Hybrid Distillation Pervaporation Research Articles

Optimal design and operation of reactive distillation systems and reactive dividing wall systems with pressure swing distillation and hybrid distillation-pervaporation

Process intensification is essential in exploring more energy-efficient processes, and key examples related to fluid separations are reactive distillation and hybrid distillation-pervaporation processes. This work will consider the reaction and separation of a general quaternary reactive system with a minimum boiling binary azeotrope AC, in a reactive distillation column where, given the thermodynamics limitations, further downstream separation is required. Low and high chemical equilibrium is considered for the reaction. For the downstream purification, both pressure swing distillation and a hybrid distillation-pervaporation process are considered. For each of the structures, their intensified equivalent dividing wall structures are also considered, including a hybrid reactive dividing wall system. It is shown that reactive distillation followed by a hybrid distillation-pervaporation system can save up to 24% energy compared to reactive distillation with pressure swing separation, and that the dividing wall column counterpart structures have lower production-based total annualised costs than the corresponding base systems.

Single- and multi-objective optimisation of hybrid distillation-pervaporation and dividing wall column structures

The separation of azeotropic mixtures is often energy intensive, thus process intensification (PI) becomes an attractive route to enhance energy efficiency. Two of the most commonly used separation intensifications are dividing wall columns and hybrid distillation-membrane processes. In this work, three typical hybrid distillation structures, distillation followed by pervaporation (D-P), pervaporation followed by distillation (P-D), and distillation followed by pervaporation then by distillation (D-P-D), are considered and compared with a hybrid dividing wall column (H-DWC) structure, which is a highly integrated process combining a dividing wall column and a pervaporation membrane network. The four structures are compared by both single-objective and multi-objective optimisation. It is shown that the D-P-D and H-DWC structures require significantly lower total annualized costs than the other two designs due to requiring smaller membrane area, as these two structures use the membrane only to help the mixture composition cross the azeotropic point.

Optimal design of hybrid distillation-membrane processes based on a superstructure approach

Considerable effort is currently being put towards process intensification to design more sustainable and energy-efficient processes. Hybrid distillation-membrane processes are prime examples of such intensified processes. In this work, different strategies are presented for how to handle the complexity of the membrane network of the hybrid process in terms of initialisation and convergence for simulation and optimisation. A superstructure approach for optimisation of membrane networks within hybrid processes is presented and verified. The energy consumption and economic performance of a hybrid distillation-pervaporation process, as well as that of the corresponding extractive distillation process, to separate a minimum-boiling azeotropic mixture are compared for different feed compositions. The impact of membrane properties and cost is also briefly considered. The results show that the total heat duty for the hybrid process is always lower than that of the extractive process for the system considered, confirming that the hybrid process is more energy efficient. In terms of total annualised cost, however, the hybrid process is found to be more economically attractive at lower feed compositions, while the extractive process is preferred for higher compositions.

Optimization of Hybrid Distillation-hydrophilic and Organophilic Pervaporation Systems

The hybrid distillation-pervaporation process is an efficient method for the removal or recovery of volatile organic compounds from their aqueous mixtures. The hybrid distillation-pervaporation process has not only shown its excellent performance in the purification of solvent mixtures but also proven to have a potential of saving energy. In this study, the hybrid distillation-pervaporation process is optimized for the treatment of low-alcohol waste solvents. Three combinations are examined: distillation with hydrophilic pervaporation, distillation with organophilic pervaporation and distillation with both pervaporation methods. The hybrid systems result in a better performance in term of energy-use compared to conventional distillation. It is observed that a combination of distillation and hydrophilic or/and organophilic pervaporation is suitable for the separation of ethanol-water mixtures and the most recommended is the third layout.Keywords: hybrid distillation-pervaporation process, pervaporation, ethanol-water separation, azeo

Application of energy-saving hybrid distillation-pervaporation process for recycling organics from wastewater based on thermoeconomic and environmental analysis

Acetonitrile and n-propanol play an indispensable role in the manufacture of perfume and photosensitive materials, and the demand for these chemicals in China is growing. In this work, a series of processes was explored for achieving sustainable and green separation of wastewater containing acetonitrile and n-propanol. The solvent with high separation performance was determined by the combination of relative volatility and biological toxicity. Based on the sequential iterative optimization sequence and taking the minimum total annual costs (TAC) as the objective function, the program written by Visual Basic software was used to optimize the parameters of the basic process. The steam recompression assisted distillation and pervaporation (PV) technology are combined to reduce the energy consumption. Through the Heat Exchanger Network Synthesis (HENs) option, the heat recovery in the process was further improved. Furthermore, exergy and environmental analyses were further used to assess the feasibility of several separation processes. The results showed that compared to the basic process, the TAC and exergy loss of vapor recompression assisted distillation process were reduced by 43.6% and 12.65%, respectively. The use of heat integration and PV technology further reduced energy consumption. The TAC and emissions of novel hybrid process were saved by 74.6% and 53.87%, respectively, which indicates the feasibility of the processes for continuously updated cleaner production.

Separation of isobutanol/water mixtures by hybrid distillation-pervaporation process: Modeling, simulation and economic comparison

Hybrid separation processes based on the membrane processes are becoming more important in practice to overcome the thermodynamic limitations of the conventional separation processes as well as to develop more sustainable and economic processes. This study focuses on the use of the hybrid distillation-pervaporation process for the separation of isobutanol/water mixtures. For engineering design of the hybrid processes, reliable modeling and simulation of the process is indispensable. For the simulation of different configurations of the hybrid processes with Aspen Plus software (Aspen Tech), a mathematical model was developed for the pervaporation process based on the solution-diffusion mechanism using the Flory-Huggins and UNIFAC thermodynamic models and Lee’s equation. The simulation was performed for the separation of isobutanol/water mixtures with various isobutanol feed concentrations (5, 7, and 15 %wt.). It was found that for both single-phase and two-phase feed solutions, the hybrid hydrophobic-hydrophilic pervaporation process was the most economical configuration to reach the desired product purity. For the hybrid hydrophobic-hydrophilic pervaporation process with feed concentrations of 5, 7 and 15 %wt., the total annual cost was 62.9 %, 58.7 %, and 58.4 %, respectively, lower than the distillation process. Furthermore, by increasing the feed concentration, the membrane area required for the pervaporation-based hybrid process enhanced.

Hybrid distillation-pervaporation in a single unit: Experimental proof of concept in a batch operation

In a Distillation-Pervaporation in a Single Unit (DPSU) system, the pervaporation unit is located inside a distillation column. Therefore, distillation and pervaporation mechanisms are carried out simultaneously in the same column section. Previously, it was theoretically demonstrated that a DPSU column is able to overcome azeotropic conditions by displacing the liquid composition due to the pervaporation. In this work, this behaviour is experimentally verified for a DPSU system in a batch operation for the separation of ethanol – isopropanol – water mixture, using a silica membrane selective to water. Several feed compositions and permeate pressures were evaluated to identify their effects on the DPSU separation performance. The distillation boundary was experimentally overcome by the DPSU system. The separation order of isopropanol and water was inverted in the DPSU system as compared to conventional distillation. Water became a saddle point for the entire composition space, allowing crossing the distillation boundary with a continuous composition profile of the residue liquid. This study experimentally proves the validity of the DPSU approach for azeotropic mixture separations.

Conceptual Design of Distillation-Pervaporation in Single Unit Columns Using Residue Curve Map Methodology

A short-cut design method based on Residue Curve Maps (RCMs) is applied to the conceptual design of Distillation-Pervaporation in a Single Unit (DPSU) columns. Unlike to a conventional hybrid distillation-pervaporation column, in a DPSU system the pervaporation module is located inside the column. The distillation and pervaporation mechanisms are fully coupled, allowing overcoming azeotropic conditions of non-ideal mixtures inside the distillation column. The simplified design method is applied to four non-ideal mixtures with different Serafimov’s topological classification: acetone-isopropanol-water (1.0-2), ethyl acetate-ethanol-methanol (2.0-2b), acetone-methyl acetate-methanol (3.1-2) and acetone-methanol-chloroform (3.1-4). The results show that it is possible to achieve a feasible separation through a DPSU column with product compositions split by distillation boundaries. Besides, the regions of a feasible separation with a DPSU column are identified. Thermodynamic limitations for a DPSU column are observed when the azeotropes generate isovolatility lines, producing different separation paths for a specified membrane selectivity. DPSU columns promise to strongly reduce the number of units and associated energy consumption in distillation trains for separating complex mixtures.

Tools for the Design of Hybrid Distillation–Pervaporation Columns in a Single Unit: Hybrid Rectifying–Pervaporation Section

Distillation–pervaporation in a single unit is a novel concept where the pervaporation membrane is located inside the distillation column as a packing bed. In this work, a simplified model, based on phase equilibrium and membrane selectivity, is derived for a DPSU column. The model provides the separation trajectories inside the column, where distillation and pervaporation mechanisms simultaneously occur. A Serafimov’s topological classification (1.0–2), specifically acetone–isopropanol–water, is evaluated. The results show that a feasible separation is achieved with product compositions separated by a distillation boundary. The stationary points are modified as compared to conventional distillation overcoming the distillation boundaries. General aspects of a DPSU column are identified to provide fundamentals in the DPSU column design.

Energy consumption in pervaporation, conventional and hybrid processes to separate toluene and i-octane

Chemical industries need to employ new process designs due to environmental policies and energy optimization because of the global energy challenge. Pervaporation has been introduced as a promising alternative for conventional processes such as distillation, known as energy intensive process, in chemical plants. In this work, the energy consumption of different processes for separation of toluene and i-octane (representatives of aromatics and aliphatic mixtures) has been evaluated, based on our previous laboratory pervaporation experiments using Polyvinyl alcohol/Graphene oxide mixed matrix membranes. Accordingly, hybrid distillation-pervaporation and cascade pervaporation systems have been compared with distillation and extractive distillation (conventional process). The results indicated that although the energy demand of hybrid system is much less than distillation, but it is not comparative with extractive distillation. However, when purification of aliphatics is required, cascade pervaporation system is more effective than extractive distillation and the energy demand for purification of i-octane is 56.1% lower in cascade pervaporation process. The results can assist engineers to design novel and low energy consumer process plants for removing aromatics from aliphatic mixtures.

Energy efficiency improvement of a bioethanol distillery, by replacing a rectifying column with a pervaporation unit

Abstract Separation methods for ethanol production are among the most energy consumption in chemical industry. The design of efficient process is part of challenges faced by process engineering. The aim of this work is to reduce the operating energy and cost of a Moroccan distillery process. The separation process of this distillery consists of a distillation, purification and rectifying column under vacuum. In this study, a hybrid distillation-pervaporation process was proposed by replacing the rectifying column, which requires more than half of the total energy of the process, with the pervaporation unit. The pervaporation unit was modeled and simulated using appropriate model. Afterwards, the design of the hybrid process has been performed coupling the obtained pervaporation model with a simulator of the separation columns. The performance of the hybrid distillation-pervaporation process has been evaluated by simulation. A reduction of about 64.5% can be obtained for the operating energy and cost compared to the industrial distillation process.

Investigation of Process Alternatives for the Separation of Ethanol, N-Butanol and Water Ternary Mixture

Biofuel production is an ever current topic, as bioethanol and biobutanol have a great potential to partially or completely replace fossil fuels in the automotive industry due to their attractive characteristics. They are usually produced by fermentation resulting in a highly diluted mixture, which poses a challenge to the downstream processing and the production of pure alcohols.In the course of this work, conventional separation systems of simple, extractive and heteroazeotropic distillation are compared with hybrid distillation-pervaporation systems for the separation of a ternary ethanol-n-butanol-water (EBW) mixture. Pervaporation (PV) is studied as an option for the final dehydration of the alcohol-water mixtures due to its great industrial potential in the separation of azeotropes. Simulations are carried out in ChemCAD® flowsheeting software, and the process alternatives are evaluated in an economic point of view, revealing the potentials and drawbacks of PV in a complex separation task.

Comparative study of conventional, reactive-distillation and pervaporation integrated hybrid process for ethyl tert-butyl ether production

Ethyl tert-butyl ether (ETBE) is widely used as an oxygenate additive to gasoline; however, a drawback in the conventional ETBE manufacture is the energy intensive product recovery process, making ETBE expensive. The purification process of ETBE involves the separation of ETBE, mixed C4 hydrocarbons and unreacted ethanol. The unreacted ethanol forms azeotropic mixtures with ETBE that are difficult to separate by distillation. In this work, a comparative study between the conventional process to produce ETBE and two alternative intensified processes is presented by means of process simulation in Aspen Plus. One of the alternative methods for improving the separation and purification section of ETBE is the use of a hybrid distillation-pervaporation process with alcohol-selective membranes, which allows to reach the target ETBE purity (95.2wt%) with a lower energy consumption and at the same time the permeate stream, with a high ethanol content, is recycled back to the reaction section. Alternatively, the production of ETBE by means of reactive distillation is analyzed for the same basis of calculation. The results show that the reactive distillation allows a significant increase in the conversion of the reactants, but in contrast the energy consumption is higher than in the other processes evaluated.

Process flowsheet analysis of pervaporation‐based hybrid processes in the production of ethyl tert‐butyl ether

AbstractBACKGROUNDThe manufacturing process of ethyl tert‐butyl ether (ETBE) involves the separation of ETBE, mixed C4 hydrocarbons and unreacted ethanol. Unfortunately, the unreacted ethanol forms azeotropic mixtures with ETBE that are difficult to separate by distillation. One of the alternative methods to overcome this limitation is the application of hybrid distillation–pervaporation processes with alcohol‐selective membranes.RESULTSSimulation tasks were carried out with the process simulation software Aspen Plus and the results of alternative process flowsheets that result from the relative location of the separation technologies (for a target product purity) have been compared on the basis of the required membrane area and energy consumption. Thus, in the case study analyzed seven pervaporation modules located on a sidestream withdrawal, with a total membrane area of 210 m2, are required to obtain 6420 kg h−1 of ETBE with a purity of 95.2 wt%. The retentate stream is returned to the column while the permeate stream, with a high ethanol content, is recycled back to feed the reactorsCONCLUSIONIncorporating pervaporation modules in the process flowsheet for production of ETBE allows unloading of the main separation unit (debutanizer column), thereby reducing energy consumption and operating costs and increasing throughput. © 2016 Society of Chemical Industry

A hybrid distillation–pervaporation system in a single unit for breaking distillation boundaries in multicomponent mixtures

This work presents a theoretical investigation of an integrated pervaporation and distillation column within a single column. The pervaporation section consists of hollow fibres, with the separation layer on the outer diameter. Vapour and liquid flow facing the separation layer while the permeate stream is removed from the inside lumen. Several advantages have been identified from the process integration. There is no need for inter-stage heating since the latent heat required for pervaporation is supplied by condensation of the vapour in the pervaporation section. Additionally, vapour induces turbulence in the liquid phase enhancing the mass and heat transfer between the liquid and the membrane surface. Also, the liquid phase within the column is close to saturated conditions, and thus its components are also close to their maximum driving force for pervaporation at the operation pressure. As a consequence, the membrane area is reduced compared to an externally connected pervaporation–distillation hybrid system (ECPDS). Due to a higher amount of liquid that is in contact with the membrane than in an ECPDS, the driving force of the transported component is improved, reducing the required membrane area. It is shown that the hybrid column is able to overcome the distillation boundaries for multicomponent mixtures and, therefore, perform separations that are not possible in a single distillation column.Two case studies of ternary mixtures are analysed. The hybrid system behaviour is studied as function of the membrane area, position of the pervaporation section and membrane wetting.

Hybrid membrane and conventional processes comparison for isoamyl acetate production

Four process alternatives for the production of isoamyl acetate, by the liquid phase esterification of acetic acid with isoamyl alcohol, were evaluated by simulation in terms of product purity, energy integration and economics. The analysis involves a transition from conventional (two structures that use acetic acid or alcohol in excess) to hybrid membrane process (two distillation–pervaporation hybrid systems). Acetate recovery is identified as a crucial factor to minimize energy costs in all considered processes. For conventional processes, the amount of energy required for separation, at low acetate recovery levels, is considerably lower if acetic acid is used in excess. For the hybrid processes, there is an optimum value of acetate recovery that minimizes the total required heat duty and membrane area. Hybrid distillation–pervaporation process allows obtaining the specified product purity with lower energy requirements and more economical tradeoffs than the considered conventional processes. The economic optimum design maximizes energy savings and minimizes total annualized costs. After optimization and energy integration, the best process alternative includes, in a hybrid system, one packed bed reactor, two pervaporation units and a distillation column.

Simulation and environmental evaluation of process design: Distillation vs. hybrid distillation–pervaporation for methanol/tetrahydrofuran separation

Separation processes are among the most energy-intensive stages in the chemical industry, and the evaluation and minimization of environmental impacts is part of the challenges faced by environmental engineering. Pressure swing distillation is a commonly used technique for separation of the mixture methanol/tetrahydrofuran (THF); the separation is not feasible with conventional distillation due to the presence of an azeotrope. In this work, the design of a hybrid process consisting of distillation and pervaporation is elaborated as an alternative for the separation and evaluated from a technical and an environmental point of view. Three different compositions of the feed stream are considered: 25, 50 and 75wt% methanol in THF and the simulation of pressure swing distillation and the hybrid process allows comparison of the energy requirements. In addition, the effect of the membrane performance on the purity of the products and the energy demand were studied. Life cycle assessment (LCA) was used to evaluate the environmental impact of both alternatives compared to incineration. From the LCA, it was observed that the hybrid process produces the lowest impact, indicating that solvent recovery is a key issue to minimize the environmental burdens. Thus, integration of membrane technology in a hybrid configuration should be considered in the design and development of more environmentally friendly processes.

REMOVED: Batch Recovery of Acetonitrile/Toluene Mixture by Hybrid Distillation-Pervaporation Process

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Synthesis, reproducibility, characterization, pervaporation and technical feasibility of preferentially b-oriented mordenite membranes for dehydration of acetic acid solution

This paper describes the development of mordenite membranes for industrial purpose to apply in dehydration processes of acetic acid (AAc) aqueous solution under high-temperature and high-pressure conditions. The membrane formation process is clarified as a function of synthesis time by investigation of the properties of permselective, crystalline state and surface morphology in the synthesized polycrystalline thin film. The crystallographic development from the random orientation to the preferred orientation of b-axis was observed in the synthesized membranes with increasing of crystallization times. The membrane performance in pervaporation was measured in a feed mixture of water (50 wt.%)/AAc (50 wt.%) to be 10.9 kg m −2 h −1 for permeate flux and to be 0.77 × 10 −6 mol m −2 s −1 Pa −1 for water permeance with separation factor ( α) of 500 at 130 °C. A technical feasibility study was undertaken for a hybrid pervaporation–distillation system to produce acetic acid with 1 wt.% of water content from a feed flow with water (55 wt.%)/AAc (45 wt.%) for 1000 kg h −1. It was a case in which dehydration from 55 wt.% to 40 wt.% water content was processed in a feed flow before distillation by pervaporation at 110 °C. Two values of (1) the energy saving ratio compared with a case of distillation alone and (2) the required membrane area were calculated to be 34% and 55 m 2, respectively, using the experimentally determined values of membrane performance. This size of the membrane module for the 55 m 2 membrane area could be a realistic scale for industrial utilizations. Therefore, the present fabrication method for mordenite membrane deserves to further technological developments of large-scale membranes and mass-production.

Numerical investigation of Membrane Dephlegmation: A hybrid pervaporation–distillation process for ethanol recovery

Ethanol is a renewable fuel that could help alleviate our dependence on fossil fuels to supply energy. Ethanol can be produced through the fermentation of sugars obtained from a variety of biomass. However, the energy intensive nature of the ethanol separation process limits the usefulness of ethanol as a biofuel. Membrane Dephlegmation is a hybrid pervaporation–distillation process that could help improve the efficiency of ethanol recovery. As opposed to most other hybrid pervaporation–distillation processes, Membrane Dephlegmation combines both processes in a single unit. In this investigation, a mathematical model of the Membrane Dephlegmation process was used to carry out a parametric study for important operating conditions and geometric variables. The impacts of feed flow rate, feed concentration, permeate pressure, reflux ratio, membrane length and membrane diameter on separation efficiency were studied. McCabe–Thiele plots were used to compare the performance of Membrane Dephlegmation to conventional distillation. Membrane Dephlegmation was shown to be more efficient than distillation, yielding ethanol concentrations above the ethanol–water azeotrope for similar operating conditions. It was also demonstrated that the inclusion of pervaporation in the hybrid process shifts the operating line below the parity line on the McCabe–Thiele plots, leading to improved separation performance relative to distillation.