Vapour–liquid equilibria of dimethyl carbonate with linear alcohols and estimation of interaction parameters for the UNIFAC and ASOG method

Isobaric vapour–liquid equilibria have been experimentally determined for the binary systems methanol+dimethyl carbonate, ethanol+dimethyl carbonate, dimethyl carbonate+1-propanol, dimethyl carbonate+1-butanol and dimethyl carbonate+1-pentanol at 101.3 kPa. The activity coefficients were calculated to be thermodynamically consistent and were correlated with the Wilson and UNIQUAC equations. Interaction parameters related to the carbonate group (OCOO) and alcohols, in ASOG and UNIFAC methods, have been determined using our experimental VLE data. The experimental results, as well as those by other authors, agree with the calculated VLE using the new ASOG and UNIFAC parameters.     

Revision of UNIFAC group interaction parameters of group contribution models to improve prediction results of vapor–liquid equilibria for solvent–polymer systems

The objective of this work was to improve the accuracy of group contribution models for prediction of solvent activities in polymer solutions by revising UNIFAC group interaction parameters using a wide range of vapor–liquid equilibrium (VLE) data of solvent–polymer systems. The group contribution models considered in this work were UNIFAC-FV, Entropic-FV, GK-FV and UNIFAC-ZM models. A total of 142 systems that consisted of 16 polymers and 36 solvents containing a large variety of solvent–polymer systems ranging from non-polar to polar substances were considered to optimize 46 pairs of group interaction parameters. Data considered were split up into systems containing alkane and cycloalkane, aromatic, and polar solvents. For athermal systems, the UNIFAC-FV model gave the best results. Therefore, the model was used in optimizing the group parameters. Revised group interaction parameters were found to improve the reliability of VLE predictions in solvent–polymer systems. A significant improvement of prediction results was achieved by UNIFAC-FV model from 20.0 to 10.8% absolute average deviation (AAD) in solvent activities for systems containing polar solvents and from 16.7 to 10.9% AAD for all systems. The prediction results of GK-FV and UNIFAC-ZM models were also improved.     

Vapor–liquid equilibrium data for the binary systems in the process of synthesizing diethyl carbonate

Vapor–liquid equilibrium data for the binary systems of carbon monoxide (CO) + diethyl carbonate (DEC) and carbon monoxide + ethyl acetate (EA) were measured at temperatures of 293.2 K, 313.2 K and 333.2 K and the elevated pressures up to 12.00 MPa. The measurements were carried out in a cylindrical autoclave with a moveable piston and an observation window. The experimental data were correlated using the Peng–Robisom (PR) equation of state (EOS) and Peng–Robinson–Stryjek–Vera (PRSV) equation of state with the two-parameter van der Waals II or Panagiotopoulos–Reid mixing rule. The interaction parameters were obtained while correlating. The comparison between calculation results and experimental data indicated that the method of PRSV equation of state with van der Waals II produced the better correlated results.     

Vapor–liquid equilibria of asymmetrical systems using UNIFAC-NRF group contribution activity coefficient model

The UNIFAC-NRF group contribution activity coefficient model is used for the calculation of vapor–liquid equilibria of binary systems of the heavy alkanes and light gases such as CH₄, C₂H₆, CO₂ and N₂. The linear combination mixing rule, LCVM, of the Huron–Vidal and Michelsen, Chen et al. modification of PSRK and Universal Group Contribution Equation of State of Ahlers and Gmehling are combined with the UNIFAC-NRF group activity coefficient model to correlation of the vapor–liquid equilibrium of both light and heavy hydrocarbons. The results show that the LCVM mixing rule combing with UNIFAC-NRF group contribution model correlate the asymmetric systems better than the LCVM-UNIFAC and the other EOS/G^E models. Also the group contribution model is used for the prediction of the phase envelope of the synthetic fluid with accurate results.     

A non-recycle flow still for the experimental determination of vapor–liquid equilibria in reactive systems

Experiments for the determination of vapor–liquid equilibrium (VLE) data with a Non-Recycle Flow Still (NFS) are described. Due to short residence times, the NFS is especially suited for systems with thermally unstable components and for reactive mixtures. VLE data of the latter are necessary for modeling reactive distillation processes. With the NFS isobaric data both at atmospheric and at reduced pressure can be gained. The potential of this technique is demonstrated and validated with the well-known, non-reactive systems methanol–ethanol and ethanol–water. The other (mainly reactive) binary mixtures investigated stem from two esterification systems (methyl formate and ethyl acetate production) and one etherification system (tert-amyl methyl ether production). The NRTL equation is used for modeling of the VLE data. The data acquired with the NFS are compared with literature data (whenever possible) or with results of group contribution methods.     

Liquid—liquid equilibria for ternary systems of water—phenol and solvents: new UNIFAC parameters for interactions between the groups ACOH/COOH and prediction

The UNIFAC group-contribution method is used to predict ternary liquid—liquid equilibrium data presented in a recent paper (Alvarez Gonzalez et al.) for the systems water/phenol/benzene, water/phenol/ethylbenzene, water/phenol/nonanoic acid, water/phenol/ethyl acetate, water/phenol/isopropyl acetate, water/phenol/n-butyl acetate, water/phenol/isoamyl acetate and water/phenol/cyclohexyl acetate at 25°C and water/phenol/n-hexyl acetate at 25, 35 and 45°C. New UNIFAC interaction parameters between the groups ACOH/COOH have been obtained.A comparison between the experimental and predicted values is presented.     

Vapor–liquid equilibrium of carbon dioxide with diethyl methylmalonate,diethyl ethylmalonate and diethyl n-butylmalonate at elevated pressures

Vapor–liquid equilibrium (VLE) data for binary mixtures of CO₂ with homologous esters of diethyl methylmalonate, diethyl ethylmalonate, and diethyl n-butylmalonate at 308.2, 318.2, and 328.2 K, respectively, over the pressure range 1.4–8.4 MPa were measured using a semi-flow apparatus. New gas solubility data for CO₂ in esters are presented, and the Henry’s law constants for CO₂ in these esters are evaluated by employing the Krichevsky–Ilinskaya (KI) equation. The VLE data were also correlated using the Soave–Redlich–Kwong and the Peng–Robinson equations of state (EOSs) with various types of mixing rules. It is shown that EOS with both the van der Waals mixing rules and the two adjustable parameters yield satisfactory correlation results.     

Modelling of high-pressure phase equilibria using the Sako–Wu–Prausnitz equation of state: II. Vapour–liquid equilibria and liquid–liquid equilibria in polyolefin systems

Phase equilibria in binary and ternary polyolefin systems are calculated using the cubic equation of state proposed by Sako–Wu–Prausnitz (SWP). Calculations were done for high-pressure phase equilibria in ethylene/polyethylene (LDPE) systems and for liquid–liquid equilibria (LLE) in systems containing either high-density polyethylene or poly(ethylene-co-propylene). The calculations for the copolymer/solvent systems are compared with those using the SAFT EOS. The two equations of state can describe UCST, LCST as well as U-LCST behaviour with similar accuracy. Whereas, the binary interaction parameter is temperature-independent for SAFT, it is found to be a function of temperature for the SWP model. Moreover, the influence of an inert gas on the LCST of the polyethylene/hexane system is investigated using the SWP EOS. The polydispersity of the different polyethylenes is considered in the phase equilibrium calculations using pseudocomponents chosen by the moments of the experimental molecular weight distributions.     

New analytic apparatus for experimental determination of vapor–liquid equilibria and saturation densities

A new experimental apparatus for performing simultaneous determination of high-pressure vapor–liquid equilibria (VLE) and saturated densities was developed in this work. The experimental methodology was verified by measuring these properties for the carbon dioxide + 1-propanol and carbon dioxide + 2-propanol systems from 313 to 363 K. The apparatus is based on the static-analytic method for VLE determinations and was slightly modified by coupling a vibrating U-tube densitometer to obtain saturated densities for both vapor and liquid phases. VLE measurements agreed with previous literature data and were correlated with the Peng–Robinson equation of state coupled to the Wong–Sandler mixing rules. Saturation densities at temperatures above 313 K have not been published up to now.     

Automated apparatus for the rapid determination of liquid–liquid and solid–liquid phase transitions

An automated apparatus developed for the determination of liquid–liquid and solid–liquid equilibrium temperatures with a resolution of 1 mK and a traceable accuracy of 0.01 K is described. The amount of light transmitted through six sample cells placed in a computer controlled thermostat is recorded at heating or cooling rates from 0.075 to 15 K h⁻¹. The construction does not require expensive optic equipment like lasers, glass fibre optics or photomultipliers, but is based on light emitting diodes (LED) as light sources and light dependent resistors (LDR) or photodiodes as detectors. As shown by the discussed examples, the instrument has a wide range of possible applications from the investigation of simple one-component and binary systems to the study of the complicated phase behavior of surfactant solutions.     

Prediction by the ASOG method of liquid–liquid equilibrium for binary and ternary systems containing 1-alkyl-3-methylimidazolium hexafluorophosphate

Ionic liquids are neoteric, environmentally friendly solvents (since they do not produce emissions) composed of large organic cations and relatively small inorganic anions. They have favorable physical properties, such as negligible volatility and wide range of liquid existence. Moreover, many different cations and anions can be used to synthesize ionic liquid, so the properties can be designed by the use of selected combinations of anions and cations. Liquid–liquid equilibrium (LLE) data for systems including ionic liquids, although essential for the design and operation of separation processes, are still scarce. However, some recent studies have presented ternary LLE data involving several ionic liquids and organic compounds such as alkanes, alkenes, alkanols, water, ethers and aromatics. In this work, the ASOG model for the activity coefficient is used to predict the LLE for 11 binary and 17 ternary systems including the ionic liquid 1-alkyl-3-methylimidazolium hexafluorophosphate plus alkanes, alkenes, alkanols, ketones, carboxylic acids and aromatics. New group interaction parameters were determined by using a modified Simplex method, minimizing a composition-based objective function. The results are satisfactory, with rms deviations of about 4%.     

Predicting vapor–liquid equilibria of fatty systems

In the present work, a group contribution method is proposed for the estimation of the vapor pressure of fatty compounds. For the major components involved in the vegetable oil industry, such as fatty acids, esters and alcohols, triacylglycerols (TAGs) and partial acylglycerols, the optimized parameters are reported. The method is shown to be accurate when it is used together with the UNIFAC model for estimating vapor–liquid equilibria (VLE) of binary and multicomponent fatty mixtures comprised in industrial processes such as stripping of hexane, deodorization and physical refining. The results achieved show that the group contribution approach is a valuable tool for the design of distillation and stripping units since it permits to take into account all the complexity of the mixtures involved. This is particularly important for the evaluation of the loss of distillative neutral oil that occurs during the processing of edible oils.The combination of the vapor pressure model suggested in the present work with the UNIFAC equation gives results similar to those already reported in the literature for fatty acid mixtures and oil–hexane mixtures. However, it is a better tool for predicting vapor–liquid equilibria of a large range of fatty systems, also involving unsaturated compounds, fatty esters and acylglycerols, not contemplated by other methodologies. The approach suggested in this work generates more realistic results concerning vapor–liquid equilibria of systems encountered in the edible oil industry.     

Prediction of liquid–liquid equilibrium for ternary systems containing ionic liquids with the tetrafluoroborate anion using ASOG

Liquid–liquid equilibrium (LLE) data for different systems involving ionic liquids are essential for design, optimization and operation of separation processes, such as recovery of valuable products and remotion of polluting agents in effluents. In this work, the ASOG model for the activity coefficient is used to predict LLE data for 32 ternary systems at 101.3 kPa and several temperatures; all the systems are formed by ionic liquids including the tetrafluoroborate anion plus alkanes, alkenes, cycloalkanes, alkanols, ketones, carboxylic acids, esters and aromatics. New group interaction parameters were determined by using a modified Simplex method, minimizing a composition-based objective function. The results, in terms of mean deviation between the experimental and calculated compositions, are satisfactory, with rms deviations of about 4%.     

Liquid–liquid equilibrium in ternary ionic liquid systems by UNIFAC: New volume,surface area and interaction parameters. Part I

Ternary liquid–liquid equilibria (LLE) data in systems involving ionic liquids has been investigated by several years, mainly due to the innovative role of ionic liquids as extraction solvents. The thermodynamic modeling of these systems has been performed almost invariably with the well-known NRTL model. In recent years, the UNIQUAC model has also been used, with structural parameters for ionic liquids determined either by empirical correlations or, more recently, through quantum mechanics calculations. In this work, the structural group volume and area parameters for the group-contribution UNIFAC method have been calculated for six ionic liquids following the quantum mechanics approach. The Density Functional Theory (DFT) was used to optimize the molecular geometry and the Polarizable Continuum Method (PCM) was used to calculate the area and volume. The obtained parameters were used to correlate LLE data for twenty-four ternary systems, totalizing 169 tie-lines. New interaction parameters were also estimated between the solvent and ionic liquid functional groups. The results are very satisfactory, with root mean square deviations between experimental and calculated compositions about 1.6%.     

Vapor–liquid equilibria for the system 1-propanol+n-hexane near the critical region

Vapor–liquid equilibria and critical point data for the system 1-propanol+n-hexane at 483.15, 493.15, 503.15 and 513.15 K are reported. The critical pressures determined from the critical opalescence of the mixture were compared with published data for the system 2-propanol+n-hexane. Phase behavior measurements were made in a modified circulating type apparatus with a view cell. These mixtures are highly nonideal because of the hydrogen bonding of 1-propanol. Modeling of the experimental data has been performed using the multi-fluid nonrandom lattice fluid with hydrogen-bonding (MF-NLF-HB) equation of state and the Peng–Robinson–Stryjek–Vera (PRSV) equation of state with Wong–Sandler mixing rule. The critical points and the critical locus were also calculated.     

Isobaric vapour–liquid equilibria for the binary systems of fuel oxygenates with aromatic hydrocarbons

Isobaric vapour–liquid equilibrium data at 720?mm?Hg for the binary systems of diisopropyl ether with o-xylene and m-xylene and dimethoxymethane with benzene and toluene are determined. A Swietoslawski type ebulliometer is used for the measurements. The experimental T?x data are used to estimate Wilson parameters and the parameters in turn are used to calculate the vapour compositions and activity coefficients. The activity coefficients are used to calculate molar excess Gibbs free energy (G ^E). All the systems studied here do not exhibit azeotropes. Excess Gibbs free energy values are positive over the entire range of composition for all the systems.     

Solid–liquid equilibria for binary and ternary systems with the Cubic-Plus-Association (CPA) equation of state

A systematic investigation of the CPA model’s performance within solid–liquid equilibria (SLE) in binary mixtures (methane + ethane, methane + heptane, methane + benzene, methane + CO₂, ethane + heptane, ethane + CO₂, 1-propanol + 1,4-dioxane, ethanol + water, 2-propanol + water) is presented. The results from the binary mixtures are used to predict SLE behaviour in ternary mixtures (methane + ethane + heptane, methane + ethane + CO₂). Our results are compared with experimental data found in the literature.     

Vapor—liquid and vapor—liquid—liquid phase equilibria for binary and ternary systems for nitrogen,ethane and methanol: Experiment and data reduction

Zeck, S. and Knapp, H., 1986. Vapor-liquid and vapor-liquid-liquid phase equilibria for binary and ternary systems of nitrogen, ethane and methanol; experiment and data reduction. Fluid Phase Equilibria, 25: 302–322.VLE and VLLE are investigated for three binary and one ternary system containing N₂, C₂H₆ and CH₃OH in a high-pressure phase equilibrium apparatus with vapor recirculation at temperatures 240 < T < 298 K and pressures 4 < p < 75 bar. Two liquid phases are observed in the systems C₂H₆CH₃OH and N₂CH₃OH. Experimental results are reported and compared with available correlations.     

Vapor–liquid equilibria of systems containing acetic acid and gaseous components. Measurements and calculations by a cubic equation of state

Isothermal pressure-composition VLE data have been measured for four systems containing acetic acid and a gaseous component. The gaseous components are carbon monoxide, carbon dioxide, hydrogen and methane. The measurements were made in a static cell and the compositions of the gas and the liquid phases were measured by a gas chromatograph. A new correlation model (ACE, Association+Cubic Equation of state) was developed. It is based on a cubic equation of state and a model for the dimerization of acetic acid. It was applied to correlate the experimetnal VLE data with good results.