Pressure-swing Distillation Process Research Articles

Improving the economy and energy efficiency of separating water/acetonitrile/isopropanol mixture via triple-column pressure-swing distillation with heat-pump technology

The separation of water/acetonitrile/isopropanol ternary mixture is difficult to achieve with conventional distillation. However, pressure-swing distillation (PSD) is one of the most effective methods. This study investigates two PSD processes with different separation order where the W-A-I separation sequence has a better performance in economy, energy consumption and environment. Several energy-saving methods, including heat integration, heat-pump and heat exchanger network, have been introduced for using the sensible heat and latent heat of the process. In addition, the T-S diagrams of overheads from each column in processes with heat-pump are utilized for discussing the feasibility of dry compression. Among all the processes, the PSD process with triple-heat-pump and heat exchanger network (PSD-THP-HEN) requires the lowest cost and energy and emits the lowest CO2, SO2 and NOx. Compared with the PSD-HEN process, 71.4% of TEC and 57.59% of TAC are saved in PSD-THP-HEN, respectively.

Dynamic control analysis of interconnected pressure-swing distillation process with and without heat integration for separating azeotrope

Abstract Dynamic controls of pressure-swing distillation with an intermediate connection (PSDIC) process of ethyl acetate and ethanol separation were investigated. The double temperature/composition cascade control structure can perfectly implement effective control when ± 20% feed disturbances were introduced. This control structure did not require the control of the flowrate of the side stream. The dynamic controllability of PSDIC with partial heat integration (PHIPSDIC) was also explored. The improved control structure can effectively control ± 20% feed disturbances. However, in industrial production, simple controller, sensitive and easy to operate, is the optimal target. To avoid the use of component controllers or complex control structure, the original product purities could be maintained using the basic control structure for the PSDIC process if the product purities in steady state were properly increased, albeit by incurring a slight rise in the total annual cost (TAC). This alternative method without a composition controller combined with the energy-saving PSDIC process provides a simple and effective control scheme in industrial production.

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.

Investigation of energy-efficient and sustainable reactive/pressure-swing distillation processes to recover tetrahydrofuran and ethanol from the industrial effluent

In this work, we report an approach for conceptual design and optimization of an energy-saving and sustainable reactive/pressure-swing distillation process to separate a ternary mixture tetrahydrofuran/ethanol/water with three azeotropes. The novel reactive/pressure-swing distillation schemes with two different separation sequences are proposed via the thermodynamic feasibility analysis. In these processes, the component of water in the ternary system is firstly removed by adding a reactant in the reactive distillation column and the remaining binary azeotropic mixture is then separated via the pressure-swing distillation. An improved genetic algorithm is employed for optimizing the proposed processes. Furthermore, the heat integration approach is adopted to further reduce the energy consumption. The evaluations illustrate that total annual cost and CO2 emissions of the proposed processes based on the proposed reactive/pressure-swing distillation with (and without) heat integration schemes could be significantly reduced by 50.16% (54.80%) and 53.00% (59.11%), and total net revenue could be decently increased with 12.19% (12.40%), compared with the existing triple-column pressure-swing distillation process. In addition, the thermodynamic efficiency of the existing process is significantly improved via the proposed reactive distillation processes.

Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations

For heat-integrated pressure-swing distillation (PSD) in which the heat release of overhead vapor condensation of high-pressure column (HPC) is completely utilized to supply the reboiler duty of low-pressure column (LPC), the operating pressure (OP) of the HPC cannot be controlled. Pressure-compensated temperature control (PCTC) is widely used to hold the controlled temperature under OP fluctuations to achieve effective control. In this paper, differential temperature control (DTC) is applied to control the sensitive-stage temperature under OP fluctuations of the HPC in the control of a variety of heat-integrated PSD processes, including both conventional and entrainer-assisted PSD, both partially and fully heat-integrated PSD, both LPC->HPC and HPC->LPC sequence, and separating both minimum-boiling and maximum-boiling azeotropes. IAE of the product purities of all the processes are calculated. Systematic comparison between DTC and PCTC is implemented. The results show that effective control can be achieved when implementing DTC in these processes and the dynamic performances of DTC and PCTC are almost the same. Therefore, DTC can be applicable in the control of heat-integrated PSD for separating binary azeotropes, which is also a good inspiration for other heat-integrated distillation processes.

Energy, economic and environmental evaluations for the separation of ethyl acetate/ethanol/water mixture via distillation and pervaporation unit

Ethyl acetate is a vital chemical raw material and is usually produced by esterification in industry. But this reaction can produce multiazeotrope mixtures of ethyl acetate/ethanol/water. In this work, triple column pressure-swing distillation process with and without heat integration and hybrid processes combining extractive distillation and pervaporation are proposed to separate a mixture of ethyl acetate/ethanol/water. Furthermore, the three processes are comprehensively compared with the triple-column extractive distillation process. Based on minimization of the total annual cost, the parameters of the all processes are optimized. The triple-column extractive distillation process has the greatest economic advantage. Additionally, the performances of the all processes in environmental protection and energy efficiency are evaluated. The energy efficiency of the combined extractive distillation and pervaporation unit process is relatively low, but its environmental impact is the lowest among the four processes.

Optimization of Pressure-Swing Distillation for iC5-Methanol Azeotropic Mixture Purification

Typical industrial technologies to produce tert-amyl methyl ether (TAME), a gasoline oxygenated additive, require some advanced purification process for methanol recovery from the reactor effluent, due to the presence of the iC5-methanol minimum boiling point azeotrope. Pressure-swing distillation (PSD) is widely used as an efficient method for separating pressure-sensitive azeotropic mixtures in industrial processes. However, it is well known that distillation units are responsible for the highest energy consumption in chemical separation facilities, reaching in some cases to 95% of the total energy cost. Thus, the objective of this work was to perform an optimization methodology of the main design and operational variables of the PSD process applied to the separation of the azeotropic iC5-methanol mixture, considering minimizing the objective function of total annual cost (TAC). For this purpose, Honeywell’s UniSim Design® Suite software was used to simulate the process flowchart and Matlab® was used to perform TAC optimization. The optimized PSD design revealed potential for saving of up to 12% per year in terms of TAC when compared to the non-optimized process, thus proving the feasibility of the optimization methodology for this specific process. Furthermore, it reinforces the main objective of the optimization technique that is to make chemical processes more economically competitive in the industrial sector.

Comparative study of Heat Pump Assisted Distillation Column and Its Application for Pressure Swing Distillation Process

Two of the well-known heat pumps assisted distillation column scheme are direct vapor recompression and bottom flashing. The comparison between the two schemes was systematically studied for binary mixture of non-azeotropic benzene-toluene system. Simulation was carried out using Aspen Plus software. The best scheme was selected based on economic evaluation (utility cost and TAC reduction). The application of both schemes was also studied for pressure swing distillation process. Pressure swing distillation is one of the most common methods for separating pressure-sensitive azeotropic system. Direct vapor recompression scheme and bottom flashing scheme can be applied to enhance the energy savings. The minimum-boiling homogeneous azeotropic mixture of methyl acetate-methanol was chosen as representative in process simulation.

Optimization of a new combined approach to reduce energy consumption in the hybrid reactive distillation–pervaporation process

This study combines feed splitting, internal heat integration, and heat integration between Pervaporation (PV) retentate streams and internal streams of reactive distillation (RD) column employed in TAME production in an attempt to optimize energy consumption in the process. All process parameters in the RD column, PV membrane process, and process energy consumption were optimized simultaneously. Further, the possibility of heat exchange between hot and cold streams was investigated by the optimization algorithm in internal heat integration in the RD column (R-HIDiC) as well as heat integration between retentate streams in PV modules and internal streams in the RD column. Accordingly, the number of heat exchangers and the heat exchange ratio of the streams was determined by the optimization algorithm. The Total Annual Cost (TAC) was adopted as the objective function to be optimized by a combination of Genetic Algorithm (GA) and Particle Swarm Optimization (PSO) algorithm. Twelve different processes were optimized and compared. Optimization results suggest that the hybrid R-HIDiC–PV process with feed splitting and heat integration reduced the energy consumption by 42 % and TAC by 45 % compared to the hybrid PV–RD process and by 47 % and 48 %, respectively, compared to the hybrid RD–Pressure swing distillation process.

Economically and thermodynamically efficient heat pump-assisted side-stream pressure-swing distillation arrangement for separating a maximum-boiling azeotrope

The feasibility and effectiveness for the two types of heat pump-assisted side-stream pressure-swing distillation arrangements (vapor recompression and bottom flashing heat pump-assisted systems) are investigated with the separation of a maximum-boiling ethylenediamine and water azeotrope as the demonstrating example. To further improve the heat recovery within the process as much as possible and reduce the excessive utilization of cold and hot utilities, the efficient Heat Exchanger Network Synthesis (HENs) analysis tool is adopted. Total annual cost (TAC), carbon footprints and thermodynamic efficiency are as the evaluation indicators to assess and screen the eco-efficient arrangement in a series of pressure-swing distillation (PSD) processes. Compared to the partially heat-integrated PSD process, the economically optimum flowsheet is the intensified self-heat recuperative vapor recompression-assisted arrangement (VRC-SSPSD-PF-HEN) since it can achieve the reductions of 59.01% in energy consumption rates, 86.60% in CO2 emissions, 12.78% in TAC and enhancement of 143.38% in thermodynamic efficiency. And the amount of heat recovery within this process is 7028.0 kW with the requirement of cold utility 395 kW and without any hot utility consumptions (electrical power is required). Besides, the exergy destroyed in each component for the optimal intensified alternative is analyzed. Result shows that the major exergy losses mainly produce in columns, especially in high-pressure column.

Optimal design and performance enhancement of heteroazeotropic and pressure-swing coupling distillation for downstream isopropanol separation

The isopropanol stream obtained by direct hydration of propylene is mainly the diisopropyl ether-isopropanol-water ternary mixture with a low concentration and multiple azeotropes that leads to high energy usage for downstream isopropanol processing. For this, a new three-column heteroazeotropic and pressure-swing coupling distillation process (TCHPSD) is proposed and further intensified by employing dividing-wall column (DWC) and vapor recompression (VRC) technologies, resulting in two energy-efficient processes (TCHPSD-DWC, TCHPSD-DWC-VRC). Rigorous simulations and a dual-staged sequential iterative method are used in the design and optimization of processes. The results show that the TCHPSD-DWC-VRC process achieves a significant reduction in total annual costs (12.0%) and energy consumptions (63.8%) in comparison with the TCHPSD process. Furthermore, thermodynamic and environmental evaluations based on exergy efficiency, pinch analysis and CO2 emissions display that this double-effect intensified process is industrially sustainable, especially for industrial sites without access to cheap heat sources.

Optimization and heat integration of hybrid R–HIDiC–PV process with the series–parallel arrangement of PV modules and recycle streams for TAME production

Tert–amyl methyl ether (TAME) production process is consisted of a reactor, a reactive distillation (RD) column and the methanol recovery section. The bottom product of the RD column is TAME while the distillate is consisted of the azeotropic mixture of methanol and isopentane (i-pentane) that can be separated by either the pervaporation (PV) membrane or conventional pressure swing distillation (PSD) and extractive distillation (ED) methods. The PV process allows the use of both series and parallel arrangements. The series arrangement has a lower membrane area compared to the parallel arrangement, while the parallel arrangement has a lower energy cost. A series–parallel arrangement with recycle streams was used in the present study to take advantage of both the series and parallel arrangements. The HIDiC method was used for reducing energy consumption in the RD column. Moreover, heat integration between PV streams and internal flows in the RD column was used to reduce PV energy consumption. The number of modules in each row, the recycle stream, the heat exchange ratio between the rectifying and stripping sections in the RD column and the heat exchange ratio between PV streams and internal RD streams were obtained by a hybrid GA–PSO algorithm. Furthermore, all RD and PV parameters were considered optimization variables and most importantly, all process variables were optimized simultaneously. According to the results, the proposed process reduced the total annual cost (TAC) by 52% and led to a 57% energetic gain compared to the conventional hybrid RD–PSD process. The proposed process also reduced TAC by 48% and led to a 40% energetic gain in comparison with the hybrid RD–PV process. This can be related to the reduced membrane area compared to the series and parallel arrangements as well as reduced energy costs of PV heaters through heat integration between PV steams and internal flows of the column.

Heat integrated technology assisted pressure-swing distillation for the mixture of ethylene glycol and 1,2-butanediol

Production of ethylene glycol (EG) from coal derived syngas has been an alternative to the petroleum route, where a certain amount of mixture product of EG and 1,2-butanediol (BDO) is inevitably side-produced as a low value-added product. Thus, designing a separation process with high economic performance for this azeotropic mixture is highly desirable. Herein, pressure-swing distillation (PSD) processes without and with aid of heat integration are designed and simulated by using Aspen Plus for recovering high purity EG and BDO from the mixture product. The results show that the CO2 emissions and total annual cost (TAC) of the four modified PSD process have been significantly reduced compared with the optimized basic PSD process. Among these processes, the full heat integrated pressure-swing distillation process has the best economic performance with TAC decreasing by 35%, while the bottom flash pressure-swing distillation process has the best environmental performance with CO2 emissions decreasing by 95%. These findings provide fundamentals for the rational design of industrial separation and purification of EG and BDO azeotrope in the coal-based EG production.

Performance Enhancement of Heat Pump with Preheater-Assisted Pressure-Swing Distillation Process

A heat pump is applied in pressure-swing distillation (PSD) for separating an isobutanol/isobutyl acetate mixture in this paper. To ensure dry compression and prevent compressor damage, a preheater is added before the compressor based on the dry fluid property of the isobutanol/isobutyl acetate mixture. In addition, the optimal preheated temperature of the overhead vapor stream may further improve the performance of the heat pump-assisted PSD process. Through optimization and analysis, the optimum superheat values of overhead vapor streams from two columns are 12 and 8.4 °C, respectively. The coefficients of performance of heat pumps achieve maximum values of 17.18 and 20, and the total annual cost of the process is minimum. Moreover, a heat exchanger network (HEN) is applied in the heat pump with preheater-assisted PSD (HPPSD) to reduce the use of steam in preheaters. Compared with the conventional PSD, the total annual costs, energy consumption, and CO₂ emission of the HPPSD-HEN process are decreased by 69.8, 83.99, and 79.58%, respectively.

Dynamic control analyses of eco-efficient partially heat-integrated side-stream pressure-swing distillation processes

Dynamic control behavior analysis for the new partially heat-integrated side-stream pressure-swing distillation arrangement is performed with the demonstrating examples of separating a minimum-boiling ethyl-acetate/ethanol azeotrope and a maximum-boiling ethylenediamine/water azeotrope. The snowball effect is observed in these systems. The contribution of this paper is to develop some novel robust and effective control schemes to eliminate or attenuate this effect for these processes. The stable regulatory control is achieved with the dual-product composition held close to their steady-state design specifications when handling the large step changes in throughput and feed composition. The feature control loops of these novel control schemes are that the flowrate in the azeotropic recycle loop from high-pressure column is, respectively, used to control the level in reflux drum and column base of low-pressure column for the minimum- and maximum-boiling azeotropes.

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process

Design and control of ethyl acetate/n-hexane azeotropic system separation via different heat-integrated pressure-swing distillation process

Efficient extractive distillation design for separating binary azeotrope via thermodynamic and dynamic analyses

Efficient and stable separation of ethyl acetate/cyclohexane mixture in an economic way is significant for the pesticide industries. The economy of the extractive distillation (ED) process performs and the pressure-swing distillation (PSD) process was compared based on total annual cost (TAC). Thermodynamic analysis was used to further modify the ED process. Two-stage preheating was applied to improve the energy use efficiency and further reduce the costs. The results show that the TAC of the ED process is lower than that of PSD process by 58.2% and the cost of the two-stage preheating extractive distillation process is 9.3% lower than traditional ED process. To separate the mixture steadily, an improved multi-proportion control structure was developed. The proportion elements change their output signals based on the initial ratios when the input signals change. The improved control structure can separate the components to 99.9 mol%. Both the economy and controllability of the modified process perform well.

Control of a pressure-swing distillation process for benzene/isopropanol/water separation with and without heat integration

Controlling the behavior of processes for the recovery of benzene and isopropanol from industrial wastewater is an important topic. In this work, dynamic control structures are investigated for the separation of azeotropic water, benzene, and isopropanol mixtures using triple column pressure-swing distillation (without heat integration, with partial heat integration, and with full heat integration). Composition and flow disturbances are utilized to examine the performance of the control structure, and four improved control structures are developed and show good control effects. The ratio of reboiler duty to mole feed flow rate control structure showed good control behavior in face of the disturbances for the ternary pressure swing distillation processes. The integral of squared error (ISE) values of the control structure was combined with the dynamic response curves to compare the performance of the control structures. The ISE value of the improved control structure with full heat integration was smaller than that of the improved control structure without heat integration and the improved control structure with partial heat integration. The total annual cost (TAC) of the full heat integration process was also lower than the values for the other three processes. Based on its control performance and TAC, the improved control structure with full heat integration was concluded to be the best of the control structures. This work can serve as a reference for industrial development.

Dynamic control analysis of partially heat-integrated pressure-swing distillation for separating a maximum-boiling azeotrope

Dynamic control behavior of partially heat-integrated pressure-swing distillation process is investigated by taking a separation of maximum-boiling ethylenediamine/water azeotrope as the example. The feasibility of using a single-end control strategy is affirmed by the method of feed composition sensitive analysis, and a series of novel control structures are developed to eliminate or attenuate the snowball effect, wherein the special control loops are that the flow in bottoms recycle line is controlled by regulating the set-point of a flow controller placing in recycle loop through two alternative ratio controllers including flow and thermal ratios. Both the robust and stable regulatory control are achieved with dual-product composition restored to their steady-state design specifications for handling large (20%) step changes in throughput and feed composition. The effectiveness of control structure with flow ratio option works better than that of another alternative taking the comprehensive consideration of product transient deviations, product offsets and settling time. Besides, there is no product offset for distillate ethylenediamine composition, although only the temperature control loops are used in the low-pressure column for control structure with thermal ratio option, which is the advantage of this control structure since the dual-end product composition control loops are required for that with thermal ratio. Of the particular importance is that the severer and stronger oscillatory effect of product composition is weakened by taking the proportional-only cascaded temperature controller for facing throughput perturbations.

Energy-efficient extractive pressure-swing distillation for separating binary minimum azeotropic mixture dimethyl carbonate and ethanol

An energy-efficient extractive pressure-swing distillation process is proposed for separating binary minimum azeotropic mixture ethanol and dimethyl carbonate. It can be observed that the minimum amount flow rate of entrainer will be decreased when the operating pressure of extractive distillation column is increased via the thermodynamic feasibility insights (i.e., residue curve map and isovolatility lines). Therefore, an extractive pressure-swing distillation process with 4 bar for the extractive distillation column is designed. Process variables of the proposed design are optimized by combining the sensitivity analysis and sequence quadratic program approaches with minimum total annual cost as objective function. Total annual cost, CO2 emissions, and exergy loss of the optimized extractive pressure-swing distillation with 4 bar for the extractive distillation column is reduced by 44.09%, 44.16% and 41.54%, respectively when compared with the existing process with 1 bar for the extractive distillation column, which mainly attributing the flow rate of entrainer decreasing from 200.020 kmol/h to 44.963 kmol/h. Furthermore, the extractive pressure-swing distillation with heat integration is studied to further reduce energy cost because the enough heat transfer temperature difference could be provided by increasing operation pressure.