Ternary Extractive Distillation Research Articles

Dynamic control investigation of an energy-saving double-thermally coupled ternary extractive distillation process

Currently, little literature has focused on the dynamic control of the economic and energy-saving double-thermally coupled ternary extraction distillation (DTCTED) systems, which demonstrates difficulties due to complex interactions between the main column and two rectifiers. The novel contribution of this paper is proposing effective and robust control structures to improve the dynamic controllability of the DTCTED process. To maintain the product purities more precisely, the key control loops employ composition-temperature cascade controls to regulate the side-vapor flowrates because the reliance on temperature control alone (CS1) is insufficient. Although this structure (CS2) can achieve the control of product purity, there could be severe oscillation in the control process. Therefore, one of the composition-temperature cascade controls is paired with the reflux ratio of the side rectifier to relax the operating freedom of the main column. The obtained structure (CS3) can brilliantly handle ±20 % throughput and various feed composition disturbances, which ensures the product purities and reduces oscillation. Additionally, control strategies based on the relative gain array (RGA) pairing criterion are explored and compared with the empirical ones. The proposed structures significantly enhance the controllability and stability of the DTCTED process, making it highly suitable for industrial applications.

Economic, environmental, exergy (3E) evaluations of recovering n-propyl acetate and n-propanol from wastewater via distillation coupled pervaporation

This work investigates an efficient and sustainable process for recovering n-propyl acetate and n-propanol from wastewater via extractive distillation coupled with pervaporation (PV). The selection of potential extractants is based on the equilibrium data between the system and the extractants in vapor-liquid phase. For the ternary extractive distillation process, we optimize it using the Non-Dominated Sorting Genetic Algorithm II with the objectives of minimizing the total annual cost and gas emissions. The PV model is integrated with the distillation process to enhance solvent recovery, while an energy-efficient scheme combined with heat integration technology and heat pump improves separation efficiency. Economic, environmental and exergy analyses are conducted to evaluate feasibility, revealing that coupling extractive distillation with PV enhances economic and environmental benefits compared to basic processes. The combination of heat pump assisted heat integration technology further improves the economy performance, environmental protection and thermodynamic efficiency, and the process selection needs to be balanced according to the actual industry.

Dynamic control analysis of eco-efficient double side-stream ternary extractive distillation process

The novel contribution of this paper is to implement the dynamic control investigation for the energy-saving double side-stream ternary extractive distillation configuration with constructing the practical and workable plumbing arrangement taking the representative example of separating a ternary benzene/isopropanol/water mixture. The new proposed control scheme achieves the stable regulatory control at rejecting the large disturbances of throughput and feed composition, wherein the particularly key control loops are controlling the product isopropanol composition by adjusting the extractant flow rate into extractive column C2 with simultaneously regulating the reflux ratio in extractive column C1 to abate the solvent dilution effect through composition cascade temperature control loops.

Energy-Saving Exploration of Mixed Solvent Extractive Distillation Combined with Thermal Coupling or Heat Pump Technology for the Separation of an Azeotrope Containing Low-Carbon Alcohol

Ternary extractive distillation (TED) is an effective and sustainable separation process for treating pharmaceutical wastewater containing ethyl acetate/isopropanol/water, corresponding to three bi...

Dynamic study in enhancing the controllability of an energy-efficient double side-stream ternary extractive distillation of acetonitrile/methanol/benzene with three azeotropes

The exploration of control strategy for the double side-stream ternary extractive distillation (denoted as DSTED) process is essential because it has a significant potential for energy-saving. However, how to effectively control the energy-efficient DSTED process is a unique and complex issue due to the additional coupled variables of double side-streams. Consequently, in this study, control schemes of the energy-efficient DSTED process for separating acetonitrile/methanol/benzene with multi-azeotrope are investigated. Firstly, a dual-temperature control strategy is proposed based on the existing single temperature control with feedforward scheme. Temperature difference control strategy is then studied to effectively reduce the offset of product purities for the disturbances of feed composition. Following that, a double-temperature difference control strategy is studied to maintain the product purities. Finally, the comparisons of product purities and energy consumption are introduced to clearly assess the stability and controllability of the different temperature control structures. Dynamic performances show that the temperature difference control structure has the best performance facing the ±10% feed disturbances.

Investigation of an energy-saving double-thermally coupled extractive distillation for separating ternary system benzene/toluene/cyclohexane

An intensified scheme for the separation of ternary azeotropic system is explored to reduce the energy consumption and recycle important organic solvents. Herein, a novel double-thermally coupled ternary extractive distillation (DTCTED) for separating azeotropic system benzene/toluene/cyclohexane (denoted as B/T/CH) is proposed to achieve energy-saving and emissions reduction. Thermodynamic feasible insights of the B/T/CH using dimethyl formamide as entrainer are firstly analyzed via residue curve maps to find separation constraints. Following that, the proposed intensified scheme is optimized via the in-house multi-objective genetic algorithm software while using total annual cost and CO2 emissions as objective functions. The results show that the total annual cost and CO2 emissions of the proposed intensified DTCTED scheme are significantly reduced by 18.60% and 20.22% compared with the existing single-thermally coupled ternary extractive distillation process. Furthermore, exergy loss and relative volatility are introduced to explore the essence of energy-saving in the proposed DTCTED scheme.

Energy-saving thermally coupled ternary extractive distillation process using ionic liquids as entrainer for separating ethyl acetate-ethanol-water ternary mixture

The major intrinsic obstacle of extractive distillation (ED) is high energy consumption. Thus it is significant to reduce the energy consumption of ED processes as low as possible. In this work, using green solvent ILs which have high selectivity, process intensification and optimizing operation parameters are adopted in the ED of ethyl acetate-ethanol-water mixture. For high-selective entrainers, ionic liquid (IL) 1-butyl-3-methylimidazolium acetate ([bmim][OAc]) is used as the solvent for the ED process of ethyl acetate-ethanol-water, and the physical properties of [bmim][OAc] are accurately defined in Aspen Plus by correlating the experimental data. To optimize the distillation sequence for process intensification, thermally coupled ternary extractive distillation (TCTED) process is adopted for the separation of the ternary mixture. Moreover, multi-objective generic algorithm with total annual cost (TAC), CO2 emissions (ECO2) and thermodynamic efficiency (η) as objective functions is used to optimize the operation parameters in order to evaluate the economy, the energy efficiency and environmental impact of alternative ternary extractive distillation processes. The result shows that the TCTED process can result in the reduction of both TAC and ECO2. So, this study can provide a reference for the separation of ethyl acetate-ethanol-water mixture in industry.

Dynamic controllability investigation of an energy-saving double side-stream ternary extractive distillation process

The investigation of dynamic controllability for the double side-streams ternary extractive distillation (DSTED) is necessary due to its advantages in energy-efficient. However, the control strategy of the energy-saving DSTED scheme is unique and complex issues owing to the wobbly of side-stream flow rate. Herein, control strategy of the energy-saving DSTED scheme is explored for separating ternary azeotropic mixtures acetonitrile/methanol/benzene. Inspiring from the control strategy of the ordinary triple-column extractive distillation scheme, the fundamental control structure CS1 is firstly designed. The control scheme CS2 with feed/side-stream (F/SS) ratio and control structure CS3 with feedforward and F/SS are then investigated to achieve higher efficiency of process control. Finally, a robust control strategy CS4 with the ratio of reboiler duty and feed flow rate and without F/SS ratio is proposed to well maintain the product purities. Moreover, additional ±15% feed flow rate and composition disturbances are added in the CS4 to assess the stability and controllability of the energy-saving DSTED. Dynamic performances illustrate that the structure CS4 can handle as well as that of confronted ±10% disturbances when the large disturbances are occurred in the real chemical process.

Control comparison of conventional and thermally coupled ternary extractive distillation processes with recycle splitting using a mixed entrainer as separating agent

This paper explores the dynamic control of thermally coupled ternary extractive distillation process containing two extractive columns with recycle splitting of mixed separating agent by taking the separation of tetrahydrofuran/ethanol/water as a demonstrating example. A series of control structures are devised and assessed by the large (20%) perturbations of throughput and feed composition, and the robust regulatory control is achieved since the purities of all three products are closely going back to their initial steady-state design specifications when facing the large (20%) feed flowrate and composition disturbances. Besides, the dynamic response performance for control strategy with product ethanol purity controlled by manipulating the reflux ratio is superior to that with manipulating solvent flowrate in terms of peak dynamic transients, settling time and steady-state offsets when facing the large (20%) throughput and feed composition disturbances for extractive rectifier column C2. The direct dynamic response performance comparisons for conventional and thermally coupled processes with mixed entrainer are also investigated and showed that there is no conflict (tradeoff) between the steady-state economics and dynamic controllability for this system.

Design optimization and operating pressure effects in the separation of acetonitrile/methanol/water mixture by ternary extractive distillation

Ternary extractive distillation is a green and sustainable separation process for the treatment of pharmaceutical wastewater containing methanol/acetonitrile and acetonitrile/water azeotropes that achieves the recovery of the acetonitrile and methanol solvents. A novel sequential iterative optimization methodology is proposed and the isovolatility curves of systems at different pressures are analyzed in this work to investigate the effect of the operating pressure on the ternary extractive distillation process. Four optimization procedures with different conditions of pressure and limits for the use of cold utilities were carried out. The optimization results showed that the optimal pressures of the first column and the third column are related to the top vapor that can be condensed by chiller water and cooling water, respectively, and the pressure of the second column is related to the effect of preheating on the third column. The ternary extractive distillation process with optimal operating pressure shows 60.1% energy cost savings and 47.0% total annual cost savings compared with the optimal process operating at atmospheric pressure. The proposed optimization method has the advantages of automatic optimization with a smaller number of simulator runs, providing a new solution for the simulator-based process optimization. The investigation of the operating pressure effect provides additional insight for the design and optimization of ternary extractive distillation.

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 a Ternary Extractive Distillation Process with Recycle Splitting Using a Mixed Entrainer

Dynamic control of the ternary extractive distillation process is complex, due to the relatively high number of operating parameters and interactions between multiple azeotropes. In this research, the control structures of the ternary extractive distillation using dimethyl sulfoxide and a mixed solvent of dimethyl sulfoxide and ethylene glycol, as the entrainer, were explored for separating tetrahydrofuran/ethanol/water. A composition with a ratio of reboiler duty to mole feed flow rate control structure was proposed to obtain good dynamic responses for the ternary extractive distillation process with dimethyl sulfoxide and mixed entrainer. Moreover, control comparisons of the ternary extractive distillation with dimethyl sulfoxide and mixed entrainer demonstrated that the dynamic performances of the extractive distillation with mixed entrainer were better compared with the process using dimethyl sulfoxide. These studies contribute to the development of controllability for ternary extractive distillation ...

Optimization of the composition of mixed entrainer for economic extractive distillation process in view of the separation of tetrahydrofuran/ethanol/water ternary azeotrope

AbstractBACKGROUNDThere are three binary azeotropes in the tetrahydrofuran/ethanol/water ternary system at atmospheric pressure. Ternary extractive distillation (ED) processes were studied to separate the ternary azeotropic mixture using two single component solvents and a mixed solvent as entrainer.RESULTBased on the sequential iterative optimization procedure, the minimal total annual costs (TACs) of the ternary extractive distillation process using ethylene glycol (EG), dimethyl sulfoxide (DMSO), and the mixture of DMSO and EG as entrainer were obtained. Compared with two single component entrainers DMSO and EG, the TAC of the extractive distillation process with mixed entrainer (60 mol% DMSO + 40 mol% EG) decreases by 6.55% and 31.88%, respectively. Furthermore, the reboiler heat duties of two extractive distillation columns (EDCs) with mixed entrainer were compared with two single component entrainers.CONCLUSIONThe results show that the optimal ED process using mixed entrainer performs better than that using single component entrainers from the perspective of economics. Moreover, there is a tradeoff between the reboiler heat duties of two EDCs, which can be adjusted by changing the entrainer performance in two EDCs. The use of mixed entrainer enhances the flexibility of the tradeoff because it only needs to change the composition of the mixed entrainer. © 2017 Society of Chemical Industry

Control comparison of conventional and thermally coupled ternary extractive distillation processes

Extractive distillation is widely used to separate binary mixtures with azeotropes that prevent separation in a single distillation column. The conventional binary extractive distillation configuration uses two columns with one key component going overhead in the extractive column and the other key component going either overhead or out the bottom of the solvent recovery column, depending on the effect of the solvent on the volatilities of the key components.Extractive distillation can also be applied to separate ternary mixtures with azeotropes. The conventional ternary extractive process requires three columns. Unconventional processes can also be used, such as thermally coupled sidestream/rectifier columns. Economic advantages of the thermally coupled process have been reported for some separations.The controllability of extractive distillation system for binary mixtures has been explored in many papers. The novel contribution of this paper is the exploration of the dynamic controllability of extractive distillation systems for a ternary mixture. The dynamics of a conventional three-column process are compared with a thermally coupled column/rectifier process.