Azeotropic Distillation Process Research Articles

Improving the performance of heterogeneous azeotropic distillation via self-heat recuperation technology

Azeotropic distillation is one of the most energy intensive processes and widely used to separate thermos-sensitive azeotropes. In this work, several heterogeneous azeotropic distillation processes based on the vapor recompression heat pump (VRHP) and self-heat recuperation technology (SHRT) are proposed to study the energy-saving performance. The results show that the heterogeneous azeotropic distillation process based on self-heat recuperation technology (HAD-SHRT) has better performance in economic and environment. In HAD-SHRT process, the sensible heat and latent heat of the vapor streams are recuperated and supplied to the reboilers. The remaining sensible heat is supplied to the preheaters through the heat exchanger network (HEN). Adding a preheater can reduce the duty of compressor by increasing the initial temperature of the stream. Compared with the conventional heterogeneous distillation process, the HAD-SHRT process can save 38.50% of TAC, 93.30% of CO2 emissions, and 80.92% of energy consumption. The thermodynamic efficiency can increase to 13.51%.

Relevance of regulatory constraints in designing pharmaceutical manufacturing processes: A case study on waste solvent recovery

This work deals with the relevance of regulatory constraints on the outcome of process design in pharmaceutical manufacturing with a case study on waste solvent recovery. The role of the investigated process was to separate and purify tetrahydrofuran from an azeotropic mixture with water and methanol. As the technologies to overcome the distillation boundary, zeolite membrane, pressure swing, azeotropic distillation, and entrainer processes were considered as alternatives, and were modeled and evaluated with regard to economy, environmental impact, and environmental, health, and safety hazards. The target concentration of recovered solvent, which cannot be altered because of regulations, was imagined to be modifiable, and two design problems, initial and extended, were formulated. A type of pressure swing process that was found to be optimal in the extended problem was equal to or better than any of the optimal alternatives in the initial design problem. Remarkably, the net present value of this alternative was about 17% larger than the maximum in the initial design problem. These results confirmed quantitatively that the way in which regulatory constraints are taken into account makes a difference in the outcome and that the appropriate formulation of a design problem is critical for pharmaceutical manufacturing processes.

Conceptual design of an extractive distillation process for the separation of azeotropic mixture of n-butanol-isobutanol-water

In many chemical processes, large amounts of wastewater containing butanol and isobutanol are produced. Given that n-butanol-isobutanol-water can form triple azeotrope, high-purity butanol cannot be recovered from the wastewater by ordinary distillation. To economically and effectively recover butanol from this kind of wastewater, 1,4-butanediol is selected as an extractant to break the formation of the azeotropes, and a double-effect extractive distillation process is proposed. The conceptual design of the proposed process is accomplished based on process simulation. With the proposed process, the purity of recovered butanol and water is greater than 99.99 wt%. In comparison with the conventional azeotropic distillation process, economic analysis shows that the operating cost of the proposed process is lower: when the capacity of wastewater treatment is 100 t·h− 1, the total operating cost decreases by 5.385 ×106 USD per year, and the total annual cost of the new process decreases by 5.249 ×106 USD per year. In addition, in the extractive distillation system, variable effects on separation purities and cost are more complex than those in the ordinary distillation system. The method and steps to optimize the key variables of the extractive distillation system are also discussed in this paper and can provide reference for similar studies.

Energy-efficient heterogeneous extractive distillation system for the separation of close-boiling cyclohexane/cyclohexene mixture

Abstract Cyclohexane and cyclohexene are close-boiling compounds with relative volatility extremely close to unity, thus, separation via conventional distillation is impractical. In this paper, an energy-efficient heterogeneous extractive distillation system using ethylene glycol as heavy entrainer is proposed. By adding ethylene glycol into the system, large liquid-liquid envelope will form. However, the principle of separation is not exclusively the formation and split of heterogeneous azeotrope like that of a typical heterogeneous azeotropic distillation process, but also because of ethylene glycol greatly enhances the relative volatility of cyclohexane over cyclohexene when treated as a heavy entrainer. The proposed heterogeneous extractive distillation column includes a top decanter and no rectifying section. After establishing the base design of the proposed system, energy-saving schemes are also suggested to further reduce the total annual cost and the annual operating cost. The results show that the proposed heterogeneous extractive distillation system with a process-to-process heat exchanger has the predominant benefit of the lowest total annual cost. To compare the optimal result of this design flowsheet with a recently published separation method utilizing two reactive-distillation columns, our proposed design is much more economical with 61.4% savings in total annual cost and 64.6% savings in annual operating cost.

Systems Design, Modeling, and Thermoeconomic Analysis of Azeotropic Distillation Processes for Organic Waste Treatment and Recovery in Nylon Plants

Nylon-6 and nylon-6,6 processes produce considerable amount of organic waste (known as light oil) consisting of n-pentanol, cyclohexanone, and cyclohexene oxide, which are difficult to separate and recover. This Article proposes six novel process designs to separate the light oil into three value-added products based on azeotropic distillation using water as an entrainer. These azeotropic distillation process designs take into account direct sequence, indirect sequence, thermal coupled column, and three types of dividing wall columns (dividing wall at the top, bottom, and middle of columns, respectively) for entrainer recovery. A conventional distillation process design for separation of the same light oil is also modeled and analyzed for comparison. High-fidelity process simulations are performed for each of the seven process designs in Aspen Plus. We further conduct exergy analyses and technoeconomic analyses to evaluate and compare the exergy efficiencies and economic performances of these seven process designs. The results indicate that the proposed azeotropic distillation process design with dividing wall at the middle of the column has the best performance in terms of both exergy efficiency and total annual cost.

Optimization of liquid–liquid extraction combined with either heterogeneous azeotropic distillation or extractive distillation processes to reduce energy consumption and carbon dioxide emissions

The mixture of propylene glycol methyl ether and water form a minimum-boiling azeotrope. To separate the binary azeotropic system, energy-saving liquid–liquid extraction combined with either heterogeneous azeotropic distillation or extractive distillation processes based upon traditional two-column heterogeneous azeotropic distillation and three-column extractive distillation processes were proposed, using chloroform and 2-ethylhexanoic acid as solvents, respectively. The minimum total annual cost (TAC), based on a sequential iterative optimization procedure, and CO2 emissions for the two processes were determined. Liquid–liquid extraction combined with heterogeneous azeotropic distillation process achieved significant reductions of 40.24% in the TAC and 45.37% in CO2 emissions compared with the traditional two-column heterogeneous azeotropic distillation process. The liquid–liquid extraction combined with extractive distillation process achieved TAC and CO2 emission reductions of 34.18% and 43.95%, respectively, compared with the traditional three-column extractive distillation process. Thus, the two processes are more attractive in terms of both economics and environmental protection.

Experimental studies and thermodynamic analysis of isobaric vapor-liquid-liquid equilibria of 2-propanol + water system using n-propyl acetate and isopropyl acetate as entrainers

Heterogeneous azeotropic distillation is a widely used technique in chemical industries for the purification of alcohols from their aqueous mixtures. This study aims at exploring the possibility of using n-propyl acetate and isopropyl acetate as entrainers for heterogeneous azeotropic distillation to effect the separation of 2-propanol + water azeotropic mixture. A novel yet simple still was constructed to measure the vapor-liquid equilibrium (VLE) and vapor-liquid-liquid equilibrium (VLLE) data for the binary and ternary systems. The isobaric VLE data for the binary systems 2-propanol + water, 2-propanol + n-propyl acetate and 2-propanol + isopropyl acetate and isobaric VLLE data for the ternary systems 2-propanol + water + n-propyl acetate and 2-propanol + water + isopropyl acetate were measured at atmospheric pressure. Subsequently, the experimental data was compared with predictions by thermodynamic models such as UNIFAC, UNIQUAC and NRTL. The feasibility of the entrainers n-propyl acetate and isopropyl acetate in separating the azeotropic mixture 2-propanol + water was studied using the Residue Curve Map (RCM). The experimental data showed the existence of a ternary homogeneous azeotrope in the 2-propanol + water + n-propyl acetate system and a heterogeneous ternary azeotrope in the 2-propanol + water + isopropyl acetate system. Since the heterogeneous azeotropic distillation process depends on the presence of ternary heterogeneous azeotrope, n-propyl acetate is not considered a suitable entrainer for the separation of 2-propanol + water mixture. Finally, a separation sequence for the heterogeneous azeotropic distillation of 2-propanol + water system using isopropyl acetate as entrainer has been proposed.

Investigation on Thermodynamics in Separation for Ethylene Glycol + Neopentyl Glycol System by Azeotropic Distillation

The isobaric vapor–liquid equilibrium (VLE) data for two binary systems of ethylene glycol (EG) + neopentyl glycol (NPG) and NPG + para-xylene (PX) have been measured under pressure of 101.3 kPa, respectively. The thermodynamic consistency of the experimental isobaric VLE data was tested by means of Herington area test. Meanwhile, the experimental isobaric VLE data have been satisfactorily correlated with Wilson, NRTL, and UNIQUAC models. A conventional azeotropic distillation process has been designed to achieve high-purity products based on preceding results. The product purities of EG and NPG can both achieved at 99.9 mol % with minimal total annual cost (TAC) through sequential iterative optimization procedure.

MINLP optimization of a heterogeneous azeotropic distillation process: Separation of ethanol and water with cyclohexane as an entrainer

Heterogeneous distillation processes are widely used in industry for the separation of azeotropic and close-boiling mixtures. This paper addresses the optimization of a heterogeneous distillation process for the separation of an azeotropic ethanol/water mixture using cyclohexane as an entrainer. Starting from a given process superstructure a MINLP problem is set up to consider continuous as well as discrete decision variables such as the feed locations and the number of stages of the distillation columns. A modified Generalized Benders Decomposition algorithm to account for non-convexities of the model equations solves the MINLP problem. The algorithm can be attached via Visual Basic for Applications (VBA) to any commercial process simulator with NLP and VBA capabilities. Various optimization runs show that the algorithm is easily applicable and returns solutions independent of the initial values.

Multiple Steady-States Analysis and Unstable Operating Point Stabilization in Homogeneous Azeotropic Distillation with Intermediate Entrainer

The steady-state multiplicity in azeotropic distillation processes has been theoretically predicted and verified experimentally for decades. However, it is a tough task to detect all the steady-state solutions. The purpose of this article is 2-fold: first, it provides a systematical study on the multiplicity in homogeneous azeotropic distillation with intermediate entrainer and a novel strategy is proposed to find all the steady-state solutions using “Design Specs/Vary” in Aspen Plus. Operating on the unstable steady-state branch benefits both energy saving and reducing capital investment with the product quality specified. Because of the great benefits that operating on the unstable steady-state branch offers, the second purpose is to present suitable control schemes to stabilize the operating point on the unstable steady-state branch to achieve robust control.

A semicontinuous approach for heterogeneous azeotropic distillation processes

The separation of azeotropes has substantial energy and investment costs, and the available methods require high capital costs for reconstruction of process plants. As an alternative, a semicontinuous configuration that utilizes an existing plant with minor modifications has been explored. In this paper, a semicontinuous, heterogeneous azeotropic distillation process is proposed and acetic acid dehydration process is used as a case study. To carry out the simulation work, Aspen HYSYS® simulation software is used along with MATLAB® and an interface program to handle the mode-transition of the semicontinuous process. Sensitivity analyses on operating parameters are performed to identify the process limits. Comparisons are made to conventional heterogeneous azeotropic distillation, and dividing-wall distillation column on the annual cost. The results proved that the semicontinuous system is the best setup in terms of total annual costs and energy requirements.

Application of Mechanical Vapor Recompression to Acetone – Methanol Separation

 Abstract—This paper proposed a novel integrated design of azeotropic mixtures distillation process based on mechanical vapor recompression (MVR). The extractive distillation of acetone - methanol binary system that forms a homogeneous minimum - boiling azeotrope was studied. Based on the simulation result, the total energy consumption of the proposed sequence is 62% less than the existing extractive distillation configuration.

Isobaric Vapor–Liquid–Liquid Equilibria for the Ternary Systems Ethanol + Water + Propyl Acetate and 1-Propanol + Water + Propyl acetate

In order to break azeotropes appearing in mixtures of water and either ethanol or 1-propanol, an azeotropic distillation process is proposed using propyl acetate as entrainer. Therefore, isobaric vapor–liquid–liquid equilibrium (VLLE) data at atmospheric pressure have been obtained for the ternary systems ethanol + water + propyl acetate and 1-propanol + water + propyl acetate. Data correlation has been carried out in four different ways and a comparison between the results obtained in each correlation has been done. The set of parameters obtained from the best correlation has been used in the VLLE estimation. Effects of using propyl acetate as entrainer in the azeotropic distillation have been discussed, and a three-column distillation sequence to separate 1-propanol and water has been proposed.

Thermodynamic Analysis and Process Simulation of Ethanol Dehydration via Heterogeneous Azeotropic Distillation

The heterogeneous azeotropic distillation process is widely used to separate nonideal binary mixtures into their constituent pure components. This method uses the addition of a third component, called an entrainer, to cause liquid–liquid phase separation over a broad range of compositions in the ternary phase diagram. Ethanol dehydration was used as a case study and diisopropyl ether and isobutyl alcohol were analyzed as possible entrainers in a heterogeneous azeotropic distillation. In this way, isobaric vapor–liquid–liquid equilibrium was measured for the ethanol + water + diisopropyl ether or + isobutyl alcohol ternary mixtures at 101.3 kPa. The data were correlated by the NRTL and UNIQUAC models, and a set of parameters for each model was obtained. A separation sequence for ethanol dehydration using diisopropyl ether was proposed. The simulation of the separation sequence was carried out satisfactorily by commercial software (Aspen Hysys) using the thermodynamic model UNIQUAC with the binary parameter...

Conceptual design of heterogeneous azeotropic distillation process for ethanol dehydration using 1-butanol as entrainer

The synthesis of a heterogeneous azeotropic distillation process for ethanol dehydration using 1-butanol as entrainer is presented. The residue curve map of the ethanol/water/1-butanol mixture is computationally generated using non-random two- liquid thermodynamic model. It is found that 1-butanol leads to a residue curve map topological structure different from that generated by typical entrainers used in ethanol dehydration. Synthesised by residue curve map analysis, the distillation flowsheet for ethanol dehydration by 1-butanol comprises a double-feed column integrated with an overhead decanter and a simple column. The double-feed column is used to recover water as the top product, whereas the simple column is used for recovering ethanol and 1- butanol. The separation feasibility and the economically near-optimal designs of distillation columns in the flowsheet are evaluated and identified by using the boundary value design method. The distillation flowsheet using 1-butanol is compared with the conventional process using benzene as entrainer. Based on their total annualised costs, the ethanol dehydration process using 1-butanol is less economically attractive than the process using benzene. However, 1-butanol is less toxic than benzene.

Breaking Azeotropes by Azeotropic and Extractive Distillation in a Dividing-Wall Column

This study gives a brief overview about using dividing-wall column (DWC) technology in azeotropic and extractive distillation processes aimed to break azeotropes. The relevant case study considered here is the bioethanol dehydration process that requires significant energy to overcome the azeotropic behaviour of ethanol-water mixture. The results of the rigorous Aspen Plus simulations show that energy savings of 10 – 20 % are possible for the novel process intensification alternative based on DWC, while using less equipment units as compared to the conventional azeotropic and extractive distillation configurations.

∞/∞-Analysis of homogeneous distillation processes

A method for the analysis of flowsheets consisting of an arbitrary number of distillation columns and mixers in conceptual process design is presented in this work. The required information on the process is reduced to a minimum: besides the fluid property model, only information on the flow sheet structure, the overall feed streams and a suitable set of desired product specifications is needed. The method is based on the study of thermodynamic limiting cases by applying ∞/∞-analysis to distillation columns. Thus, the attainable distillate and bottom compositions are described by the invariant manifolds of the singular points of the respective vapor–liquid equilibria. The approach based on residue curve maps or distillation line diagrams is general and not limited to the number of components or azeotropes. Only homogeneous azeotropes are discussed in the present work. The nonlinearity in the resulting short-cut model is only introduced by the fluid properties. By applying a suitable linearization to the separatrices of the vapor–liquid equilibria the invariant manifolds of the singular points are represented by linear elements. This results in piece-wise linear sub-models for the attainable product compositions. Brute force enumeration of the combined linear sub-models allows finding of all solutions reliably and robustly. Hence, comprehensive feasibility and multiplicity analysis are possible. An overview of the method is given followed by some examples for its application to a number of azeotropic distillation processes.

Synthesis of La0.85Sr0.15Ga0.8Mg0.2O3 − δ powder by carbonate co-precipitation combining with azeotropic-distillation process

La0.85Sr0.15Ga0.8Mg0.2O3−δ (LSGM1520) powder is synthesized by a carbonate co-precipitation coupling with azeotropic-distillation process. The composition of the as-prepared precipitate is determined by X-ray diffraction (XRD), elemental analysis (EA), thermogravimetric and differential scanning calorimeter (TG-DSC) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The post-distilled precursor is submitted to various thermal treatments and characterized by XRD and transmission electron microscopy (TEM). The results show that the components of the powder calcined at 1000°C contain a main perovskite phase and small amounts of secondary phases (namely LaSrGaO4 and LaSrGa3O7). TEM observation reveals that the powder has a narrow grain size distribution, which turns out to be suitable for sintering (>97% relative density for a pellet sintered at 1400°C during 4h). The conductivity of sintered pellets is measured and the highest conductivity at 800°C of LSGM1520 is 0.186Scm−1, which is nearly three times as high as that of La0.8Sr0.2Ga0.8Mg0.2O3−δ (0.0644Scm−1) prepared by the similar carbonate method. It suggests that a new route of synthesizing Sr- and Mg-doped lanthanum gallate (LSGM) with good sinterability has been developed.

Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 3. Azeotropic Mixtures with Light Entrainer.

This article shows how knowledge of the location of univolatility lines and residue curve analysis helps in assessing the feasibility of extractive distillation of minimum-boiling (minT) or maximum-boiling (maxT) azeotropic mixtures or low-relative-volatility (low-α) mixtures (A–B) by using a light-boiling entrainer (E), in accordance with the general feasibility criterion of Rodriguez-Donis et al. [Ind. Eng. Chem. Res. 2009, 48 (7), 3544−3559]. Considering all possible locations of the univolatility line αAB, three minT azeotropic mixtures with a light entrainer (1.0–2 class), namely, ethanol–water with methanol, ethanol–toluene with acetone, and methyl ethyl ketone–benzene with acetone; three maxT azeotropic mixtures with a light entrainer (1.0–1a class), namely, water–ethylenediamine with methanol, acetone–chloroform with dichlomethane, and propanoic acid–dimethyl formamide with methyl isobutyl ketone; and one low-α mixture with a light entrainer (0.0–1 class), namely, ethyl acetate–benzene with acetone, were studied in a stripping extractive column. For the 1.0–2 class, both A and B can be recovered as the bottom product, depending on the location of αAB = 1, which sets limiting values for the entrainer feed flow rate FE/LT for one of the product. In addition, the feasible region of the extractive distillation process is larger than for the azeotropic distillation process. For the 1.0–1a class, the product is either A or B, depending on the location of αAB = 1, which sets a minimum value of (FE/LT)min for one of the product. For the 0.0–1 class, feasibility depends on the existence αAB = 1. When it does not exist, B is the unique possible product. When it does, both A and B are products, with B below a maximum value of (FE/LT)max,B and A above a minimum value (FE/LT)min,A.

Preparation of ZnO Nanoparticles and Photocatalytic H2 Production Activity from Different Sacrificial Reagent Solutions

ZnO nanoparticles were synthesized via a direct precipitation method followed by a heterogeneous azeotropic distillation and calcination processes, and then characterized by X-ray power diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption measurement. The effects of Pt-loading amount, calcination temperature, and sacrificial reagents on the photocatalytic H2 evolution efficiency from the present ZnO suspension were investigated. The experimental results indicate that ZnO nanoparticles calcined at 400 °C exhibit the best photoactivity for the H2 production in comparison with the samples calcined at 300 and 500 °C, and the photocatalytic H2 production efficiency from a methanol solution is much higher than that from a triethanolamine solution. It can be ascribed to the oxidization of methanol also contributes to the H2 production during the photochemical reaction process. Moreover, the photocatalytic mechanism for the H2 production from the present ZnO suspension system containing methanol solution is also discussed in detail.