Homogeneous Azeotropes Research Articles

Possible Existence of a Negative (Positive) Homogeneous Azeotrope When the Binary Mixture Exhibits Positive (Negative) Deviations from Ideal Solution Behavior (That is, When gE is Positive (Negative))

The objective of this note is to give proof that the existence of a positive (or, respectively, negative) homogeneous azeotrope is not linked to the sign (positive or negative) of the molar excess Gibbs energy function (gE) but rather to the curvature of gE. We demonstrate that when gE is concave (or, respectively, convex), a binary system may exhibit a positive (or, respectively, negative) azeotrope. Because a concave or convex function may indifferently be positive or negative, when gE is positive (or, respectively, negative), a binary system may exhibit a negative (or, respectively, positive) azeotrope.

Azeotropic behaviour of (benzene + cyclohexane + chlorobenzene) ternary mixture using chlorobenzene as entrainer at 101.3 kPa

In this paper, the azeotropic behaviour of the (benzene + cyclohexane + chlorobenzene) ternary mixture was experimentally investigated with the aim of enhancing the knowledge for the feasible use of chlorobenzene as an entrainer for the azeotropic distillation of the binary azeotrope. Such a study has not been reported in the literature to the best of the authors’ knowledge. (Vapour + liquid) equilibria data for (benzene + cyclohexane + chlorobenzene) at 101.3 kPa were obtained with a Othmer-type ebulliometer. Data were tested and considered thermodynamically consistent. The experimental results showed that this ternary mixture is completely miscible and exhibits an unique binary homogeneous azeotrope, an unstable node at the conditions studied, and the propitious topological characteristics (residual curve map and relative volatility) to be separated. Satisfactory results were obtained for the correlation of equilibrium compositions with the UNIQUAC activity coefficients model and also for prediction with the UNIFAC method. In both cases, low root mean square deviations of the vapour mole fraction and temperature were calculated. The capability of chlorobenzene as a modified distillation agent at atmospheric condition is discussed in terms of the thermodynamic topological analysis. A conceptual distillation scheme with reversed volatility is proposed to separate the azeotropic mixture. In order to reduce the operational cost requirements of the sequence of columns proposed, the range for optimal reflux and the ratio for feed flow conditions were studied.

Dehydration of tetrahydrofuran by pervaporation using a composite membrane

Tetrahydrofuran (THF) is a strong aprotic solvent, commonly used in the pharmaceuticals industry due to its broad solvency for both polar and non-polar compounds. THF and water form a homogeneous azeotrope at 5.3 wt.% water thus simple distillation is not feasible to dehydrate THF below this concentration. Pervaporation offers a solution since it is not governed by vapour–liquid equilibria. However many polymer-based pervaporation membranes are cast utilizing THF as the casting solvent and so these membranes have a tendency to swell excessively in its presence. This results in poor separation performance and poor long-term stability and thus renders these membranes unsuitable for THF dehydration. In this study, a new membrane available from CM Celfa, CMC-VP-31 has been tested for the dehydration of THF. The membrane shows excellent performance when dehydrating THF with a flux of over 4 kg m −2 h −1 when dehydrating THF containing 10 wt.% water at 55 °C dropping to 0.12 kg m −2 h −1 at a water content of 0.3 wt.%. The permeances of water and THF in the membrane were calculated to be 11.76 × 10 −6 and 7.36 × 10 −8 mol m −2 s −1 Pa −1, respectively, at 25 °C and found to decrease in the membrane with increasing temperature to values of 6.71 × 10 −6 and 1.63 × 10 −8 mol m −2 s −1 Pa −1 at 55 °C. The flux and separation factor were both found to increase with an increase in temperature thus favouring the operation of CMC-VP-31 at high temperatures to optimize separation performance.

Characteristics of activity coefficient models for liquid solutions

AbstractLiquid–phase activity coefficient models (or excess Gibbs energy models) with three or fewer adjustable parameters are often sufficient to model the liquid solutions present for the vapor–liquid equilibria (VLE) or the vapor–liquid–liquid equilibria (VLLE) calculations of phase equilibria. Our purpose here is to show the flexibility of three such equations in the correlation and prediction of (1) extrema and inflection points on the popular ln γi vs. x1 diagram for binary solutions, (2) liquid–liquid phase splitting, and (3) homogeneous azeotropes. The empirical equations investigated here are (a) the two‐constant Margules model, (b) the van Laar model, and (c) the three‐constant NRTL model. New mathematical procedures lead to new graphs and equations, which allow the reader to identify the presence of any of the above three phenomena by inspection without performing detailed calculations such as a Gibbs energy minimization for liquid phase splitting. © 2004 American Institute of Chemical Engineers AIChE J, 50: 854–861, 2004

Homotopy continuation based prediction of azeotropy in binary and multicomponent mixtures through equations of state

A method to compute all the azeotropes in homogeneous binary and multicomponent mixtures for entire two-phase pressure range is described. The method is based on solving the necessary condition of azeotropy for all the possible solutions through homotopy continuation approach. The method is mathematically guaranteed to predict all the possible azeotropes and is in close agreement with experimental data for any equation of state that can adequately represent the phase behavior. Both vapor and liquid phase non-idealities are incorporated using fugacity coefficients from the Peng–Robinson–Stryjek–Vera equation of state with the Wong–Sandler mixing rules. The method is also capable of predicting the value of bifurcation pressure where homogeneous azeotropes will appear or disappear. Polyazeotropy in binary mixtures is a singular case of vapor-liquid equilibrium and can also be computed by solving the necessary condition of azeotropy in binary mixtures for multiple solutions through homotopy continuation based approach. The approach can also systematically search the entire two-phase pressure range for the appearance, disappearance and persistence of azeotropy and polyazeotropy in binary and multicomponent mixtures.

Reliable computation of binary homogeneous azeotropes of multi-component mixtures at higher pressures through equation of states

A method to compute binary homogeneous azeotropes in multi-component mixtures at elevated pressures through the equation of state approach is developed. The method is capable of predicting the homogeneous azeotropes and is in close agreement with experimental data. At higher pressures, vapor and liquid phase non-idealities are incorporated using vapor and liquid phase fugacity coefficients from Peng–Robinson–Stryjek–Vera equation of state with Wong–Sandler mixing rules. The method is also capable of predicting the exact value of bifurcation pressure where homogeneous azeotropes may appear or disappear. The method can predict the azeotropes at elevated pressures and is independent of equation of state and mixing rules. The method is also capable of predicting the double azeotropy in binary mixtures. The method is tested with Ethanol-Water, Isopropanol-Water, Carbon dioxide-Ethane-Ethylene and Ammonia-R-125 systems. The highly non-linear system of equations is solved by homotopy continuation approach.

Novel hybrid separation processes for solvent recovery based on positioning the extractive heterogeneous-azeotropic distillation

The solvent recovery is often the separation of highly non-ideal mixtures. The separation and recovery of quaternary solvent mixtures coming from printing and medicine factories are investigated. The components of the six quaternary mixtures studied in form of heterogeneous and homogeneous azeotropes of minimum boiling point. The mixtures can be categorised into three groups according to their VLLE behaviours. After studying their behaviours, three novel hybrid separation processes based on the extractive heterogeneous-azeotropic distillation, a special kind of new distillation, are developed and recommended for each group of solvents. In the novel processes, beside the extractive heterogeneous-azeotropic distillation, ordinary distillations and phase separation units are also used utilising the fact that the combination of such units, the hybrid processes, offer a higher variety of the possibilities for the separation of highly non-ideal mixtures. The separation processes are verified experimentally and the agreements between the simulated and measured data prove to be rather favourable. A strategy is recommended for the use of the novel hybrid processes developed according to the VLLE behaviour of the non-ideal quaternary mixtures.

Vapor−Liquid Equilibrium Measurements and Correlation of the Binary Refrigerant Mixture Propane (HC-290) + 1,1,1,2,3,3,3-Heptafluoropropane (HFC-227ea) at 278.15, 293.15, and 308.15 K

Isothermal vapor−liquid equilibria for the binary system propane (HC-290) + 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea) were measured at 278.15, 293.15, and 308.15 K using a recirculation apparatus in which the vapor phase was forced through the liquid. The phase composition at equilibrium was measured by gas chromatography; calibration of the response was made with gravimetrically prepared mixtures. The system shows a major deviation from Raoult's law, with the formation of a homogeneous azeotrope at a mole fraction of propane of about 0.8. The uncertainties in pressure, temperature, and vapor- and liquid-phase composition measurements were estimated to be no more than ±1 kPa, ±0.02 K, and ±0.002 in the mole fraction, respectively. The data were reduced using the Carnahan Starling De Santis (CSD) equation of state (EoS) and the Lemmon−Jacobsen (LJ) Helmholtz energy mixture model. A comparison was made with VLE calculations from REFPROP 6.0 for both the experimental data and the data reduction models.

Froth Heights on Dual-Flow Trays with a Heterogeneous Binary Azeotropic System and a Heterogeneous Ternary System with a Homogeneous Azeotrope

Visual froth height measurements and the clear liquid heights on 20% free area dual-flow trays, operated at total reflux, have been obtained on the homogeneous system of water−steam, on the heterogeneous systems of ethyl acetate−water and ethyl acetate−ethanol−water, and in the homogeneous region near the homogeneous ternary azeotrope of that ternary system. The experimental results were obtained under distilling conditions at a total pressure of 101.3 kPa for a range of liquid and vapor densities and vapor velocities. The churn flow conditions on the dual-flow trays at total reflux were found to have the characteristic of constant volume fraction liquid in the froth for all systems investigated: ΦL = 0.291; hf < 0.300. A correlating equation for the froth height that contains the impact pressure was found for all systems investigated to be hf = 2.625(1/2ρVu2) with hf < 0.300. A dimensionless correlating form, based on a modified Froude number, was found to be suitable for all systems: FrM = 280.0 × 10-6(ρV/ρL)-1/2 with hf < 0.300. The clear liquid height was found for all systems to follow hCL = ΦLhf with hf < 0.300. The dimensionless correlation for froth heights for all systems could be converted to a flooding vapor velocity relationship at total reflux for dual-flow trays by ufl = 0.0283√Z(ρV/ρL)-3/4 with Z < 0.300.

Prediction of Homogeneous Azeotropes with Interval Analysis Techniques Exploiting Topological Considerations

In this paper, we present an efficient method for the prediction of homogeneous azeotropes. The method is an adaptation of a former method based on interval analysis techniques. An interval Newton with generalized bisection (IN/GB) technique is used to find all the roots of a set of equations representing the azeotropy condition. The novel contribution is to combine this robust technique with the Zharov−Serafimov topological index theory. By checking the topological consistency, it is possible to avoid the numerical verification of the nonexistence and therefore to reduce significantly the total computation time. In addition, a simplified model is selectively used at the first stage of the algorithm for providing good starting points for the second stage, where the full model is used for solution refining. In this way, more computation time is saved without compromising the reliability of the method. As a result, the performance of the method is comparable to the one of the fastest local methods.

Critical Distillation Experiments in a Region near the Homogeneous Ternary Azeotrope in the System Ethyl Acetate−Ethanol−Water

A nine-tray distillation column has been used to critically examine a constant-temperature region near the ternary homogeneous azeotrope in the system ethyl acetate-ethanol-water. Liquid samples withdrawn from the trays show an almost constant ethanol composition for a specific charge to the reboiler. An examination of the experimental discrete distillation lines on a portion of the ternary phase diagram showed that the constant-temperature region had been covered and an indication of a different location of the ternary homogeneous azeotrope. Process simulation studies could be expected to be difficult with existing parameters in thermodynamic models, under these conditions.

Comments on “Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water”

Comments on “Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water”

Rebuttal to the Comments of J. Gmehling on “Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water”

ADVERTISEMENT RETURN TO ISSUEPREVCorrespondenceRebuttal to the Comments of J. Gmehling on “Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water”Ian A. FurzerView Author Information Department of Chemical Engineering, University of Sydney, Sydney, NSW 2006 Australia Cite this: Ind. Eng. Chem. Res. 2001, 40, 1, 494–495Publication Date (Web):December 7, 2000Publication History Published online7 December 2000Published inissue 1 January 2001https://doi.org/10.1021/ie000750hCopyright © 2001 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views199Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (16 KB) Get e-AlertsSUBJECTS:Algorithms,Azeotropes,Ethyl groups,Liquid liquid equilibrium,Vapor liquid equilibrium Get e-Alerts

Computation of heteroazeotropes. Part I: Theory

This paper describes an algorithm for the computation of the homogeneous and heterogeneous azeotropes present in a multicomponent mixture. The approach (which is an extension of an approach developed by Fidkowski, Malone and Doherty (1993, Computers and Chemical Engineering, 17, 1141–1155) for the computation of homogeneous azeotropes) is independent of the representation of the nonideality of the system and the topology of the liquid–liquid region. Furthermore, the approach can be readily extended to handle any number of liquid phases in equilibrium. The second paper in this series discusses how the approach can be used to compute efficiently changes in equilibrium structure with parameters such as pressure (i.e., the appearance and disappearance of azeotropes and heteroazeotropes) and contains several numerical examples of the approach described in this paper.

Optimization of a Wastewater System Containing the Ternary Homogeneous Azeotropic System Ethyl Acetate−Ethanol−Water

A wastewater stream containing minor amounts of ethyl acetate and ethanol could produce clean water with a low solvent composition by the use of direct steam injection or by the use of a distillation column. A problem that arises in this system is the approach to a homogeneous azeotrope in the distillate as the number of ideal stages is increased. Higher compositions of ethanol can be produced at low distillate flow rates by limiting the number of ideal stages. The prediction of the azeotrope in this system requires new UNIFAC vapor−liquid equilibrium interaction parameters, which have been determined. Simulation of a distillation column at total reflux then predicts a maximum in the ethanol composition which could be recovered and recycled in the plant. The value of this recycled ethanol can exceed the steam operating costs for the wastewater plant. A cost optimization shows that there is a cost-feasible region that satisfies the composition constraints when the reflux ratio is between 10 and 30, with lo...

Reliable nonlinear parameter estimation in VLE modeling

The reliable solution of nonlinear parameter estimation problems is an important computational problem in the modeling of vapor–liquid equilibrium (VLE). Conventional solution methods may not be reliable since they do not guarantee convergence to the global optimum sought in the parameter estimation problem. We demonstrate here a technique that is based on interval analysis, which can solve the nonlinear parameter estimation problem with complete reliability, and provides a mathematical and computational guarantee that the global optimum is found. As an example, we consider the estimation of parameters in the Wilson equation, using VLE data sets from a variety of binary systems. Results indicate that several sets of parameter values published in the DECHEMA VLE Data Collection correspond to local optima only, with new globally optimal parameter values found by using the interval approach. When applied to VLE modeling, the globally optimal parameters can provide significant improvements in predictive capability. For example, in one case, when the previously published locally optimal parameters are used, the Wilson equation does not predict experimentally observed homogeneous azeotropes, but, when the globally optimal parameters are used, the azeotropes are predicted.

Computing Homogeneous Azeotropes Using Interval Analysis

Determining the existence of homogeneous azeotropes, together with their composition and temperature, is important from both theoretical and practical standpoints in the analysis of phase behavior and in the synthesis and design of separation systems employing distillation. We describe a new method that reliably locates any and all homogeneous azeotropes for multicomponent mixtures, and also verifies the nonexistence of homogeneous azeotropes if none are present. The method is based on interval analysis, and provides a mathematical and computational guarantee that all azeotropes are located. The technique is general purpose and can be applied in connection with any thermodynamic model describing vapor-liquid equilibrium. An example using a five-component mixture modeled with the NRTL equation is presented.

Recent advances in global optimization for process synthesis, design and control: Enclosure of all solutions

Recent advances in global optimization for process synthesis, design and control are discussed. After a review of the chemical engineering contributions, we focus on the enclosure of all solutions of nonlinear constrained systems of equations. Important theoretical results are presented accompanied with computational studies on the enclosure of multiple steady states and all homogeneous azeotropes.

Interval analysis for thermodynamic calculations in process design: a novel and completely reliable approach

Recently, a robust new computational technique, based on interval analysis, has been developed for solving the difficult nonlinear problems arising in the modeling of phase behavior. This technique can be used, with mathematical and computational guarantees of certainty, to find the global optimum of a nonlinear function or to enclose any and all roots of a system of nonlinear equations. As shown in the applications here to phase stability analysis and to the location of homogeneous azeotropes, it provides a method that can guarantee that the correct result is found; thus, eliminating computational problems that may potentially be encountered with currently available techniques. The method is initialization independent; it is also model independent, straightforward to use, and can be applied in connection with any equation of state or activity coefficient model.

Vapor−Liquid Equilibria for Ethanol + Hept-1-yne and Butyric Acid + Butyric Anhydride

Experimental (x, y, P) measurements of ethanol + hept-1-yne at 55 °C and 75 °C and butyric acid + butyric anhydride at 120 °C and 155 °C were obtained in an isothermal circulating glass still. The vapor pressure of hept-1-yne was measured from 43 °C to 100 °C. Ethanol + hept-1-yne exhibits moderate positive deviations from ideal behavior and a minimum-boiling homogeneous azeotrope at both temperatures. Butyric acid + butyric anhydride exhibits weak positive deviations, and no azeotrope was observed.