Batch Extractive Distillation Research Articles

A novel vapor recompressed batch extractive distillation: Design and retrofitting

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

Evolutionary Algorithm Based Multiobjective Optimization of Vapor Recompressed Batch Extractive Distillation: Assessing Economic Potential and Environmental Impact

Despite generating enormous interest, the full landscape of process intensification and multiobjective optimization (MOO) remains unexplored in the area of batch extractive distillation (BED). This...

Comparison of batch heteroazeotropic distillation operational strategies for the dehydration of isopropanol

The dehydration of isopropanol (B) from a mixture containing methyl ethyl ketone (A) and toluene (E) as pollutants by batch heteroazeotropic distillation (BHAD) is studied by dynamic simulation. The water (C) content of the feed is much lower than that of the BC azeotrope. Isopropanol can be obtained by conventional batch distillation under high reflux ratio and considerable loss. Toluene is a potential entrainer forming a ternary heteroazeotrope BCE.Dehydration is feasible by Mode II, Strategy A of BHAD, by which the whole amount of E-rich phase is refluxed, that of E-lean phase is withdrawn as distillate. Since the production is very slow due to the high (E-rich/E-lean) phase ratio, different operational strategies are studied in order to make the production faster without significant decrease in isopropanol recovery. These include taking a homogeneous fore-cut to remove methyl ethyl ketone, and Strategy B of Mode II, where one part of the E-rich phase is also withdrawn as distillate.A novel operational policy is proposed, as well, that is a combination of Strategies A and B. The application of cyclohexane (D) as entrainer and batch extractive distillation with dimethyl sulfoxide (F) are also studied.

Extractive distillation: Advances in conceptual design, solvent selection, and separation strategies

Abstract Extractive distillation (ED) is one of the most promising approaches for the separation of the azeotropic or close-boiling mixtures in the chemical industry. The purpose of this paper is to provide a broad overview of the recent development of key aspects in the ED process involving conceptual design, solvent selection, and separation strategies. To obtain the minimum entrainer feed flow rate and reflux ratio for the ED process, the conceptual design of azeotropic mixture separation based on a topological analysis via thermodynamic feasibility insights involving residue curve maps, univolatility lines, and unidistribution curves is presented. The method is applicable to arbitrary multicomponent mixtures and allows direct screening of design alternatives. The determination of a suitable solvent is one of the key steps to ensure an effective and economical ED process. Candidate entrainers can be obtained from heuristics or literature studies while computer aided molecular design (CAMD) has superiority in efficiency and reliability. To achieve optimized extractive distillation systems, a brief review of evaluation method for both entrainer design and selection through CAMD is presented. Extractive distillation can be operated either in continuous extractive distillation (CED) or batch extractive distillation (BED), and both modes have been well-studied depending on the advantages in flexibility and low capital costs. To improve the energy efficiency, several configurations and technological alternatives can be used for both CED and BED depending on strategies and main azeotropic feeds. The challenge and chance of the further ED development involving screening the best potential solvents and exploring the energy-intensive separation strategies are discussed aiming at promoting the industrial application of this environmentally friendly separation technique.

Extractive Distillation Approach to the Removal of Dimethyl Disulfide from Methyl Tert-Butyl Ether: Combined Computational Solvent Screening and Experimental Process Investigation

Our present work focused on the extractive distillation desulfurization from methyl tert-butyl ether (MTBE). By using dimethyl disulfide (DMDS) as the model compound contained in MTBE, the intermolecular interactions that happen among solvent, DMDS, and MTBE were analyzed and defined, and the interaction energies were calculated by applying density functional theory method. The interactions between solvents and DMDS are found to be van der Waals and weak hydrogen bond forces. The distributions of DMDS in solvents and MTBE also are calculated using dissipative particle dynamics. According to the computational results coupled with batch extractive distillation experiment using constant reflux ratio, dimethyl sulfoxide has the strongest interaction with DMDS and, therefore, exhibits the highest efficiency for DMDS removal. In addition, the reflux ratio-programmed batch extractive distillation (RRPED) process was developed. Under the suitable operation conditions of RRPED process, the sulfur content of produc...

Simulation and experiment for ethanol dehydration using low transition temperature mixtures (LTTMs) as entrainers

In this work, the separation of ethanol-water azeotrope which was choosing low transition temperature mixtures (LTTMs) as entrainers was investigated through process simulation and batch extractive distillation experiment. Based on the vapor-liquid equilibrium (VLE) curves of ethanol-water with LTTMs and the residual curves of LTTMs-ethanol-water, glycolic acid–choline chloride 3:1(GC3:1) was selected as the entrainer to simulate ethanol-water mixtures separation, and the sensitive analysis was performed in order to determine the main design variables. On this basis, the traditional process was further improved through the optimization of heat exchanger network, and the energy consumption was reduced by 46.24% and 37.00% compared with the ethylene glycol and 1-Ethyl3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), respectively. In addition, GC3:1 was synthesized and used as solvent to separate the mixture of ethanol-water in the batch extractive distillation, which can obtain high-purity ethanol at the top of distillation column. Fourier Transform Infrared Spectrum (FT-IR) was used to analyze the recycled GC3:1, and it suggested that the chemical properties of GC3:1 were stable and GC3:1 could be reused depending on the infrared spectrum of used GC3:1. The advantage of GC3:1 as entrainer for the separation of ethanol-water azeotrope was proved through the combination of process simulation and experiment.

Modeling of batch extractive distillation

New data on the concentration profiles in a packed column during extractive distillation of benzene–heptane mixture in the presence of N-methylpyrrolidone as a separating agent have been obtained. A calculation method for the process based on partial mass transfer coefficients in the vapor and liquid has been proposed. The calculated and experimental data have been compared. It has been shown that both continuous and batch extractive distillation are calculated more precisely using the proposed model compared to the equilibrium model.

Simulation and Experimental Research of Cyclohexane Isopropyl Alcohol Azeotropic Solvent Separation During Chemical and Pharmaceutical Process

In this paper, a cyclohexane-isopropanol azeotrope separation process was studied, respectively general simulation the separation process. The steady-state pressure swing distillation process, while at the laboratory of transformer rectification section, reduction pressure distillation column and intermittent small scale experimental atmospheric tower portion. Salt pressure swing distillation experiments, have achieved good results. This article will use dynamic simulation of distillation processes to separate these two processes in line, especially in heterogeneous batch azeotropic distillation and batch extractive distillation, distillation is an attempt to design and method of open up. The general process for separating a cyclohexane-isopropanol azeotrope was simulated optimization studies, including a total theoretical plate number of each section of the tower. Each column operating parameters have been best products of cyclohexane and isopropanol concentrations were reached more than 99.9wt%.

Optimization of a batch extractive distillation process with recycling off-cuts

A multiple step solvent recovery distillation process is optimized where the components form several azeotropes, and the off-cuts are recycled. Both conventional and extractive batch distillation are studied. The recovery of methanol from an industrial waste solvent mixture (acetone–methanol–tetrahydrofuran–water–toluene) is rigorously simulated and optimized. The first fore-cut is incinerated; the second fore-cut, the after-cut and the hold-up are recycled to the next batch in order to decrease the loss of methanol. The optimization of both processes is performed by a genetic algorithm coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization of the batches is performed consecutively, with the objective function being the profit of the actual batch. The optimization variables are the reflux ratios of the steps (fore-cuts, main cut), duration of fore-cut withdrawals and for the batch extractive distillation the flow rate and duration of entrainer (water) feeding. The effects of the recycling of the off-cuts on the charge composition and on the optimal values of the parameters are studied, and the optimized batch distillation and batch extractive distillation processes are compared with each other and with the batch distillation process used in the plant. The extractive process gives a 67% higher profit than the optimized batch distillation, whose profit was in turn by 25% higher than without optimization. The environmental impact is also assessed by calculating the related CO2 emission and the waste water production. The specific CO2 emission (kg CO2/kg product) is by 20% lower for the extractive process than for the optimized and by 22% lower than for the non-optimized batch distillation.

Neural Network Based Model Predictive Control of Batch Extractive Distillation Process for Improving Purity of Acetone

In a pharmaceutical industry, batch extractive distillation (BED), a combination process between extraction and distillation processes, has been widely implemented to separate waste solvent mixture of acetone-methanol because of minimum-boiling azeotrope properties. Normally, water is used as solvent and semi-continues mode is proposed to improve purity of acetone. The solvent is charged into the BED column until the purity of a desired product is achieved. After the total reflux start-up period is ended, a dynamic optimization strategy is applied to determine an acetone distillate composition profile maximizing the weight of the distillate product (acetone). The acetone distillate composition profile is used as the set point of neural network model-based controllers: the neural network direct inverse model control (NNDIC) and neural network based model predictive control (NNMPC) in order to provide the acetone composition with the purity of 94.0% by mole within 9.5 hours. It has been found that although both NNDIC and proportional integral derivative (PID) control can maintain the distillate purity on its specification for the set point tracking and in presence of plant uncertainties, the NNMPC provides much more satisfactory control performance and gives the smoothest controller action without any fluctuation when compared to the NNDIC and PID.

Optimisation of a batch extractive distillation process with off-cut recycle

The recovery of methanol from an industrial waste solvent mixture (acetone (A) – methanol (B) – THF (C)–water (D) – toluene (E)) by a batch (BD) and batch extractive distillation (BED) process was simulated and optimised. For both processes a production cycle consists of six consecutive batches. The first fore- cut is incinerated; the second fore-cut, the after-cut and the hold-up are recycled to the next batch in order to decrease the loss of methanol. The optimization of both processes was performed by a genetic algorithm (GA) coupled with a professional flow-sheet simulator performing the dynamic simulation. The optimization of the batches was performed consecutively, with the objective function being the profit of the actual batch. The optimization variables were the reflux ratios of the steps (fore-cuts, main cut), duration of fore-cut withdrawals and for the BED the flow rate and duration of entrainer (water) feeding. The effects of the recycling of the off-cuts on the charge composition and on the optimal values of the parameters were studied, and the optimised BD and BED processes were compared.

Off-cut Recycle for Batch and Batch Extractive Distillation Separation of a Multicomponent Azeotropic Mixture

The influence of recycling off-cuts for the batch and batch extractive distillation separation of a four component (methanol- THF- water- toluene) waste solvent mixture of a pharmaceutical plant is studied by rigorous dynamic simulation. The evolution of the charge composition, of the amount of fresh feed and that of methanol product are determined for six consecutive productions of batch rectification. As an alternative of the traditional batch distillation, batch extractive distillation by using water as entrainer is also studied. Water feeding is applied during the heating-up phase, in order to decrease the methanol concentration in the column top, in this way reducing methanol loss with the fore-cuts. The profit of the productions is calculated on the basis of the operational and incineration costs and the price of the methanol. The influence of the volume of the first fore-cut, which is later incinerated, on the profit of the whole production process is also investigated and its optimal amount is determined for both separation methods. For the extractive process the profit of the regeneration is higher, the optimal volume of the first fore-cut is lower, which means a reduction in the air pollution caused by the incineration.

A new batch extractive distillation operational policy for methanol recovery

The recovery of methanol from a multicomponent aqueous waste solvent mixture was studied. The components form several minimum azeotropes, of which the methanol-THF and methanol-toluene azeotropes limit the recovery of methanol by traditional batch distillation (BD). THF and toluene are removed in the fore-cut, causing a significant loss of methanol. The addition of water decreases both methanol-THF and methanol-toluene relative volatility, and therefore by feeding water as entrainer, methanol loss can be decreased. A new BED operational policy is suggested, where water feeding is applied only during the heating-up of the column (BED1). Compared to BD, at the end of the heating-up, the concentration of organic pollutants is increased, and that of methanol is significantly decreased in the top of the column. Water feeding can continue during the fore-cut (BED2), but this increases the amount of fore-cut and dilutes the mixture from which methanol is recovered. Laboratory experiments were performed in a packed column to compare the BD and the two BED operational policies. The highest recovery was obtained by BED1, the lowest one by BD. The preliminary and posterior rigorous dynamic simulation of the experiments was made with a professional dynamic flowsheet simulator. Industrial-size pilot productions of BD and BED1 in a 50 bubble cap tray column also showed a 5% increase in methanol recovery.

Extractive distillation: recent advances in operation strategies

AbstractExtractive distillation is one of the efficient techniques for separating azeotropic and low-relative-volatility mixtures in various chemical industries. This paper first provides an overview of thermodynamic insight covering residue curve map analysis, the application of univolatility and unidistribution curves, and thermodynamic feasibility study. The pinch-point analysis method combining bifurcation shortcut presents another branch of study, and several achievements have been realized by the identification of possible product cut under the following key parameters: reflux ratio, reboil ratio, and entrainer-feed flow rate ratio. Process operation policies and strategy concerning batch extractive distillation processes are summarized in four operation steps. Several configurations and technological alternatives can be used when extractive distillation processes take place in a continuous or batch column, depending on the strategy selected for the recycle streams and for the main azeotropic feeds.

General Model for Studying the Feasibility of Heterogeneous Extractive Batch Distillation

By extending our former model for batch heteroazeotropic distillation, a general model is developed for the batch heterogeneous extractive distillation. An entrainer-rich and an entrainer-lean phase are present in the decanter, where the holdup of both phases can be reduced, kept constant, or increased, thanks to batch operation mode. Any fraction of both phases can be refluxed or withdrawn as distillate. The entrainer is fed continuously either onto one of the plates of the column, or into the decanter. The still path equation is derived for both cases. A discussion is given on the literature occurrence and practical applicability of the 16 possible operational policies, and the effect of continuous entrainer feeding on the still path direction of all operational policies is determined. The still path directions are validated by rigorous simulations for multiple operational policies for the mixture of ethanol, water, and n-butanol.

Use of glycerol as entrainer in the dehydration of bioethanol using extractive batch distillation: Simulation and experimental studies

In this paper the dehydration of bioethanol via extractive batch distillation using glycerol as entrainer is studied. Simulation and experimental tests were carried out in order to use glycerol to produce bioethanol with a composition higher than that of the azeotropic point. The results are compared to those reported using ethylene glycol and ionic liquids as entrainers for the same separation. The simulation and experimental results indicate that it is possible to produce high purity bioethanol that can be used as a fuel oxygenate. Among the entrainers used in the experimental tests, the glycerol presented the best performance in terms of the purity in the distillate. Also, it is important to highlight that glycerol has a lower cost in comparison to ethylene glycol and ionic liquids and that is considered a by-product in the biodiesel production.

Extension of Thermodynamic Insights on Batch Extractive Distillation to Continuous Operation. 2. Azeotropic Mixtures with a Light Entrainer

We have studied the continuous extractive distillation of minimum- and maximum-boiling azeotropic mixtures with a light entrainer. The ternary mixtures belong to class 1.0-2 and 1.0-1a diagrams, each with two subcases depending on the location of the univolatility line. The feasible product and feasible ranges of the operating parameters reboil ratio (S) and entrainer/feed flow rate ratio for the continuous process (FE/F) were assessed. Equations were derived for the composition profiles of the stripping, extractive, and rectifying sections in terms of S and FE/F. Class 1.0-1a processes enable the recovery of only one product because of the location of the univolatility line above a minimum value of the entrainer/feed flow rate ratio for both batch and continuous processes. Given a target purity, a minimum reboil ratio S also exists; its value is higher for the continuous process than for the batch process, for the continuous process where stricter feasible conditions arise because the composition profile of the rectifying section must intersect that of the extractive section. Class 1.0-2 mixtures allow either A or B to be obtained as a product, depending on the feed location on the composition triangle. Then, the univolatility line location sets limiting values for either the maximum or minimum of the feed ratio FE/F.

Extension of Thermodynamic Insights on Batch Extractive Distillation to Continuous Operation. 1. Azeotropic Mixtures with a Heavy Entrainer

We have studied the batch and continuous extractive distillation of minimum- and maximum-boiling azeotropic mixtures with a heavy entrainer. These systems exhibit class 1.0-1a and 1.0-2 ternary diagrams, each with two subcases depending on the location of the univolatility line. The feasible product and feasible ranges of the operating parameters reflux ratio (R) and entrainer/feed flow rate ratio for continuous (FE/F) and batch (FE/V) operation were assessed. Class 1.0-1a processes allow the recovery of only one product because of the location of the univolatility line above a minimum value of the entrainer/feed flow rate ratio for both batch and continuous processes. A minimum reflux ratio R also exists. For an identical target purity, the minimum feed ratio is higher for the continuous process than for the batch process, for the continuous process where stricter feasible conditions arise because the composition profile of the stripping section must intersect that of the extractive section. Class 1.0-2 ...

Batch extractive distillation of mixture methanol-acetonitrile using aniline as a asolvent

Methanol and acetonitrile form a minimum azeotrope at 336.74 K, which contains methanol 76.89 mas%. The simulation and the experiment to separate the mixture by batch extractive distillation using aniline as entrainer is performed. Based on the experimental and simulative VLE data, aniline is chosen to be the suitable solvent. The sensitivity analysis about the number of stages, the refl ux ratio, the solvent feed stage and the solvent fl ow rate is conducted to obtain the optimal parameters and confi guration of the extractive distillation column with minimal energy requirements. The most appropriate confi guration is 30 theoretical stages. The optimal entrainer feeding stage is 8 with a solvent fl ow rate of 20kg/h and the refl ux ratio of 2.0, respectively. The simulation results show the effect of the main variables on the extractive distillation process. The experiment is carried out to corroborate the feasibility of the separation of methanol-acetonitrile by batch extractive distillation.

Purification of bioethanol using extractive batch distillation: Simulation and experimental studies

Among biofuels, bioethanol has increased in importance in many countries because it can be used directly or mixed with gasoline in combustion engines. The production of bioethanol in a fermentative process usually gives a dilute solution from which the bioethanol must be obtained in high concentration in order to be used as biofuel. The separation of an azeotropic mixture of ethanol and water using batch and semi-batch distillation was studied considering ethylene glycol and ionic liquids as entrainers. The simulation and experimental results indicate that the separation is favored using ethylene glycol in comparison to the use of ionic liquid; however, the ionic liquid is considered a green solvent and the use of ethylene glycol could be forbidden in the near future.