Jürgen Gmehling

PSRK: A Group Contribution Equation of State Based on UNIFAC

Abstract A group contribution equation of state called PSRK (Predictive Soave-Redlich-Kwong) which is based on the Soave-Redlich-Kwong equation (Soave, 1972) has been developed. It uses the UNIFAC method to calculate the mixture parameter a and includes all already existing UNIFAC parameters. This concept makes use of recent developments by Michelsen (1990b) and has the main advantage, that vapor-uquid-equilibria (VLB) can be predicted for a large number of systems without introducing new model parameters that must be fitted to experimental VLB-data. The PSRK equation of state can be used for VLB-predictions over a much larger temperature and pressure range than the UNIFAC γ-ϕ-approach and is easily extended to mixtures containing supercritical compounds. Additional PSRK parameters, which allow the calculation of gas/gas and gas/alkane phase equilibria, are given in this paper. In addition to those mixtures covered by UNIFAC, phase equilibrium calculations may also include gases like CH4 C2H6, C3H6, c4H10, CO2, N2, H2 and CO.

Development of an universal group contribution equation of state: I. Prediction of liquid densities for pure compounds with a volume translated Peng–Robinson equation of state

Abstract With a view to the development of an universal group contribution equation of state, the Peng–Robinson (PR) equation of state (EOS) has been modified to obtain a better description of saturated liquid densities for the pure compounds. A simple improved volume translation together with a temperature dependent volume correction deliver an accurate representation of this property near and far from the critical point for polar and non-polar substances. The fitted parameters have been generalized as a function of the critical compressibility factor. The results are compared with the results of the original PR and the Soave–Redlich–Kwong (SRK) EOS.

A gE model for single and mixed solvent electrolyte systems: 1. Model and results for strong electrolytes

Abstract Li, J., Polka, H.-M. and Gmehling, J., 1994. A gE model for single and mixed solvent electrolyte systems. 1. Model and results for strong electrolytes. Fluid Phase Equilibria, 94: 89-114. A gE model for electrolyte systems has been developed which is based on results from statistical thermodynamics and takes into account the interactions between all species present in the electrolyte solution. In this model the electrolyte solution is treated as a nonelectrolyte solution plus charge interactions, and it is assumed that the charge interactions show two effects, direct and indirect. The indirect effect differs not only from the long-range electrostatic interaction but also from the short-range interaction for nonelectrolyte solutions. With the help of a large data base the required parameters (164 in number) have been fitted for 10 solvents, 18 cations and 10 anions. The model parameters have been used to calculate the VLE behavior, osmotic coefficients and mean ion activity coefficients for a large number of systems with high accuracy.

Transesterification processes by combination of reactive distillation and pervaporation

The development of a reactive distillation process for the production of n-butyl acetate by transesterification of methyl acetate with n-butanol is presented. Thermodynamic aspects of the quaternary system n-butyl acetate–n-butanol–methyl acetate–methanol are discussed and UNIQUAC interaction parameters derived using the Dortmund Data Bank (DDB) are given. The reaction kinetics of the heterogeneously by a strongly acidic ion-exchange resin (Amberlyst 15) catalyzed reaction has been investigated and the kinetic constants for a pseudohomogeneous kinetic model are presented. Pervaporation experiments using Pervap 2255 membranes have been conducted for the separation of the methanol–methyl acetate binary mixture which forms the distillate stream of the reactive distillation column. Reactive distillation experiments have been performed using the structured catalytic packings Katapak-S (Sulzer Chemtech) and Katapak-SP (type SP 11, Sulzer Chemtech). Important operating conditions (reflux ratio, total feed rate) have been varied experimentally. The experimental results are presented in comparison with simulation results. An equilibrium stage model for the modeling of the distillation is capable of describing the composition profiles quantitatively. Finally, a new process, combining reactive distillation with pervaporation, has been developed and investigated by means of simulation studies. It has been shown that the combination of reactive distillation with pervaporation is favorable since conversions close to 100% can be obtained with a reasonable size of the reactive section.

Further development, status and results of the PSRK method for the prediction of vapor-liquid equilibria and gas solubilities☆

Abstract Since Huron and Vidal (1979) developed the basic idea of so called GE mixing rules, similar models have been proposed by different authors. The aim of all recent developments of GE mixing rules is to combine the successful GE models or group contribution methods with equations of state to enalbe the description of vapor-liquid equilibria at high temperatures and pressures including supercritical compounds. The group contribution equation of state PSRK (predictive Soave-Redlich-Kwong) as suggested by Holderbaum and Gmehling (1991) combines the UNIFAC model (Hansen et al., 1991) with the SRK equation of state. In this work the range of applicability of the PSRK method was extended by the introduction of additional gases and the determination of the missing interaction parameters between the following gases: CH4, CO2, CO, Ar, NH3, H2S, H2, O2, N2 and the original UNIFAC structural groups. The VLE results of the PSRK model have been compared with other predictive equations of state (MHV2 (Dahl and Michelsen, 1990), Lermite and Vidal (1992), LCVM (Boukouvalas et al. (1994)), Wong et al. (1992), UNIWAALS (Gupte et al. (1986)), GCEOS (Skjold-Jorgensen (1984), Tochigi et al. (1990)). Furthermore a comparison between experimental and predicted VLE and Henry coefficients is presented. The PSRK mixing rule can also be used to introduce other GE models into the SRK equation of state. The results show, that for any GE model the parameters derived from VLE can be used to enable reliable predictions of phase equilibria, whereby usually excellent results are obtained for alarge temperature range. The thermodynamic analysis of GE mixing rules enables a reduction of all approaches to one general AE mixing rule. From this formalism the derivation of the PSRK, and other, GE mixing rules can be easier understood.

Prediction of vapor-liquid equilibria in mixed-solvent electrolyte systems using the group contribution concept

Abstract The LIQUAC model is widely used to predict reliably vapor–liquid equilibria (VLE), osmotic coefficients and mean ion activity coefficients for electrolyte systems. It consists of a Debye–Huckel term, the UNIQUAC term and the osmotic virial equation for the middle-range contribution. The aim of this work is to provide a model based on the group contribution concept that can be used to predict phase equilibria in mixed-solvent electrolyte systems. Therefore, in the LIQUAC model the UNIQUAC equation has been substituted by the original UNIFAC equation and group interaction parameters have been introduced into the middle-range term. With the help of a large data base, 234 group interaction parameters for seven solvent groups, 13 cations and seven anions have been fitted. The model parameters have been used to calculate the VLE behavior, osmotic coefficients and mean ion activity coefficients for a large number of systems with high accuracy.

Review of thermophysical property measurements on mixtures containing MTBE, TAME, and other ethers with non-polar solvents

Abstract IUPAC has sponsored three international workshops on vapor–liquid equilibria and related properties in binary and ternary mixtures of ethers, alkanes, and alkanols with the objective of developing a set of recommended values. Particular interest has focused on methyl tert -butyl ether (MTBE, methyl 1,1-dimethylethyl ether), tert -amyl methyl ether (TAME, 1,1-dimethylpropyl methyl ether), ethyl tert -butyl ether (ETBE, ethyl 1,1-dimethylethyl ether), dipropyl ether (DPE), diisopropyl ether (DIPE, bis(1-methylethyl) ether) and other selected ethers that are used or are being considered as gasoline additives to improve the octane rating and reduce exhaust pollution. From a detailed literature search and from contact with researchers currently working in the field, a comprehensive review of the mixtures and properties (both binary and ternary) that have been studied or are presently under study is presented here. This information will allow workers in the field to ascertain the mixture classes and types where sufficient data are now available and where further property measurements are required.

PSRK group contribution equation of state: revision and extension III

Abstract The application range of the predictive Soave–Redlich–Kwong (PSRK) group contribution equation of state (EOS) for the prediction of vapor–liquid equilibria (VLE) and gas solubilities was extended by the introduction of additional structural groups (epoxides, HF, HI, COS) and fitting of 98 pairs of group interaction parameters to experimental phase equilibrium data. These data were systematically measured for the extension of PSRK, or taken from literature and compiled in the Dortmund Data Bank (DDB). Typical results are presented for various systems. Additionally, new experimental VLE data are given for the binary system propylene oxide+benzene at 323.15 K. The new data were required to fit the interaction parameters between the epoxy and the aromatic CH group.

Solid-liquid equilibria in binary mixtures of organic compounds

Abstract Solid-liquid phase equilibria for the systems idane/nitrobenzene, indane/1,2-dichloroethane, indane/1,4-dioxane, ndane/dodecane, acenaphthene/1,4-xylene, tetrachloromethane/2-dodecanone, tetrachloromethane/2-undecanone, 1,2-xylene/1,3-xylene, 1,4-xylene/1,3-xylene, and 1,2-xylene/1,4-xylene were measured visually using the synthetic method. The measured systems were calculated by means of the group contribution method UNIFAC and modified UNIFAC (Dortmund). If necessary, solid-solid transitions were taken into account in the calculations. The systems selected are of technical interest and can also be used for checking and the further development of the group contribution method modified UNIFAC (Dortmund).

High-pressure vapor—liquid equilibria for mixtures containing one or more polar components: Application of an equation of state which includes dimerization equilibria

Abstract Perturbed-hard-chain theory is extended to include chemical dimerization equilibria for strongly polar molecules. Using four adjustable molecular parameters, the extended theory gives good representation of the PVT properties of polar fluids, including water, alcohols and ketones. For nonpolar fluids only three adjustable parameters are required. Straightforward extension to mixtures requires one characteristic binary parameter for “physical” interactions and, for polar-polar mixtures, another for “chemical” interactions. The combined “physical and chemical” theory gives good representation for a variety of binary mixtures containing polar and/or nonpolar components. Particular attention is given to the systems methanol-water and ethanol-water where good results are obtained at pressures ranging from atmospheric to over 100 bars.