Vapor Liquid Phase Equilibrium Research Articles

UNIFAC PREDICTION OF VAPOR LIQUID EQUILIBRIA INVOLVING GAMMA-VALEROLACTONE DERIVATIVE SYSTEMS

Researchers have studied the hydrogenation of Gamma-Valerolactone (GVL) over Ru/C to produce 2-methyltetrahydrofuran (2-MTHF), a biomass-based platform chemical with potential as a biofuel and green solvent. Other byproducts of this reaction include 2-butanol (2-BuOH), 2-pentanol (2-PeOH), and 1,4-pentanediol (1,4-PDO). In this study, UNIFAC activity coefficient models were used to predict the vapor-liquid equilibrium of several systems included in the process to explain the phase behavior which is important in purification process. The accuracy of the UNIFAC model is tested by comparing the experimental boiling points for the binary system of 2-propanol + 1-butanol and the vapor-liquid equi-librium of the GVL + 2-MTHF system. From this comparison, the Root Mean Square Deviation (RMSD) values for the boiling point measurements are obtained to be 3.153%, and for the liquid and vapor phases in the vapor-liquid equilibrium measurements, the RMSD values are 1.934% and 0.298% respectively. These RMSD values indicate the level of accuracy of the UNIFAC model in representing the experimental data for both boiling point measurements and vapor-liquid equilibrium phase behavior. The prediction results of vapor-liquid equilibrium data for GVL derivative systems showed that the 2-BuOH + 2-MTHF system does form an azeotrope when the mol fraction of 2-BuOH is 0.0031 at 79.780C. The calculation was performed using ChemCAD commercial software for chemical process modeling and simulation

Application of ionic liquid extractant in enhanced separation of 2-propanol-n-hexane azeotrope system

2-Propanol and n-hexane are widely used (as) chemical reagents in electronic, pharmaceutical, and chemical industries. An efficient separation of the azeotropic system of 2-propanol-n-hexane is of profound practical significance. By using the conductor-like screening model for real solve (COSMO-RS) predictive model, ionic liquids as extractants for separating the azeotropic system of 2-propanol-n-hexane were evaluated with selectivity coefficients (S) and capacity (C) as the evaluation indexes. Based on the evaluation results, one high-performance extractants named hydroxylamine Cl (C8A19) was selected from 435 kinds of ionic liquids designed by combining 29 kinds of anions and 15 kinds of cations. Moreover, the reliability of the model in predicting the vapor–liquid phase equilibrium behavior of 2-propanol-n-hexane system was verified. Then, the effect of C8A19 on the vapor–liquid phase equilibrium of the 2-propanol-n-hexane system was investigated theoretically and experimentally. The results show that the azeotrope of the system can be broken when the molar fraction of C8A19 is 0.02, denoting that C8A19 can be used for enhanced separation of 2-propanol-n-hexane system. On the basis of the aforementioned study, the selectivity mechanism of the extractant was analyzed from the perspective of microscopic molecular interactions by using the descriptor (σ-profiles) of COSMO-RS. This study provides both theoretical and data support for further designing high-performance ionic liquid extractants and extraction process.

Effect of glucose–citric acid deep eutectic solvent on the vapor–liquid equilibrium of an aqueous ethanol solution

Objectives. To study the effect of a deep eutectic solvent (DES) based on glucose and citric acid on the vapor–liquid equilibrium of an aqueous solution of ethanol.Methods. A qualitative and quantitative analysis of the conditions of vapor–liquid equilibrium in an ethanol–water–DES ternary mixture was performed based on the open evaporation method and the measurement of TPxy data using a Świętosławski ebulliometer. Since the volatility of the DES is negligible in comparison with that of water and ethanol, the composition of the vapor phase was measured by means of Karl Fischer titration. The conditions of vapor–liquid phase equilibrium were modeled using the UNIFAC model.Results. The open evaporation method was used to determine the curves of residual concentrations for the ethanol–water–DES mixture at various DES concentrations and compositions (glucose–citric acid ratios). TPxy data was obtained for the mixture produced by adding 30 wt % DES to an aqueous solution of ethanol at atmospheric pressure. Studies show that DES based on glucose and citric acid has a significant effect on the relative volatility of ethanol in aqueous solution, leading to the disappearance of the azeotropic point. This effect is due to only the presence of glucose. Citric acid does not change the composition of the equilibrium phases, but rather increases the solubility of glucose in aqueous ethanol solutions. This is especially important at high ethanol concentrations, since glucose is poorly soluble in ethanol.Conclusions. Addition of DES based on glucose and citric acid to an aqueous solution of ethanol leads to the disappearance of the azeotropic point. DES can thus be considered as a promising entrainer for extracting ethanol from aqueous solutions using extractive distillation. Modeling of the conditions of vapor–liquid equilibrium in the ethanol–water–DES system using the UNIFAC model showed a satisfactory level of accuracy. The error in the calculated data increases with increasing the glucose concentration, while remaining acceptable for practical use.

Study on separation of acetonitrile and methanol azeotropic system using tetraethylammonium chloride-based deep eutectic solvents

Large quantities of waste streams containing mixed acetonitrile (ACN) and methanol (MeOH) are generated during pharmaceutical and chemical production. The polarity of these two substances is extremely similar, resulting in the formation of an azeotrope at room temperature and atmospheric pressure. In this study, deep eutectic solvents (DESs) were selected as extractants for the separation of ACN-MeOH binary azeotrope. To obtain suitable DESs, the σ-profiles of ACN, MeOH, DESs were calculated using the COSMO-SAC model, and the results demonstrated that the DESs synthesized when tetraethylammonium chloride (TEAC) was chosen as the hydrogen bond acceptor (HBA) and acetamide as the hydrogen bond donor (HBD) could effectively break the azeotropy of ACN and MeOH. Therefore, four DESs were synthesized with molar ratios of TEAC: acetamide = 1: n (n = 1, 2, 3, 4) for subsequent ACN-MeOH-DESs ternary vapor–liquid phase equilibrium (VLE) experiments at 101.3 kPa to determine the optimal extractant. The measured VLE data revealed the higher separation of DES TEAC-2acetamide on the ACN-MeOH binary azeotrope compared with other DESs. Afterward, the NRTL model was adopted to calculate the binary interaction parameters between ACN/MeOH and DESs. The results of the fitting indicated agreement with the experimental data. Finally, the separation mechanism was further analyzed using the interaction energy analysis, improved independent gradient model (IGMH), and the theory of atoms in molecules (AIM). The results indicated that the strong interaction between DESs and MeOH is the primary factor in the ability of DESs to break the azeotrope of the system.

The Vapor–Liquid Phase Equilibrium Line for Water within the Framework of the Renormalization Group Theory

The Vapor–Liquid Phase Equilibrium Line for Water within the Framework of the Renormalization Group Theory

Force Field for Calculation of the Vapor-Liquid Phase Equilibrium of trans-Decalin

Based on the TraPPE force field, previously unknown values of the parameters of the intermolecular interaction potential of trans-decalin were determined. Parametrization was carried out using experimental data on saturated vapor pressure and density at atmospheric pressure. The found parameters make it possible to adequately describe the boiling and condensation lines of trans-decalin and also predict the critical values of pressure, density, and temperature with satisfactory accuracy. Calculations of vapor-liquid phase equilibrium conditions for a binary CO2—trans-decalin mixture in supercritical conditions for CO2 were carried out. When quantitatively comparing the calculated values with experimental data, an underestimation of pressure at a temperature of 345.4 K by 30% is observed, which decreases to 5% for temperatures up to 525 K.

Vapor-liquid equilibrium data and performance analysis on binary mixture of R32 and R1216 for residential air condition system

In order to accurately evaluate the performance of R32 and unsaturated fluorinated olefins (HFOs) binary mixtures in residential air condition (RAC) system, the vapor-liquid phase equilibrium (VLE) data of R32 and R1216 binary mixture has been measured with a liquid phase circulation system in the temperature range from 285 to 315 K. The experimental data were correlated by Peng-Robinson (PR) equation of state with Huron-Vidal (HV) mixing rule and non-random two-liquid (NRTL) activity coefficient model. Maximum deviation of the pressure and the mole fraction was 1.38% and 0.013, respectively. The azeotropic behavior was observed for the R32 and R1216 binary mixture when the mole fraction of R32 was around 0.9. The RAC system with standard refrigeration, heating and variable evaporation temperature operating condition was simulated. The cycle performance of binary mixtures of R32 + R1216, R1234yf and R1234ze(E) at different concentrations was compared. The azeotrope R32/R1216 (molar ratio 0.9/0.1) has an extremely low GWP, the COP, refrigeration/heating capacity per unit volume and condensation pressure close to pure R32, and lower discharge temperature. At the same time, it also has well variable operating conditions performance and can be considered as a drop-in replacement for R32 and R410A in RAC systems.

Separation process and mechanism of cyclohexane/ethanol system using deep eutectic solvents based on betaine and choline chloride

The efficient separation of azeotropes is of great significance for the effective recovery and utilization of chemical raw materials and environmental protection. This study investigated the separation efficiency and mechanism of deep eutectic solvents (DESs) with different combinations and ratios of hydrogen bond acceptors (HBA) and hydrogen bond donors (HBD) for cyclohexane/ethanol azeotropic systems. Through vapor-liquid phase equilibrium experiments, the effects of different DESs and different HBD: HBA molar ratios as solvents on the phase behavior of cyclohexane/ethanol azeotropic system were studied, and different combinations and molar ratios of DESs with the best separation performance were obtained. The effective separation of azeotropes by DESs is primarily due to the stronger molecular surface electrostatic potential of ethanol compared to that of cyclohexane, which results in a stronger interaction between the DESs and ethanol. Finally, through process simulations, a cyclohexane/ethanol extractive distillation separation process using a DES as the main solvent was established. The results showed that the separation effect of DESs increased with the increase of the interaction force between DESs and ethanol, achieving efficient recovery of chemical raw materials. This study established a safe and efficient separation process using DESs, which is of great significance for environmental protection and the development of safety processes.

A study on the vapor–liquid equilibria of vinyl acrylate-acetic acid and vinyl acetate-acetic acid with GEMC method

Vinyl acetate (VAc) is one of the widely utilized industrial organic raw materials. In the acetoxylation of ethylene to vinyl acetate, there is a by-product vinyl acrylate. However, the vapor–liquid phase equilibrium data of this component with acetic acid and vinyl acetate have not been reported. Here, by Density Functional Theory calculations, we fitted the TraPPE-UA force field parameters of vinyl acrylate. The vapor–liquid phase equilibrium data of the vinyl acrylate-acetate and vinyl acrylate-vinyl acetate binary systems were calculated using the Gibbs Ensemble Monte Carlo (GEMC) method. The calculated phase equilibrium data were utilized to fit the binary interaction parameters of the NRTL equations for the binary systems which were used for the separation process simulation of the vinyl acrylate, acetic acid and vinyl acetate systems. It was verified that the TraPPE-UA force field parameters fitted in this paper have high accuracy. The results clarify the concentration distribution of vinyl acrylate gas–liquid phase components in the distillation column, which builds the foundation for the development of the separation process.

Vapor–Liquid Equilibrium Phase Behavior of Binary Systems of Carbon Dioxide with Eugenol or Guaiacol

Vapor–Liquid Equilibrium Phase Behavior of Binary Systems of Carbon Dioxide with Eugenol or Guaiacol

Preparation of high-purity copper through vacuum distillation

Copper is capable of maintaining strong competitiveness in the metal materials market for its prominent ductility, thermal conductivity, and electrical conductivity. As more rigorous purity requirements of industrial sputtering targets and aerospace have been raised, the clean and efficient production of high-purity copper turns out to be an urgent problem over the past few years. In this paper, the possibility of removing impurities from copper melt was investigated by integrating theoretical calculations and experiments, and the separation coefficient and vapor-liquid equilibrium phase diagram of copper and impurity elements were determined and plotted using the molecular interaction volume model (MIVM). Moreover, the effects of the distillation temperature, the holding time, and the system pressure on the experimental results were discussed. As indicated by the results, with the rise of the temperature and with the extension of the holding time, the purity of copper was first increased and then decreased, and the purity of residual copper reached 99.9993% at 1473 K temperature, 1.5 h holding time, and 5 Pa pressure, and the method effectively separated impurities from copper raw materials. Besides, no waste water or waste gas emission was generated in the experiment.

Separation of fuel additives based on mechanism analysis and thermodynamic phase behavior

tert-butanol and ethyl acetate, as fuel additives and oxygenated fuels, can improve fuels quality and reduce exhaust emissions. Therefore, the recovery of these compounds from azeotropic systems is of great significance. Ionic liquids (ILs) are promising green solvents for separating azeotropic systems. In this study, an efficient extraction strategy based on 1-butyl-3-methylimidazolium acetate ([Bmim][AC]) is proposed. The mechanism by which ILs enable the separation of binary alcohol-ester azeotropes was revealed by evaluating the lowest conformational energy through combining an independent gradient model based on the Hirshfeld partition (IGMH) and frontier molecular orbitals, to preliminarily screen the extractants. The range of extractants was further reduced by a vapor–liquid phase equilibrium (VLE) experiment, and a modeling method for separating the alcohol–ester system and recovering the solvent using [Bmim][AC] and 1-ethyl-3-methyl-3-imidazolium acetate ([Emim][AC]) is established. Under the optimal operating conditions, the use of [Bmim][AC] can reduce the total annual cost (TAC) per year by 17.78%, and the emissions of CO2, SO2, and NO can be reduced by 10.86%. In this study, a comprehensive method for screening extractants is proposed, and the simulation process is optimized in combination with the economic and environmental impact. The results have important guiding significance for realizing efficient, energy-saving, and green azeotropic separation systems in industry.

Holding water in a sieve—stable droplets without surface tension

Our understanding of supercritical fluids has seen exciting advances over the last decades, often in direct contradiction to established textbook knowledge. Rather than being structureless, we now know that distinct supercritical liquid and gaseous states can be distinguished and that a higher order phase transition - pseudo boiling - occurs between supercritical liquid and gaseous states across the Widom line. Observed droplets and sharp interfaces at supercritical pressures are interpreted as evidence of surface tension due to phase equilibria in mixtures, given the lack of a supercritical liquid-vapor phase equilibrium in pure fluids. However, here we introduce an alternative physical mechanism that unexpectedly causes a sharpening of interfacial density gradients in absence of surface tension: thermal gradient induced interfaces (TGIIF). We show from first principles and simulations that, unlike in gases or liquids, stable droplets, bubbles, and planar interfaces can exist without surface tension. These results challenge and generalize our understanding of what droplets and phase interfaces are, and uncover yet another unexpected behavior of supercritical fluids. TGIIF provide a new physical mechanism that could be used to tailor and optimize fuel injection or heat transfer processes in high-pressure power systems.

Effect of salt-based deep eutectic solvent on vapor-liquid equilibrium for the mixture of 2-propanol and water

Salt-based deep eutectic solvents (DESs) (i.e, ethylene glycol-choline chloride-MgBr2 (1: 0.6: 0.05) and ethylene glycol-choline chloride-MgCl2 (1: 0.6: 0.05)) have been proposed in this work for the separation of the azeotrope of 2-propanol and water (H2O). Based on the newly determined experimental data for the systems (2-propanol + H2O + DESs), revised LIQUAC model was developed for describing the vapor-liquid phase equilibrium of the system (2-propanol + H2O + DESs). Comparisons of model calculated and experimental measured values proved that the model presented here provides a reliable method for correlating the vapor-liquid equilibria data. Furthermore, both the VLE experiments and the model were used to study the effect of salt-based deep eutectic solvent on vapor–liquid equilibria. It was revealed that ethylene glycol-choline chloride-MgCl2 (1: 0.6: 0.05) is more promising than ethylene glycol-choline chloride-MgBr2 (1: 0.6: 0.05) as entrainer for the separation of mixture (2-propanol + water).

Vapor-liquid equilibrium data for binary mixture of 1,1,2,3,3,3-Hexaflfluoro-1-propene (R1216) and trans-1,3,3,3-Tetraflfluoropropene (R1234ze(E)) at temperatures from 275 to 315 K

In this work, the vapor–liquid phase equilibrium (VLE) data of R1234ze(E) and R1216 binary mixtures has been investigated experimentally and theoretically. The VLE data for the binary system of R1234ze(E) + R1216 were measured with a recirculation system at five temperatures range from 275 to 315 K. The experimental results were correlated by Peng-Robinson equation of state combined with Huron-Vidal mixing rule or Wong-Sandler mixing rule and non-random two-liquid activity coefficient model, and van der Waals mixing rule. The calculated values were in well agreement with the experimental results, with the maximum deviations of the pressure and the mole fraction of the vapor phase within 0.87% and 0.016, respectively. The average absolute deviations of the pressure and the mole fraction of the vapor phase between the experimental values and calculated values were 0.35% and 0.005, respectively.

Isobaric Vapor–Liquid Equilibrium Experiment of Methyl Acetate + Ethanol Containing Different Ionic Liquids at 101.3 kPa

Vapor–liquid phase equilibrium experiments for the binary system of methyl acetate + ethanol and ternary systems of methyl acetate + ethanol + 1-ethyl-3-methylimidazole acetate ([EMIM][OAC]), methyl acetate + ethanol + 1-butyl-3-methylimidazole acetate ([BMIM][OAC]), and methyl acetate + ethanol + 1-ethyl-3-methylimidazolium methanesulfonate ([EMIM][MeSO3]) were conducted at 101.3 kPa. The results show that all three extractants can effectively break the azeotrope of methyl acetate + ethanol. The ILs produce a salting-out effect on methyl acetate and increase the relative volatility of methyl acetate to ethanol. The NRTL model has been chosen to correlate the experimental data. The ARD (average relative deviation) of the activity coefficient of NRTL for the binary system of methyl acetate + ethanol and ternary systems of methyl acetate + ethanol + [EMIM][OAC], methyl acetate + ethanol + [BMIM][OAC], and methyl acetate + ethanol + [EMIM][MeSO3] is 1.22, 1.88, 1.64, and 1.57%, respectively, indicating the good applicability of NRTL.

Equation of State Associated with Activity Coefficient Model Based on Elements and Chemical Bonds

A new element- and chemical bond-dependent GE-EoS model(SRK-UNICAC) is proposed to consider the deviation of the vapor and liquid phases from the ideal state. The SRK-UNICAC model combines the UNICAC model and the SRK cubic equation of state. It uses the original interaction parameters of the UNICAC model and uses this model to calculate the GE. The SRK-UNICAC model predicted vapor-liquid equilibria for 87 binary systems under low- and medium-pressure conditions, 12 binary systems under high-pressure conditions, and 14 ternary systems; a comparison of the predictions with five other activity coefficient models were also made. The new model predicted the vapor-phase fraction and bubble-point pressure, and temperature for the binary system at high pressure, with a mean relative error of 3.75% and 6.58%, respectively. The mean relative errors of vapor-phase fraction and bubble-point temperature or bubble-point pressure for ternary vapor–liquid phase equilibrium were 6.50%, 4.76%, and 2.25%. The SRK-UNICAC model is more accurate in predicting the vapor–liquid phase equilibrium of high-pressure, non-polar, and polar mixtures and has a simpler and wider range of prediction processes. It can therefore be applied to the prediction of vapor–liquid equilibrium.

Correlating Pure Component Properties with MOSCED Solubility Parameters: Enthalpy of Vaporization and Vapor Pressure

Tools to predict vapor–liquid phase equilibria are indispensable for the conceptualization and design of separation processes. Modified separation of cohesive energy density (MOSCED) is a solubility-parameter-based method parameterized to make accurate predictions of the limiting activity coefficient. As a solubility-parameter-based method, MOSCED can not only make quantitative predictions, but can shed light on the underlying intermolecular interactions. In the present study, we demonstrated the ability of MOSCED to correlate the enthalpy of vaporization and vapor pressure at a specific temperature using multiple linear regression. With this addition, MOSCED is able to predict vapor–liquid phase equilibria in the absence of reference data. This was demonstrated for the prediction of the Henry’s constant and solvation free energy of organic solutes in water, which was found to be superior to mod-UNIFAC. In addition to being able to make phase equilibrium predictions, the ability to correlate the enthalpy of vaporization and vapor pressure offers the opportunity to include additional properties in the regression of the MOSCED parameters. Given this success, we additionally attempted to correlate a wide range of physical properties using a similar expression. While, in some cases, the results were reasonable, they were inferior to the correlations of the enthalpy of vaporization and vapor pressure. Future efforts will be needed to improve the correlations.

Theoretical calculation and experimental investigation on vacuum gasification separation of Ag-Cu-Au ternary alloy

In this study, an innovative method for vacuum gasification separation of Ag-Cu-Au alloy was proposed. The saturated vapor pressure of each component is calculated theoretically, and the activities of Au-Cu and Ag-Cu-Au alloys are calculated by molecular interaction volume model (MIVM). The results show that the activities of Au-Cu alloy calculated by MIVM is accurate and reliable. Based on activity prediction, the separation coefficients of Au-Cu alloy were calculated. The results show that the separation coefficients of Au-Cu alloy are between 0.0037 ∼ 0.6626 in the temperature range of 1337–1773 K. Subsequently, the vapor-liquid equilibrium composition and vapor-liquid equilibrium phase diagram of Au-Cu and Ag-Cu-Au alloys were calculated, and the vapor-liquid equilibrium measurement experiments of Ag-Cu-Au alloy were carried out. The results show that vacuum gasification is challenging to realize the separation of Au-Cu alloy. During the vacuum gasification separation process of Ag-Cu-Au alloy, silver volatilizes into the vapor phase. When the pressure is 10 Pa and the mole fractions of silver, copper and gold in the liquid phase are 0.2, 0.1 and 0.7, respectively, the equilibrium temperature is 1545.5 K, and the mole fractions of silver, copper and gold in the vapor phase are 0.994, 0.002 and 0.004 respectively. The corresponding experimentally determined mole fractions of silver, copper, and gold in the vapor phase were 0.9666, 0.0333, and 5.89 × 10−5, respectively. In addition, the distribution and occurrence state of each element in the vacuum separation process of Ag-Cu-Au alloy were determined by EPMA.

Calculating the Enthalpy of Vaporization of Ethanol, n-Heptane, Isooctane, and a Binary Mixture of Isooctane + n-Heptane from Their Vapor Pressure Data

ConspectusA key physical property of volatile liquids is vapor pressure (VP). Volatile organic compounds (VOCs) are a classification of compounds directly associated with low boiling points, high rates of evaporation, and high flammability. The majority of chemists and chemical engineers were directly exposed to the odor of simple ethers, acetone, and toluene in the air while taking an organic chemistry laboratory course as an undergraduate student. These are just a few examples of the numerous VOCs produced by the chemical industry. When toluene is poured into a beaker from its reagent bottle, its vapors readily evaporate at ambient temperature from this open container. When the cap is securely placed back on the reagent bottle of toluene, a dynamic equilibrium develops and exists in this closed environment. This chemical concept is known as a vapor-liquid phase equilibrium. A crucial physical property of spark-ignition (SI) fuels is high volatility. In the United States, most of the vehicles traveling on the road today have SI engines. Gasoline is the fuel used to power these engines. It is a major product manufactured by the petroleum industry. This fuel is petroleum based since it is a refined product of crude oil consisting of a mixture of hydrocarbons, additives, and blending agents. Thus, gasoline is homogeneous solution of VOCs.The VP as a function of temperature of a pure VOC can readily be measured using an ebulliometer. The VP is also known in the literature as the "bubble point pressure". In this investigation, the VP as a function of temperature was acquired for the VOCs ethanol, isooctane (2,2,4-trimethylpentane), and n-heptane. The latter two VOCs are primary reference fuels components found in 87, 89, and 92 grade gasoline. Ethanol is an oxygenate additive of gasoline. The VP of a homogeneous binary mixture of isooctane and n-heptane was also acquired using the same ebulliometer and methodology. In our work, an enhanced ebulliometer was used to collect the VP data in our work. It is known as the vapor pressure acquisition system. The devices that comprise the system automatically acquire the VP data and log it into an excel spreadsheet. The data are readily transformed into information to compute the heat of vaporization (ΔHvap). The results described in this Account compare quite favorably to the literature values. This validates our system for performing fast and reliable VP measurements.