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Extractive distillation is widely accepted and commercialized for separating azeotrope mixtures, but using traditional organic solvents leads to intrinsic obstacles such as the high energy requirement and solvent-related environmental problems. Benefiting from the development of green solvents, using ionic liquids instead of traditional solvents as entrainers for extractive distillation has attracted wide attention. This paper presents a multi-objective optimization strategy to integrate the design and control of the ionic liquid-based extractive distillation processes. In the optimization processes, the condition number (CN) and total annual cost (TAC) are minimized as the objective functions to evaluate the control properties and design of three different separation systems. The optimization results are shown by the Pareto front, which is based on trade-offs between controllability and economics. The environmental impact is evaluated by the environmental impact potential of energy for each system in a posterior stage during the optimization processes. Designs with minimum TAC (PT), trade-off designs between TAC and CN (PO) and designs with minimum CN (PC) on Pareto front are optimized and compared. The results show that the increase of reflux ratio can improve the control properties for the ionic liquid-based extractive distillation processes. Furthermore, the dynamic simulation of PT and PO are carried out to compare their dynamic responses based on the same dynamic control structure, and PO shows better performance in the aspects which include maximum deviation and residual error of dynamic response.

As a process intensification technology, semicontinuous distillation uses less equipment to achieve the separation of multiple components. However, there is still a lack of systematic guidance for the design of semicontinuous distillation. In this paper, we propose a new method to guide the design of semicontinuous distillation via multi-objective optimization (MOO) and control. Conventional continuous distillation, dividing wall column (DWC) distillation and semicontinuous distillation for separation of n-alkanes are optimized through multi-objective genetic algorithm (MOGA). Several different control schemes are proposed for semicontinuous distillation, and the temperature-concentration cascade control scheme CS5 is selected as the optimal control scheme. The economic benefits of semicontinuous distillation based on dynamic simulation are evaluated by the comparison with the conventional continuous distillation and DWC under a series of throughput. It is found that the total annual cost (TAC) of the semicontinuous distillation is smaller than that of conventional continuous distillation when the annual throughput is less than 7.73 × 104 kmol/yr. And the TAC of the semicontinuous distillation is less than that of DWC when the annual throughput is less than 5.29 × 104 kmol/yr. Therefore, we can conclude that the semicontinuous distillation has better economic benefits than the other two configurations within the smaller annual throughput.

For the treatment of toluene exhaust gas, absorption is widely applied because of its advantages of mature technology and high efficiency, and research for the development and performance of absorb...

Dynamic process intensification technology is an emerging technology of process intensification. It adopts a nonsteady-state operation mode, which can improve the time-averaged performance of the r...

Methanol and methylal form a minimum boiling point azeotrope and cannot be separated by conventional distillation. In this paper, the azeotrope was separated by extractive distillation with cyclohe...

Ethyl propionate is usually produced from esterification of propionic acid and ethanol in the industry. However, the purification of ethyl propionate remains a challenge because the unreacted ethan...

Considering the separation of 1-butanol and water, extraction has received increasing attention because of the advantages of easy operation and low energy consumption. In this work, deep eutectic s...

The application of ionic liquids in separating complex ternary azeotropic system via extractive distillation (ED) is investigated. Five configurations using 1-butyl-3-methylimidazolium dicyanamide ...

Deep eutectic solvents (DESs) as novel entrainers can be used for the separation of azeotropic mixture, and have received much attention in recent years. However, the researches about DESs mainly focus on vapor–liquid equilibrium (VLE) and extractive distillation experiment. In this work, an overall extractive distillation process for ethanol dehydration using ChCl/Urea (1:2) as entrainer is investigated. The physical properties of the DES are defined by correlating the experimental data. Three thermodynamic methods are employed to describe the phase behavior of ethanol–water–ChCl/Urea (1:2) system. COSMO-based theory is adopted to explain the differences in separation performance among ChCl/Urea (1:2), glycerol and [EMIM][BF4]. The design parameters of extractive distillation process are optimized by multi-objective generic algorithm (MOGA) with minimum total annual cost (TAC), minimum CO2 emissions E C O 2 and maximum efficiency indicator of extractive section (EExt) as objective functions. In addition, the control structure of extractive process is studied by Aspen Dynamics, and the proposed control structure could resist fresh feed flow rate and composition disturbances. The results show that ChCl/Urea (1:2) exhibits better separation performance in ethanol dehydration compared with glycerol and [EMIM][BF4]. Both COSMOSAC model relying on molecular information and NRTL model based on experimental data can well describe the vapor–liquid behavior containing ChCl/Urea (1:2). Entrainer purity plays an important role in extractive distillation process, and a proper concentration rather than nearly pure entrainer should arouse our attention in extractive distillation process. DESs as promising novel entrainers can be used in extractive distillation industrial for separating azeotrope.

Reactive dividing wall column (RDWC) is a highly integrated configuration where reaction and separation take place in a single equipment simultaneously. In this study, three self-heat recuperative ...

Reactive dividing wall column (RDWC) is the integration of reactive distillation and dividing wall column, which simultaneously has the advantages of both process intensification techniques. Howeve...

In this paper, a steady state model and three control structures of different pressure thermally coupled reactive distillation process for isoamyl acetate synthesis are proposed. The process is firstly designed in Aspen Plus to build a steady state model, economic analysis is then adopted to optimize process parameters. The optimized process shows 39.65% saving on operating cost and 1.25–19.05% saving on TAC with the payback period varies from 5 to 10 years. Three control structures including one basic structure (BC) and two improved structures (IC1, IC2) are proposed. IC1 uses a composition/feed ratio controller to decrease residual errors, and a feed composition ratio controller is added in IC2 to achieve better control behaviors. ±10% feed flowrate/feed water composition disturbances are added to the control structures and the control behaviors are studied. The selections of control structures are based on the control behaviors. IC2 with better control behaviors under feed composition disturbance is recommend for the process.

In this work, three deep eutectic solvents (DESs), which are sulfolane + tetrabutylammonium bromide 3:1 (molar ratio, ST3:1), sulfolane + tetrabutylammonium bromide 7:1 (molar ratio, ST7:1), and ethylene glycol + trimethylamine hydrochloride 5:1 (molar ratio, ET5:1), were prepared and used as extractants for the separation of benzene and cyclohexane mixture by liquid–liquid extraction. Liquid–liquid equilibrium (LLE) data for the three ternary systems of benzene + cyclohexane + DESs were measured at 303.15 and 323.15 K under atmospheric pressure. The Othmer–Tobias equation was used to validate the consistency of the experimental tie-lines data and the regression coefficients R2 were all close to 1. Meanwhile, distribution coefficient (β), selectivity (S), and performance index (PI) were used to evaluate the performance of the three DESs, and the result indicates that the DESs ST3:1 and ST7:1 as extractants are more feasible for the separation of benzene and cyclohexane mixture compared to ET5:1. In additi...

In this paper, the mixture of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate was separated by middle-vessel batch distillation with feeding in middle-vessel and process control characteristics were researched. The steady state simulation results in Aspen Plus were exported to Aspen Dynamics. Then control effect of liquid level control with HighSelector, composition control (structure1, structure2) and temperature control (proportional action, proportional integration action) were proposed. Composition control structure 2 and temperature control with PI action were investigated to achieve a good control effect.

The dividing wall column (DWC) is considered as a major breakthrough in distillation technology and has good prospect of industrialization. Model predictive control (MPC) is an advanced control strategy that has acquired extensive applications in various industries. In this study, MPC is applied to the process for separating ethanol, n-propanol, and n-butanol ternary mixture in a fully thermally coupled DWC. Both composition control and temperature inferential control are considered. The multiobjective genetic algorithm function “gamultiobj” in Matlab is used for the weight tuning of MPC. Comparisons are made between the control performances of MPC and PI strategies. Simulation results show that although both MPC and PI schemes can stabilize the DWC in case of feed disturbances, MPC generally behaves better than the PI strategy for both composition control and temperature inferential control, resulting in a more stable and superior performance with lower values of integral of squared error (ISE).

Data for two systems of isobaric vapor–liquid equilibrium (VLE), n-heptane + sec-butyl acetate (SBAC) and methylcyclohexane + SBAC, were determined under atmosphere with an Ellis vapor–liquid equilibrium still. The Herington method and Wisniak test were employed to determine the thermodynamic consistency of the two systems. The experimental results of n-heptane + SBAC and methylcyclohexane + SBAC were correlated by three activity coefficient models, which are the nonrandom two-liquid, universal quasichemical, and Wilson, and the correlation results fit well with experimental data. The binary interaction parameters of these models were obtained, and the results showed that these models can give good predictions. The VLE data provide theoretical basis and data support for the further study on separation of n-heptane + SBAC and methylcyclohexane + SBAC.

In this work, the separation of ethanol-water azeotrope which was choosing low transition temperature mixtures (LTTMs) as entrainers was investigated through process simulation and batch extractive distillation experiment. Based on the vapor-liquid equilibrium (VLE) curves of ethanol-water with LTTMs and the residual curves of LTTMs-ethanol-water, glycolic acid–choline chloride 3:1(GC3:1) was selected as the entrainer to simulate ethanol-water mixtures separation, and the sensitive analysis was performed in order to determine the main design variables. On this basis, the traditional process was further improved through the optimization of heat exchanger network, and the energy consumption was reduced by 46.24% and 37.00% compared with the ethylene glycol and 1-Ethyl3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), respectively. In addition, GC3:1 was synthesized and used as solvent to separate the mixture of ethanol-water in the batch extractive distillation, which can obtain high-purity ethanol at the top of distillation column. Fourier Transform Infrared Spectrum (FT-IR) was used to analyze the recycled GC3:1, and it suggested that the chemical properties of GC3:1 were stable and GC3:1 could be reused depending on the infrared spectrum of used GC3:1. The advantage of GC3:1 as entrainer for the separation of ethanol-water azeotrope was proved through the combination of process simulation and experiment.

A novel heat pump-assisted azeotropic dividing wall column (HP-ADWC) has been proposed for the separation of a maximum-boiling ethylenediamine (EDA)/water system in this paper. Compared with conventional azeotropic distillation (CAD), HP-ADWC allows 42.93% energy savings and 24.36% total annual cost (TAC) savings if the payback period is assumed to be 8 years. To achieve the energy and economic benefits, this novel design must be controllable. However, it is challenging to control this complex and highly integrated HP-ADWC process since there are more interactive variables and fewer degrees of freedom than classic DWC process. In this paper, the dynamic controllability of HP-ADWC is studied by Aspen Dynamics and an effective control structure named CS4 is proposed, which works pretty well for the disturbances in both feed rate and feed composition.

Reactive distillation presents a distinct advantage for the combination of reaction and separation. However, when reactants are the lightest and the heaviest components and products are the intermediate ones, the configuration should be well designed to maintain the merits of the reactive distillation. In this work, two new processes, whose reactive distillation column with one side stream (RDC-S1) and with two side streams (RDC-S2) are proposed for dimethyl adipate production by the esterification of adipic acid with methanol. The two new processes are simulated using Aspen Plus and analyzed with minimum total annual cost (TAC) as the objective function. Then the carbon dioxide emissions of the proposed processes are calculated. The RDC-S1 and RDC-S2 processes are compared with the conventional reactive distillation process and the reactive distillation column with a top-bottom external recycle process. The results show that RDC-S2 process requires the lowest energy and has the smallest carbon dioxide emissions when compared with other processes. Thus considering the remarkable economic and environmental benefits, RDC-S2 is an attractive configuration for the production of dimethyl adipate.

Liquid–liquid equilibria (LLE) data for the water + cyclohexanone + solvents (toluene or p-xylene) ternary systems were reported at 303.15 and 323.15 K under 101.3 kPa. The distribution coefficient (D) and separation factors (S) were calculated to evaluate the separating efficiency of the selected solvents. Besides, both the Hand and the Bachman correlation equations were used to ascertain the reliability and consistency of the obtained LLE data. The nonrandom two-liquid (NRTL) and the universal quasi-chemical activity coefficient (UNIQUAC) models were both applied to correlate the experimental results for the studied ternary systems with the RMSD% values of these two models as low as 0.16. Also, the binary interaction parameters were obtained for these two correlation models.

The heat integrated reactive distillation is beneficial on energy saving and economy compared with conventional reactive distillation. However, the dynamic controllability is unfavorable due to the complexities of system. In this paper, five different control structures for the isopropyl acetate synthesis are presented as considering both product purities and safety. The integral of absolute error (IAE) and process stream index (PSI) are used to quantify the dynamic performances. The result shows that four enhanced control schemes can achieve better dynamic performances compared with the basic control structure. Based on the four improved control structures, the control structure with temperature difference controller shows the best performance, as involving the overshoot, recovery time, IAE, and PSI, since it improves the tuning stability and adjusts the temperature difference of exchange heat process between the high-pressure column and the low-pressure column.

In order to make full use of the sensible heat of the heavy entrainer adopted in the extractive distillation, an industrial separation case that focuses on the separation of benzene/cyclohexane mixture using sulfolane as entrainer is studied in this work. Furthermore, several retrofitted processes are proposed using the basic case. A side reboiler that utilizes the self-heat or external heat as the heat source is introduced in the separation system to reduce the energy requirement. The economic feasibilities of these sequences are estimated by calculating the total annual cost. Moreover, the thermodynamic analysis and carbon dioxide emissions indexes are also considered to evaluate the energy efficiency and environmental impacts of the modified designs. The simulation results show that the extractive distillation with heat integration 2 (EDHI2) design, which utilizes the entrainer stream to heat the side reboiler and the bottom reboiler, is the most energy-conserving sequence. In addition, the EDHI2 seque...

To screen suitable low transition temperature mixtures (LTTMs) as solvents for the extraction process of a benzene and cyclohexane mixture, the extraction performance of the LTTMs (25 hydrogen-bond donors (HBDs) and 13 hydrogen-bond acceptors (HBAs)) was assessed based on COSMO-SAC predictions of infinite dilution activity coefficients of benzene and cyclohexane in different LTTMs. The effects of the molar ratio of HBD to HBA on extraction efficiency were also observed in the meantime. It is found that the LTTM sulfolane-tetrabutylammonium bromide 5:1 (ST 5:1), which has excellent extraction performance, is the most promising solvent. To explain the difference of extraction efficiency of various LTTMs, σ-profiles were adopted to study the molecular interactions between LTTMs and benzene or cyclohexane. The analysis for geometry, interaction energy, independent gradient model (IGM) and atoms in molecules (AIM) was performed to explain interaction mechanisms between benzene/cyclohexane and HBD/HBA. Moreover...

Thermally coupled distillation is designed to reduce energy requirements and achieve environmental benefits in chemical engineering development processes. In this study an attractive different pressure thermally coupled reactive distillation (DPTCRD) process was proposed for the hydrolysis of methyl acetate, and the DPTCRD process was optimized to evaluate its economic feasibility. The calculation results clearly demonstrated that the total annual cost of this thermally coupled sequence can be saved by 7.49% and its exergy consumption is reduced by 40.07% compared with conventional reactive distillation. In addition, the controllability of this promising sequence was evaluated, and the dynamic results showed that the system with improved control structure can maintain stable operation and handle large feed upsets effectively.

Recent advances in dividing wall column (DWC) have led to renewed interest in the design or redesign of many industrial processes. For the distillation system of cumene production, the existing design alternatives have the potentials of energy savings and consequently the reduction of total annual cost (TAC) and energy consumption. In this paper, cumene production based on the real industrial process is simulated in a conventional process using commercial process simulator Aspen Plus, and two DWC distillation processes are introduced. Then optimization study for the proposed DWC distillation processes is performed based on the TAC calculation with sensitivity analysis to investigate the effects of operating parameters. The results indicate that the optimum DWC distillation process works well for the production of cumene, and the corresponding TAC is reduced significantly accompanied by substantial energy savings.

Process intensification is aimed at reducing energy consumption and capital investment, as well as achieving environmental benefits by integrating different processes. Heat pump and dividing wall column distillations are two representative examples of such design technology. In this study, the performance of heat pump assisted dividing wall column, a recent technology combining both heat pump and dividing wall column, is investigated for a reactive distillation system and a heterogeneous azeotropic distillation system. Vapor from top of the dividing wall column is recompressed and used to drive the side reboiler. Economic and thermodynamic efficiencies and the carbon dioxide emissions of the novel processes and the dividing wall column processes have been estimated. The results indicate that applying the heat pump technology to the dividing wall columns can achieve operating cost savings and also increase the installed capital cost, which means that companies who can afford higher investment should consider the heat pump assisted dividing wall columns for better return in the long run. Besides, heat pump assisted dividing wall columns are beneficial for cases where clean and highly effective electricity generation technologies are adopted.

Supported Pt nanoparticle catalysts were prepared by combing a chemical reduction method with an ultrasonic sonication loading method. Several techniques including transmission electron microscopy (TEM), nitrogen sorption technique and pyridine adsorption Fourier-transform infrared (Py-IR) were applied to characterize the physicochemical properties of these catalysts. The catalytic performance of catalysts was evaluated in the dehydrogenation of propane. The influence of the preparation method of Pt nanoparticles, the ratio of Polyvinyl Pyrrolidone (PVP) to Pt, loading method and different supports on the catalytic performance was investigated. PVP is useful for controlling the size of Pt nanoparticles and a PVP/Pt ratio of 15 is favorable to achieve a good catalytic performance. NaBH4 reduction is better than ethanol refluxing in preparing Pt nanoparticles. The ultrasonic sonication is effective to load the Pt nanoparticles onto the support channels. The mesoporous alumina proved to be a good catalyst support due to its high surface area and unique pore structure.

This paper considers the design and control of the separation of benzene and cyclohexane process via extractive distillation in a dividing wall column. To aid the separation, furfural is used as the heavy boiling entrainer. The optimal flow sheet with minimum energy requirements has been established using the multiobjective genetic algorithm with constrains. Three control strategies are proposed: the basic control strategy uses four composition controllers, and two improved control strategies with and without vapor split ratio use temperature controllers that are more practical in application than the basic control strategy. The dynamic simulations reveal that the three control strategies can object to the feed disturbances well. The dynamic responses of two improved control structures show that vapor split ratio as a manipulated variable can maintain the product purities at their set points when a feed disturbance is introduced.

The minimum vapor flow method and Vmin diagram are applied to the design of a reactive dividing wall column (RDWC) in this work. A shortcut design method for the conventional dividing wall columns based on the Underwood equations has been extended by introducing a new parameter that eliminates the effects of the reaction to allow conceptual design of the RDWC. Taking the syntheses of methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and dimethyl ether (DME) as design cases, the results show that the minimum vapor flow method and the Vmin diagram can be well applied to the conceptual design of a RDWC in different reaction systems.