Triple-column Pressure-swing Distillation Research Articles

Conceptual process design and process optimization of triple-column pressure-swing distillation for the separation of ternary mixtures embedding two azeotropes with different feed composition via thermodynamic insights and genetic algorithm

In this article, we take the tetrahydrofuran (THF)/ethanol (ETOH)/methanol (MeOH) as an example to investigate the process design of the triple-column pressure-swing distillation (TCPSD) for the separation of Serafimov’s class 2.0-2b mixtures with different feed composition. Two basic topology structures (TSI, TSII) and two separation sequences (SSI, SSII) are investigated, then, process optimization with total annual cost (TAC) as objective function is conducted via genetic algorithms. Heat integration (HI) is also applied to TCPSD. From a new perspective, the separation of THF/ETOH/MeOH can be regarded as the azeotropic distillation for THF/ETOH with MeOH as azeotropic agents based on thermodynamic features of Serafimov’s class 2.0-2b mixtures. The feasible topology structure and separation sequence of TCPSD for Serafimov’s class 2.0-2b mixtures depend on the feed composition and operating pressure. The feed composition is divided into three regions according to the concentration of methanol in azeotropic distillation column. The two critical points are azeotropic points at allowed minimum and maximum operating pressure. Especially, when feed composition is below azeotropic point at allowed minimum operating pressure, TSI is not feasible due to less MeOH as azeotropic agents. Furthermore, TCPSD combining pure azeotropic agents (ATPSD) can be developed based on this new insight. Then, two feed compositions are used to illustrate the detailed conceptual design of three topology structures as well as corresponding two separation sequences and their economic performance. The results show that when feed composition is 0.4ETOH/0.25THF/0.35MeOH, TSI and TSII are feasible, the best economical configurations without and with heat integration is TSII-SSII and TSII-SSII-HI. When feed composition is 0.4ETOH/0.4THF/0.2MeOH, TSII and ATPSD are feasible, the best economical configurations without and with heat integration is ATPSD-SSI and ATPSD-SSI-HI. Furthermore, ATPSD-SSI and ATPSD-SSI-HI have 18.28% and 19.38% TAC reduction than TSII-SSI and TSII-SSI-HI, respectively. In summary, feasible and the best economic topology structure and separation sequence of TCPSD for Serafimov’s class 2.0-2b mixtures depend on the feed composition and operating pressure. In addition, the proposed ATPSD shows good economic performance for Serafimov’s class 2.0-2b mixtures.

Improving the economy and energy efficiency of separating n-propanol/water/tetrahydrofuran via triple-column pressure-swing distillation and azeotropic combining pressure-swing distillation

The triple-column pressure-swing distillation (TPSD) and novel azeotropic combining pressure-swing distillation (APSD) processes were designed for separating the n-propanol/water/tetrahydrofuran ternary mixture. The application of heat-integration and vapor-recompressed heat pump technologies in the abovementioned processes were explored to achieve energy conservation. The total annual cost (TAC), total energy consumption (TEC), gas emission, and exergy analysis were conducted to evaluate the proposed processes. APSD displayed a greater economic performance when compared with TPSD. The ADLH-VR-HI exhibited the highest energy and economic performance. It also showed a 54.32 % reduction in the TAC and 67.19 % reduction in the TEC when compared with TPSD. The total exergy efficiency of the ADLH-VR-HI process was 6.02 %, which indicated that applying heat-integration and vapor-recompressed heat pump is suitable for saving energy and improving exergy efficiency.

Towards energy saving and carbon reduction of pressure-swing distillation for separating the ternary azeotropic mixtures by thermodynamic insights and process intensification

The recovery and separation of organic solvents such as tetrahydrofuran (THF), ethanol (EtOH), and methanol (MeOH) are important to protect the environment and save resources. Such ternary mixture has two azeotropes and one distillation boundary that makes separation difficult to be carried out using ordinary distillation technique. In this work, we developed a systematic approach for heat-integration (HI) and vapor recompression heat pump (VRHP) assisted triple-column pressure-swing distillation (TCPSD) for the recovery and separation of these valuable compounds. Firstly, the thermodynamics topological analysis is introduced to evaluate the feasibility of TCPSD for separating the ternary azeotropic mixture THF/EtOH/MeOH. Different separation sequence is determined via the combination of residue curve, component balance line, isovolatility curve, and distillation boundary. Subsequently, the potential application of HI and VRHP technologies is additionally explored for further minimizing the energy consumption and it is found that both process intensification technologies provide significant improvement in terms of economic, environmental impact, and energy efficiency. Relative to the traditional TCPSD, the application of VRHP technology to the TCPSD sequence B, in particular, provides 43.5% and 76.4% reduction in TAC and CO2 emission, respectively, while it improves the energy efficiency 100.4%.

Economic and Energy-Saving Heat Pump Assisted Triple-Column Pressure-Swing Distillation for the Separation of Methanol/Ethyl Acetate/Methyl Via Thermodynamic Insights and Multi-Objective Optimization

Economic and Energy-Saving Heat Pump Assisted Triple-Column Pressure-Swing Distillation for the Separation of Methanol/Ethyl Acetate/Methyl Via Thermodynamic Insights and Multi-Objective Optimization

Application of heat pump technology to recover 1,4-dioxane and acetonitrile from wastewater via triple-column distillation

• An effective method to recover 1,4-dioxane and acetonitrile from wastewater. • Heat pump technology is applied for thermal efficiency enhancement. • Temperature-entropy diagram is taken for illustrating the heat pump process. • The splitting arrangement is the optimal process. An effective method of triple-column pressure-swing distillation is introduced to recover 1,4-dioxane and acetonitrile from wastewater in this study. In order to save energy, heat pump technology is applied for utilizing the latent heat of the overheads. Besides, the heat exchange network is used for optimizing the heat exchange of the process. For better analysis of the heat pump process, the temperature-enthalpy diagram is taken to present the utilization, heat recovery and pinch point. And the temperature-entropy diagram is adopted to illustrate the thermodynamic parameters of the overhead during the heat exchange process. Several different processes with heat pump are designed and the triple-heat pump assisted pressure-swing distillation with splitting arrangement is the optimal process with the second-law efficiency of 1.45%. Compared with the conventional pressure-swing distillation, the savings of total annual cost and total energy consumption are 45.83% and 65.82% and the reduction of greenhouse gas emissions are 62.36% in CO 2 , 63.72% in SO 2 and 63.72% in NO x .

Improved design of separation system for the recovery of benzene and isopropanol from wastewater

In order to recover valuable benzene and isopropanol from wastewater, development of energy-efficient design flowsheet of this separation system is a relevant design problem in industry and worthy of investigation. The available separation methods in open literature were to either use a triple-column pressure swing distillation or by combining heterogeneous azeotropic distillation and pressure-swing distillation. Although the above two separation methods having the favorable feature of not introducing any foreign component into the system, the economics and energy consumption of the above separation design flowsheets can still be significantly improved. The purpose of this paper is to develop an improved design flowsheet for this separation task, not ever seen in open literature, making use of natural liquid–liquid splitting in a decanter and arranging the distillation sequence so that one of the preceding column to be designed as a stripper to preserve latent heat of this column’s top vapor stream. Further energy-saving schemes of this separation system were also thoroughly investigated. It is found that the economics of our proposed heat-integrated separation system can significantly cut 75.1% and 66.2% in total operating cost and total annual cost, respectively, as compared to that of the best separation system recently proposed in open literature.

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.

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.

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.

Heat-integrated triple-column pressure-swing distillation process with multi-recycle streams for the separation of ternary azeotropic mixture of acetonitrile/methanol/benzene

The steady-state economics and dynamic controllability of heat-integrated triple-column pressure-swing distillation (TCPSD) process are explored by taking the separation of ternary mixture of acetonitrile, methanol and benzene as demonstrating example. The performance evaluation indicators of second-law efficiency and CO2 emissions are employed to rank different arrangements except only reference of total annual cost (TAC). Compared to the conventional process, the economically optimum flowsheets are the partially heat-integrated processes (Cases 1 and 2) since it can reduce about 20.00% in TAC, 35.19% in energy-saving and enhancement of 48.77% in thermodynamic efficiency. Dynamic control of the economic efficient processes are also investigated. A series of control structures are developed and assessed by the throughput and feed composition disturbances, which are divided to two categories including control schemes with or without split ratio of the distillate stream of second column. The snowballing effect is efficiently attenuated by control schemes (CS4 and CS5) with the ratio strategy to adjust the recycle stream flowrate for partial Case 1. These control strategies are also applied to partial Case 2, the stable regulatory control is achieved, yet oscillation phenomena for the response of condenser heat removal of second column exists for control strategies without split ratio scheme, while it is efficiently handled by the split ratio scheme coupling with pressure compensated temperature-composition cascade control strategy.

Pressure-Swing Dividing Wall Column with Multiple Binary Azeotropes: Improving Energy Efficiency and Cost Savings through Vapor Recompression

This work introduces a novel thermal integration scheme for a pressure-swing distillation train used to separate a mixture of methanol/benzene/acetonitrile. This mixture typically forms three azeotropes as shown through developing its residue curve map with two distillation boundaries at atmospheric pressure. This ternary mixture is traditionally separated via a triple column pressure-swing distillation (TCPSD) scheme, in which, all columns operate at different pressures. Here, the first two columns of the TCPSD are proposed to be replaced by a single column having a dividing wall that allows heat transfer through it. Thus, the resulting scheme is called pressure-swing dividing wall column (PSDWC). Aiming to improve its performance, further advancement is subsequently made by developing the heat intensified PSDWC (HiPSDWC) and vapor recompressed PSDWC (VRPSDWC). The performance of these proposed schemes is evaluated in the context of energy saving and total annual cost (TAC). Among these configurations, i...

Effect of multi-recycle streams on triple-column pressure-swing distillation optimization

Different structures of multi-recycle triple-column pressure-swing distillation (TCPSD) are synthesized and explored. Acetonitrile/methanol/benzene ternary mixture is set as a case to identify the applicability of different multi-recycle TCPSD flowsheets. Four multi-recycle flowsheets are analyzed and compared with convention TCPSD process and rigorous steady-state simulations are implemented using Aspen Plus. Operating parameters are optimized by using the sequential iterative optimization procedure when the split fraction changes with the objective function of minimum total annual cost. Two structures are found that distillate compositions surpass the distillation boundaries at finite reflux ratios. However, the results show that different multi-recycle TCPSD processes are feasible.

Heat Integration and Control of a Triple-Column Pressure-Swing Distillation Process

Heat integration and dynamic characteristics are critical for the triple-column pressure-swing distillation (TCPSD) processes that are used to separate ternary or multicomponent systems. In this study, rigorous steady-state simulations of heat-integrated TCPSD processes are optimized using Aspen Plus, and dynamic strategies for the different TCPSD processes are explored using Aspen Dynamics. When ±20% feed flow rates and composition disturbances are introduced, the composition/temperature cascade control structure (CSB), which uses stage 19 as the temperature-sensitive stage in the second column, exhibits better controllability than the CSA, which uses stage 4 as the temperature-sensitive stage. Three cases of partial heat integration are studied, and the first case, which uses an auxiliary condenser, is the most economic. The dynamic control strategies of the first and second cases handle ±10% feed disturbances well; however, the CSE can attain good controllability when ±20% feed disturbances are introdu...

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.

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.