Pressure Swing Batch Distillation Research Articles

Pressure-Driven Batch Distillation Optimal Control for Ethanol-Water Separation

Ethanol-water separation by pressure-swing batch distillation in a double-batch rectifier system is a process under investigation. In this work, a complete global solution to the optimal control problem in the form of a sequential synthesis of controlled trajectories is derived. During this study, the optimal reflux strategy through cyclic operation was extended to the separation of a second non-ideal minimum boiling azeotrope of industrial importance. The optimal cyclic reflux ratio operating policy, brought significant reductions in time duration, going up to even 50%. Consequently even more significant reductions in energy expenditure, since the derived discontinuous energy function tends to show cyclic “behavior” as well. Lastly, the proposed strategy provides the possibility to highly recover the desired product even within a single period, and finally maybe even the most importantly, flexibility in operating different units within the time frame.

Process design and multi-objective optimization for separation of ternary mixtures with double azeotropes via integrated quasi-continuous pressure-swing batch distillation

An multivessel double-column pressure-swing batch distillation process and a triple-column integrated quasi-continuous distillation process were designed to separate ternary mixtures with double azeotropes of ethyl acetate-methanol-water. The process feasibility was analyzed based on ternary phase diagram. Based on a production capacity of 100 kmol/batch, the corresponding control strategy was proposed to achieve the effective separation of the mixture. Taking the minimum total annual cost as the objective function, the process parameters of the double-column process were optimized to determine the optimal operating pressure. Exergy loss of distillation column was calculated to evaluate the thermodynamic performance of the process. To further improve the separation efficiency of the process, a third column was integrated in the double-column batch distillation process to separate the methanol-water mixture directly. Combined with sequential iterative optimization sequence and multi-objective optimization algorithm, the triple-column process parameters were optimized, and the trade-off between equipment cost and carbon dioxide was realized. Thermal integration technology was adopted to further reduce the energy consumption of the triple-column process. The results show that the carbon dioxide emissions and total annual cost of the double-column process are 1.323 × 106 kg/y and 2.107 × 105 $/y. The purity of ethyl acetate and water was 99.9 mol%. While the purity of methanol was 99.5 mol%. The total annual cost and emission of the triple-column process were 1.993% and 1.890% higher than that of the double-column process, respectively, but the methanol purity was further improved to 99.9 mol%. Compared with the double-column process, the total annual cost and carbon dioxide emissions of the triple-column process with thermal integration technology were reduced by 1.281% and 17.337%.

Design and comprehensive analysis of a novel pressure-swing batch distillation process for the separation of a binary azeotrope with various boiling behaviors

Batch distillation is widely employed in the fine chemical industry because of its operational flexibility. The mixture of n-heptane and isobutanol exhibits a special azeotropic phenomenon by which it changes from a minimum-boiling azeotrope to a maximum-boiling one with increasing pressure. However, the traditional double column batch rectifier and double column batch stripper processes cannot separate the mixture efficiently. Therefore, the double-column batch stripper–rectifier (DCBS-R) process was designed to obtain high-purity products, based on the azeotropic phenomenon. Further, control structures are explored to achieve stability, and the final purities of the separated products are over 99.9%. Each batch of raw materials is 100 kmol, and the expected annual production capacity is 800 batches. Additionally, a precooler of the low-pressure column (LPC) is introduced to reduce the exergy destruction by exergy analysis. The equipment cost and CO2 emissions are analyzed afterward to optimize the process, based on the multi-objective optimization method. Further, the number of stages and the pressure of the columns are optimized. The optimal obtained total annual cost (TAC) and CO2 emissions of the DCBS-R process are 2.26 × 105 $/y and 4.92 × 105 kg/y, respectively. The partial heat integration is studied to further improve the process performance, thus obtaining TAC and CO2 emissions of 2.22 × 105 $/y and 3.80 × 105 kg/y, which are 7.1% and 22.76% lower than the values obtained from the optimal process, respectively.

Separation of ternary mixture with double azeotropic system by a pressure-swing batch distillation integrated with quasi-continuous process

Two pressure-swing batch distillation processes, which are double-column batch stripper process and its integration with quasi-continuous process named triple-column process, were designed and investigated to separate the tetrahydrofuran/methanol/water ternary system. There are two azeotropes in the system and previous studies about batch distillation to separate such mixtures are insufficient. Based on the residue curve maps, the feasibility of the processes was analyzed. Control structures were explored to implement efficient separation and ensure the safety and stability of the process. The minimum total annual cost was used to optimize the processes. The double-column batch stripper process can separate the tetrahydrofuran and water well but the methanol purity is only 99.4 mol%. To improve the separation effect, a third column was integrated in the batch distillation process to separate the methanol/water mixture directly. The new triple-column process has the characteristics of batch distillation and continuous distillation. The results show that the minimum TAC of double-column batch stripper process is 147,815 $/y which is a little lower than that of triple-column process by only 3.2%. The final compositions of tetrahydrofuran and water are same in the two processes, which are 99.9 mol% for water and 99.85 mol% for tetrahydrofuran, but the methanol purity is different. The methanol is 99.4 mol% in the double-column process while 99.9 mol% in the triple-column process. The improved methanol purity reflects the high separation efficiency and it is beneficial for the environmental protection.

Design and control of an energy-efficient alternative process for separation of Dichloromethane-Methanol binary azeotropic mixture

Design and control of an energy and cost efficient separation process is deduced amongst several evaluated separation alternatives for Dichloromethane-Methanol binary mixture. Separation process evaluation for this specific binary mixture has not received much attention in the open literature so far. In the present study, several other significant alternatives (Pressure swing distillation, Extractive distillation and Azeotropic distillation) for the separation of the mixture have been explored and compared with the single reported work published earlier wherein separation using pressure swing batch distillation method has been discussed. Steady state analysis reveals that out of these evaluated alternatives; Extractive distillation is the best method in terms of economics and energy efficiency. The TAC of the extractive distillation method (best amongst four alternatives studied including the published work of PSBD method) was found to be 27.62% less than that of the second best from the list, which is Pressure Swing Batch Distillation method (Heat integration variant). The saving by extractive distillation method will result in significant benefits based on the futuristic surge in compound annual growth rate in the production of Dichloromethane-Methanol. Further, a plantwide control structure is designed for the recommended extractive distillation flow sheet which is further evaluated for throughput and composition disturbances. The present study will be helpful in designing the real process plants for the separation of Dichloromethane-Methanol binary mixture.

Optimization of Pressure-Swing Batch Distillation with and without Heat Integration for Separating Dichloromethane/Methanol Azeotrope Based on Minimum Total Annual Cost

Pressure-swing batch distillation was investigated to separate the binary azeotrope of dichloromethane/methanol. Based on the robust control of a composition–flow rate cascade control structure, minimum total annual cost, instead of conventional energy consumption, was studied to optimize the process. Different cooling mediums of cooling water and refrigerated water were applied and compared based on a 323 K reflux-drum criterion. Heat integration was also studied to realize further reduction of total annual cost. The results show that the difference of the costs is small when the lower-pressure column was operated at 1 and 1.6 atm. However, heat integration reduces the cost by 11.3% and shows advantage in energy consumption, which is 53.8% lower than that of the process without heat integration.

Separation of a Chloroform–Acetone–Toluene Mixture by Pressure-Swing Batch Distillation in Different Column Configurations

In this paper, a new, triple-column configuration application is introduced to separate ternary mixtures by pressure-swing batch distillation. This study investigates the separation of a chloroform–acetone–toluene ternary mixture in different column configurations (a combination of the batch stripper and the double-column batch rectifier, the double-column batch rectifier, and the triple-column configuration) by a feasibility study and by rigorous simulation and compares these processes at two different charge compositions by its overall specific energy consumption. The influences of the most important operational parameters are studied for all processes, and the performances of the column configurations are compared. On the basis of the results, we state that the triple-column configuration is more efficient than the other column configurations investigated.

Reactive pressure swing batch distillation by a new double column system

Ethyl-acetate is generally produced by the esterification reaction of ethanol with acetic-acid. Since the reaction is equilibrium-limited, the use of reactive distillation is an attractive option. A new double-column system is suggested for ethyl-acetate production by applying reactive pressure swing batch distillation. The system was investigated by a feasibility study based on the analysis of reactive and non-reactive residue curve maps. Two different process options were found to be feasible. In the first option, the reactive column operates at the lower pressure (1.01 bar), and the non-reactive column that removes ethyl-acetate from the system operates at the higher pressure (10 bar). The second option allows the reactive column to operate at the higher pressure (10 bar), and the non-reactive column removes water at the lower pressure (1.01 bar). The first process option was studied by rigorous simulation based on less simplifying assumptions using a professional dynamic simulator. The influence of the most important operation parameters was also studied.

Separation of an Acetone−Methanol Mixture by Pressure-Swing Batch Distillation in a Double-Column System with and without Thermal Integration

Pressure-swing batch distillation in a double-column system is suggested for the separation of an acetone−methanol pressure-sensitive azeotropic mixture. The studied column configuration is the double-column batch stripper in open mode. We investigated this separation by rigorous simulation using a professional dynamic flow-sheet simulator. The influence of the most important operational parameters is studied. The energy demand of the separation is converted to carbon dioxide emission. The two columns can be thermally integrated to save energy. The effectiveness of thermal coupling is also investigated at different pressure gaps.

Pressure swing batch distillation by double column systems in closed mode

Two new double column systems operated in closed mode are suggested for pressure swing batch distillation. These configurations are investigated by feasibility studies based on several simplifying assumptions (e.g., infinite plate number, no stage hold-up) and are compared with double column batch rectifier and double column batch stripper in open mode. We study the configurations also by rigorous simulation based on less simplifying assumptions using a professional dynamic simulator. For the different configurations the influence of the most important operational parameters is studied. The results obtained for open and close modes are compared. The calculations and the simulations are performed for a binary minimum (acetone–n-pentane) and for a maximum (ethylene-diamine–water) azeotrope mixture.

Feasibility of separation of ternary mixtures by pressure swing batch distillation

Feasibility of the pressure swing batch distillation separation of ternary homoazeotropic mixtures in different single and double column configurations is investigated by assuming maximal separation. Feasibility regions where the ternary mixture can be separated into its pure components (by applying in at least one step pressure swing) and the separation steps for the recommended configurations are determined. The method is presented in details for the most frequent types of ternary mixtures with minimum azeotrope(s).

Regular and inverted batch process structures for pressure swing distillation: a case study

AbstractThe main focus of this paper is on the comparison of the inverted and the regular pressure swing batch distillation processes for the separation of a homogenous azeotropic mixture. On the basis of a successful, experimentally validated rigorous model, a simulation study to identify the differences between the two processes and the influences of different structures on them is carried out. This identification of influences helps in finding out a heuristic base of the most suitable batch structure for a given separation problem. Especially the influence of the feed flow rate on the processes and the differences between the results on operation with different pressures will be addressed. Furthermore advantages, disadvantages and the limitations of both processes will be shown. In the end the best way of operating the pressure swing batch distillation will be presented depending on the product purity and the feed concentration for a given example. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

OPERATION AND CONTROL OF NEW PRESSURE SWING BATCH DISTILLATION SYSTEMS

OPERATION AND CONTROL OF NEW PRESSURE SWING BATCH DISTILLATION SYSTEMS

Separation of a Ternary Homoazeotropic Mixture by Pressure Swing Batch Distillation

The separation of a ternary mixture (n-pentane-acetone-cyclo-hexane) with two binary minimum azeotropes is studied by feasibility studies and rigorous simulation calculations. By the feasibility studies based on the analysis of the vessel paths in the residue curve maps at the two different pressures (PI, PII) the separation steps are determined for the two configurations studied (batch stripper (BS), double column batch stripper (DCBS)). The rigorous calculations are performed by the CCDColumn professional dynamic flow-sheet simulator. For the DCBS two operational policies are compared.

Feasibility of new pressure swing batch distillation methods

The pressure swing distillation in different batch column configurations is investigated by feasibility study and rigorous simulation calculations. Besides studying the well known batch configurations (rectifier, stripper, middle vessel column) we also suggest two novel configurations such as double column batch rectifier (DCBR) and double column batch stripper (DCBS). The alternate application of a batch rectifier and a batch stripper is also studied. The feasibility method is based on the assumption of maximal separation. The results of the feasibility studies are verified by rigorous simulations based on less simplifying assumptions. The calculations are made by a professional dynamic flow-sheet simulator for the separation of a minimum (ethanol–toluene) and a maximum boiling (water–ethylene-diamine) azeotropic mixture. The different column configurations are compared. The DCBS (for the separation of the minimum azeotrope) and the DCBR (for the maximum azeotrope) showed several advantages (e.g. only one production step without pressure change, lower energy consumption) compared with the other configurations.

Pressure Swing Batch Distillation for Homogeneous Azeotropic Separation

The separation of the homogeneous azeotropic mixture acetonitrile/water by pressure swing distillation (PSD) is considered. In this work, the PSD is operated as a discontinuous (batch) process and two basic batch modes, regular and inverted, are investigated. The processes are analysed and a rigorous dynamic model for both batch PSD processes is formulated. The model takes a cold and empty column as an initial condition. Because of the lack of experimental data, in particular for the inverted batch distillation new experiments were carried out. The regular and the inverted batch PSD consist of two steps, a low pressure and a high pressure run, and experimental results are shown for each step. The simulations fit the experiments with good accuracy. Using the validated model, a simulation study to discuss different batch processes is carried out and an alternative inverted batch process is proposed.