Extractive Distillation Process Research Articles

Multi-objective optimization and performance evaluation for the recovery of isopropanol and benzene from effluent via side-stream extractive distillation with intermediate reboiler processes

Side-stream extractive distillation typically requires the introduction of expensive high-pressure steam, which is not conducive to economic benefits. A heuristic approach is to introduce an intermediate reboiler in side-stream extractive distillation to reduce the use of high-pressure steam and thus lower economic costs. In this article, three side-stream extractive distillation with intermediate reboiler processes are proposed to recover the benzene and isopropanol from chloramphenicol production effluent. Taking into account economic, environmental, and entropy production indicators, an evolutional genetic algorithm is used to conduct the multi-objective optimization for the three processes. After obtaining the optimal operation parameters, the corresponding heat integration processes are proposed. Following that, the six process are compared to the optimal double side-stream extractive distillation process (D-SSED) in literature. It indicates that all six processes have good economic potential, especially the single side-stream extractive distillation with intermediate reboiler process with heat integration (S-SSEDIR-2-HI), which is the optimal scheme. Compared to the D-SSED process, it can reduce total annual cost (TAC) by 29.02 %, CO2 emission by 36.14 %, and entropy production by 44.07 %.

Energy and cost-efficient ionic liquids extractive distillation for producing electronic and polymer-grade propylene with emphasis on feedstock variability

The separation of propylene/propane is the main source of electronic or polymer-grade propylene. However, the current industrial method faces significant challenges due to high theoretical stages and energy consumption. In this work, an extractive distillation process using ionic liquids (ILs) 1-butyl-3-methylimidazolium trifluoroacetate ([BMIM][TFA]) is proposed to overcome these difficulties. Based on quantum chemical calculations, the mechanism of separation of propylene/propane is analyzed, and the mechanism behind the performance differences of various anions is explored. Optimal designs for extractive distillation processes are investigated for varying propylene/propane feed compositions, targeting electronic and polymer-grade propylene. A comparison of traditional distillation, heat pump distillation, and ILs extractive distillation evaluates both energy consumption and economic factors. The results suggest that both the cation and anion contribute to the separation of propylene/propane, with the cation having a greater effect than the anion. The separation is enhanced by the π-π stacking, C-H···π, and π···H···O interactions between [BMIM][TFA] and propylene, which strengthen the affinity for propylene over propane. Compared to traditional distillation, ILs extractive distillation reduces energy costs by 64.1% to 82.1% for polymer-grade propylene and by 69.5% to 84.0% for electronic-grade propylene, with theoretical stages dropping from 210–240 to 46–78 and 250–280 to 64–98, respectively. It also cuts total annual cost by 2.0% to 37.4% for polymer-grade and 7.4% to 39.2% for electronic-grade propylene compared to heat pump distillation. The extractive distillation using [BMIM][TFA] performs best, indicating substantial potential for separating propylene/propane.

Economical process design of reactive-extractive distillation combining variable pressure and heat integration for separating a ternary azeotropic mixture

Research and development of environmentally friendly processes that can generate significant profits has always been a focus of attention in pharmaceutical and chemical fields. In this study, a novel reactive-extractive pressure-swing distillation (REPSD) process was designed to separate tetrahydrofuran (THF)-methanol-water (TMW) ternary azeotropic mixtures. Ethylene oxide (EO) is reacted with water to form ethylene glycol (EG) in a reactive distillation (RD) column, which removes the water from the mixture. Then, the THF-methanol (TM) mixture is separated by extractive distillation (ED) and pressure-swing distillation (PSD). A multi-objective genetic algorithm (MUOGA) with total annual cost (TAC) and total capital cost (TCC) as objective functions, along with heat integration techniques were used to optimise the designed REPSD process. Optimal operating conditions to achieve maximum economic benefits were obtained for the process. Subsequently, the environmental benefits of the process were evaluated. The results showed that the proposed REPSD with heat integration can significantly reduce the TAC and CO2 emissions by 29.1 and 26.9 %, respectively, compared to existing optimal heat integration extractive distillation (HIED) processes. This study provides a new perspective on the separation and purification of ternary azeotropic mixtures.

The design and control of heat-integrated EDWC processes for the separation of THF/IPA/water

Extractive dividing wall columns (EDWC) and heat integration are effective process intensification strategies for separating azeotropes. In this study, the steady-state and dynamic control for the separation of tetrahydrofuran/isopropanol/water using a combination of EDWC and heat integration with intermediate reboilers are systematically investigated. The feasibility of the extractive distillation process is evaluated by analyzing the thermodynamic characteristics of the mixture through phase diagrams, and the three-column extractive distillation (TCED) process is established as the basic process. To enhance the energy and economic efficiencies, as well as environmental sustainability, three improved processes are proposed. Compared with TCED, the optimal process (E-EDWC-HI2) reduces the total annual costs, energy consumption, and CO2 emissions by 22.35 %, 41.77 %, and 26.28 %, respectively. In addition, a dynamic control structure is proposed for the E-EDWC-HI2, which exhibits robustness against disturbances in the feed flow rate and composition. This study provides guidance for the design and dynamic control of complex distillation processes.

A new strategy to design the purification process of ethyl tertiary butyl ether gasoline additive via hybrid extractive-reactive distillation

Here we propose a new strategy for designing the purification process of ethyl tertiary butyl ether (ETBE) gasoline additive. Our proposal suggests replacing the last two columns of the triple-column extractive distillation process from previous work with a single reactive distillation column. This column incorporates an ethylene oxide hydration reaction, yielding ethylene glycol, which can be utilized as a solvent for extractive distillation. This replacement is able to reduce the total number of columns, the amount of solvent needed, and significantly decreases total energy consumption up to 32 % compared to the original process. Furthermore, it benefits from the redistribution of energy between different steam-grade utilities, enabling significant reduction in operational costs. These advantages result in a 3−22 % cost decrease compared to the original process. Overall, the proposed process exhibits significant improvements in energy efficiency and cost reduction with respect to the original process with and without heat integration from previous research.

Integrating different fidelity models for process optimization: A case of equilibrium and rate-based extractive distillation using ionic liquids

We integrate equilibrium and rate-based models to formulate a hybrid optimization scheme for designing an ionic liquid-based extractive distillation process for mixed-refrigerant separation. The equilibrium model assumes vapor–liquid equilibrium at each stage but challenges arise with low-volatility, high-viscosity solvents, which drive the system away from equilibrium. The rate-based approach considers mass and heat transfer rates, giving more accurate representation. We compare the two models for separating R-410A, an azeotropic mixture of R-32 and R-125, using [EMIM][SCN] ionic liquid as entrainer. Analyzing over 4300 simulations with various dimensionality reduction and topological analysis techniques, we find that predictions from the two models exhibit similar trends, but the overestimation in equilibrium-based purities sometimes leads to infeasible process designs. The proposed optimization algorithm thus combines the strengths of the two models to locate feasible and optimal designs.

Towards on energy-saving and cost-reducing heterogeneous azeotropic distillation process for separating n-butanol/isobutanol/water

N-butanol, isobutanol, water can form a ternary azeotropic mixture, which is often separated by special distillation methods in the chemical industry. In our previous work, an efficient extractive distillation process was proposed for the separation of this mixture. This work focuses on developing another efficient heterogeneous azeotropic distillation (HAD) process for the same goal. Firstly, according to thermodynamic analysis, a basic HAD process is proposed and optimized to minimize both the total annual costs (TAC) and CO2 emissions. Three HAD enhanced processes using dividing-wall column, vapor recompression heat pump and pressure-swing thermal couple distillation are designed and heuristically optimized. Finally, the performance of these schemes is analyzed from four aspects: economy, environment and exergy (3E). The results demonstrate that, in comparison to the basic process, the enhanced process HADWC-HPTC reduces TAC by 27.44 %, CO2 emissions by 80.01 %, and exergy loss by 62.57 %.

An innovative quick-decision strategy for evaluating the applicability of extractive distillation process with a preconcentration column in separating high-concentration organic waste liquid

In the face of the high energy consumption challenge in separating high-concentration organic waste liquid through extractive distillation (ED), the concept of preconcentration provides a new strategic direction. Therefore, it has become crucial to determine the suitability of the ED process with a preconcentration column for processing such complex mixture. Taking this into consideration, the study proposes an innovative quick-decision method that utilizes thermodynamic analysis of ternary phase diagram to determine the ratio of theoretical product flowrate at the bottom of the preconcentration column to the feed flowrate, which serves as the basis for deciding whether to choose the ED process with a preconcentration column for handling such separation tasks. Three azeotropic systems with different thermodynamic characteristics are chosen as case studies: cyclohexane/ethyl acetate/ethanol (Case 1), ethyl acetate/ethanol/water (Case 2), and n-hexane/ethyl acetate/acetonitrile (Case 3). The task of separating the above three systems is accomplished through the application of both three-column extractive distillation configuration (TCED), and four-column extractive distillation configuration (FCED). The objective functions for multi-objective optimization of all separation configurations include the minimum total annual cost (TAC), the minimum entropy generation and the minimum CO2 emissions. The research findings indicate that when the ratio of theoretical product flowrate at the bottom of the preconcentration column to the feed flowrate is not less than 0.56, or when there is a significant concentration difference among the components in the feed stream, the FCED configuration exhibits clear advantages over the TCED configuration in terms of economic, environmental, and thermodynamic aspects.

Energy-efficient heat pump-assisted pre-concentration integrated with sequential [EMIM][BF4] and ethylene glycol-based extractive distillation for enhanced recovery of ethanol and isopropyl alcohol from wastewater

Recovering ethanol and isopropyl alcohol (IPA) from wastewater offers significant economic and environmental advantages. In this work, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and ethylene glycol (EG) are proposed as double entrainers for separating IPA/ethanol/water mixtures. The novel process sequentially uses [EMIM][BF4] to separate ethanol/water and IPA/water azeotropes, followed by EG for near-boiling mixture of ethanol/IPA. Energy-economic comparisons of extractive distillation process using single and double entrainers are performed. To address the issue of high water content in mixtures, the heat pump-assisted pre-concentration (HPP) integrated with extractive distillation processes are proposed. Subsequently, the effect of water content in the mixtures on process performances are analyzed. The results indicate that compared to using a single entrainer [EMIM][BF4] or EG process, the double entrainers process reduces energy cost and total annual cost (TAC) by 19.9% to 45.3% and 18.6% to 52.7%, respectively. The HPP scheme effectively reduces the mole fraction of water from 60% to 26.05%, further decreasing energy costs by 4.2% to 22.2%. The energy cost and TAC of the double entrainers process decreases by 4.8% to 50%, and 2.8% to 52.1% compared with the single entrainer process under HPP schemes. The double entrainers [EMIM][BF4]-EG process shows promising prospects from energy and economic perspectives.

Separation of ethanol/n-hexane azeotrope by imidazolium ionic liquids: Experimental study and mechanism analysis

In the process of producing low-carbon alcohols from coal, azeotropic waste containing ethanol and n-hexane is generated. To prevent environmental risks and resource waste from solvent loss, this study selected green solvent ionic liquids (ILs) for their separation. First, we screened five anions with high selectivity based on the conductor-like screening model for realistic solvents (COSMO-RS), and through various quantum chemical calculations, we found that the anions play a significant role in the separation of the two components, with [HSO4]− showing the best separation performance. Second, we predicted the phase equilibrium data for ILs containing [HSO4] − in the azeotropic system, considering practical factors such as price and viscosity, and selected [EMIM][HSO4], [BMIM][HSO4], and [HMIM][HSO4] for experiments. The results indicated that simpler cation side chains enhance the separation capability of the system. Then, a toxicity analysis of the ILs ensured their biocompatibility and feasibility. Finally, we established the extraction distillation process and visualized the interactions between the ILs and the azeotropic system through molecular dynamics simulations. This work provides theoretical guidance for the separation of alcohols and alkanes in the industry.

Exploration and multi performance evaluation of process intensification for separation of ethyl tert-butyl ether/ethanol from wastewater

Ethyl tert-butyl ether is a green gasoline additive that enhances fuel efficiency and can play an essential role in improving fuel performance. This study explored the separation of wastewater containing ethyl tert-butyl ether and ethanol by changing the pressure and adding reactions based on extractive distillation, using the synergistic effect of the entrainer, pressure, and chemical reaction. By utilizing coupling technology and process intensification concepts, developed a comprehensive series of intensified processes that have clarified the interaction mechanisms between the extractive distillation process (EDP), pressure swing extractive distillation process (PSEDP), and reactive extractive distillation process (REDP). Studying the separation and purification mechanisms of products and intermediates during the reaction process provides theoretical and practical support for optimizing chemical processes. Comparative analysis showed that the reactive extraction pressure swing distillation process (REPSDP) had preeminent economic and environmental benefits. The total annual cost of PSEDP, REDP, and REPSDP was reduced by 5.88 %, 1.68 %, and 10.08 %, respectively, compared with EDP. The gas emissions of PSEDP, REDP, REPSDP, and REPSDP with heat integration process (HI-REPSDP) are all lower than those of EDP. HI-REPSDP saves 47.59 % of gas emissions compared to EDP, highlighting its environmental benefits. HI-REPSDP has the best energy efficiency, reducing energy consumption by 47.58 % compared to EDP, significantly improving the energy utilization rate. It was found that the introduction of heat integration technology had a significant improvement effect. This research has crucial theoretical and practical value and provides guidance and reference for achieving a clean and efficient production process.

Furfural purification and production from prospective agricultural waste of oil palm empty fruit bunch: Simulation, design and economic assessments

Furfural is potentially produced from lignocellulose waste of biorefinery processes and is widely used as a value-added in various chemical industries. However, the purification of furfural should be conducted to obtain high purity. This work aims to synthesize, design, and optimize the furfural production using some alternative distillation processes by simulation using Super Pro and ASPEN software. The pretreatment process of producing crude furfural from empty fruit bunch waste is also evaluated. The production cost of $0.23/kg of crude furfural (5 %) was obtained in the preliminary process. In the purification process, the sequenced distillation process was less prospective than the extractive distillation based on the simulation basis and economic evaluation. The extractive distillation using n‑butyl chloride performed better than toluene and benzene as the furfural recovery, and the purity was 98.60 % and 99.94 %, respectively. The payback period (PBP), internal rate return (IRR), and net present value (NPV) also indicated the great performance of the extractive distillation process with values of 1.24 years, 36.04 %, and $14,591,500, respectively. Therefore, the simulation, design, and economic evaluation presented promising results that are feasible for plant establishment.

Extractive distillation using salt-based deep eutectic solvent as entrainer for separating acetonitrile-water mixture

Salt-based deep eutectic solvents (DESs) have been proposed in this work for the separation of the azeotrope of acetonitrile and water (H2O). The vapor–liquid equilibrium experiments indicated that (ChCl:U:CaCl2)1:2:0.36 exhibits an higher selectivity among all of the entrainers investigated and eliminates the azeotropic point of acetonitrile and water mixture. Moreover, the calculated values by NRTL model coincide well with the experimental data for the systems (acetonitrile + H2O + (ChCl:U:CaCl2)1:2:0.36). Based on the thermodynamic study, the conceptual process design was established to evaluate the competitiveness of the suggested entrainers for the separation of acetonitrile and water. It was determined that the thermodynamic efficiency (η) in the extractive distillation (ED) process utilizing the new salt-based DESs entrainers increases 60.31 % compared with the benchmark entrainer ethylene glycol (EG). Conversely, the ED process using (ChCl:U:CaCl2)1:2:0.36) entrainer can reduce the total annual cost (TAC) by about 7.81 % and the CO2 emissions (ECO2) by 14.74 %. The ED process using (ChCl:U:CaCl2)1:2:0.36) as entrainer shows the high energy efficiency, low economy cost and low CO2 emissions with a great industrial application prospect when compared to the bench marked process.

Dimethyl carbonate/methanol separation by azeotropic distillation with water: An alternative process driven by low-pressure steam

This study reported a conceptual design of dimethyl carbonate/methanol (DMC/MET) separation via an azeotropic distillation (AD) process with water as the entrainer. Water can form a minimum azeotrope with DMC, stripping DMC from MET via a distillation column. Meanwhile, the liquid–liquid equilibrium can lift the DMC fraction from the azeotropic composition to a much higher level with a decanter. It enables the subsequent distillation column to produce pure DMC. The techno-economic analysis after process optimization demonstrated that the total annualized cost (TAC) of the AD process is 13.8 % lower than the conventional extractive distillation (ED) process. Subsequently, heat integration and double-effect distillation were introduced to further increase the energy efficiency. The improved AD process is also superior to the improved ED process (31.7 % energy cost and 4.1 % TAC saved). Moreover, the moderate temperature of the reboilers of the AD process with water as the entrainer further elevates its superiority since industrial waste heat can be applied in this case.

Process-driven solvent screening for efficient extractive distillation using interpolative rational functions

When designing extractive distillation processes, using selectivity and capacity at infinite dilution alone is hard to identify the real optimal solvent with minimal process cost. To overcome this problem, a new process-driven solvent screening approach is developed. As simple and reliable surrogate models, rational functions (algebraic fractions such that the numerator and the denominator are polynomials) and multivariate polynomials (a subset of rational functions) are trained to interpolate vapor–liquid equilibria with thermodynamic consistency. The surrogate models can directly be embedded into superstructure-based extractive distillation process design to obtain optimal solutions within a few seconds. This enables to evaluate the real process performance of numerous solvents efficiently. Incorporating the accelerated process design strategy, a multi-level solvent screening framework is proposed and exemplified for the separation of a close-boiling mixture ethylbenzene/styrene. The solvent C2H2Br4 ultimately enables a cost reduction of 27.9 % compared to the industrially used benchmark solvent sulfolane.

Mechanism analysis and performance comparison of extractive distillation with different extractants for separating methyl tert-butyl ether/methanol mixture

Methyl tert-butyl ether (MTBE) is an important chemical raw material and fuel additive commonly used in the chemical industry and can form minimum boiling azeotrope with methanol (MeOH). In this article, extractive distillation processes with common-extractant (diethylene glycol, DG), counter-extractant (chlorobenzene, CB) and ionic liquid ([MIM][HSO4]) for the separation of MTBE and MeOH binary azeotrope are investigated simultaneously for the first time. Moreover, five quantum chemical calculation methods of σ-profiles, electrostatic potential, interaction energy, Hirshfeld surface and weak interaction are used simultaneously for the first time to reveal the extractive distillation mechanism of different extractants in detail. Finally, three extractive distillation processes (CED-IL, CED-DG, CED-CB) are established and optimized with total annual costs (TAC) and CO2 emissions as objectives. Their performances are comprehensively compared from the aspects of economy, environment, energy, exergy and inherent safety under the optimal conditions. The results demonstrate that, in comparison to the CED-DG process, the CED-IL process reduces TAC by 31.0%, total energy consumption (TEC) and gas emissions by 27.7%, process route index (PRI) by 36.4% and increase thermodynamic efficiency by 46.4%, while the CED-CB process increases TAC by 29.1%, TEC and gas emissions by 23.2%, PRI by 22.1% and reduce thermodynamic efficiency by 11.4%.

Control of extractive distillation processes with preconcentration for the separation of ternary azeotropic mixture ethyl acetate-ethanol–water in the face of multiple feed disturbances

The integration of preconcentration and solvent recovery functions is one of the effective ways to save energy consumption of extractive distillation processes for separating ternary azeotropic mixtures with a high content of one composition. However, the integration of various functions inevitably increases the difficulty of constructing robust control structures. In this paper, different proportion-integration (PI) control structures are investigated for the four-column extractive distillation with preconcentration process, while different PI and PI with model prediction controller (MPC) hybrid control structures are proposed for the three-column extractive distillation with integrated distillation column (TCED-IDC) process to deal with feed disturbances via taking the separation of ternary azeotropic mixture ethyl acetate-ethanol–water as a case study. The control structures are tested via introducing multiple feed disturbances including one feed flowrates disturbance and three feed compositions disturbances. The dynamic test comparison results show that the integration of preconcentration and solvent recovery functions causes a larger transient deviation in terms of dynamic responses of the individual optimal control structures. In addition, the integral of squared error of the TCED-IDC process are reduced by about 22 times after introducing the MPC in the face of feed disturbances.

Dynamic control investigation of an energy-saving double-thermally coupled ternary extractive distillation process

Currently, little literature has focused on the dynamic control of the economic and energy-saving double-thermally coupled ternary extraction distillation (DTCTED) systems, which demonstrates difficulties due to complex interactions between the main column and two rectifiers. The novel contribution of this paper is proposing effective and robust control structures to improve the dynamic controllability of the DTCTED process. To maintain the product purities more precisely, the key control loops employ composition-temperature cascade controls to regulate the side-vapor flowrates because the reliance on temperature control alone (CS1) is insufficient. Although this structure (CS2) can achieve the control of product purity, there could be severe oscillation in the control process. Therefore, one of the composition-temperature cascade controls is paired with the reflux ratio of the side rectifier to relax the operating freedom of the main column. The obtained structure (CS3) can brilliantly handle ±20 % throughput and various feed composition disturbances, which ensures the product purities and reduces oscillation. Additionally, control strategies based on the relative gain array (RGA) pairing criterion are explored and compared with the empirical ones. The proposed structures significantly enhance the controllability and stability of the DTCTED process, making it highly suitable for industrial applications.

GC-MS and Sensory Analysis of Aqueous Extracts of Monovarietal American Hops, Produced Using the Synergy Pure™ Extraction Technique.

Aqueous extracts from four different American hops varieties (Mosaic, Chinook, Citra, and Centennial) were produced using the Synergy Pure technique, an innovative extraction distillation process developed by Synergy Flavours, a global specialist in the manufacturing of flavors, extracts and essences. This process is able to preserve and maximize the aromatic characteristics without increasing the bitterness of the final product. Therefore, the aim of this work is to identify the volatile and sensory characteristics of these extracts, with the additional aim to assess their suitability for brewing. GC-MS and sensory analyses were carried out on the four different aqueous extracts. The results highlighted the presence of 33 volatile compounds in a quantity that allowed us to identify the characteristics of the varieties under investigation in each extract. Sensory analysis was carried out using the expert sensory profiling technique. The results regarding the olfactory analysis of the extracts allowed us to define the aroma profiles of the four extracts, highlighting their strong correspondence with the characteristic of the varieties under investigation. Finally, the results showed that the aqueous extracts produced using the Synergy Pure extraction technique had a richer aroma profile, highlighting its higher aptitude in beer production.

A novel intermediate heat exchange intensified extractive pressure-swing distillation process for efficiently separating n-hexane-tetrahydrofuran-ethanol

The new intensified strategy can be used in special distillation processes to achieve energy savings. Through analyzing the influence of different extractants and pressure on the separation performance of n-hexane-tetrahydrofuran-ethanol. system, extractive pressure-swing distillation process (EPSD) using dimethyl sulfoxide as extractant was proposed. Multi-objective optimization was performed to definite the best operating parameters of EPSD. Based on the phenomenon that the temperature of high-temperature column top is lower than low-temperature column bottom, making it impossible to perform traditional thermal integration, an intermediate heat exchange intensified process (IHE-EPSD) was developed. The performance influencing factors and heat exchange network of IHE-EPSD were analyzed to obtained the optimal IHE-EPSD process. Three heat integration schemes of the IHE-EPSD were designed to further save energy consumption. Finally, the processes were assessed from economy, energy, environment and exergy. The results indicate that the IHE-EPSD process exhibits excellent separation performance, achieving the efficient separation of n-hexane-tetrahydrofuran-ethanol.