Conventional Extractive Distillation Research Articles

Evaluation on the separation effect and extractant recovery efficiency of extractive distillation for separating ethyl acetate/methanol with ionic liquids as extractants

For the purpose of recycling resource and cleaner production, the extractive distillation schemes with different ionic liquids as extractants are proposed to separate ethyl acetate and methanol. In fact, the evaluation of extractants should not just focus on the separation effect, the effectiveness for the recovery of extractants which has a great influence on the overall benefits of extractive distillation process also need to be paid more attention, especially for the ionic liquids (ILs). On the basis of the VLE diagram, σ-Profiles, and interaction energy based on molecular dynamics, the separation effects of the selected extractant are following the order of 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) > 1-ethyl-3-methylimidazolium diethyl phosphate ([EMIM][DEP]) > dimethyl sulfoxide (DMSO). However, the decomposition temperature of [EMIM][DEP] is much higher than that of [EMIM][OAc], which leads to the better effectiveness for extractant recovery. Then, several recovery configurations are explored owing to different decomposition temperature of selected ILs. The result shows that the heat integration assisted the process with [EMIM][DEP] as extractant which utilizes two-stage evaporators extractant recovery configuration has a better performance than other processes and can reduce 35.07% of TAC, 37.59% of energy consumption and 37.36% of gas emission compared with conventional extractive distillation process with DMSO as extractant

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).

Are process-intensified extractive distillation always energetically more efficient?

The thermally coupled, dividing wall column, and side-stream configurations are some of the energy-intensified techniques widely applied to the extractive distillation for improving the energy efficiency. Today, several heuristics are available for analysing the energy-saving efficiency of these intensified techniques for ideal distillation system but there is no heuristic available for analysing the complex distillations system. Therefore, it has not yet been established what variables affect the energy-savings and under what particular conditions the intensified processes for these complex distillation systems present energy-savings. In this work, we aim to provide insights and preliminary conclusions that open a field of study for a more detailed and in-depth analysis for future researches through three different case studies where their corresponding intensified configurations do not provide any energy-saving relative to the conventional extractive distillation (CED). Based on our preliminary analysis, we attributed this to the poor values of interconnecting flowrate or composition and high column internal vapour flowrate. Our results also revealed the possibility of extending several heuristics, previously developed for evaluating the energy-saving efficiency in ideal distillation system, for complex distillation. Lastly, several recommendations are given that were derived from our simulation results and the analyses we carried out on existing publications.

Economic, environmental, and exergy analysis of an efficient separation process for recovering low-carbon alcohol from wastewater

Extractive distillation separation is a continuous and effective process for the separation of industrial wastewater components. In this study, a method to recover high-purity ethanol and isopropanol from industrial wastewater via extractive distillation has been proposed. Three enhanced energy-saving processes were developed to reduce the economic costs and environmental impact of distillation processes. The process operation parameters with the best economic performance were obtained based on a sequential iterative optimization method with the total annual cost as the objective function. Results show that, thermally coupled technology can effectively reduce the economic cost. Compared with the conventional extractive distillation process, the total annual cost of the thermally coupled extractive distillation process was the lowest, accounting to a reduction of 33.14%. The heat recovery rate of the heat pump-assisted thermally coupled extractive distillation process was the highest (1979 kW), and the total energy consumption was the lowest (5762.4 kW). The gas emission (2432.72 kg/Y), GWP (1246.42 kg CO2-Eq), AP (2.23 kg SO2-Eq), HTP inf (38.66 kg DCB-Eq), Eco tox (20.04 CTUe), and exergy loss (20.73%) of the heat pump-assisted thermally coupled extractive distillation process were the lowest. This work has important guiding significance for the efficient recovery of low-carbon alcohols from industrial wastewater and promoting cleaner production in the chemical industry.

Comparative optimal design and effective control of different pressure extractive distillation for separating acetone - Methanol

Acetone and methanol are critical industrial feedstocks as well as organic solvents. Previous studies on the separation of the minimum-boiling azeotrope acetone-methanol by pressure-swing extractive distillation have shown superiority in terms of energy and cost savings. However, the pressure-varying configuration inevitably requires high-grade heat steam. To surpass the limitation, a novel different pressure extractive distillation strategy is proposed in this paper. The conceptual design of the different pressure extractive distillation configuration is carried out from thermodynamic insights, and the feasible ranges of entrainer/feed flow rate ratio and reflux ratio are determined. The design parameters are optimized by an improved non-dominated sorting genetic algorithm. Compared with the conventional extractive distillation process, the total annual cost (TAC) and CO2 emissions of the proposed process are reduced by 22.17% and 48.14%, respectively. An alternative different pressure extractive distillation process with feed preheating is then obtained by changing feed thermal condition, which has a 24.08% reduction in TAC and a 48.33% reduction in CO2 emissions in comparison with the conventional extractive distillation process. Compared with the existing heat-integrated pressure-swing extractive distillation process, the new process has a 2.90% and 22.36% reduction in TAC and CO2 emissions, respectively. Subsequently, two control schemes are presented by calculating controllability indicators in the steady-state design stage. The results illustrate that the improved control scheme with multiple feedforward control loops performs the best robustness.

Design and optimisation of novel hybrid side-stream reactive-extractive distillation for recovery of isopropyl alcohol and ethyl acetate from wastewater

For the first time, we developed a novel side-stream double-column reactive-extractive distillation (SS-DCRED) for the recovery of isopropanol (IPA) and ethyl acetate (EA) from wastewater. Starting with the conceptual design and optimisation of a double-column reactive-extractive distillation (DCRED) using particle swarm optimisation (PSO), we designed and optimised next the SS-DCRED, which is the main contribution of this work. In addition, a reactive-extractive dividing wall column (REDWC) was also developed as we intend to benchmark the SS-DCRED with the REDWC, which is available in literature. The performance of the SS-DCRED was also compared against the DCRED and the best heat-integrated conventional extractive distillation (HI-CED) using ionic liquid (ILs) and ethylene glycol (EG) from previous work based on total energy consumption, TAC, environmental performance, and thermodynamic efficiency. Overall, the total energy consumption, TAC, and environmental performance of the SS-DCRED are 51%, 40%, and 51% lower with respect to the HI-CED using ILs and are 63%, 56%, and 63% lower than the HI-CED using EG from previous work. Likewise, it is also better than the REDWC by about 8%, 4%, and 9% in terms of total energy consumption, TAC, and environmental emissions with respect to the REDWC. These significant enhancement highlights the superiority of our proposed SS-DCRED.

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.

Process evaluation for the separation of acetonitrile-water using extractive distillation with deep eutectic solvents as entrainers

Deep Eutectic Solvents (DESs) show properties that make them effective as environmental-friendly entrainers for extractive distillation. However, the technical and economic evaluation via process simulation and the method of screening a suitable DES for a given azeotropic system are less studied. In this work, the extractive distillation process for acetonitrile dehydration with glycolic acid/choline chloride 3:1 (GC3:1) as entrainer is studied. Firstly, the σ-profiles based on the COSMO-SAC model are employed to select an appropriate DES entrainer. Then, the feasibilities of GC3:1 and ethylene glycol (EG) as entrainer are further studied by the analysis of residue curve maps. Finally, the design and optimization of the extractive distillation process for acetonitrile dehydration with GC3:1 and EG are conducted. The results demonstrate that the conventional extractive distillation process with GC3:1 entrainer gives 13.40% and 9.64% reduction in TAC over the conventional and heat-integrated extractive distillation processes with EG as entrainer, respectively. The TAC of the GC3:1 process is further reduced by 3.14% after heat integration. In addition, the control scheme of the extractive distillation process with GC3:1 entrainer is studied by Aspen Dynamics, and the proposed control structure is effective in managing operational stability.

Energy‐Saving Separation of the Ethanol‐tert‐Butanol‐Water Azeotrope System Based on an Ionic Liquid

AbstractThe separation requirements of the ethanol‐tert‐butanol‐water system are difficult to meet due to the formation of azeotropes under normal pressure. After screening the four most important ionic liquids, i.e., [BMIM][BF4], [EMIM][Cl], [HMIM][Cl], and [EMIM][AC], ionic liquid [EMIM][AC] was selected as extractant, and quantum chemical calculations based on COSMO‐SAC theory were carried out to analyze the mechanism of the separation process. An ethanol‐tert‐butanol‐water extractive distillation process was designed, optimized with the goal of the lowest total annual economic cost, and the cost of carbon dioxide emissions was calculated. To further save energy, a heat pump distillation process was designed and compared with the conventional ionic liquid process. The annual total cost of the heat pump distillation process is reduced by 10.11 %, and carbon dioxide emission costs are reduced by 61.9 %. Comparison with the conventional extractive distillation process and its modified process revealed economic advantages for the ionic liquid extractive distillation process and its heat pump version.

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.

Design and Control of Extractive Dividing Wall Column for Separating Dipropyl Ether/1-Propyl Alcohol Mixture

The focus of this work is the study of the extractive dividing wall column (EDWC) for separating the azeotropic mixture of dipropyl ether and 1-propyl alcohol with N, N-dimethylacetamide (DMAC) as the entrainer. Three separation sequences are investigated, including a conventional extractive distillation sequence (CEDS), EDWC and a pressure swing distillation sequence (PSDS). The static simulation results showed that the EDWC with DMAC as the entrainer is more economically attractive than CEDS and PSDS. Subsequently, a control structure CS1 based on a three-temperature control loop and a control structure CS2 with the vapor split ratio as the manipulated variable are investigated for the EDWC. Their dynamic control performances are evaluated by facing large feed flow rates and composition disturbances. The results showed that the CS1 can deal with feed flow rate disturbance effectively. However, the transient deviation is large and the settling time is too long when facing feed flow composition disturbances. The CS2 can quickly and effectively deal with feed flow rate and composition disturbances, and it can maintain the two products at high purity.

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%.

Sustainable wastewater treatment via extractive distillation process with ionic liquid as entrainer for the separation of ethyl acetate/isopropanol/water

To recycle isopropanol and ethyl acetate from wastewater by extractive distillation, 1-butyl-3-methylimidazolium acetate ([BMIM][OAc]) is considered to be an appropriate entrainer by comparing with ethylene glycol on VLE diagram and σ-Profiles, respectively. Then, the extractive distillation processes with [BMIM][OAc] as entrainer are proposed. Since the degradation temperature of [BMIM][OAc] requires the entrainer recovery section of processes to operate under high vacuum, one-stage evaporator and one stripping column configuration is determined to recycle entrainer [BMIM][OAc]. After optimizing the IL processes, the heat integration technology is applied to the optimized processes. Compared conventional extractive distillation process with EG as entrainer, the heat integration assisted IL process with appropriate entrainer recovery configuration which uses IPA as stripping agent can reduce 24.76% of TAC, 45.64% of energy consumption and 45.52% of gas emission.

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.

Design and eco-efficiency analysis of sustainable extractive distillation process combining preconcentration and solvent recovery functions for separating the tetrahydrofuran/ethanol/water ternary multi-azeotropic mixture

It is of great significance to design a sustainable extractive distillation separation configuration that can implement efficient separation of the ternary multi-azeotropic mixtures with a large single component content and propose a feasible and accuracy sustainable evaluation method. This is because the extractive distillation separation scheme with preconcentration should be designed for the particularity of such ternary multi-azeotropic azeotropes. To fill this gap, the paper designs a novel and sustainable three-column extractive distillation process containing one integrated distillation column (TCED-IDC) with both preconcentration and solvent recovery functions and two extractive distillation columns taking the separation of the tetrahydrofuran/ethanol/water ternary multi-azeotropic mixtures containing large amounts of water as an example. Simultaneously, economic optimization of the TCED-IDC process as well as the conventional three-column extractive distillation (TCED) process and the four-column extractive distillation (FCED) process is implemented to determine economically optimal design parameters via minimizing the total annual costs (TAC) using genetic algorithm. Following that, environmental and thermodynamic evaluations are comprehensively conducted to prove the advantages of the TCED-IDC process. The TCED-IDC separation schemes achieves 79.05%/8.47% reduction in CO2 emissions and 71.92%/9.57% economic cost savings compared to the TCED and the FCED schemes, and the corresponding thermodynamic efficiency is 7.87%. Moreover, an extended Eco-efficiency Comparison Index (ECI) method is proposed to perform the eco-efficiency analysis covering economic, environmental, and thermodynamic aspects for the three extractive distillation separation processes proposed. The analysis results demonstrate that the integration of preconcentration and solvent recovery functions improve the eco-efficiency compared to the other two separation schemes, and the corresponding ECI reaches 91.57% and achieves 1.42% points increase compared to the FCED scheme.

Eco-efficient heat-integrated extractive distillation process using ionic liquid as entrainer for ethyl acetate-isopropyl alcohol-water mixture

Ethyl acetate-isopropyl alcohol-water is a common ternary mixture in pharmaceutical and chemical industries, containing multiple binary minimum azeotropes. Highly efficient separation for this mixture is of great significance to reduce environmental risk, recover valuable resource and maintain eco-sustainability. In this work, various enhanced extractive distillation processes using ionic liquid (IL) as entrainer are compared with conventional extractive distillation process (CED) in terms of the reductions of cost, energy and carbon emissions. First of all, ethylene glycol (EG) and 1-ethyl-3-methylimidazolium acetate ([BMIM][OAC]) as the most promising conventional and IL entrainers are screening out through quantum chemistry calculation based on COSMO-SAC model. Secondly, two methods of improving energy efficiency such as differential pressure heat integration and divided-wall column are applied to the CED process. Finally, the resulting six configurations are optimized by simulated annealing algorithm, taking minimum total annual cost (TAC) as goal, and subsequently evaluated from four aspects of TAC, annual capital cost (ACC), annual operating cost (AOC) and CO2 emission. The results show that the new heat-integrated extractive distillation configuration with [BMIM][OAC] as entrainer, known as EDHI-IL is the best solution for ecological efficiency. As compared to the CED process, TAC, ACC, AOC and CO2 emission of this process are reduced by 38.86%, 36.51%, 41.41% and 41.36%, respectively.

Towards sustainable separation of the ternary azeotropic mixture based on the intensified reactive-extractive distillation configurations and multi-objective particle swarm optimization

The separation of ternary azeotropic systems has received significant interest as it enables the recovery of value-added organic solvents, subsequently contribute towards environmental protection. In this work, we propose a novel approach that involves the conceptual design, multi-objective optimization, and process evaluations for developing two different processes, i.e., double-column reactive-extractive distillation (DCRED) and reactive-extractive dividing wall column (REDWC), for the separation of ethanol/tert-butanol/water ternary azeotropic mixture. The conceptual design of the proposed processes was conducted using kinetic and thermodynamic analysis while optimal operating conditions of the established processes were obtained via multi-objective particle swarm optimization algorithm. Then, both developed processes were evaluated based on the total annual cost (TAC), CO2 emissions, and thermodynamic efficiency. From the steady-state simulation, DCRED and REDWC provides a TAC of 1.056 × 106 US$ and 1.117 × 106 US$, respectively. Likewise, it provides CO2 emissions of 731.27 kg/h and 733.42 kg/h, respectively. The energy efficiency of the DCRED and REDWC were found to be 1.285% and 1.055%, respectively. Relative to the conventional extractive distillation process, the TAC and CO2 emission for the proposed DCRED reduced significantly by 55.4% and 61.8%, respectively. Similar reduction was also observed for the REDWC which provides 52.8% and 61.7% lower TAC and CO2 with respect to the conventional process. In addition, the thermodynamic efficiency of the developed DCRED and REDWC processes are improved by 40.4% and 15.3% in comparison to the conventional extractive distillation scheme.

Investigation on energy-efficient extractive distillation for the recovery of ethyl acetate and 1,4-dioxane from industrial effluent

Conventional extractive distillation processes have been proposed to separate the ternary ethyl acetate-1,4-dioxane-water system with azeotropes. Energy-efficient extractive thermally coupled processes with heat integration have been developed to reduce energy consumption. A macro-analysis of the energy, exergy, economy, and environment is conducted to estimate the economic and environmental benefits. The results proved that an extractive dividing-wall column with a heat-integrated process possessed the greatest energy-saving potential, delivered best economic performance and exhibited highest exergy efficiency. Compared to those of a conventional direct extractive distillation process, the total energy requirement and total annual investment cost are reduced by 28.18% and 24.28%, respectively, by the best energy-saving process. The total exergy efficiency of it is 1.779%. The proposed cleaner and sustainable extractive dividing-wall column configuration could achieve energy saving, investment reduction, and effectively enhance the exergy efficiency.

Optimal modes of side-section flow in heat-pump-assisted extractive distillation systems for separating allyl alcohol–allyl acetate mixtures with butyl propionate

Objectives.To investigate the influence of side-section flow modes on the energy efficiency of apartially thermally coupled distillation sequence (PTCDS) with a vapor recompression heat pumpfor the extractive distillation of an allyl alcohol–allyl acetate mixture with n-butyl propionate andidentify modes under which the combined use of a PTCDS and heat pump are the most efficient.Methods.Mathematical modeling in the Aspen Plus V10 software package was used as the mainresearch method. The local composition equation of the non-random two-liquid model was usedas a model for describing the vapor–liquid equilibrium, while the Redlich–Kwong model was usedto consider the non-ideal vapor phase. When modeling the conventional extractive distillationscheme and PTCDS, parametric optimization was carried out according to the criterion of the totalenergy costs in the column reboilers. For the economical evaluation, Aspen Process EconomicAnalyzer V10.1 tools were used.Results.For extractive distillation of a mixture of allyl alcohol (30 wt %) and allyl acetate (70 wt %)with n-butyl propionate as an entrainer, the minimum energy consumption was achieved at thesame side-section flow mode for the variants of a PTCDS with and without a heat pump. Thereduction in energy costs relative to the conventional scheme was 20% for the sequence withouta heat pump and 38% for that with a heat pump. An economic assessment was made of thebest options in comparison with the conventional extractive distillation scheme. The PTCDS witha heat pump had an advantage over the sequence without a heat pump only for long periods ofoperation.Conclusions.For the extractive distillation of an allyl alcohol–allyl acetate mixture, the optimalmodes for the combined use of a PTCDS with a vapor recompression heat pump coincide with theoptimal modes for a PTCDS without a heat pump.

Optimal design and control of an energy-efficient triple-side-stream quaternary extractive distillation process

Dynamic control of extractive distillation process with multiple liquid side-streams is challenging although it has an energy-saving potential. In this work, the optimal design and control of a high-efficient triple-side-stream quaternary extractive distillation process (TSQED) is presented for separating acetone/methanol/butanone/tert‑butanol. All operating parameters are optimized by a simulated annealing based systematic method, resulting in the reduction of total annual costs by 9.37%, energy consumption by 18.76%, and CO2 emissions by 33.17% as compared with conventional extractive distillation process. Subsequently, three control structures (CS1, CS2, and CS3) are proposed and demonstrated according to different side-stream flowrate control strategy. In the CS1, the side-stream flowrate is proportional to feed flow. In the CS2, the side-stream flowrate is proportional to reboiler vapor flow. In the CS3, and temperature-sensitive plate in distillation column is identified and cascaded by side-stream flowrate. By contrast, CS3 is far better than CS1 and CS2 in terms of dynamic responses and integral performance criteria. This attributes to the virtuous effect of the inferential temperature control on side-stream flowrate in the whole process control of TSQED. Finally, the feedforward control of QR/F is added in the CS4 to further improve the effectiveness of CS3.