Separation Of Azeotropic Mixtures Research Articles

Molecular mechanism of efficient separation of isopropyl alcohol and isooctane by extractive distillation

In this paper, a method of extracting isopropyl alcohol and isooctane system from industrial wastewater of fuel oil by extractive distillation is proposed to realize resource utilization of waste and reduce environmental pollution. Isooctane and isopropyl alcohol are both products obtained from petroleum refining, which are widely used in many fields. In this study, the quantum chemical was used to determine that glycerol (Gl) and N, N-dimethylacetamide (DMAC) were the best extractants to separate Isopropanol and isopropyl alcohol. The intermolecular electrostatic interaction and reaction site between the extractant and the system were determined by electrostatic potential (ESP) analysis. Inter-complex compounds and weak interactions were analyzed by interaction region indicator (IRI). The independent gradient model based on Hirschfeld partition (IGMH) was used to visualize the electron density of the molecule. Meanwhile, the simulation process of azeotropic mixture separation of IPA and ISO by extractive distillation was established, and the process was optimized by a sequential iterative method. The economic and environmental were used to evaluate and analyze the process, and the azeotropic mixture separation was realized. Compared with Gl, the extractive distillation separation of isopropyl alcohol and isooctane by DMAC reduces the total annual cost by 5 %, energy consumption, and reduces the greenhouse gas emissions by 1 %, and has greater environmental protection and economic benefits. This work is guided by quantum chemical calculation and reveals the interaction mechanism of solvent separation azeotropic mixture from the microscopic level, which provides an important reference value for realizing high efficiency, energy saving, and green separation of azeotropic mixture in industry.

Principle and Feasibility Study of Proposed Hydrate-Based Cyclopentane Purification Technology

The separation of azeotropic mixtures has conventionally been one of the most challenging tasks in industrial processes due to the fact that components in the mixture will undergo gas–liquid phase transition at the same time. We proposed a method for separating azeotropes using hydrate formation as a solid–liquid phase transition. The feasibility of hydrate-based separation is determined by analyzing the crystal structure and chemical bonds of hydrate. Taking the azeotrope cyclopentane and neohexane in petroleum as an example, cyclopentane (95%) was purified to 98.56% yield using the proposed hydrate-based cyclopentane purification technology. However, this is difficult to achieve using conventional distillation methods. The proposed method is simple in operation and yields a good separation effect. This study provides a new method for separating cyclopentane and neohexane.

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.

Separation of Azeotropic Mixtures of Ethyl Acetate + Methylcyclohexane: Vapor–Liquid Equilibrium Measurements

It is a challenge to separate ethyl acetate from methylcyclohexane because of the azeotropic phenomenon. To provide a basis for the design of the separation process, the isobaric vapor–liquid equilibria for an ethyl acetate + methylcyclohexane binary system were measured at 101.3 and 20.0 kPa using a modified Othmer-type still. The results show that ethyl acetate and methylcyclohexane form a miscible azeotropic mixture with minimum boiling temperature (349.99 K at 101.3 kPa), of which the composition varies slightly with decreasing pressure (≤101.3 kPa). It implies that ethyl acetate cannot be separated from methylcyclohexane by pressure-swing distillation. The azeotropy of ethyl acetate and methylcyclohexane disappears in the presence of decane (∼0.5 mole fraction), which means that ethyl acetate can be separated from methylcyclohexane by extractive distillation with decane as an entrainer.

Separation of n-hexane-ethanol azeotropic mixture using choline chloride +1,4-butanediol deep eutectic solvents

For an environmentally friendly and economical separation process of ethanol from n-hexane which is hard to handle due to the azeotrope, the liquid-liquid extraction was carried out by using choline chloride (ChCl) based deep eutectic solvents (DESs) in different molar ratios with 1,4-butanediol: DES1 (ChCl:1,4-butanediol=1:3), DES2 (ChCl:1,4-butanediol=1:4), and DES3 (ChCl:1,4-butanediol=1:5). The liquid-liquid phase equilibrium was performed on the n-Hexane (1) + Ethanol (2) + DES (3) systems at 298.15 K and atmospheric pressure. The binodal curve is determined by using the turbidity method. The various physico-chemical properties such as refractive index, viscosity, and density were measured for compositions in the binodal point. The equilibrium compositions of liquid-liquid phase equilibrium were determined from the refractive index value at the binodal points, and were predicted by COSMO-SAC model. The miscibility area predicted by COSMO-SAC model became larger as the molar ratio of 1,4-butanediol in DES increased, that is, DES3 shows the most miscible area. While in the experimental results, the miscibility depending on DES-type does not show a large difference. The experimental values for PI shows the order of DES2 (ChCl:1,4-butanediol=1:4)> DES1 (ChCl:1,4-butanediol=1:3)> DES3 (ChCl:1,4-butanediol=1:5) at less 3 wt% concentration of ethanol, but at higher concentration range (>3 wt%) DES3 shows the best value. Both of DES2 and DES3 are profitable to adopt in the extraction process of ethanol from n-hexane owing to the high performance index, high distribution coefficient, and high selectivity. The experimental results show the possibility of DESs as an alternative to ionic liquids in the separation of azeotropic mixtures, taking into account the properties of DES such as low price, uncomplicated manufacturing methods, environmentally friendly, and low toxicity.

Thermodynamic efficiency of membrane‐assisted distillation processes

AbstractMembrane processes are considered as comparably mild separation processes offering the potential for significant energy savings compared with azeotropic distillation processes. Despite higher investment and material costs, they are of particular interest for improving the energy efficiency in the chemical industry. However, energy savings of more than 20%–30% are rarely reported and even a general superiority can be disputed. To further elucidate this controversial, the current study pursues a quantitative assessment of the thermodynamic efficiency of pervaporation and vapor permeation processes with stand‐alone distillation and hybrid membrane‐assisted distillation processes for the separation of azeotropic mixtures. The results confirm the case‐dependent potential of distillation processes to outperform membrane‐assisted separations in terms of energy efficiency, considering proper heat integration. Although energy efficiency is becoming significantly important, it should be considered in the context of economic performance to determine an optimal trade‐off and to select the best process alternative during conceptual process design.

Highly efficient chitosan-based bio-polymeric membranes embedded with green solvent encapsulated MIL-53(Fe) for methanol/MTBE separation by pervaporation

An emerging family of solvents known as deep eutectic solvents has been heralded as a sustainable alternative to traditional solvents. Due to the low compatibility with polymeric materials, the direct use of a deep eutectic solvent (DES) as a solvent is still in the challenging phase. Therefore, we have developed a novel strategy to add DES into the polymer matrix. We have encapsulated MIL-53(Fe) using the choline chloride and ethylene glycol DES mixture and incorporated it into the chitosan polymer matrix. This study prepares chitosan-based biodegradable and sustainable membranes by adding different nanofillers such as DES, MIL-53(Fe), and DES@MIL-53(Fe) for methanol/MTBE azeotropic mixture separation. The prepared nanofillers and bio-degradable membranes are characterized using various analytical techniques such as FESEM, HRTEM, AFM, FTIR, XRD, TGA, XPS, mechanical strength, and wettability. The best separation results are found for the DES@MIL-53(Fe)/CS membranes because the membrane exhibit the characteristic of both components together. The highest total flux and methanol selectivity are observed for the F4 membrane, which is 2329 g m−2 h−1 and 207.06. Based on the surface characteristics and performance study, the DES@MIL-53(Fe)/CS membrane can have better potential in wastewater treatment and other membrane-based separation processes.

Design and control of a novel single-column extractive distillation with internally circulated intermediate boiling entrainer

The effective separation of binary azeotropic mixtures is one of the main difficult problems for distillation processes. For the azeotropic mixture separation, additional columns and energy are always needed compared with the non-azeotropic mixture separation. To reduce the equipment cost and energy consumption of the extractive distillation, a novel single-column extractive distillation with internally circulated intermediate boiling entrainer is proposed in this paper. In the proposed distillation column, the entrainer has no need to be withdrawn and recycled into the column, and the binary minimum boiling point azeotropic mixture can be separated completely by one distillation column. Due to there is no outside recycled stream, the entrainer cannot be added into the column directly in its steady state design. To solve this problem, a two-column model is proposed to simulate the whole column in this paper. Three binary minimum boiling point azeotropic mixture separation cases show that the proposed column has high separation and energy efficiencies. In addition, the effective control strategies of the proposed column are studied in three cases, and excellent control performances are achieved by the proposed control strategies. This work proposes a new energy saving way for the extractive distillation to separate the binary azeotropic mixtures.

Effects of Energy Intensification of Pressure-Swing Distillation on Energy Consumption and Controllability.

The aim of process integration is the efficient use of energy and natural resources. However, process integration can result in a more precise process operation, that is, it influences controllability. Pressure-swing distillation processes are designed for the separation of azeotropic mixtures, but their inherent heat integration option can be utilized to significantly reduce their energy consumption. One maximum-boiling and three minimum-boiling azeotropes are considered to study and compare the nonintegrated and integrated alternatives with the tool of mathematical modeling where ASPEN Plus and MATLAB software are used. The results show that the heat-integrated alternatives result in 32-45% energy savings that are proportional to the emission reduction and the consumption of natural resources. As far as the operability is concerned, the heat-integrated alternatives show worse controllability features than the nonintegrated base case. This can be due to the loss of one controllability degree of freedom. This recommends using more sophisticated control structures for the sake of safe operation if process integration is applied.

Screening of ionic liquids as green entrainers for ethanol water separation by extractive distillation: COSMO-RS prediction and aspen plus simulation

Ionic liquids (ILs) have been demonstrated as promising alternatives to conventional entrainers in separation of azeotropic mixtures mostly investigating phase equilibrium and process design scenarios. However, proper selection of ILs for a specific task always remains challenging. Hence a simulation tool, i.e. conductor like screening model for real solvents (COSMO-RS) was applied to address this challenge. Furthermore, screened ILs were simulated as entrainers for ethanol water separation by extractive distillation. The current study also aims to demonstrate a systematic approach to retrofit existing processes, by employing ILs as green entrainers. Screening of twenty-five (25) ILs was carried out using COSMO-RS to select suitable ILs as green entrainers based on activity coefficient, capacity and selectivity. Results illustrated that tetramethylammonium chloride ([TMAm][Cl]) due to its strong hydrogen bonding ability was found to be the best ILs entrainer. Moreover, in order to reduce the operating costs without compromising desired product purity (ethanol purity ≥99.5% in top product), the selected ILs (8 kg/h) in a mixture with ethylene glycol (72 kg/h) were simulated using Aspen plus v.11. The simulation results revealed that by combining tetramethylammonium chloride (2 kg/h) with ethylene glycol (78 kg/h) reduced 7.26 tons of CO2 emissions/year through heat integration by saving 1.49*108 kJ/year energy besides minimizing operating costs. In conclusion, the systematic selection of ILs as green entrainers in combination with ethylene glycol and then the appropriate simulation of the whole system will ultimately reduce the cost of the separation process and reduce the emission of greenhouse gases as well utilization of toxic conventional entrainers.

Effect of choline lactate ionic liquid as entrainer on the thermodynamic properties of alcohols + water azeotropic mixtures

Ionic liquids could be used as entrainer in the azeotropic mixture separation process efficiently. Accordingly, the thermodynamic properties of ionic liquid choline lactate ([Ch][Lac]) as a potential entrainer have been studied in different azeotropic mixtures. In this respect, the density and speed of sound for binary systems containing (water + [Ch][Lac]) (ethanol/ 1-propanol/ 2-propanol) + [Ch][Lac])] and also ternary systems with different mass percent from alcohol-containing (water + alcohol + [Ch][Lac]) have been measured under a pressure 871 hPa at different temperatures T = (288.15 to 318.15) K. These data are used to calculate standard partial molar volume (Vφ0), and the limiting apparent molar compressibility (κφ0) using the Redlich-Mayer model besides the intermolecular free length (Lf) and relative association (RA) to interpret the existing interaction in the azeotropic mixture of the studied alcohols. Also, the scaled particle theory is used as a microscopic approach. All of the properties have been analyzed to interpret the interactions between the components of the mixture and 2-propanol has stronger interactions with the [Ch][Lac] in the azeotrope composition. The results suggest that the [Ch][Lac] could be used as an entrainer to separate 2-propanol more efficiently rather than the other studied alcohols.

Imidazolium Chloride Ionic Liquid Mixtures as Separating Agents: Fuel Processing and Azeotrope Breaking.

Relevant chemical separations for the petrochemical and chemical industries include the removal of aromatic hydrocarbons from aliphatics, the desulfurization and denitrification of fuels, and the separation of azeotropic mixtures containing alkanols. In an attempt to contribute to the development of novel technologies, the potentialities of imidazolium chloride ionic liquid (IL) mixtures as separation agents were investigated. Selectivities, capacities, and solvent performance indices were calculated through the activity coefficients at infinite dilution of organic solutes and water in the imidazolium chloride IL: [C8mim]Cl, [C12mim]Cl, and the equimolar mixture of [C4mim]Cl and [C12mim]Cl. Results show that the imidazolium chloride IL might be appropriately tailored for specific purposes, in which an increase in the proportion of cations containing larger alkyl chains tends to increase the overall affinity with organic solutes. The IL designer solvent concept was explored by comparing the IL equimolar mixture results with the intermediary [C8mim]Cl. The COSMO-RS thermodynamic model was also applied, showing it to be a promising tool for a fast qualitative screening of potential separation agents for specific separation processes.

Fabrication of ternary polyvinyl alcohol/tetraethyl orthosilicate/silicotungstic acid hybrid membranes for pervaporation dehydration of alcohol

Herein, we present simple method of fabrication and pervaporation application of organic/inorganic ternary nanocomposite membranes. These are obtained from novel combination of poly(vinyl alcohol)/tetraethyl orthosilicate (PVA/TEOS) along with incorporation of silicotungstic acid (STA) nanoparticles via solution casting method. Physico-chemical structure has been confirmed by using various characterization tools. Pervaporation efficiency of these new nanocomposite membranes in terms of flux and separation factor is investigated for one of the important processes of ethanol separation (azeotropic mixture separation) from its aqueous solution. Dramatically boosted pervaporation separation efficiency by PVA/TEOS membranes has been observed as a result of STA incorporation. The results are also confirmed by calculating diffusion coefficients and activation energies using Fick’s and Arrhenius equations, respectively.

Process intensification by integration of distillation and vapor permeation or pervaporation - An academic and industrial perspective

Since membrane separations, such as vapor permeation (VP) or pervaporation (PV), are not limited by vapor-liquid equilibrium, their coupling with distillation can exert a synergistic effect, overcome the thermodynamic limits of distillation, and improve energy efficiency, especially suitable for the separation of azeotropic mixtures that otherwise requires special distillation processes. Therefore, there is an increasing number of such studies, and it is of great significance to comprehensively explore the process integration of distillation with VP or PV. This review first introduces the mechanism model of membrane separation and membrane materials, then comprehensively summarizes the academic research in terms of hybrid configurations of distillation with VP or PV in the following aspects: separation of azeotropic or close-boiling mixtures, promoting reactions by selectively removing a product, and energy savings, providing guidelines for subsequent application and future research. Finally, this review gives typical industrial cases of distillation and membrane-coupled separation processes and highlights some deficiencies of current research in this area.

Analysis and performance enhancement of heat pump technology assisted pressure-swing distillation process in the separation of azeotropic mixtures

In this paper, vapor recompressed heat pump assisted pressure-swing distillation process (VRC-PSD) is proposed to explore the ethyl acetate/n-hexane and THF/ethanol/water separating process based on the method explored for defining optimal vapor recompressed heat pump assisted distillation process in our early work. In binary separating process, the VRC-ABR-PSD and VRC-PRE-PSD configurations, respectively, reduce the 52.927% and 52.427% in TAC. And the VRC-ABR-PSD and VRC-PRE-PSD process applied in the separation of THF/ethanol/water ternary azeotrope can reduce TAC by 62.640% and 58.752%.The result demonstrates that all VRC-PSD schemes perform better than the corresponding PSD scheme in terms of economic, energy saving and thermodynamic efficiency. And VRC-PSD scheme with auxiliary bottom reboiler performs better than the VRC-PSD scheme with preheater. Meanwhile, the VRC-PSD assisted with heat integration schemes show better performance than those schemes without heat integration. For the separation of THF/ethanol/water ternary azeotrope, the VRC-ARB-HI-PSD and VRC-PRE-HI-PSD scheme reduce TAC by 67.359% and 63.257%.

Comparison of Controllability Features of Extractive and Pressure Swing Distillations on the Example of Tetrahydrofuran Dewatering.

The controllability study is an integral part of chemical process design. In this work, the controllability of two special distillation techniques, extractive distillation and pressure swing distillation, designed for the separation of azeotropic mixtures is investigated with dynamic tools. The control design interface of Aspen Plus and Matlab are applied for the modeling and evaluation of the two systems. Dynamic controllability indices are determined and aggregated in a desirability function. The results are compared to obtain efficient help for process design activity. The pressure swing distillation shows significantly better controllability features than the extractive distillation. The reason can be the fact that in the case of the extractive distillation, a third compound, the extractive agent, is added to the system to carry out the separation, therefore making the system more complex. As far as the selection of manipulated variables is concerned, in the case of the extractive distillation, the reflux flows should be preferred to the reflux ratios but in the case of the pressure swing distillation, the reboiler heat loads are preferred to the reflux ratios since those are closer to the controlled compositions. Both separation systems show worse controllability features if the product purity requirement is approaching to the pure products, that is, close to 100%. Although the energy consumption of the pressure swing distillation is higher than that of the extractive distillation, it has the inherent feature that it can be automatically heat integrated due to a column operated at high pressure and, as a consequence, higher temperatures.

Construction of MoS2 hybrid membranes on ceramic hollow fibers for efficient dehydration of isopropanol solution via pervaporation

Due to environmental issues and intense competition in the marketplace, industries and governmental organizations invest in new technology research to improve productivity, environmental protection, and cost-efficiency. Pervaporation is a membrane-based separation technology, which is cost-effective, environmentally friendly, and efficient in the separation of azeotropic mixtures. Here, we report the fabrication of a hybrid membrane based on molybdenum disulfide (MoS2) material, which can be used to dehydrate alcohol through a pervaporation process. Ceramic hollow fiber (CHF) membrane was used as a substrate in MoS2hybrid membrane, and TiO2 intermediate layer was constructed to reduce the macropores on the CHF surface. Polyethyleneimine (PEI) was used as a binder in the fabrication of the MoS2 layer. MoS2-PEI layer was prepared by vacuum suction method and then crosslinked with trimesoyl chloride (TMC) to prevent the hybrid layer from swelling in an aqueous solution. We investigated the morphology and physicochemical characteristics of the hybrid membranes by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and water contact angle (WCA) measurements. The fabricated MoS2hybrid membrane possesses a permeation flux of 5697 g m-2h−1 and separation factor of 320 in a 90 wt% isopropanol aqueous solution at 343 K. In this study, we provide a comprehensive understanding of the fabrication of MoS2hybrid membrane on the CHF membrane for efficient dehydration of isopropanol via the pervaporation process.

Systematic Design and Evaluation of Energy-Efficient Alternatives of Heterogeneous Azeotropic Distillation: Furfural Case Study

Separation of azeotropic mixtures receives special attention for their impact on various significant industrial processes. Because of the non-ideal behaviour of these mixtures, it is impossible to separate them by conventional distillation. Instead of a single distillation unit, a system of multiple operations is to be employed. Heterogeneous azeotropic distillation (HAD) is an example of this kind of systems, where entrainers are applied to modify the behaviour of the mixture. The selection of the best separation system is a key objective during the synthesis of the process network. However, synthesis of HAD is especially difficult because of the complex interaction between its continuous and discrete features. Therefore, traditional separation network synthesis tools are incapable of solving this problem. In this work, the properties of the ternary vapor-liquid-liquid equilibrium diagram are exploited for systematically identifying plausible operating units that perform the separation of the azeotrope. Subsequently, energy consumption of the entire network is estimated through rigorous simulation. The P-graph framework is employed to represent the system’s structure. Additionally, its combinatorial algorithms generate a rigorous superstructure for the synthesis problem, and the set of n-best designs that minimize energy consumption. The method is illustrated by synthesizing the dehydration of furfural through HAD. The results demonstrate that it constitutes a valuable tool for the designer by being effective in the systematic identification and assessment of HAD alternatives.

Heat-Integrated Pervaporation–Distillation Hybrid System for the Separation of Methyl Acetate–Methanol Azeotropes

Pervaporation is typically considered an energy-efficient technology for the separation of azeotropic mixtures. However, the vaporization of the permeate leads to a temperature drop in the residual...

Recent Advances of Pervaporation Separation in DMF/H2O Solutions: A Review.

N,N-dimethylformamide (DMF) is a commonly-used solvent in industry and pharmaceutics for extracting acetylene and fabricating polyacrylonitrile fibers. It is also a starting material for a variety of intermediates such as esters, pyrimidines or chlordimeforms. However, after being used, DMF can be form 5–25% spent liquors (mass fraction) that are difficult to recycle with distillation. From the point of view of energy-efficiency and environment-friendliness, an emergent separation technology, pervaporation, is broadly applied in separation of azeotropic mixtures and organic–organic mixtures, dehydration of aqueous–organic mixtures and removal of trace volatile organic compounds from aqueous solutions. Since the advances in membrane technologies to separate N,N-dimethylformamide solutions have been rarely reviewed before, hence this review mainly discusses the research progress about various membranes in separating N,N-dimethylformamide aqueous solutions. The current state of available membranes in industry and academia, and their potential advantages, limitations and applications are also reviewed.