Joule-Thomson coefficients and Joule-Thomson inversion curves for pure compounds and binary systems predicted with the group contribution equation of state VTPR

In this work the accuracy of the prediction of Joule-Thomson coefficients for the gases CO₂ and Ar and the binary systems CO₂-Ar and CH₄-C₂H₆ was examined using the group contribution equation of state VTPR. Furthermore the experimental and correlated data of Joule-Thomson inversion curves of a few compounds including carbon dioxide, nitrogen, benzene, toluene, methane, ethane, ethylene, propyne, and SF₆ were compared with the results of the group contribution equation of state VTPR, the Soave-Redlich-Kwong (SRK), the Peng-Robinson (PR) and the Helmholtz equation of state (HEOS). Moreover, Joule-Thomson inversion curves for pure fluids, binary (CH₄-C₂H₆, N₂-CH₄, CO₂-CH₄), and ternary systems (CO₂-CH₄-N₂, CH₄-C₂H₆-N₂, CO₂-CH₄-C₂H₆) were calculated with VTPR and compared to the results of SRK, PR, HEOS and the molecular simulation results of Vrabec et al. It was found that the calculated values for the Joule-Thomson coefficients and Joule-Thomson inversion curves are in good agreement with the experimental findings.     

Prediction of Antoine constants using a group contribution method

Vapor pressure is one of the important properties necessary for process design. Antoine equation has been widely used to evaluate the vapor pressures. This article deals with the proposal of a method for predicting the Antoine constants using a group contribution method. The 1817 compounds treated here are grouped into six classes. The group contribution parameters for each class have been determined using a regression analysis. The group contribution method with help of experimental normal boiling point has good results for predicting the vapor pressures.     

Modeling alcohol + water + hydrocarbon mixtures with the group contribution with association equation of state GCA-EoS

The growing interest on first- and second-generation biofuels requires the development of thermodynamic tools with predictive capacity for mixtures containing a wide variety of organo-oxygenated compounds, water and hydrocarbons. Modeling this type of mixtures is challenging due to the presence of association and solvation effects. In this work, we present a revision of the group contribution with association equation of state (GCA-EoS) parameters, with the purpose of extending and improving the predictive capacity of the model for systems containing water, alcohols and hydrocarbons.     

Vapor–liquid equilibrium data and critical points for the system H2S+COS. Extension of the PSRK group contribution equation of state

Isothermal vapor–liquid equilibrium data for the binary system hydrogen sulfide+carbonyl sulfide were measured in the temperature range from 232 to 293 K using the static-synthetic technique. From the isothermal P−x data, the azeotropic conditions were derived. The critical line of this system was visually detected in a flow apparatus. Interaction parameters for this binary system were fitted simultaneously to all the experimental VLE and critical data for the Predictive Soave–Redlich–Kwong group contribution equation of state.     

Calculating poly(ethylene-co-acrylic acid)-solvent phase behavior with the SAFT equation of state

Statistical Associating Fluid Theory (SAFT) is used to model the cloud-point behavior of poly(ethylene-co-acrylic acid), with up to 7 mol % acid content, in propane, butane, propylene, butene, and dimethyl ether at temperatures to 250°C and pressure to 2600 bar. The values for the pure component temperature-independent segment volumes, nonspecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers contain modest amounts of acrylic acid repeat units. Two different approaches are used to determine values of the pure component energy of hydrogen bonding, ?/k, and the binary interaction parameter, k_ij. In one approach, ?/k for acid dimerization is obtained from literature spectroscopic data and a constant value of k_ij is fit to each copolymer-solvent cloud-point curve. Increasing the value of k_ij shifts the predicted cloud-point curves to higher temperatures and pressures. For the five solvents used in this study, k_ij decreased steadily in the range of 0.040 to ?0.025 as the acid content in the copolymer increased. The predicted cloud-point curves are in good agreement with experimental data, and the impact of hydrogen bonding on the phase behavior is well represented, even if k_ij is set equal to zero. For the second approach, ?/k is set to ～ 90% of the value obtained from spectroscopic data as determined from a fit of a single poly(ethylene-co-acrylic acid)-butane cloud-point curve, while k_ij is fit to the corresponding polyethylene-solvent system. This approach requires less mixture data than the previous approach, and the calculated cloud-point curves are also in good agreement with experimental data, except for the EAA-DME systems. © 1995 John Wiley & Sons, Inc.     

Extension of the group-contribution lattice-fluid equation of state

This work focuses on the extension of the numbers of group parameters and application of the group-contribution lattice-fluid equation of state (GCLF EOS). The new group parameters of the GCLF EOS were evaluated by means of the volume translated Peng–Robinson equation of state (VTPR EOS) and the UNIFAC model. Values for 20 main groups and 33 subgroups are added into the current parameter matrix. The procedure used in this work can also be used to evaluate group parameters for the groups not present in the current matrix. Some examples are given to show the reliability of the new group parameters. Two new applications of the GCLF EOS are present: the effect of polymeric additive to solvents in extractive distillation and prediction of the crystallinity of polymers in the presence of gas.     

Correlations for describing gas-to-ionic liquid partitioning at 323 K based on ion-specific equation coefficient and group contribution versions of the Abraham model

Chromatographic retention measurements were measured for a wide range of solutes on 1-methyl-3-ethylimidazolium tris(pentafluoroethyl)trifluorophosphate, ([MEIm]⁺[FAP]⁻), and 1-(3-hydroxypropyl)pyridinium tris(pentafluoroethyl)trifluorophosphate, ([1-PrOHPy]⁺[FAP]⁻), stationary phases at 323 K. The measured retention factors were combined with published infinite dilution activity coefficient, gas solubility data and retention factor data to yield gas-to-anhydrous ionic liquid (IL) partition coefficients at 323 K for 2349 different solute-IL combinations. The compiled partition coefficient data were analyzed using the ion-specific equation coefficient and the functional group contribution versions of the Abraham solvation parameter model. Ion-specific equation coefficients were calculated for 25 cations and 14 anions. In addition, values were calculated for 14 cation functional groups and 14 anions. The calculated ion-specific equation coefficients and calculated functional group values described the experimental 323 K partition coefficient data to within standard deviations of 0.10 and 0.13 log units, respectively.     

Excess volume of mixing and equation of state theories

Equation-of state theories of Flory and of Sanchez and Lacombe describe both enthalpy and volume of mixing of binary systems using single component properties and only one binary parameter X₁₂. We have evaluated this parameter from literature enthalpy data for numerous mixtures of two aromatic hydrocarbons, of alkanes with aromatic compounds, and of alkanes with carbonyl compounds. We have used this X₁₂ for calculation of excess volumes and compared the results with our previously measured experimental data. The agreement was fair for mixtures of two nonpolar components. Nevertheless, mixtures containing either cyclohexane or benzene displayed anomalies that could be traced to special packing of molecules in these compounds when pure. For mixtures of carbonyl compounds with alkanes, the theories predicted the qualitative trends correctly, but the quantitative agreement was rather poor. These results tend to support a model in which the enthalpy(cohesive energy) is inversely proportional to volume (as in the theories considered) only for dispersive interaction. When polar-polar interactions are involved, the dependence of excess volume on the excess enthalpy is much weaker.     

Predictive use of a SAFT EOS for phase equilibria of some hydrocarbons and their binary mixtures

A systematic study of several hydrocarbons with a SAFT equation of state (EOS) is presented. First, it is shown that the phase behavior of the whole family of n-alkanes may be represented with the use of only three parameters. The approach is then extended to moderately branched alkanes, alkenes and ring compounds using one additional property, namely normal boiling point. Binary mixtures are also investigated and reasonable results are obtained with no additional binary parameters.     

A proposed equation of correlation for the study of thermodynamic properties (density,viscosity, surface tension and refractive index) of liquid binary mixtures

The literature on the physicochemical properties of liquid binary mixtures shows that most such systems exhibit nonlinear behavior. As a result, rigorous data and equations capable of affording a reliable estimate of the behavior of such mixtures are needed.     

Potential of thermodynamic tools (group contribution methods, factual data banks) for the development of chemical processes

Reliable knowledge of the thermophysical properties of pure compounds and their mixtures in the whole composition and a wide temperature and pressure range is a vital prerequisite for the computer aided synthesis, design and optimization of chemical processes. At the beginning of the development of thermodynamic models, the main interest was directed to the development of predictive g^E-models for vapor–liquid equilibria (VLE) of subcritical compounds. Today group contribution equations of state are available which can also handle supercritical compounds, very asymmetric systems and even systems with strong electrolytes. These sophisticated models together with factual data banks (e.g. the Dortmund Data Bank) are powerful software tools for the reliable development of chemical processes and other applications of industrial interest. In this paper, the status of the different approaches and important applications of industrial interest using thermodynamic information derived from factual data banks or by using sophisticated predictive thermodynamic models will be presented.     

Application of a new equation of state to liquid refrigerant mixtures

A new general equation of state recently reported for pure liquids has been developed to predict the volumetric and thermodynamic properties of six binary and two ternary liquid refrigerant mixtures (including HCs and HFCs mixtures) at different temperatures, pressures, and compositions. The results show this equation of state can be used to reproduce and predict different thermodynamic properties of liquid refrigerant mixtures within experimental errors. The composition dependence of the parameters of this equation of state has been assumed as quadratic functions of mole fraction. Using these mixing rules, the agreement between calculated and experimental densities is better than 0.6% for binary mixtures and 2.3% for ternary mixtures. To compare the performance of this new equation of state against other well-known methods such as the COSTALD method, the density of some refrigerant mixtures, for which the parameters of COSTALD were available, has been computed and compared with those of this new equation of state.     

Chemical applications of topology and group theory

The 60 even permutations of the ligands in the five-coordinate complexes, ML ₅, form the alternating group A ₅, which is isomorphic with the icosahedral pure rotation group I. Using this idea, it is shown how a regular icosahedron can be used as a topological representation for isomerizations of the five-coordinate complexes, ML ₅, involving only even permutations if the five ligands L correspond either to the five nested octahedra with vertices located at the midpoints of the 30 edges of the icosahedron or to the five regular tetrahedra with vertices located at the midpoints of the 20 faces of the icosahedron. However, the 120 total permutations of the ligands in five-coordinate complexes ML ₅ cannot be analogously represented by operations in the full icosahedral point group I _h, since I _his the direct product I×C₂ whereas the symmetric group S ₅ is only the semi-direct product A ₅S₂. In connection with previously used topological representations on isomerism in five-coordinate complexes, it is noted that the automorphism groups of the Petersen graph and the Desargues-Levi graph are isomorphic to the symmetric group S ₅ and to the direct product S ₅×S ₂, respectively. Applications to various fields of chemistry are briefly outlined.     

On the prediction of equilibrium phase behavior of amino acids in aqueous and aqueous-electrolyte solutions using SAFT equation of state

We present an approach based on the statistical associating fluids theory (SAFT) to predict the solubility of amino acids in aqueous and aqueous-electrolyte solutions. This approach can describe the association interactions and their effects on the solubility of amino acids. Using the experimental data of activity coefficients of amino acids in water, the parameters of SAFT model for amino acids are obtained. The solubility of several amino acids in the temperature range of 273.15–373.15 K is predicted. Results obtained from the model are in a good accordance with the experimental data. Also, we examine the effect of pH on the solubility of dl-methionine. Addition of an extra amino acid to the binary solution of amino acid + water makes the system more complex. To check the accuracy of model, we study the ternary solution of dl-serine + dl-alanine + water and dl-valine + dl-alanine + water. Predicted results depict that the proposed model has the ability to describe the ternary solution of amino acids, accurately. Finally, the solubility of amino acids in aqueous-electrolyte solutions is investigated. The long-range interactions caused by the presence of ions affects the solubility of amino acids, leading them to be salted in or out. To treat this kind of interaction, the restrictive primitive mean spherical approximation (RP-MSA) is coupled with the SAFT equation of state. The proposed model can accurately predict the solubility of amino acids in aqueous-electrolyte solutions.     

Estimation of pure component properties. Part 4: Estimation of the saturated liquid viscosity of non-electrolyte organic compounds via group contributions and group interactions

A new group contribution method for the prediction of pure component saturated liquid viscosity has been developed. The method is an extension of the pure component property estimation techniques that we have developed for normal boiling points, critical property data, and vapour pressures. Predictions can be made from simply having knowledge of the molecular structure of the compound. In addition, the structural group definitions for the method are identical to those proposed for estimation of saturated vapour pressures. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. The new method is based on liquid viscosity data for more than 1600 components. Results of the new method are compared to several other estimation methods published in literature and are found to be significantly better. A relative mean deviation in viscosity of 15.3% was observed for 813 components (12,139 data points). By comparison, the Van Velzen method, the best literature method in our benchmarking exercise produced a relative mean deviation of 92.8% for 670 components (11,115 data points). Estimation results at the normal boiling temperature were also tested against an empirical rule for more than 4000 components. The range of the method is usually from the triple or melting point to a reduced temperature of 0.75–0.8. Larger than average deviations were observed in the case of molecules with higher rotational symmetry, but no specific correction of this effect was included in this method.     

Solubility of hydrocarbons in water: Experimental measurements and modeling using a group contribution with association equation of state (GCA-EoS)

In this communication, new experimental data on the solubility of n-hexane, cyclo-hexane and iso-octane in pure water are reported. The data have been measured using a static-analytic technique that takes advantage of a Rolsi™ sampling device in the temperature range of 298–353 K and at pressures up to 0.5 MPa. The experimental data measured in this work at 298 K have been compared with some selected data from the literature and good agreement is found. A group contribution plus association equation of state, namely the GCA-EoS, is used to model the phase equilibrium of water + hydrocarbon (C₂ to n-C₆, cy-C₆, i-C₄ and i-C₈) system. The predictions of the model are found in good agreement with the experimental data measured in this work and some selected data from the literature.