed to optimize the extractive distillation process, with the total annual cost as the constraint objective. Significant findingsThe results show that p-xylene can facilitate the separation of acetone / n-heptane, with high efficiency and low energy consumption, when using a double distillation column. Among the four separation processes developed, the p-xylene side-stream extractive distillation process delivers the best economic and environmental performance, with a total annual cost of 6.04 × 105 $/y and CO2 emissions of 1114.66 kg/y. Compared to the case of traditional p-xylene extractive distillation and benzene side-stream extractive distillation processes, the total annual cost of the p-xylene side-stream extractive distillation process was reduced by 9.56% and 49.22%, respectively, while the corresponding CO2 emissions were reduced by 15.71% and 48.85%.

Novel temperature-control strategy for single column side-stream extractive distillation process with intermediate-boiling entrainer

A simple, novel, and energy-saving single column side-stream extractive distillation (SSED) process was recently proposed in literature, for separating the azeotropic mixture of methanol (MeOH) and toluene (TOL) using triethylamine (Et3N) as an intermediate boiling entrainer. However, within the limited progress regarding the control of this process, composition controllers were required to maintain stringent product specifications in the face of disturbances. In view of this, our work firstly uncovers the feasibility of establishing control strategies without using composition loops. The research scope also covers the revision of thermodynamic properties in between MeOH and Et3N, re-design of the process with systematic optimization, development and evaluation of four control schemes. With thorough analyses, a dual-temperature control structure with three measurement (i.e. a side-stream temperature control loop, and a temperature difference control loop in the extractive section of the SSED column) was found to satisfactorily reject the specified feed disturbances (i.e. ±20% change in flowrate and composition). Notably, the loop adjusting the makeup flowrate to control the side stream temperature, which has not been proposed to the single column SSED process, greatly reduced the settling time under disturbances. Comparing with other control structures in literature, the one proposed in this work provides good control performances, but in a manner that is more industrially maneuverable.

An intensified energy-saving architecture for side-stream extractive distillation of four-azeotrope mixtures considering economic, environmental and safety criteria simultaneously

Side-stream extractive distillation is used in separating azeotropic mixtures due to its advantages in energy-saving. However, environmental and safety aspects should also be considered in most chemical industries. Thus, this work focuses on thermodynamic analysis, multi-objective optimization and multi-criteria decision making. The main contributions of this work are developing the intensified side-stream extractive distillation for complex ternary azeotropic mixture, obtaining the trade-offs between the economic, environmental and safety impacts of SSED processes and determining the best sustainable SSED process according to objective mathematical analysis. A systematic intensified architecture including conceptual design, multi-objective optimization and multi-criteria decision making is proposed. Firstly, three strategies of side-stream extractive distillation (i.e., SSED-1, SSED-2, and SSED-3) are proposed via the thermodynamic analysis including quaternary phase diagram. Subsequently, the three strategies are optimized via the multi-objective particle swarm algorithm simultaneously using total annual costs (TAC), CO2 emission and process route index (PRI) as objective functions. Finally, the optimal economic, environmental and safety performance of such a complex system is determined by the technique for order of preference by similarity to ideal solution method with entropy weighting information. The results indicate that the introduction of the side-stream for extractive distillation could decrease the exergy loss and increase the thermodynamic efficiency. The SSED-1 process shows that the best performance in economic, safety and environmental aspects, which reduce 19.21% of TAC, 5.24% of PRI and 16.80% of CO2 emission, respectively.

Towards sustainable separation and recovery of dichloromethane and methanol azeotropic mixture through process design, control, and intensification

AbstractBackgroundHere we analysed the possibility of improving the sustainability performance for the recovery of dichloromethane and methanol from a binary azeotropic mixture using different energy‐intensified extractive distillation‐based processes: side‐stream extractive distillation (SSED), thermally coupled extractive distillation (TCED), and extractive dividing wall column (EDWC). The sustainability performance of the different processes was analysed based on three main factors: total annual cost (TAC), CO2 emissions, and condition number.ResultsThe EDWC was found to give the best improvement in terms of TAC and CO2 emissions by about 18% and 21%, relative to conventional extractive distillation (CED). These however were traded‐off by the increase in conditional number (CN) by 186 times, signifying a complex dynamic characteristic for the EDWC. Thus, the SSED was suggested as an alternative sustainable option as it also provides significant improvement in TAC and CO2 emissions by about 11%, and 18% with respect to the CED, whilst providing the least reduction in operational controllability, as evidenced by the marginal increase in the CN of about 1.5 times. We also investigated the dynamic performance of the SSED and found that the SSED provides identical dynamic performance in handling both ±10% throughput and ±5% feed composition disturbances as those of the CED.ConclusionAmong the different processes, SSED is the best sustainable alternative that provides compromised steady‐state (i.e. TAC and CO2 emissions) and dynamic (i.e. control) performance for the recovery of dichloromethane and methanol. © 2022 Society of Chemical Industry (SCI).

Comparison of different extractive distillation processes for chloroform/n‐hexane separation: design and control

AbstractBackgroundWhen extracting total glycosides from Panax notoginseng, a waste liquid containing chloroform and n‐hexane will be produced. These waste liquids are not separated and recycled in time, which will not only waste resources but also cause environmental pollution. Chloroform and n‐hexane form an azeotrope which cannot be separated by ordinary distillation methods. This study proposes three extractive distillation processes to separate the chloroform/n‐hexane azeotrope: conventional extractive distillation (ED), side‐stream extractive distillation (SSED) and extractive dividing wall column (EDWC). The total annual cost (TAC) and carbon dioxide (CO2) emissions of the three options were compared, and the optimal process was selected. Furthermore, this research developed dynamic control of the optimal process.ResultsCompared with ED, from the perspective of economic indicators, the SSED process showed 18.9% reduction in TAC yet the EDWC process showed 33.2% reduction in TAC. In terms of CO2 emission indicators, the EDWC process also is more advantageous. Three control structures thus were developed for EDWC: applying ±5% or ±10% feed flow disturbance, and feed composition disturbance. The results show that CS3 with temperature composition cascade control structure can perfectly control all disturbances.ConclusionThis paper designs an economical, environmentally friendly and controllable chloroform/n‐hexane azeotropic separation process, which can provide a reference for the industrial application of chloroform/n‐hexane separation. © 2022 Society of Chemical Industry (SCI).

Different extractive distillation processes for isopropanol dehydration using low transition temperature mixtures as entrainers

Low transition temperature mixtures (LTTMs) are effective and environmental-friendly entrainers for extractive distillation. However, process intensification for the LTTMs extractive distillation process is less studied. This paper provides a techno-economic study for the separation of isopropanol and water by extractive distillation using ChCl/EG1:2 as entrainer. Firstly, the σ-profiles based on the COSMO-SAC model, the residue curve maps and univolatility lines are used to investigate the advantages of ChCl/EG1:2 over ethylene glycol. Then, the conventional extractive distillation (CED) system with EG or ChCl/EG1:2 entrainers are simulated and optimized by non-dominated sorting genetic algorithm-II (NSGA-II) method with targets of minimum total annual cost (TAC), minimum CO2 emissions and minimum global energy consumption (GEC). The TAC of the CED process using ChCl/EG1:2 as entrainer is reduced by 13.75% than that of the process using ethylene glycol as entrainer. Finally, in order to reduce energy consumption, the processes of extractive dividing wall column (EDWC) and the side-stream extractive distillation system (SED) with ChCl/EG1:2 as entrainer are simulated and optimized. The results show that the EDWC with ChCl/EG1:2 can save 23.83% of TAC, 23.43% of CO2 emissions and 22.66% of GEC compared with the CED process using EG as entrainer.

Design and control of an energy intensified side-stream extractive distillation for binary azeotropic separation of n-hexane and ethyl acetate

In this work, we explored, for the first time, the possibility of improving the performance of conventional extractive distillation (CED) for the separation of n-hexane and ethyl-acetate system using dimethylformamide (DMF) as solvent through retrofitting it to an energy-intensified side-stream extractive distillation (SSED). This is since the application of the energy-intensified processes have never been explored in any of the existing studies for the n-hexane and ethyl-acetate system using DMF as solvent. Prior to the investigation, we first bridged the gap of previous study (Ind. Eng. Chem. Res.2018, 57, 32, 11050–11060) where using DMF was found to be more economical relative to using n-methyl-2-pyrrolidone (NMP) as solvent but previous study did not explicitly compared the environmental and dynamic performances of both processes. The environmental performance evaluated based on the CO2 emission revealed that using DMF is much more environmentally sustainable relative to that using NMP. Likewise, DMF also provides better dynamic performance by about 3 times, as indicated by the sum of integral absolute error (SIAE), when both processes are tested under ± 10% feed flowrate and ± 5% feed composition disturbances. Therefore, it is used as a base case for subsequent comparison against the retrofitted energy-intensified SSED. Relative to the base case, the proposed SSED reduces the energy consumption, TAC, and CO2 emission by 26%, 19%, and 26%, respectively, indicating its economic and environmental advantages. It additionally provides 4 times better dynamic performance as reflected by the SIAE and it generally provides a lower transient deviation and can maintain both products at their desired purities.

Insights on sustainable separation of ternary azeotropic mixture tetrahydrofuran/ethyl acetate/water using hybrid vapor recompression assisted side-stream extractive distillation

The energy-efficiency of the traditional distillation-based processes are low, which results in waste of resources and environmental pollution. Therefore, a sustainable extractive distillation (ED) process should be developed to reduce energy consumption and CO2 emissions while improve the energy efficiency. In this work, a systematic approach is developed for the first time, for the separation of ternary azeotropic mixture containing Tetrahydrofuran (THF)/Ethyl acetate (EtAC)/Water via the combination of side-stream distillation and vapor recompression heat pump techniques. Firstly, the conceptual design of the various intensified schemes such as single (or double) side-stream(s) ED configurations are developed. Subsequently, the developed configurations were optimized using mesh adaptive direct search algorithm to obtain the optimal operating conditions of the established processes. Vapor recompression heat pump technique is used to further reduce the energy consumption. The sustainability of the various established configurations is assessed via the comparison of total annual cost (TAC), CO2 emissions, energy consumption, and thermodynamic efficiency. Overall, it was revealed that the TAC, CO2 emissions, and energy-consumption for the integrated vapor recompression assisted side-stream ED process were reduced by 33%, 49%, and 38%, respectively, relative to the conventional triple column ED. Likewise, the thermodynamic efficiency was improved by 52%.

Design and control of side-stream extractive distillation to separate acetic acid and cyclohexanone from wastewater by varying pressure

A large amount of wastewater containing acetic acid and cyclohexanone is produced during the production of ε-caprolactone. It is necessary to recycle acetic acid and cyclohexanone from wastewater. In this paper, the feasibility analysis for the separation of acetic acid/ cyclohexanone/ water with a near-azeotrope and an azeotrope which is pressure sensitive is carried out based on the residue curve map (RCM). And two sequences of conventional extractive distillation are determined. In order to prevent the remixing effect in conventional extractive distillation, four configurations of side-stream extractive distillation by varying pressure are proposed and optimized. The results show that the single liquid side-stream extractive distillation configuration SED1 is the optimal configuration in terms of economy, environmental protection, energy efficiency and safety. Compared with the optimal conventional extractive distillation configuration CED1, the total annual cost (TAC) of SED1 is reduced by 6.6%, and CO2 emissions are reduced by 11.9%. Subsequently, three proportion-integral (PI) control structures and a model predictive control (MPC) structure are proposed for SED1. The robustness and controllability of PI and MPC systems are compared by calculating integral absolute error (IAE). The findings indicate that the MPC structure has the best performance among all control structures.

Dynamic controllability comparison of different side-stream extractive distillation processes with intermediate boiling entrainer

It is of great significance to simultaneously consider the economy and controllability for promoting the sustainability of the process industry. In the paper, the controllability of different energy-efficient side-stream extractive distillation (SSED) processes using intermediate boiling entrainer including two double column side-stream extractive distillation (DC-SSED) processes and one single column side-stream extractive distillation (SC-SSED) process are explored for separating the methanol/toluene azeotrope with triethylamine as entrainer. The side stream withdrawal locations of the DC-SSED processes are located in the rectifying section (DC-SSED (a)) and extraction section (DC-SSED (b)), respectively. The recycled intermediate boiling entrainer concentration is 45 mol% for the SC-SSED process. The two robust control strategies constructed for the DC-SSED (b) process are also suitable for the DC-SSED (a) process in resisting the same feed disturbances, which do not adopt the construction concept of the feasible control strategy for the SSED separation process with heavy entrainer. The difference between the two novel control strategies exists in how to control the methanol product purities via reflux ratios. Simultaneously, the two robust control strategies are constructed to resist the same feed disturbances for the SC-SSED process and compared to the two DC-SSED processes in terms of dynamic performances. The dynamic performances demonstrates that the DC-SSED (a) process with worst energy and economic performances is superior to the SC-SSED process and the DC-SSED (b) process from the perspective of the total integral squared error. However, the number of control loops used in the control strategies constructed for the SC-SSED process with optimal energy and economic performances is much smaller than that used in the control strategies constructed for the DC-SSED process, especially the number of composition control loops. Overall, the dynamic performances and economic performances of different processes may not be consistent, and the paper provides some advice for the construction of the robust control strategies for the SSED separation processes with intermediate boiling entrainer.

Insights on Sustainable Separation of Ternary Azeotropic Mixture Tetrahydrofuran/Ethyl Acetate/Water Using Hybrid Vapor Recompression Assisted Side-Stream Extractive Distillation

Insights on Sustainable Separation of Ternary Azeotropic Mixture Tetrahydrofuran/Ethyl Acetate/Water Using Hybrid Vapor Recompression Assisted Side-Stream Extractive Distillation

Novel Temperature-Control Strategy for Single Column Side-Stream Extractive Distillation Process with Intermediate-Boiling Entrainer

Novel Temperature-Control Strategy for Single Column Side-Stream Extractive Distillation Process with Intermediate-Boiling Entrainer

Design and control of energy-saving double side-stream extractive distillation for the benzene/isopropanol/water separation

A new energy-saving double side-stream extractive distillation (SSED) is proposed for the benzene/isopropanol/water separation. The energy-saving alternative can further reduce 13% in TAC and 14.31% in CO2 emission in comparison to the conventional arrangement. Five control structures (CSs) are developed to control conventional (CS1 and CS2) and energy-saving (CS3-CS5) double SSED. The response of five CSs are studied by ±10% feed flowrate and ±20% composition disturbances, and the performances of five CSs are quantitatively assessed by two criteria, deviation from the production target (DPT) and integral absolute error in product purity (IAE). It is found that CS1 fails to handle effectively the feed flowrate disturbance, but CS2 has good dynamic behavior in the face of both feed flowrate and composition disturbances. The values of DPT and IAE for CS2 are obviously smaller than CS1. CS3, CS4 and CS5 all can resist feed flowrate and composition disturbances, but CS4 and CS5 receive more favorable control outputs than CS3. The values of DPT and IAE for CS4 and CS5 are very close, and both are smaller than those for CS3.