Pressure-swing Distillation Research Articles

Continuous diisobutylene manufacturing: Conceptual process design and plantwide control

The complete process design cycle encompassing flowsheet synthesis, design and controllability evaluation is studied for continuous DIB manufacturing. The residue curve map tool is applied to synthesize two new flowsheets, FS1 and FS2, exploiting pressure swing distillation. A unique feature of these is the use of a decanter for recovery and recycle of water, which allows maintaining the reactor tert-butyl alcohol content at the desired level for suppressing the side reaction. Unlike the literature flowsheet (FS0), this innovation makes it possible to achieve both high conversion and high yield for an economically superior design. Between FS1 and FS2, FS1 is found to be superior with significantly lower capital and energy costs as well as lower fresh water consumption. A “smart” control strategy for holding the single-pass reactor conversion and the overall process yield towards economic process operation is also developed. Rigorous dynamic simulations demonstrate the controllability of FS1 and FS2.

Separation of an azeotropic mixture of dimethyl carbonate and methanol via partial heat integration pressure swing distillation

AbstractA method for dimethyl carbonate and methanol separation using pressure swing distillation is presented, and the optimum design is proposed by minimizing the total annual cost as the objective function. It is revealed that compared with no heat integration pressure swing distillation (HIPSD), partial HIPSD reduces the total annual cost by 20.01%. This paper presents a criterion for selection of the temperature control stage in the low‐pressure column (LPC), the temperature profile of which is quite close to linear. Additionally, the influences of the temperature stage in the LPC on the dynamic responses in the partial HIPSD are investigated. The results show that the composition/temperature cascade control structure with stage 10 or 31 selected as the control stage in the LPC can achieve efficient controllability of the process, even for large feed flow rates and composition disturbances. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Design and control of extractive dividing wall column and pressure-swing distillation for separating azeotropic mixture of acetonitrile/N-propanol

This paper addresses the design and the control analysis of the extractive dividing wall column and the pressure-swing distillation for separating acetonitrile (MeCN)/n-propanol system using Aspen Plus and Aspen Dynamics. The steady state design of the two processes was optimized by minimizing the total annual cost (TAC) via a sequential iterative optimization procedure. On the basis of the steady-state results, the dynamic control of the two processes and the comparison between them were presented. The results show that the pressure-swing distillation has the advantages for the economic savings and the control stability compared with the extractive dividing wall column process.

Effect of feed temperature on economics and controllability of pressure-swing distillation for separating binary azeotrope

The mixture of methyl acetate and methanol created a minimum-boiling azeotrope which can be separated by pressure-swing distillation. The designs and optimizations of eight processes with eight different feed temperatures were studied to explore the effect of feed temperature on economics. Total annual cost (TAC) as the objective function reduced first and then increased with feed temperature increasing. Dynamic control of three typical temperature points was made. The designed process with feed temperature at 334.15K (vapor-liquid) had the minimum TAC, while the best dynamic control performance was found for the design process with feed temperature at 323.15K (cold). The choice of feed temperature should be considered from the perspectives of both TAC and the dynamic control performance.

Control of a triple-column pressure-swing distillation process

Abstract The separation of the ternary mixture of acetonitrile, methanol and benzene into three high-purity products is complicated by the presence of three binary azeotropes that divide the ternary diagram into three distinct regions. Fortunately the compositions of two of these azeotropes change significantly with pressure. The economic optimum flowsheet has been developed in a recent paper in the literature that uses a process with three columns operating at different pressures. Three high-purity products are produced as bottoms streams from the three columns with the distillate of the third column recycled back to the first column. The plantwide dynamic controllability of this complex, non-ideal interacting process is studied in this paper. An effective control structure is developed that controls one temperature in each column. Pressure compensation in the low-pressure column improves load rejection of both throughput and feed composition disturbances. No on-line composition measurement is required.

Control of fully heat-integrated pressure swing distillation for separating isobutyl alcohol and isobutyl acetate

Design and control of fully heat-integrated pressure swing distillation for separating isobutyl alcohol and isobutyl acetate are explored. The steady state design and dynamic simulation are performed via Aspen Plus and Aspen Plus Dynamics, respectively. Some control structures for this process are put forward to hold the products purities. It is found that the control structure with pressure-compensated temperature control can effectively address feed flow rate and composition disturbances despite of small flaw. In order to address to this small flaw, the control structure with a cascade connection of pressure-compensated temperature and composition control is proposed and this control structure can precisely maintain the products purities.

Application of a simulated annealing algorithm to design and optimize a pressure-swing distillation process

Abstract The design and optimization of pressure-swing distillation (PSD) have a critical impact on its economics. An optimization method based on simulated annealing algorithm (SAA) was proposed. The move generator and cooling schedule of the SAA were discussed, and suitable parameter settings were investigated. Two cases of PSD with and without heat integration were optimized by the SAA-based optimization method using procedures of pressure specified and pressure optimized. The results of the process without heat integration were compared with conventional optimization methods. For the acetone-methanol system, the total annual cost (TAC) shows a 5.69% decrease with the pressure specified and a 17.32% decrease with the pressure optimized. For the methanol-chloroform system, the TAC shows a 1.79% decrease with the pressure specified and a 9.04% decrease with the pressure optimized. The SAA-based optimization method has the advantages of a high probability to obtain the global optimum, automatic calculation, and less computing time.

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%.

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 pressure-swing distillation with the low pressure column performing at 30kPa and the atmospheric pressure column at 101kPa. 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%.

Effect of Pressure on the Azeotrope of the Mixture Isoamyl Acetate–Isoamyl Alcohol at 50.00, 101.32, 250.00, and 350.00 kPa

In this work the phase equilibrium data for the mixture isoamyl acetate (iAAc) + isoamyl alcohol (iAA) at pressures of 50.00, 101.32, 250.00, and 350.00 kPa in a dynamic recirculation cell (Fischer Labodest VLE model 602) were measured. The existence of a minimum boiling point azeotrope and the effect of the pressure on the azeotropic composition were determined. The data obtained experimentally were evaluated by means of a thermodynamic consistency analysis to validate the data quality and to use it in data regression to obtain the adjusted aij parameters for the nonrandom two-liquid (NRTL) model at each system pressure. Finally, a pressure swing distillation separation scheme is proposed. The main operating conditions of this separation alternative are defined by simulations in the Aspen Plus software platform in order to obtain high-purity components.

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.

The partial heat-integrated pressure-swing reactive distillation process for transesterification of methyl acetate with isopropanol

A novel partial heat-integrated pressure-swing reactive distillation process is designed for the transesterification reaction of methyl acetate and isopropanol. Aspen Plus is used to investigate the steady state for obtaining the optimal configurations of the processes. The partial heat-integrated pressure-swing reactive distillation process can save 33.41% energy consumption and 27.16% total TAC in comparison with conventional reactive distillation process. The basic and improved control structures for the partial heat-integrated pressure-swing reactive distillation process are studied using Aspen Dynamic. The improved control structure can deal with the feed disturbances very well and maintain product purities with acceptable transient deviations and settling times.

Separation of acetonitrile/methanol/benzene ternary azeotrope via triple column pressure-swing distillation

Abstract Acetonitrile/methanol/benzene mixture forms more than one different azeotropes and its triangular diagram presents several distillation boundaries at atmospheric pressure. A process named as triple column pressure-swing distillation (TCPSD) was proposed to separate this complex ternary system. The feasibility of the process was confirmed using residue curve maps and rigorous steady-state simulations were implemented on Aspen Plus. On basis of minimum total annual cost, several operating parameters were optimized by pressure-swing optimization software using the sequential iterative optimization procedure and the economics of TCPSD were compared with four different separation configurations. The results demonstrated that the A-M-B separation configuration was the most optimal column sequence in global optimization to separate acetonitrile/methanol/benzene azeotropic mixture using TCPSD. TCPSD may arouse the interest of researchers in various fields and can assist engineers to select the optimal separating process.

Purification of tetrahydrofuran from its aqueous azeotrope by extractive distillation: Pilot plant studies

Tetrahydrofuran (THF) is an important chemical which is useful in various applications. THF forms an azeotrope with water which is homogeneous and minimum boiling. Several techniques have been used for breaking this azeotrope including membranes, pressure swing distillation and extractive distillation. This work explores the possibility of using extractive distillation for dehydration and purification of tetrahydrofuran. Pilot scale distillation column experiments are presented in batch, semi batch and continuous mode using 1,2-propanediol and dimethyl sulfoxide as the entrainers. Use of dimethyl sulfoxide helps produce greater than 99% pure THF by mass.

Design and control of pressure-swing distillation for azeotropes with different types of boiling behavior at different pressures

The mixture of n-heptane and isobutanol presents minimum- and maximum-boiling azeotropes as the pressure changes. Two different pressure-swing distillation (PSD) processes are available for this mixture if the pressure of the low-pressure column is set as atmospheric. The steady states of the two available PSDs are optimized by minimizing the total annual cost (TAC) following a sequential iterative optimization procedure. On the basis of the steady-state results, the dynamic control of the two available PSDs and a comparison between them are presented. The conventional PSD (CPSD) is more economical but less controllable than the unusual PSD (UPSD), which has seldom been studied in the published literature. These two different PSD processes should be considered for the separation of this type of mixture according to their advantages.

압력변환 증류공정을 이용한 Methyl Ethyl Ketone-Cyclohexane 공비혼합물의 전산모사

Methyl Ethyl Ketone(MEK)-Cyclohexane(CH) 이성분계 공비 혼합물의 분리를 위해 압력변환 증류공정(Pressure-Swing Distillation, PSD)을 사용하여 저압-고압 컬럼 배열 공정과 고압-저압 컬럼 배열 공정에 전산모사 및 공정 최적화를 수행하였다. 저압 컬럼과 고압 컬럼 상부 MEK의 조성, 이론단수, 원료 주입단 순으로 공정 최적화를 수행하였다. 공정 최적화 수행 결과, 저압-고압 컬럼 배열 공정의 총 재비기의 heat duty 값은 11.7667 Mkcal/h이었으며, 고압-저압 배열 공정의 총 재비기의 heat duty 값은 10.3484 Mkcal/h로 고압-저압 공정의 heat duty 값이 저압-고압 공정 보다 약 12.05%정도 감소됨을 확인 할 수 있었다. The modelling and optimization of Methyl Ethyl Ketone (MEK)-Cyclohexane (CH) separation process were performed using pressure-swing distillation with a low-high pressure column and a high-low pressure column configuration. The optimization was performed for the number of theoretical stages, and the location of the feed tray of low column and high column to obtain high-purity MEK at the top. The total reboiler heat duty at the low-high pressure column configuration and high-low pressure column configuration were at 11.7667 Mkcal/h and at 10.3484 Mkcal/h, respectively. The results showed that total reboiler heat duty could be reduced to 12.05% using a high-low pressure column configuration.

Pressure swing distillation of azeotropic mixture – A simulation study

Summary The aim of this work is to simulate a pressure-swing distillation column for the separation and purification of ethanol from the ethanol–water binary system. The choice for this system is due to the importance of the ethanol–water separation. A steady-state equilibrium-stage model based on normalised MESH equations is used to simulate pressure-swing distillation column applied for the production of ethanol. All the work has been carried out using Aspen Plus simulator, version 13.2. Among the activity coefficient models available, the WILSON-RK model with binary parameters predicted by the Aspen Plus simulator is shown to be the most accurate to correlate the experimental vapor-/liquid equilibrium (VLE) data available for the ethanol–water system. The simulation has been satisfactorily carried out for a mixture of 20 mol% ethanol in water at 1 atm pressure and 90 °C with a molar flow rate of 100 kmol/h. The adjusting parameters include D/F ratio and reflux ratio of the two columns to get water purity of 99.5 mol% from the bottom of the Low Pressure Column (LPC) and the ethanol purity of 99.7 mol% from the bottom of High Pressure Column (HPC).

Modeling and Optimization Study of Pressure-Swing Distillation for the Separation Process of Acetone–Methanol Mixture with Vapor–Liquid Equilibrium Analysis

The azeotropic point of the binary system of acetone–methanol varies sensitively depending on the pressure change. This principle can be applied in order to obtain substantially pure acetone and methanol by using two distillation columns operated in sequence at two different pressures. The process of separation through this mechanism is known as pressure-swing distillation (PSD). This study mainly focused on the modeling and optimization of the PSD process as an effective method of separating an azeotropic mixture of acetone–methanol. The proper thermodynamic model to be used in the simulation was selected based on the prediction of the liquid activity model which gives the best fit for the experimental vapor–liquid equilibrium data of the involved binary system. For the simulation works, PRO/II with PROVISION v9.2 was utilized to create a model of PSD using two column configurations, a low–high pressure (LP+HP) column configuration and a high–low pressure (HP+LP) column configuration. The optimum theoretical number of stages, reflux ratios and feed stage locations were determined for the low-pressure (LP) column and high-pressure (HP) column to minimize the heat duty. Since PSD operates at different pressures, the hot and cold utility consumption is quite large. Therefore, heat integration was applied to the system to eliminate the high– and low– temperature utility consumption of the reboiler and condenser.

A review of ternary azeotropic mixtures advanced separation strategies

In most multi-component systems, the predominant non-ideality occurs which lead to the occurrence of an azeotrope. The ternary systems classification and study are summarized in first part of this review. The next part covers thermodynamic knowledge of residue curve maps, univolatility and unidistribution curves. A feasibility criterion based on thermodynamic properties of ternary diagram is presented, they are considered as powerful tool for the flow-sheet development and conceptual design. Separation of azeotropic mixtures and close boiling mixtures require non-conventional distillation processes, among which the leading processes are pressure-swing distillation if the composition of the azeotrope changes significantly with pressure, azeotropic distillation, extractive distillation, reactive distillation, and salt-effect distillation. The final section provides an overview of concepts, history, and recent strategies in these non-conventional distillations.

에탄올-n-헵탄 공비 혼합물의 분리를 위한 압력변환 증류공정 연구

In the present study, modelling and optimization of ethanol-n-heptane separation process were performed using pressure-swing distillation. The pressure-swing distillation process optimization was performed to obtain high purity ethanol and high purity n-heptane into a low-high pressure columns configuration and a high-low pressure columns configuration. The results of pressure-swing distillation process simulation and optimization using high-low pressure column configuration showed a reduced total reboiler heat duty at 5.8% which confirmed a more economical energy consumption.