Entrainer Recovery Column Research Articles

ECONOMIC STUDY OF CONVENTIONAL AND IMPROVED EXTRACTIVE DISTILLATION SYSTEM USING ASPEN ECONOMIC ANALYSER

Simulation and the economic analysis of a conventional and an improved extractive distillation system has been carried out. Aspen plus and the Aspen Economic Analyser were used to simulate and generate data tables and charts while the non-random two liquid physical property was selected for the process. The case study adopted is the separation of Isopropyl alcohol (IPA) – water (H2O) azeotrope mixture using dimethyl sulfoxide (DMSO) as the entrainer. Maintaining the optimum parameters, an improved configuration was designed to improve economic efficiency by reducing the amount and cost of utility requirements. The modification involved the addition of heat exchangers to make use of the available sensible heat from the entrainer stream to be recycled. The heat exchangers serve as preheaters for both column feed streams by using the excess sensible heat from the entrainer recovered as heat source. Results showed that the utility cost requirement for the extractive distillation column and the entrainer recovery column decreased from 49.4 $/hr to 41.9 $/h and from 57.7 $/hr to 47.2 $/h respectively. The total system utility cost requirement also decreased by 167,589 $/year in the proposed modification. Keywords: economic analysis; extractive distillation; heat integration; process simulation

A systematic process synthesis method towards sustainable extractive distillation processes with pre-concentration for separating the binary minimum azeotropes

A systematic process synthesis method is investigated towards sustainable extractive distillation with pre-concentration. To approach energy saving, it is one of the common senses to eliminate the infamous remixing effects. In detail, the energy consumption bottleneck is initially analyzed to come at the inspiration to replace the pre-concentration column with a pre-stripper. Afterwards, a two-column scheme is synthesized by combining the pre-stripper with either the extractive distillation column or entrainer recovery column. Finally, an extractive dividing wall column (EDWC) scheme is synthesized. A fair comparison of all configurations is given under a simulation-based framework employing a stochastic algorithm to optimize all decision variables including the usually arbitrarily fixed operating pressure. The results demonstrate two-column schemes to be more promising, saving more than 30% of economic and environmental costs, and improving energy efficiency by 1–2 times compared to the conventional system. Besides, EDWC structures are not always advantageous in sustainability.

Energy‐Efficient Process with a Decanter to Separate Toluene‐Methanol‐Water Ternary Azeotropic Mixtures

AbstractAn extractive distillation process with two columns and a decanter was proposed to separate ternary toluene‐methanol‐water azeotropic mixtures in a previous study. Based on this process, six processes were established to explore further energy‐efficient schemes to separate the ternary azeotropic system. The optimal parameters of the process were determined in terms of the minimum total annual cost (TAC). The processes with heat integration perform better than those with a side stream or thermal coupling in terms of energy savings and TAC reduction. A process in which both the feed stream of the extractive distillation column and the entrainer recovery column are preheated by the entrainer recycle stream can reduce energy consumption by up to 27.69 % and TAC by 21.36 %.

Control of extractive distillation processes with intermediate impurities removed as a side withdrawal from the extractive distillation column

AbstractBACKGROUNDThe design and control of extractive distillation (ED) for separating azeotropes has been widely investigated. However, most researches only deal with simple binary azeotropes without considering impurities. In fact, in industrial practices, intermediate impurities can be removed as a side withdrawal from the extractive distillation column. The dynamic control of such processes has not been investigated. Furthermore, there are many heat‐integrated alternatives of basic ED sequence. When considering impurities withdrawn, the dynamic control of these alternatives may face some difficulties. Thus, this article aims to establish the effective control structures of ED processes for separating azeotropes with intermediate impurities, including basic sequence and heat‐integrated alternatives. Ethanol dehydration is selected to be explored, including a basic sequence (BS), a heat‐integrated sequence (HIS) which combines the pre‐concentration column and the entrainer recovery column into one column and the thermodynamic equivalent sequence of the HIS (TEHIS). Overall assessment of the dynamic performances of these sequences is implemented.RESULTSFor all the sequences, the dynamic performance with entrainer recycling stream being proportional to the extractive distillation column (EDC) feed is better than being proportional to the fresh feed. Meanwhile, large negative transient deviations in the water product purity and intensive fluctuations of sensitive‐stage temperatures can be observed for the HIS, but not for the TEHIS.CONCLUSIONSThe TEHIS is the best sequence considering both economics and dynamics. These sequences and the analyses of their dynamic controllability are valuable in practice for multicompoent azeotropes purification. © 2020 Society of Chemical Industry

Practical controllability and systematic tuning in a control system of bioethanol purification

For a system of bioethanol purification based on extractive distillation, this work addresses the problem of determining the better control configuration and the systematic tuning of the PI controllers in a framework of physical insight. The purification system is a distillation column train consisting of a preconcentration column, a dehydration column and a entrainer recovery column. To establish the control loops, a parameter called Operability Index (OI) was proposed and applied. All possible control loops were evaluated, and unlike typical works, also impurities in the product streams were considered as control outputs. The outcomes suggested that less control effort is achieved by controlling impurities than controlling purities; this means, the OI for impurities were lower than the ones for purities, and the control configuration was easily established by choosing loops of small OI. In the next step of tuning the linear PI controller for each loop, an approach of stable pole assignment was followed. Through this technique, all controllers were tuned simultaneously, and the values of the controller gains were calculated directly from the static gains and a pseudo time constant identified for every loop; this pseudo time constant corresponds to the best first order dynamics matched to the dynamics of the control output with respect to unit change of the control input. Through simulations in Aspen Plus Dynamics®, the performance of controlling impurities was illustrated and compared with the one of controlling purities, and the simultaneous tuning of controllers was demonstrated.

A new sulfolane aromatic extractive distillation process and optimization for better energy utilization

Extractive distillation (ED) processes are widely used for the separation of aromatic and non-aromatic hydrocarbons. Approximate boiling points of components and azeotropes in the mixture need solvents to aid the separation processes. A considerable mass flowrate and recovery of solvents in separation processes leads to significant energy requirement. This study provides a new extractive distillation process for the efficient separation of aromatic and non-aromatic hydrocarbons aided by sulfolane solution. A flash tank and a semi-lean solution stream are introduced to modify existing extractive distillation processes to reduce the reboiler heat duty of the entrainer recovery column and improve the separation performance of the extractive distillation column. The NRTL-RK property method and rigorous unit models in Aspen Plus are used to simulate new and existing processes. No-databank model parameters are regressed to improve the accuracy of simulations. A coordinative strategy is proposed to optimize the significant operating parameters for new and existing processes by combining Aspen Plus with MATLAB. Compared with the optimal existing extractive distillation process, the new extractive distillation process reduces the operating costs by 8.9% when heat integration is not considered, and 13.04% of the total annual cost can be reduced when a heat exchanger network is considered.

Energy-saving thermally coupled ternary extractive distillation process by combining with mixed entrainer for separating ternary mixture containing bioethanol

The major intrinsic obstacle of extractive distillation is the high energy consumption. It is an actual problem for reducing energy consumption of extractive distillation processes. Two thermally coupled ternary extractive distillation processes were studied to separate the ternary azeotropic mixture tetrahydrofuran/ethanol/water using a single component solvent (dimethyl sulfoxide) and a mixed solvent (dimethyl sulfoxide and ethylene glycol) as entrainer. The optimal conditions of all ternary extractive distillation processes were obtained based on the minimal total annual cost. Thermodynamic efficiency and CO2 emissions index were also considered to evaluate the energy efficiency and environmental impact of alternative ternary extractive distillation processes. The results show that the use of mixed entrainer can result in reduction in both energy consumption and total annual cost for the same ternary extractive distillation configuration. Comparisons of the conventional ternary extractive distillation process and thermally coupled ternary extractive distillation process 1 (combining extractive distillation column with entrainer-recovery column) with mixed entrainer show that a thermally coupled extractive distillation sequence with a side rectifier present the best results. However, thermally coupled ternary extractive distillation process 2 (combining extractive distillation column with entrainer-recovery column) does not show good result due to existence of remixing effect.

Control of Highly Heat-Integrated Energy-Efficient Extractive Distillation Processes

In our previous papers, two highly heat-integrated energy-efficient extractive distillation processes were presented by combining a preconcentration distillation column with an extractive distillation column or entrainer recovery column (Ind. Eng. Chem. Res. 2014, 53, 7121; Chem. Eng. Sci. 2015, 135, 166). However, these novel synthesis systems with highly heat-integrated configurations may exhibit complicated issues of dynamic controllability. Thus, this paper extends the previous work to investigate the dynamic controllabilities of these new synthesis systems. The singular value decomposition method is applied to analyze the temperature profiles and select the appropriate control trays. As the main column is highly heat-integrated from two columns, several degrees of freedom are lost. Thus, three temperature control loops are installed in the combined column. The dynamic performances of each system are tested by introducing ±20% disturbances of feed flow rate and composition, respectively. The results s...

Pressure-Swing Distillation for Separating Pressure-Insensitive Minimum Boiling Azeotrope Methanol/Toluene via Introducing a Light Entrainer: Design and Control

In this paper, pressure-swing distillation (PSD) is applied to separate pressure-insensitive minimum boiling azeotrope methanol/toluene via introducing chloroform as a light pressure-swing entrainer. The feasibility of this process is verified by analyzing the residue curve maps. Both partially and fully heat-integrated PSD processes are implemented. The steady-state designs of these processes are optimized based on total annual cost (TAC). In this extended PSD process, the high-pressure column (HPC) serves as the homogeneous azeotropic distillation column, while the low-pressure column (LPC) serves as the entrainer recovery column. It is found that the HPC has large temperature slope in the stripper section while with relatively flat trend above. This unique phenomenon makes it beneficial to reduce the energy consumption by preheating the feed and recycling stream using low-grade heat. Both conventional and partially heat-integrated extractive distillation processes with aniline as the entrainer are also...

Transesterification of Methyl Acetate with Isobutanol in a Reactive and Extractive Distillation Column with Ionic Liquid as Catalyst and Molecular Liquid as Entrainer

The reaction kinetics of transesterification of methyl acetate with isobutanol catalyzed by ionic liquid 1-sulfobutyl-3-methylimidazolium hydrogensulfate was measured. The reaction kinetic data were correlated by the ideal homogeneous model and nonideal homogeneous model, and the corresponding kinetic parameters were obtained. A reactive and extractive distillation (RED) process was proposed to conduct the transesterification, and the process was simulated based on the analysis of vapor–liquid equilibrium and reactive residue curve maps. High purities of products and high conversions of reactants can be achieved by the RED process. Effects of operating and structural parameters of the RED column and entrainer recovery column were investigated. Moreover, a lab-scale RED experiment was conducted to verify the reliability of the simulation process, and the simulation results agreed well with the experiment.

Dynamic Simulation and Control of a Complete Industrial Acetic Acid Solvent Dehydration System in Purified Terephthalic Acid Production

In the production of purified terephthalic acid (PTA), the acetic acid solvent dehydration system is a typical heterogeneous azeotropic distillation system. In this work, a rigorous process simulation of the complete industrial acetic acid solvent dehydration process is conducted. To achieve both the bottom- and top-product specifications, remove the accumulated p-xylene (PX), and recycle the methyl acetate (MA) despite feed flow rate disturbances, a suitable control strategy of this complete system is proposed. The control strategy requires only a side draw and organic reflux to control the tray temperatures of the dehydration column, the bottom heating steam to control the tray temperature of the PX purification column, and top-product reflux to control the tray temperature of the entrainer recovery column; this strategy can be easily implemented in industry for wider applications. From dynamic simulation and analysis, the control strategy can maintain the product purities, overcome the drawback of the ...

Criterion of the energy effectiveness of extractive distillation in the partially thermally coupled columns

The aim of this work is the statement of the reasons for different energy effectiveness of extractive distillation systems with the partially coupled heat and material flows (PCEDS) for various mixtures and entrainers. The estimation of the effectiveness was performed for PCEDS application for the separation of seven binary mixtures with different initial compositions and various entrainers. The criterion of the summary power consumption in the reboilers of the columns under the optimal operating parameters was used. It has been concluded on the basis of the obtained results that PCEDS effectiveness depends on the value of the reflux ratio in the entrainer recovery column of the conventional extractive distillation flowsheet. If the reflux ratio in that apparatus has a small value, then the energy consumption decrease due to the use of PCEDS will be insignificant. The criterion for the evaluation of the PCEDS energy efficiency for binary mixtures separation has been formulated as follows: PCEDS is useful if the reflux ratio at the entrainer recovery column has a value equal to or greater than 1.

Energy-Efficient Extractive Distillation Process by Combining Preconcentration Column and Entrainer Recovery Column

An energy-efficient two-column process based on a conventional extractive column process is explored by combining a preconcentration column and entrainer recovery column, which provides potential energy savings and capital investment reduction. Two case studies are demonstrated to verify the above-mentioned energy and economic advantages: the separation of isopropyl alcohol–water using DMSO as the entrainer and the separation of acetonitrile–water using ethylene glycol as the entrainer. In both cases, based on the global economic optimization, a design with optimized operation conditions for the conventional and improved processes is developed. It is revealed that the new process offers energy savings of 13.7% and 16.3%, respectively, and a similar reduction in total annual costs as compared to those of the conventional process.

Design and Control of an Extractive Distillation System for Benzene/Acetonitrile Separation Using Dimethyl Sulfoxide as an Entrainer

A method for benzene/acetonitrile separation using extractive distillation is presented, and dimethyl sulfoxide (DMSO) is selected as the entrainer. Steady state and dynamic simulations for this process are implemented by commercial simulators (Aspen Plus and Aspen Dynamics). On the basis of global economic optimization, a design with optimized operation conditions for this process is developed. Two single temperature control structures with fixed reflux ratio or fixed reflux-to-feed ratio and a dual-end temperature control structure for entrainer recovery column are presented to evaluate the dynamic performance with feed flow rate and feed composition disturbances, and the last structure is quite effective.

Control of Benzene–Cyclohexane Separation System via Extractive Distillation Using Sulfolane as Entrainer

Benzene and cyclohexane (CYH) can be separated via extractive distillation using sulfolane (SULF) as entrainer. In this Article, the steady state of an extractive distillation system has been simulated using the RadFrac model in Aspen plus, and the controllability of this system with feed flow rate and feed composition disturbances has been studied in Aspen Dynamics. Sensitivity analysis is used to obtain optimal operation conditions. The common control scheme for extractive distillation is infeasible. Two control structures are demonstrated in this Article. Each control structure has three main temperature controllers, two in the extractive distillation column and one in entrainer recovery column. Although both control structures can solve all disturbance issues and maintain the product purities very close to the set points, the dynamic responses of initial control structure have large transient deviation when +20% feed flow rate disturbance is introduced, while the improved control structure can overcome this obstacle.

Design and Control of Extraction Distillation for Dehydration of Tetrahydrofuran

AbstractDesign and control of an extractive distillation system for tetrahydrofuran (THF) dehydration with ethylene glycol as entrainer is investigated. The main module is a two‐column system containing an extractive distillation column, whose top stream is the desired product THF, and an entrainer recovery column. Economic analysis with total annual cost as the objective function is developed. Two kinds of control strategies are explored for THF dehydration. The responses reveal that the control structure with fixed reflux ratio cannot maintain the bottom liquid level of the entrainer recovery column, while the control scheme with fixed reboiler heat duty/feed flow ratio exhibits good control performance in spite of large deviations in feed flow rate and feed composition.

Design and Control of a Complete Azeotropic Distillation System Incorporating Stripping Columns for Isopropyl Alcohol Dehydration

As demonstrated by Pham and Doherty [Chem. Eng. Sci.1990, 45, 1823] in an ethanol dehydration process and by Arifin and Chien [Ind. Eng. Chem. Res.2007, 46, 2535] in an isopropyl alcohol dehydration process, a three-column heterogeneous distillation sequence which contains a preconcentrator column, an azeotropic column, and an entrainer recovery column is more energy saving than two-column and four-column sequences. The three-column sequence for the isopropyl alcohol (IPA) dehydration process, according to Arifin and Chien, is more energy-saving than the two-column sequence, but the capital cost of the entire sequence is more expensive than that of the two-column sequence. Because the reflux ratio used either in the preconcentration column or the recovery column of the three-column IPA dehydration system is quite small, these two conventional distillation columns are both replaced by a stripping column, and in this study a new separation scheme is thereby developed. The economic analysis of the proposed system shows there is more saving in energy and capital costs than the two- and three-column sequences aforementioned. Further, in developing a plant-wide control structure, a tray temperature control loop is implemented in each of the three columns which regulates reboiler duty in order to maintain the bottom product compositions for the new scheme, and ratio control of the organic reflux flow to the feed flow rate of the azeotropic column is used to reject feed rate disturbance. The purities of water achieved in the preconcentrator and entrainer recovery columns are greater than 99.88 mol %, and the IPA purity in the product stream is greater than 99.99985 mol %. Closed-loop responses to ±20% changes in fresh feed rate and feed H2O composition show that the proposed strategy has good control performance.

Design and Control of an Isopropyl Alcohol Dehydration Process via Extractive Distillation Using Dimethyl Sulfoxide as an Entrainer

In this paper, design and control of an isopropyl alcohol (IPA) dehydration process via extractive distillation have been investigated. The heavy-boiling entrainer used to aid the separation is dimethyl sulfoxide (DMSO). The design flowsheet includes an extractive distillation column and an entrainer recovery column with the top product of the extractive distillation column to be IPA and the top product of the entrainer recovery column to be water. The bottom product of the entrainer recovery column is the recovered DMSO which is recycled back to the extractive distillation column. The optimal design flowsheet of this complete process has been established showing that the total annual cost and the needed steam cost of this design flowsheet is significantly less than a competing design flowsheet via heterogeneous azeotropic distillation. A very simple overall control strategy has also been proposed which requires only one tray temperature control loop in each column to hold the high-purity specifications o...

Startup of Homogeneous Azeotropic Distillation Sequences with Multiple Steady States

The operability of an azeotropic sequence, which consists of an azeotropic distillation column with multiple steady states and an entrainer recovery column with the corresponding recycle stream, is analyzed by dynamic simulation during its startup. The goal is to study the effect of the recycle stream on the start-up performance. The well-known benzene−heptane−acetone (BHA) system is studied. Given open-loop (manual) start-up strategies, the way in which the system reaches different steady states by applying different start-up configurations and/or policies can be observed through the temperature profile evolutions. These are generated using different initial charges in one or both columns, and by applying different schedules for the evolution of the operative variables. Indeed, a partition of the start-up policy space yielding different solutions is achieved. Therefore, it is possible to identify a set of critical values for the supervision of the startup. Based on these results, very simple closed-loop ...

Simulation and optimization of heterogeneous azeotropic distillation process with a rate-based model

A rate-based simulation method for sieve tray columns is developed with the correlations of clear liquid height and mass transfer rate that were obtained in our previous experiments of the homogeneous and heterogeneous ternary distillation with a sieve tray column. The simulation method is applied to an ethanol dehydration process that consists of a dehydration column and an entrainer recovery column. In the simulation study, the effects of tray specification, overhead vapor concentration, locations of main feed and recycle flow, reflux ratio and recycle flow rate on separation performance of the columns are investigated. The simulation results show that increase of the reflux ratio and recycle flow rate decreases the necessary number of trays of the dehydration column to achieve a specified separation, but it increases the heat duties of the process. Then, the economical analysis of the process is carried out, and the optimum operation conditions of the process are discussed.