Environmental,economic and exergy analysis of separation of ternary azeotrope by variable pressure extractive distillation based on multi-objective optimization

In this work,the ternary azeotrope of tert-butyl alcohol/ethyl acetate/water is separated by extractive distillation(ED)to recover the available constituents and protect the environment.Based on the conductor like shielding model and relative volatility method,ethylene glycol was selected as the extractant in the separation process.In addition,in view of the characteristic that the relative volatility between components changes with pressure,the multi-objective optimization method based on nondominated sorting genetic algorithm II optimizes the pressure and the amount of solvent cooperatively to avoid falling into the optimal local solution.Based on the optimal process parameters,the proposed heat-integrated process can reduce the gas emissions by 29.30%.The heat-integrated ED,further coupled with the pervaporation process,can reduce gas emission by 42.36%and has the highest exergy efficiency of 47.56%.In addition,based on the heat-integrated process,the proposed two heat pump assisted heat-integrated ED processes show good economic and environmental performance.The double heat pump assisted heat-integrated ED can reduce the total annual cost by 28.78%and the gas emissions by 55.83%compared with the basis process,which has a good application prospect.This work provides a feasible approach for the separation of ternary azeotropes.

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

Extractive distillation(ED) is one of the most promising approaches for the separation of the azeotropic or closeboiling 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.

Computer-aided ionic liquid design for alkane/cycloalkane extractive distillation process

A computer-aided ionic liquid design(CAILD) study is presented for the frequently encountered alkane/cycloalkane separations in petrochemical industry. Exhaustive experimental data are first collected to extend the UNIFAC-IL model for this system, where the proximity effect in alkanes and cycloalkanes is considered specifically by defining distinct groups. The thermodynamic performances of a large number of ILs for 4 different alkane/cycloalkane systems are then compared to select a representative example of such separations. By applying n-heptane/methylcyclohexane extractive distillation as a case study, the CAILD task is cast as a mixed-integer nonlinear programming(MINLP) problem based on the obtained task-specific UNIFAC-IL model and two semi-empirical models for IL physical properties. The top 5 IL candidates determined by solving the MINLP problem are subsequently introduced into Aspen Plus for process simulation and economic analysis, which finally identify 1-hexadecyl-methylpiperidinium tricyanomethane([C_(16)MPip][C(CN)_3]) as the best entrainer for this separation.

Extractive Distillation of Methyl Acetate-Methanol Azeotrope Using [DMIM]DMP as Solvent

In order to separate methyl acetate and methanol azeotrope, the ionic liquid(IL) 1,3-dimethylimidazolium dimethylphosphate([DMIM]DMP) was used as the solvent. The Aspen Plus software was used to design and optimize the extractive distillation process. Under the optimized conditions, the mass fractions of methyl acetate and methanol were both above 99.5%. Compared with the dimethyl sulfoxide(DMSO) process, the [DMIM]DMP process has the advantages of saving energy and lower equipment investment cost. The result shows that using [DMIM]DMP as the solvent to separate a methyl acetate and methanol azeotrope has better prospect in industrial application.

Simulation of 1,3-Butadiene Production Process by Dimethylfomamide Extractive Distillation

Nowadays, extractive distillation is the main technique to produce 1,3-butadiene. This study simulated the 1,3-butadiene production process with DMF extractive distillation by Aspen Plus. The solvent ratio is the most important parameter to the extractive distillation process. The article has given out the proper solvent ratios, reflux ratios, distillate ratios, and bottom product ratios of the columns. It also discusses the thermal loads of several columns. The results of simulation are consequently compared with the plant data, which shows good accordance with each other.

Design, Optimization and Control of Extractive Distillation for Separation of Ethyl Acetate-Ethanol-Water Mixture Using Ionic Liquids

In this work, the process simulation of pressure-swing distillation(PSD) and extractive distillation(ED) using ionic liquid(IL) 1-butyl-3-methylimidazolium acetate([bmim][OAc]) as the entrainer for separation of ethyl acetateethanol-water mixture is performed. The design parameters of the two distillation processes are optimized with the minimum total annual cost(TAC) serving as the objective function. The results show that the TAC saving of ED process is 35.27% in comparison with that of PSD process in the case of achieving the same purity and yield of ethyl acetate.In addition, the dynamic controllability of ED process is further studied. The traditional two-point temperature control structure is proposed for the ED process, and it works pretty well while taking into account the disturbances in both feed rate and feed composition.

Batch Extractive Distillation in a Column with a Middle Vessel

Batch extractive distillation was studied in a column with amiddle vessel. The process was simulated by a constant holdup modeland solved by two point implicit method. Acetone and methanol mixturewas separated in such a setup using water as solvent. The simulationagrees well with experimental results. The experimental andsimulation results show that the solvent at the bottom and theproduct at the top of the column can be withdrawn simulataneously fora long period of time. It needs more time for the solvent to reachhigh purity than that required for the more volatile component toreach high purity, so that the time to withdraw solvent from thebottom is delayed.

Simulation for Transesterification of Methyl Acetate and n-Butanol in a Reactive and Extractive Distillation Column Using Ionic Liquids as Entrainer and Catalyst

A new reactive and extractive distillation process with ionic liquids as entrainer and catalyst （RED-IL）was proposed to produce methanol and n-butyl acetate by transesterification reaction of methyl acetate with n-butanol. The RED-IL process was simulated via a rigorous model, and high purity products of methanol and n-butyl acetate can be obtained in such a process. The effects of reflux ratio, feed mode, holdup, feed location, entrainer ratio and catalyst concentration on RED-IL process were investigated. The conversion of methyl acetate and purities of products increase with the holdup in column, entrainer ratio and catalyst content. An optimal reflux ratio exists in RED-IL process. Comparing to the mixed-feed mode, the segregated-feed mode is more effective, in which the optimal feed locations of reactants exist.

Behaviour of Tributylamine as Entrainer for the Separation of Water and Acetic Acid with Reactive Extractive Distillation

A new separation method, reactive extractive distillation, was put forward for separating water and acetic acid. The separation mechanism was analyzed through infrared spectra technique. Isobaric vapor-liquid equilibrium (VLE) data at 101.33 kPa for the binary or ternary systems consisting of water, acetic acid and tributylamine were measured. The activity coefficients were correlated by using Wilson, NRTL, and UNIQUAC Equations.The VLE experiment showed that tributylamine could enhance the relative volatility of water to acetic acid. An extractive distillation experiment was carried out and proved that tributylamine was a good extractive solvent.

Solvent Selection for Extractive Distillation by the Universal Quasichemical Functional Group Activity Coefficient(UNIFAC) Group Contribution Method

A method to select solvent for extractive distillation is proposed by UNIFAC group contribution. Solventselectivity can be divided into two parts: the partial combinatorial solvent selectivity and the partial residual solventselectivity. The properties of partial combinatorial and residual solvent selectivity are demonstrated. In most cases,the partial residual solvent selectivity is predominant. The candidate groups of solvent can be selected by groupinteraction parameter using UNIFAC group interaction parameter table as a guide.

Extractive distillation of the benzene and acetonitrile mixture using an ionic liquid as the entrainer

The benzene and acetonitrile azeotropic mixture was proposed to be separated by extractive distillation using an ionic liquid(IL)as the entrainer.The suitable IL was selected by the COSMO-RS model,and 1-ethyl-3-methylimidazolium tetrafluoroborate([EMIM][BF_(4)])was considered as the suitable entrainer mainly due to its high selectivity,low viscosity,and low price.The experimental vapor pressure data of the IL-containing systems(benzene+[EMIM][BF_(4)]and acetonitrile+[EMIM][BF_(4)])were measured in the full concentration range.The results show that acetonitrile has a stronger interaction with IL than benzene,and the low deviations between the experimental and UNIFAC predicted values show the reliability of the UNFIAC model.The UNIFAC predicted vapor-liquid equilibrium data of the benzene+acetonitrile+dimethyl sulfoxide(DMSO)/[EMIM][BF_(4)]system show that the relative volatility of benzene to acetonitrile is higher when the entrainer is[EMIM][BF_(4)].The process simulation results show that[EMIM][BF_(4)]can reduce the material and energy consumptions compared with DMSO.

The Separation of Catechol from Carbofuran Phenol by Extractive Distillation

In this study, extractive distillation has been applied to separate catechol （CAT） from carbofuran phenol （CFP） with high purity and yield. The relative volatility of CFP to CAT was measured, and the choice of separating agents was investigated. The experimental results indicated that CFP/CAT is an azeotropic system with an azeotropic point at 93.40℃/0.400 kPa and an azeotropic mixture containing 49.96% of CFP and 50.04% of CAT. Data from the determination of the relative volatility have shown that separating agents such as diglycol and 4-butylcatechol （4-TBC） are able to increase the relative volatility up to 1.90. In one shot process batch extractive distillation of CFP mixture with 3% （by mass） diglycol as separating agent, the purity and yield of the obtained CFP was 99.0% and 95.0%, respectively, while the distillation without separating agent provided a purity and yield of only 98.0% and 90.0%, respectively, There was no residual separating agent found in the product.

Conceptual design of an extractive distillation process for the separation of azeotropic mixture of n-butanol-isobutanol-water

In many chemical processes, large amounts of wastewater containing butanol and isobutanol are produced.Given that n-butanol-isobutanol-water can form triple azeotrope, high-purity butanol cannot be recovered from the wastewater by ordinary distillation. To economically and effectively recover butanol from this kind of wastewater, 1,4-butanediol is selected as an extractant to break the formation of the azeotropes, and a doubleeffect extractive distillation process is proposed. The conceptual design of the proposed process is accomplished based on process simulation. With the proposed process, the purity of recovered butanol and water is greater than 99.99 wt%. In comparison with the conventional azeotropic distillation process, economic analysis shows that the operating cost of the proposed process is lower: when the capacity of wastewater treatment is 100 t·h^(-1), the total operating cost decreases by 5.385 ×10~6 USD per year, and the total annual cost of the new process decreases by 5.249 ×10~6 USD per year. In addition, in the extractive distillation system, variable effects on separation purities and cost are more complex than those in the ordinary distillation system. The method and steps to optimize the key variables of the extractive distillation system are also discussed in this paper and can provide reference for similar studies.

Design and Operation of Batch Extractive Distillation with Two Reboilers

This paper proposes a modified operation mode of batch extractive distillation with two reboilers. The seoaration of ethanol and water using as ethylene glycol is well done to validate the feasibility, of this mode. The pilot-plant experimental data under the identical operational conditions between the regular mode and the modified mode are in particular discussed. The studied results prove more practical advantages of tile.modified mode over the regular mode such as easier operation control, more flexibility and higher separation efficiency etc. So it suppues certain guidance for the industrial application of batch extractive distillation process.

Molecular interaction mechanism in the separation of a binary azeotropic system by extractive distillation with ionic liquid

Ionic liquids(ILs)have shown excellent performance in the separation of binary azeotropes through extractive distillation[1].But the role of the ionic liquid in azeotropic system is not well understood.In this paper,COSMO-RS model was applied to screen an appropriate IL to separate the binary azeotrope of ethyl acetate(EA)and ethanol and 1-octyl-3-methylimidazolium tetrafluoroborate([OMIM][BF4])was selected.The Quantum Mechanics(QM)calculations and molecular dynamics(MD)simulation are performed to study the interactions between the solvent molecules and[OMIM][BF4],in order to investigate the separation mechanism at the molecular level.The nature of the interactions is studied through the reduced density gradient(RDG)function and quantum theory of Atom in Molecule(QTAIM).Hydrogen bonds and van der Waals interactions are the key interactions in the complexes.The results of MD simulations indicate that the introduction of ILs has a prominent effect on the interaction between the solvent molecules,especially on reducing the number of hydrogen bonds among the solvent molecules.The radial distribution function(RDF)reveals that the interaction between the cation and solvent molecules will increase while the concentration of ILs increases.This paper provides important information for understanding the role of ILs in the separation of the azeotropic system,which is valuable to the development of new entrainers.

Effect of thermodynamic parameters on prediction of phase behavior and process design of extractive distillation

Extractive distillation was investigated for separation of the minimum azeotrope of n-propanol/water, via the Aspen Plus simulation platform. Experimental data of n-propanol/water, which could pass the thermodynamic consistency test, were regressed to get suitable binary interaction parameters(BIPs) by the UNIQUAC thermodynamic model. The azeotrope system was heterogeneous in the simulation with built-in BIPs, which was contrary to the experimental data. The study focused on the effect of thermodynamic parameters on the prediction of phase behavior, and process design of extractive distillation. N-methyl-2-pyrrolidone(NMP) and ethylene glycol were used as solvents to implement the separation. Processes with built-in and regressed BIPs were explored,based on the minimum total annual cost(TAC). There were significant differences in the phase behavior simulation using different thermodynamic parameters, which showed the importance of BIPs in the design and optimization of extractive distillation.

A Quasi-steady-state Model for Numerical Simulation of Batch Extractive Distillation

Batch extractive distillation(BED)is a special method used in the distillation process by adding a solvent into the batch distillation column to alter the relative volatility of the components and improve the separation. A comprehensive design and simulation method is required due to the complexity of BED.In this study,a quasi-steady-state model for BED is proposed,the derivation and solution of the model are presented.This shortcut model can be used to simulate the composition and temperature of the reboiler,the top and other plates of the column in a batch extractive distillation operation.The calculated values are in good agreement with the experimental data.The results show that the quasi-steady-state model is a practical method because of some advantages such as high precision and fast calculation.

Process Design for Separating C4 Mixtures by Extractive Distillation

C4 components are useful in industry and should be separated as individuals. A new process was proposed to separate them by extractive distillation, with the advantages of low equipment investment, energy consumption and liquid load in the columns. One principle to improve the extractive distillation process was put forward. Moreover, the analysis of operation state of the new process was done. There were eight operation states found for the whole process, but only one operation state was desirable. This work provides a way to effectively separate C4 mixtures and helps the reasonable utilization of C4 resource.

[EMIM][DCA] as an entrainer for the extractive distillation of methanol-ethanol-water system

The ionic liquid(IL)1-ethyl-3-methylimidazolium dicyanamide([EMIM][DCA])was selected as an appropriate entrainer for the extractive distillation of the methanol-ethanol-water mixture.The COSMO-RS model was applied to screen out the appropriate solvents considering selectivity and solvent capacity together.Isobaric vapor-liquid equilibrium(VLE)experiments for the two systems of methanol-water and ethanol-water with different amounts of[EMIM][DCA]added were conducted at 101.3 kPa.The experimental data showed that[EMIM][DCA]exhibits an obvious salting effect for the methanol(or ethanol)-water mixture and eliminates the azeotropic point of ethanol-water.Moreover,the predicted values by UNIFAC-Lei model coincide well with experimental data.The separation mechanism was further explained in combination with surface charge density distribution(σ-profiles),excess enthalpy(HE),and binding energy.In addition,the flow charts were designed to evaluate the improvement of energy consumption with[EMIM][DCA]as the entrainer when compared to ethylene glycol(EG).The simulation results demonstrated that[EMIM][DCA]is more energy efficient than EG.

Separation of Benzene and Cyclohexane by Batch Extractive Distillation

Azeotropic liquid mixture cannot be separated by conventional distillation. But extractive distillation or combination of the two can be valid for them. An experiment to separate benzene and cyclohexane by batch extractive distillation was carried out with N, N-dimethylformide （DMF）, dime- thyl sulfoxide （DMSO） and their mixture as extractive solvent. The effect of the operation parameters such as solvent flow rate and reflux ratio on the separation was studied under the same operating conditions. The results show that the separation effect was improved with the increase of solvent flow rate and the reflux ratio; all the three extractive solvents can separate benzene and cyciohexane, with DMF being the most efficient one, the mixture the second, and DMSO the least. In the experiment the best operation conditions are with DMF as extractive solvent, the solvent flow rate being 12.33 mUmin, and the reflux ratio being 6. As a result, we can get cyclohexane from the top of tower with the average product content being 86.98%, and its recovering ratio being 83.10%.