Process design and intensification of multicomponent azeotropes special distillation separation via molecular simulation and system optimization

This work provides an overview of distillation processes,including process design for different distillation processes,selection of entrainers for special distillation processes,system integration and intensification of distillation processes,optimization of process parameters for distillation processes and recent research progress in dynamic control strategies.Firstly,the feasibility of using thermodynamic topological theories such as residual curve,phase equilibrium line and distillation boundary line to analyze different separation regions is discussed,and the rationality of distillation process design is discussed by using its feasibility.Secondly,the application of molecular simulation methods such as molecular dynamics simulation and quantum chemical calculation in the screening of entrainer is discussed for the extractive distillation process.The thermal coupling mechanism of different distillation processes is used to explore the process of different process intensifications.Next,a mixed integer nonlinear optimization strategy for the distillation process based on different algorithms is introduced.Finally,the improvement of dynamic control strategies for different distillation processes in recent years is summarized.This work focuses on the application of process intensification and system optimization in the design of distillation process,and analyzes the challenges,prospects,and development trends of distillation technology in the separation of multicomponent azeotropes.

Economy, environmental assessment and energy conservation for separation of isopropanol/diisopropyl ether/water multi-azeotropes via extractive distillation coupled pervaporation process

This wok proposed the extraction distillation coupled pervaporation(ED+PV) technology process using two different solvents to separate isopropanol(IPA) and diisopropyl ether(DIPE) from DIPE/IPA/H_(2)O ternary heterogeneous azeotropes in industrial wastewater from the synthesis of isopropanol in this study.Based on strict design specifications, simulation and sequential iteration methods are used for process design and optimization. Compared to the ethylene glycol(EG)-EG+H_(2)O process and the 1,3-propanediol(PDO)-IPA+H_(2)O process, the total annual cost(TAC) of the EG-IPA+H_(2)O process decreased by 20.76% and 7.86%(PDO). Compared to the EG-EG+H_(2)O process, the TAC of the PDO-IPA+H_(2)O process reduced 14%, but the global warming potential(GWP) and human toxicity of the PDO-IPA+H_(2)O process increased 11.3% and 4.07% respectively. Compared to the PDO-IPA+H_(2)O process, the EG-IPA+H_(2)O process saves 7.86%(TAC), 9.78%(GWP) and 9.85%(human toxicity). The ED+PV process with EG is superior to PDO in factors of TAC, energy consumption, human toxicity and environment. The EG-IPA+H_(2)O process changed the separation order of the products of the multi-azeotropic system, reduced the cost and energy conservation of the system, and enhanced the environmental protection evaluation of the process, is the best process through life cycle assessment for analyzing the economy, energy conservation, environmental assessment and human toxicity, designing cleaner products, controlling waste discharge, and promoting the chemical purification industry. This work provides a new process design and optimized separation ideas, will have a good guiding significance for the research and application separation of multi-azeotropic mixture with mixed solvents in organic wastewater from the cleaner chemical production, has been up to standard wastewater discharge process, and realized the development goal of carbon peak and carbon neutrality in the sustainable development of chemical clean industry.

Investigation of energy-efficient heat pump assisted heterogeneous azeotropic distillation for separating of acetonitrile/ethyl acetate/n-hexane mixture

The conventional distillation is hard to accomplish the separation of acetonitrile/ethyl acetate/n-hexane mixture. Herein, a heterogeneous azeotropic distillation(HAD) without adding entrainer is proposed to separate ternary mixture. The proposed scheme is optimized via the simulated annealing algorithm and minimum total annual cost(TAC) is used as objective functions. To minimize energy consumption,heat pump is added on the basis of optimal heterogeneous azeotropic distillation and heat integration technology is used to further improve the energy recovery. The TAC, gas emission, energy consumption and exergy destruction are used to discuss the economy and environmental protection of processes.Among all the processes, the heat pump with higher preheating temperature(HPT) assisted HAD process by combining with heat integration(HAD-HPT-HI) has best performances on economic, environment,energy and exergy. Compared with conventional HAD process, the HAD-HPT-HI achieves the reductions of 52.17%, 68.86%, 65.87% and 65.46% on TAC, total energy consumption, gas emissions and exergy destruction, respectively.

Separation of fuel additives based on mechanism analysis and thermodynamic phase behavior

tert-butanol and ethyl acetate,as fuel additives and oxygenated fuels,can improve fuels quality and reduce exhaust emissions.Therefore,the recovery of these compounds from azeotropic systems is of great significance.Ionic liquids(ILs)are promising green solvents for separating azeotropic systems.In this study,an efficient extraction strategy based on 1-butyl-3-methylimidazolium acetate([Bmim][AC])is proposed.The mechanism by which ILs enable the separation of binary alcohol-ester azeotropes was revealed by evaluating the lowest conformational energy through combining an independent gradient model based on the Hirshfeld partition(IGMH)and frontier molecular orbitals,to preliminarily screen the extractants.The range of extractants was further reduced by a vapor–liquid phase equilibrium(VLE)experiment,and a modeling method for separating the alcohol–ester system and recovering the solvent using[Bmim][AC]and 1-ethyl-3-methyl-3-imidazolium acetate([Emim][AC])is established.Under the optimal operating conditions,the use of[Bmim][AC]can reduce the total annual cost(TAC)per year by 17.78%,and the emissions of CO_(2),SO_(2),and NO can be reduced by 10.86%.In this study,a comprehensive method for screening extractants is proposed,and the simulation process is optimized in combination with the economic and environmental impact.The results have important guiding significance for realizing efficient,energy-saving,and green azeotropic separation systems in industry.

A new combination process of distillation with salt extraction for separating organic solvent-water azeotropes

A novel process which can purify the organic solvents from their azeotropes with water is proposed. In this process,water can be drained off both from bottom and overhead of tower at the same time,and the organic solvent is concentrated in the tower and accumulated in the middle vessel at last. So the progress is time-shortened and energy-saving. The product purity is 99. 8% and the product yield is more than 99.5%. Simulation of liquid-liquid equilibrium (LLE) and the equipment operation data agree well with the experiment.

QSPR modeling of azeotropic temperatures and compositions for binary azeotropes containing lower alcohols using a genetic function approximation

Binary azeotropes, which contain two chemicals with a relative volatility of 1, are very common in the chemical industry. Understanding azeotropes is essential for effectively separating binary azeotropes containing lower alcohols. Experimental techniques and ab initio approaches can produce accurate results;however, these two processes are time consuming and labor intensive. Although thermodynamic equations such as UNIFAC are widely used, experimental values are required, and it is difficult to choose the best groups to represent a complex system. Because of their high efficiency and fast calculation speed, quantitative structure–property relationship(QSPR) tools were used in this work to predict the azeotropic temperatures and compositions of binary azeotropes containing lower alcohols. The QSPR models for 64 binary azeotropes based on centroid approximation and weighted-contribution-factor approximation were established using the genetic function approximation(GFA) procedure in Materials Studio software, and a leave-one-out cross-validation procedure was conducted.External tests of an additional 16 azeotropes were also investigated, and high determination coefficient values were obtained. The best QSPR models were explained in terms of the molecular structure of the azeotropes,and good predictive ability was obtained within acceptable prediction error levels.

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.

Comparison of continuous homogenous azeotropic and pressure-swing distillation for a minimum azeotropic system ethyl acetate/nhexane separation

Continuous homogenous azeotropic distillation(CHAD) and pressure-swing distillation(PSD) are explored to separate a minimum-boiling azeotropic system of ethyl acetate and n-hexane. The CHAD process with acetone as the entrainer and the PSD process with the pressures of 0.1 MPa and 0.6 MPa in two columns are designed and simulated by Aspen Plus. The operating conditions of the two processes are optimized via a sequential modular approach to obtain the minimum total annual cost(TAC). The computational results show that the partially heat integrated pressure-swing distillation(HIPSD) has reduced in the energy cost and TAC by 40.79% and 35.94%, respectively, than the conventional PSD, and has more greatly reduced the energy cost and TAC by 62.61% and 49.26% respectively compared with the CHAD process. The comparison of CHAD process and partially HIPSD process illustrates that the partially HIPSD has more advantages in averting the product pollution, energy saving, and economy.

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 and Analysis on Multiple Steady States of an Industrial Acetic Acid Dehydration System

In this work, an industrial acetic acid dehydration system via heterogeneous azeotropic distillation is simulated by Aspen Plus software. Residue curves are used to analyze the distillating behavior, and appropriate operating region of the system is determined. Based on steady states simulation, a sensitivity analysis is carried out to detect the output multiple steady states in the system. Different solution branches are observered when the flow rates of the feed stream and the organic reflux stream are selected as manipulated variables. The performance of the column under different steady states is different. A method is oroposed to achieve the desired steady state.

Effect of methylimidazolium-based ionic liquids on vapor–liquid equilibrium behavior of tert-butyl alcohol + water azeotropic mixture at 101.3 kPa

Three ionic liquids(ILs),1-ethyl-3-methylimidazolium bromine([EMIM]Br),1-butyl-3-methylimidazolium bromine([BMIM]Br),and 1-hexyl-3-methylimidazolium bromine([HMIM]Br),were used as the solvent for separation of {tert-butyl alcohol(TBA)+ water} azeotrope.Vapor–liquid equilibrium(VLE)data for {TBA + water + IL}ternary systems were measured at 101.3 k Pa.The results indicate that all the three ILs produce an obvious effect on the VLE behavior of {TBA + water} system and eliminate the azeotropy in the whole concentration range.[EMIM]Br is the best solvent for the separation of {TBA + water} system by extractive distillation among the three ILs.The experimental VLE data for the ternary systems are correlated with the NRTL model equation with good correlations.Explanations are given with activity coefficients of water and TBA,and the experimental VLE-temperature data for {TBA or water + IL} binary systems.

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.

Application of the Chemical-Looping Concept for Azoetrope Separation

The need for the separation of azeotropic mixtures for the production of high-end chemicals and resource recovery has spurred significant research into the development of new separation methods in the chemical industry.In this paper,a green and sustainable method for azeotrope separation is proposed based on a chemical-looping concept with the help of reversible-reaction-assisted distillation.The central concept in the chemical-looping separation(CLS)method is the selection of a reactant that can react with the azeotrope components and can also be recycled by the reverse reaction to close the loop and achieve cyclic azeotrope separation.This paper aims to provide an informative perspective on the fundamental theory and applications of the CLS method based on the separation principle,reactant selection,and case analysis,for example,the separation of alkenes,alkane,aromatics,and polyol products.In summary,we provide guidance and references for chemical separation process intensification in product refining and separation from azeotropic systems for the development of a more sustainable chemical industry.

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.

Separation process of butanol-butyl acetate-methyl isobutyl ketone system by the analysis to residual curve and the double effect pressure-swing distillation

The separation of ternary mixture of butanol, butyl acetate, and methyl isobutyl ketone(MIBK) was initially analyzed by the residual curve. In this process, MIBK was chosen as the azeotropic agent during the first step of separation. The optimum mass ratio of extra MIBK was 1.6 in the modified feed stream according to the residual curve. Thus on this condition the top product was butanol-MIBK azeotrope while the bottom product was butyl acetate in the preliminary separation of the mixture. Then the butanol and MIBK azeotrope was separated by the double effect pressureswing distillation with the low pressure column performing at 30 kPa and the atmospheric pressure column at 101 kPa. The optimal operating conditions were then obtained by using Aspen Plus to simulate and optimize the process. The results showed that the mass purities of butanol, butyl acetate, and MIBK were all more than 99% and reached the design requirements. Additionally, compared with the traditional distillation with outside heating, the double effect pressure swing distillation saved the reboiler duty by 48.6% and the condenser duty by 44.6%.

Effects of imidazolium-based ionic liquids on the isobaric vapor–liquid equilibria of methanol+dimethyl carbonate azeotropic systems

The separation of methanol(MeOH)and dimethyl carbonate(DMC)is important but difficult due to the formation of an azeotropic mixture.In this work,isobaric vapor–liquid equilibrium(VLE)data for the ternary systems containing different imidazolium–based ionic liquids(ILs),i.e.MeOH+DMC+1-butyl-3-methy-limidazolium bis[(trifluoromethyl)sulfonyl]imide([Bmim][Tf2N]),MeOH+DMC+1-ethyl-3-methyl-imidazolium bis[(trifluoromethyl)sulfonyl]imide([Emim][Tf2N]),and MeOH+DMC+1-ethyl-3-methylimidazolium hexafluorophosphate([Emim][PF6])were measured at 101.3 kPa.The mole fraction of IL was varied from0.05 to 0.20.The experimental data were correlated with the NRTL and Wilson equations,respectively.The results show that imidazolium-based ILs were beneficial to improve the relative volatility of MeOH to DMC,and[Bmim][Tf2 N]showed a much more excellent performance on the activity coefficient of MeOH.The interaction energies of system components were calculated using Gaussian program,and the effects of cation and anion on the separation coefficient of the azeotropic system were discussed.

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.

Process optimization of an industrial acetic acid dehydration progress via heterogeneous azeotropic distillation

The simulated process model of the HAc dehydration process under actual overloaded condition was conducted by amending the model of standard condition in our previous work using the process data collected from actual production. Based on the actual process model, the operation optimization analysis of each plant(HAc dehydration column, decanter and NPA recycle column) was conducted using Residue Curve Maps(RCMs),sensitivity analysis and software optimization module. Based on the optimized parameters, the influence of feed impurity MA and the temperature of decanter on the separating effect and energy consumption of the whole process were analyzed. Then the whole process operation optimizing strategy was proposed with the objective that the total reboiler duty Q Total of C-1 and C-3 reaches the minimum value, keeping C-1 and C-3 at their optimized separation parameters obtained above, connecting all the broken recycle and connection streams, and using the temperature of D-1 as operation variable. The optimization result shows that the total reboiler duty Q Total of the whole process can reach the minimum value of 128.32 × 10~6 k J·h^(-1) when the temperature of decanter is 352.35 K, and it can save 5.94 × 10~6 k J·h^(-1), about 2.56 t·h^(-1) low-pressure saturated vapor.

Biodiesel Production from Waste Edible Oils and Grease Containing Free Fatty Acids

Till now, most part of the biodiesel is produced from the refined vegetable oils using methanol as feedstock in the presence of an alkali catalyst. However, large amount of waste edible oils and grease are available. The difficulty with alkali-catalyzed esterification of these oils is that they often contain large amount of free fatty acids （FFA）, polymers and decomposition products. These free fatty acids can quickly react with the alkali catalyst to produce soaps that inhibit the separation of the ester and glycerine. An esterification and transesterification process is developed to convert the high FFA oil to its monoesters, The first step, the acidcatalyzed esterification with glycerine and these FFA reduces the FFA content of the oil and grease to less than 3%, and then an azeotropic distillation solvent is used to remove the water. The major factors affecting the conversion efficiency of the process such as glycerol to free fatty acid molar ratio, catalyst amount, reaction temperature and reaction duration are analyzed, The second step, alkali-catalyzed transesterificatiou process converts the products of the first step to its monoesters and glycerol, and then the glycerol is recycled for utilization in the first step. Technical indicators of the biodiesel product can meet the ASTM 6751 standard.

Design and control of methyl acetate-methanol separation via heat-integrated pressure-swing distillation

Design and control of pressure-swing distillation(PSD) with different heat integration modes for the separation of methyl acetate/methanol azeotrope are explored using Aspen Plus and Aspen Dynamics. First, an optimum steady-state separation configuration conditions are obtained via taking the total annual cost(TAC) or total reboiler heat duty as the objective functions. The results show that about 27.68% and 25.40% saving in TAC can be achieved by the PSD with full and partial heat integration compared to PSD without heat integration. Second,temperature control tray locations are obtained according to the sensitivity criterion and singular value decomposition(SVD) analysis and the single-end control structure is effective based on the feed composition sensitivity analysis. Finally, the comparison of dynamic controllability is made among various control structures for PSD with partial and full heat integration. It is shown that both control structures of composition/temperature cascade and pressure-compensated temperature have a good dynamic response performance for PSD with heat integration facing feed flowrate and composition disturbances. However, PSD with full heat integration performs the poor controllability despite of a little bit of economy.