Vapor-liquid Equilibrium Diagrams Research Articles

Influence of supercritical fluid parameters on the polyimide aerogels in a high-efficiency supercritical drying process

A semi-continuous supercritical drying process was proposed to greatly improve the drying efficiency in producing polyimide aerogels. The influence of supercritical fluid parameters such as pressure and temperature on the aerogel properties were systematically investigated, based on the vapor-liquid equilibrium diagram of the ethanol-CO2 binary system. Results showed supercritical drying efficiency was critical for the comprehensive properties of the aerogel, because solvent retention in the aerogel after drying could cause depressurization-induced shrinkage and a subsequent change in nano-structure in the vacuum drying that ensued. By continuous scCO2 flushing at 90 °C and 16 MPa with the total drying time as short as 3 h, the aerogel showed a satisfactory shrinkage as low as 11.5%, a large specific surface area as high as 344.3 m2/g. Our findings also showed that the subcritical drying condition slightly below the critical mixture pressure of the binary system could provide special interest.

DEVELOPMENT OF SOLVENTS ALCOHOL MIXTURE SEPARATION TECHNOLOGY

The paper is devoted to the development of a technology for the regeneration of caprolactam solvents containing n-butanol, amyl alcohol, cyclohexanone, cyclohexanol, as well as isoamyl alcohol and cyclopentanone in impurity amounts. To study the phase equilibrium and the separation process, a computational experiment using AspenPlus V.10.0 was selected. The parameters of the Non Random Two Liquid equation allow reproducing the vapor-liquid equilibrium data and azeotropic properties of the system with a relative error not exceeding 5%. Separation of the mixture by conventional distillation is difficult, which is caused by the presence of three binary azeotropes, as well as three pairs of components characterized by close volatility. The structure of the vapor-liquid equilibrium diagram becomes more complex due to the appearance of new azeotropes with a decrease in pressure. A technological flowsheet for solvent regeneration based on the use of continuous distillation was proposed. The flowsheet contains five columns. At the first stage, preliminary fractionation of the mixture is assumed (the mode of sharp distillation in the first column) with complete separation of cyclohexanone and cyclohexanol in the bottom (vacuum distillation is used to separate this pair) and of a mixture of butanol and amyl alcohol with impurity components in the distillate. Extractive distillation with ethylene glycol was proposed to purify butanol and amyl alcohol from impurities. In the presence of the latter, the volatility of butanol increases in relation to other components. The fourth column is designed for the regeneration of the separating agent. Amyl alcohol separation is provided on the bottom of fifth column. The column operation parameters (the number of stages, the feed stage, the reflux ratio, the ratio of the quantities of the initial mixture and the separating agent) that meet the minimum energy consumption and ensure the production of commercial-quality substances are determined.

Vapor–liquid behavior of phenol and cumene in ternary and quaternary mixtures

AbstractBACKGROUNDAlthough phenol is a key intermediate in the plastics and polycarbonate industry, it is also a toxic component that requires removal from dilute aqueous streams, potentially by liquid–liquid extraction (LLX). For LLX, cumene is suggested as a solvent as it is already present in processes in the polycarbonate industry. For the recovery of cumene from phenol by distillation, knowledge on vapor–liquid equilibrium (VLE) behavior is important, in combination with how this is affected by other components possibly present as an impurity or explicitly added as a solvent. This was investigated in this work.RESULTSThe binary cumene–phenol system shows a tangent pinch in the binary VLE diagram. Addition of a range of impurities and solvents showed that hydrogen bond accepting compounds strongly improve the relative volatility of the mixture, whereas dodecane, not capable of forming hydrogen bonds, has a negative effect on the relative volatility.CONCLUSIONAddition of polar components with hydrogen bonding abilities, i.e. ketones or ethers, affected the relative volatility of cumene over phenol the most positively. Combining two types of components results in similar effects, and clear synergistic effects could not be shown based on current VLE measurements. Addition of an apolar component in combination with polar components with hydrogen abilities had only a minor effect on the relative volatility. © 2021 The Authors. Journal of Chemical Technology and Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry (SCI).

Extension of the Classification of Three-Component Systems Containing Binary Biazeotropic Components and Not Containing Ternary Azeotropes

The separation strategies of mixtures are determined by knowledge of their structures of phase equilibrium diagrams. In this paper, in two independent ways, namely, by constructing K = 1 lines and on the basis of the analysis of the transformations of the phase diagrams when the external conditions change, all thermodynamically possible subtypes of the phase portraits of the trajectories of the open equilibrium evaporation of three-component systems containing binary biazeotropic components and not containing ternary azeotropes are determined. An atlas of structures of vapor–liquid equilibrium diagrams of the indicated systems is created (116 diagrams in total).

Areas of energy advantage for flowsheets of separation modes for mixtures containing components with similar volatilities

Objectives. The conditions for the effective application of the sharp distillation technique (without a component distributed between the distillate and bottom flows) for the separation of quaternary zeotropic mixtures containing components with similar volatilities were determined. The area of energy advantage for the flowsheet based on the preliminary fractionation of the mixture, compared with the flowsheet, the first distillation column of which works based on the indirect separation mode, was identified for an ethyl acetate–benzene–toluene–butyl acetate system. Energy savings of up to 20% were achieved. The direct and indirect distillation modes can become competitive when the point of the original composition is located near single K-surfaces or in a region with a different ratio of distribution coefficients. Sharp distillation is not suitable for the separation of a mixture containing a pair of components exhibiting relative unity volatility with medium boiling points.Methods. The mathematical modeling in the Aspen Plus V.10.0 software package was chosen as the research method. The simulation was based on the Wilson local composition equation. The relative errors in the description of the phase equilibrium did not exceed 3%.Results. The structure of the vapor–liquid equilibrium diagram and diagram of surfaces of the unit component distribution coefficients were studied for the ethyl acetate–benzene–toluenebutyl acetate and acetone–toluene–butyl acetate–o-xylene systems. Flowsheets based on the sharp, indirect (both systems), or direct (second system) distillation modes were proposed. The distillation process was simulated, and the parameters of the column work were determined (the quality of the substances meets the State Standard requirements of the Russian Federation for minimal energy consumption).Conclusions. Recommendations regarding the use of sharp distillation for the separation of quaternary mixtures containing components with similar volatilities were devised.

Analysis of Mutual Transformations of the Structures of the Diagrams of Ternary Systems via the Formation of Binary Boundary Tangential Azeotropes

A consideration has been made of mutual transformations of the structures of the vapor–liquid equilibrium diagrams of ternary systems without ternary azeotropes and with monoazeotropic and biazeotropic binary components through the formation of a binary boundary tangential azeotrope with varying external conditions. Specific features of the appearance of biazeotropy at the boundaries of the concentration simplex have been determined for ternary systems with different types of structures of the vapor–liquid equilibrium diagrams.

Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations: Basic and explanatory data.

This data article contains basic and explanatory data of “Differential temperature control in heat-integrated pressure-swing distillation for separating azeotropes to deal with operating pressure fluctuations” [1], including thermodynamic models, vapor-liquid equilibrium diagrams, steady-state flowsheets, temperature profiles of columns, description and setpoint units of the abbreviation of inventory control loops, description of control loops of control flowsheet with DTC, control flowsheets of PCTC and DTC, temperature and composition tuning constants, faceplates and flowsheet equations, dynamic performances and integral absolute errors. It also contains other important information.

Isothermal measurement and modeling of VLE properties for 2,3,3,3-tetrafluoroprop-1-ene + trifluoromethane + tetrafluoromethane ternary system at temperatures from 253.15 K to 273.15 K

Abstract At present, the difficulty in the research of auto cascade refrigeration system lies in the selection of the mixed refrigerant ratio and the design of system process. Accurate thermodynamic data is the key to solve those problems. In this paper, isothermal vapor liquid equilibrium (VLE) behavior was experimentally studied for the strongly-zeotropic ternary mixture 2,3,3,3-tetrafluoroprop-1-ene (R1234yf) + trifluoromethane (R23) + tetrafluoromethane (R14) at 253.15 K, 263.15 K, and 273.15 K. The pressures and the vapor mass fractions were found to be thermodynamically consistent and were satisfactorily correlated with the NRTL-RK model and the MUNIFAC-SRK model. The average absolute relative deviations of pressure (AARD-p), and the average absolute deviations of vapor phase mass fraction (AAD-y1, AAD-y2 and AAD-y3) are less than 0.25%, 0.0032, 0.0048 and 0.0040 for the MUNIFAC-SRK model, respectively, which are better than those of 0.4%, 0.0138, 0.0198 and 0.0049 for the NRTL-RK model. The results of the MUNIFAC-SRK model showed excellent agreement with the experimental values. The isothermal three-dimensional VLE behavior and the isothermal-isobaric ternary VLE diagrams under 1500 kPa were also established using a flash calculation method.

Thermodynamic and Topological Analysis of Phase Diagrams of Quaternary Systems with Internal Singular Points

A review of the literature published in Russia and abroad on the experimental studies of phase equilibria, methods for analyzing and predicting phase diagram structures, and simulating problems of the vapor–liquid equilibrium (VLE) of quaternary systems containing internal singular points is presented. A complete set of parameters that adequately describe the liquid–vapor and liquid–liquid equilibrium is obtained for the following four systems: acetone–chloroform–ethanol–water, acetone–chloroform–propanol-2–water, chloroform–ethanol–cyclohexane–water, and ethyl acetate–methyl ethyl ketone–cyclohexane–propanol-2. The methodology for determining the structure of the VLE diagram and predicting the presence of an internal azeotrope in the systems under study and in a model system that contains binary azeotropes and a quaternary azeotrope is illustrated. Possible ways for evolutionary changes in the structure of the VLE diagram with a variation in the pressure are shown, and the Poincare indices of boundary single azeotropes and a double tangential azeotrope are determined.

Development of an in-line evaporation unit for the production of gas mixtures containing hydrogen peroxide – numerical modeling and experimental results

Hydrogen peroxide (H2O2) is a typical surface sterilization agent for packaging materials used in the pharmaceutical, food and beverage industries. We use the finite-elements method to analyze the conceptual design of an in-line thermal evaporation unit to produce a heated gas mixture of air and evaporated H2O2 solution. For the numerical model, the required phase-transition variables of pure H2O2 solution and of the aerosol mixture are acquired from vapor-liquid equilibrium (VLE) diagrams derived from vapor-pressure formulations. This work combines homogeneous single-phase turbulent flow with heat-transfer physics to describe the operation of the evaporation unit. We introduce the apparent heat-capacity concept to approximate the non-isothermal phase-transition process of the H2O2-containing aerosol. Empirical and analytical functions are defined to represent the temperature- and pressure-dependent material properties of the aqueous H2O2 solution, the aerosol and the gas mixture. To validate the numerical model, the simulation results are compared to experimental data on the heating power required to produce the gas mixture. This shows good agreement with the deviations below 10%. Experimental observations on the formation of deposits due to the evaporation of stabilized H2O2 solution fits the prediction made from simulation results.

Separation of Antimony from Copper in Vacuum Distillation

Experiment of vapor-liquid equilibrium (VLE) for Cu-Sb alloy in the range of 1150 to 1550 K at 10 Pa was investigated. The experimental data are compared with those calculated using Wilson equation, and a good agreement between the experimental and calculated values is obtained. A thermodynamic consistency of experimental VLE data and calculated values were tested by Herington test and Van Ness test, respectively. It can be seen that Cu3Sb is the main phase of the alloy from XRD pattern. The VLE diagram can be employed for designing the process and phase separation in vacuum distillation.

Experimental investigation and modeling of phase equilibria for Cu-Bi and Cu-Bi-Sb alloys in vacuum distillation

The measurements of vapor-liquid equilibrium (VLE) for Cu-Bi and Cu-Bi-Sb alloys in vacuum distillation were performed. We calculated the VLE diagrams of Cu-Bi and Cu-Bi-Sb alloys at 10 Pa by Wilson equation only using binary parameters. Thermodynamic consistency tests of experimental data for the binary and ternary systems were discussed using the Van Ness method. The calculated results are in good agreement with the experimental data. The VLE data can be used for designing the purification process and phase separation of crude copper in vacuum metallurgy.

SB-PB-AG ALLOY PROCESSING BY VACUUM DISTILLATION

The paper relevance is determined by the need to create an environmentally safe, high-performance and cost-efficient integrated vacuum distillation technology for the processing of lead-containing middling products and wastes, in particular, a Sb-Pb-Ag (SPA) alloy resulting from the recovery of silicate slag from copper anode slime melting to obtain sellable mono-element concentrates of an­timony, lead and silver. Laboratory studies were carried out on SPA alloy processing with the calculations of «T—x» temperature-com­position VLE (vapor liquid equilibrium) diagrams to analyze the behavior of Sb-Pb and Pb-Ag binary alloys during processing, select preliminary system temperature and pressure, and assess component separation efficiency in the following conditions: T = = 900+2100 K, P = 1+133 Pa, т = 8+16 hours. The aim of the study was to investigate the effect of temperature and pressure in the system, the duration of sublimation on the completeness of extraction and the degree of antimony, lead and silver separation from the SPA composition. Activity coefficients of binary alloy components when constructing VLE diagrams were calculated using the MI- VM (molecular interaction volume model). The information is obtained regarding the effect of temperature and vacuum level on the degree of sublimation and separation of metals from Sb—Pb and Pb—Ag compositions of different contents. Saturated vapor pressures were calculated for Sb (p* = 273.664+ 67436.9 Pa), Pb (0.149+485.9), Ag (5.05440 -5 -6.558) at T = 1073+1773 K. It was demonstrat­ed that the high values of the pSb /PPb = 1832.98+138.79, рр ь /pA g = 2948.16+74.09 ratio and lgPsb = 2.099+3.33 and lgPp b = 1.813+ +3.944 separation factor create theoretical prerequisites for a selective isolation of these metals by vacuum distillation, when anti­mony and lead are successively enriched in the gas phase (Ps^ > 1, Pp b > 1), and silver — in the liquid phase. The molar fraction of hard-to-sublimate lead/silver in the gaseous phase ур Ь /уA g = (1.55+982)T0 -3 /(36+772)T0 -3 is increased with rising temperature 894+1601/1399+2099 K, pressure 1.33+133 Pa and metal content in the alloy x Pb /x Ag = 0.9+0.9999/0.9+0.99. The MIVM model was used to calculate the activity factors of antimony Ysb = 0.832+0.999, lead yp b = 0.474+1.0, YA g = 0.331+0.999 for Sb/Pb and Pb/Ag al­loys with the following composition 0.1+0.9/0.9+0.1 in the investigated temperature range. The found dependences of the amount and composition of polymetallic alloy sublimation products on the process parameters are important for practical application due to the development of a principal technology for SPA processing by vacuum distillation.

Re-established congruent vapor-liquid diagram and fluctuation aspects of isotope theory-I (H2O-D2O-T2O)

The well-established vapor-pressure isotope effects (VPIEs) are independently corroborated in the set of isotopes H2O-D2O-T2O by the recently proposed congruent vapor-liquid (CVL) diagram only at the vaporization of liquid (l) phase. The striking discrepancies with the expected IE-trends following from the Bigeleisen-Mayer formulation at the condensation of vapor (v) phase have been revealed. The obvious failure of the classical second virial coefficient determined for dilute gas (g) phase to represent the actual predominance of repulsive collective interactions between particles in the so-called overheated v-phase (termed the interphase by CVL-methodology) needs the additional experimental and/or simulation confirmation. This conclusion corresponds qualitatively to that obtained for pair interactions in the about ideal-gas v-phase by Van Hook, Rebelo and Wolfsberg. The crucial distinctions between the fluctuation CVL-diagram and the deterministic, mean-field (mf) by nature, description of the first-order phase transition by its vapor-liquid equilibrium (VLE) diagram are discussed.

The Analysis of the Mutual Transformations of the Structures of Diagrams of Ternary Systems via the Formation of Binary Internal Tangential Azeotropes

The mutual transformations of the structures of vapor–liquid equilibrium diagrams of ternary systems containing zeotropic, monoazeotropic, and biazeotropic binary components via the formation of a binary internal tangential azeotrope in the case of varying external conditions are considered. The characteristic features of the appearance of binary biazeotropy in ternary systems belonging to different types of structures of vapor–liquid equilibrium diagrams are found. The mutual transformation of vapor–liquid phase diagrams of systems of classes 3.0.0-1 and 3.[2.0.0].0-2a is illustrated via a computational experiment using an isobutyl acetate–acetic acid–sulfolane system as an example.

Comparison of extractive distillation separation sequences for acetonitrile/methanol/benzene multi‐azeotropic mixtures

AbstractBackgroundThe extractive distillation‐based separation of a multi‐azeotropic mixture has several optional solvents and schemes. The screen of a suitable solvent was performed and diverse extractive distillation sequences were compared for separating the specified mixture of acetonitrile/methanol/benzene.ResultAs a solvent breaking all binary azeotropes, chlorobenzene was selected over aniline on the basis vapor–liquid equilibrium diagrams and infinite dilution factors. Four separation sequences were optimized by the sequential iterative procedure on the basis of minimal total annual cost (TAC), and CO2 emissions were calculated. Among four sequences, sequence III, composed of two extractive distillation columns and one solvent recovery column, is the best scheme from environmental and economic viewpoints. Simple partial heat integration was further implemented and can save 20.08% and 8.86% in terms of energy cost and TAC.ConclusionThe results demonstrate that the separation of acetonitrile/methanol/benzene is fully achievable using common extractive distillation with chlorobenzene as solvent. Moreover, there is a trade‐off between heat transfer in the reboiler‐condenser and corresponding energy consumption variations due to pressure changes when considering heat integration. © 2018 Society of Chemical Industry

Vapor Liquid Equilibria for Acetic Acid–Acetaldehyde–Crotonaldehyde System: Gibbs Ensemble Molecular Simulation for Pure Components and Binary Systems and NRTL Model Prediction for Ternary System

The vapor–liquid equilibrium (VLE) for the system acetic acid, acetaldehyde, and crotonaldehyde was investigated by combining the Gibbs ensemble Monte Carlo (GEMC) method and activity coefficient models prediction. The VLE of above pure components and their binary systems were first studied using GEMC method. Based on the strong association characteristics of acetic acid, the revised TraPPE-UA-D force field was developed with quantum chemistry methods for the VLE calculation of the acetic acid system. The original and mixed TraPPE-UA force field was introduced for the VLE calculation of the acetaldehyde and crotonaldehyde system, respectively. The results showed that the predictions agreed fairly well with the average relative deviations of the saturated densities smaller than 4.60%. Moreover, the binary VLE diagram was calculated using the above force fields. The simulation results of the mole composition were in good agreement with the experimental values, which verified the high simulation accuracy of ...

Harmless, industrial vacuum-distillation treatment of noble lead

This paper introduces a new process to process noble lead by vacuum distillation, which is produced from the fire reduction smelting of lead anode slime with a large number of valuable and precious metals. Lead anode slime is important as a raw material for the extraction of precious metals. However, some of the shortcomings of the traditional process, such as serious pollution, complex processes, large resource consumption, and low metal recovery rate, must be overcome. Based on a study of the saturated vapor pressure in the metal and vapor–liquid equilibrium diagram of a binary system, we carried out a large-scale recovery experiment for bismuth and lead with the enrichment of silver and copper. The experimental results show that the copper and silver contents in the residue are higher than 80%. Secondary continuous vacuum distillation resulted in a residue with a Ag content of less than 20 g/t. At the same time, the direct yield of silver from the whole process is higher than 99%, and the evaporation contents of Pb and Bi are above 90%. Achieved a comprehensive recovery of valuable metals recycling.

Application of vacuum distillation in refining crude lead

This paper introduces a new process for refining crude lead by vacuum distillation. The saturated vapor pressures of lead and impurity elements were calculated, and the removal effect of impurity elements was quantitatively predicted using the vapor-liquid equilibrium diagram. In addition, the low temperature followed by high temperature vacuum distillation method and the high temperature followed by low temperature method were adopted to adjust the order of impurity removal. The refining effect was experimentally studied using these two methods, and the best parameters were determined. The predictions are in close agreement with the experimental results. Based on theoretical and experimental analyses, a new, clean and efficient process for refining crude lead was developed. First, the crude lead was distilled by vacuum distillation at 10 Pa and 1673 K for 30 min, and then, the volatiles and residues were collected. Second, the volatiles were vacuum distilled at 10 Pa and 1273 K for 30 min. The removal rates of Cu, Sn, Ag, Zn, Sb and Bi were 99.73%, 99.72%, 96.23%, 90.78%, 74.80% and 8.82% respectively, and the purity of Pb reached 99.03%.

Development of Predictive Methods of Water–Heavy Oil Phase Equilibrium for Supercritical Water Upgrading Process

Predictive methodology was developed for water-hydrocarbon systems under high temperature and pressure conditions based on reported phase equilibrium data using the Peng-Robinson equation of state (EOS) for vapor-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE). The available experimental data for hydrocarbons with low molecular weight and interaction parameter, kij, with/without a size parameter, lij, included in the Peng-Robinson EOS were fitted to experimental data and accumulated for constructing a predictive equation for hydrocarbons with high molecular weight. As a result, lij was found to be negligible for VLE in water-hydrocarbon systems, and only the fitting parameter kij was necessary in some hydrocarbon and water systems. Consequently, prediction of VLE diagrams was possible using the estimated kij in the Peng-Robinson EOS for water-hydrocarbon systems under high temperature and pressure conditions.