Time filter

Source Type

Oldenburg, Germany

Ince E.,Istanbul University | Lalikoglu M.,Istanbul University | Constantinescu D.,DDBST GmbH
Journal of Chemical and Engineering Data

Liquid-liquid equilibria (LLE) of water + acetic acid + dimethyl carbonate were experimentally specified at (298.2, 308.2, and 318.2) K. Each diagram was obtained through specifying binodal curves and tie-lines. The reliability of the experimental tie-line data was calculated by the Othmer-Tobias correlation. The nonrandom two-liquid (NRTL) and unified quasichemical activity coefficient (UNIQUAC) models were used to obtain the binary interaction parameters of the experimental tie-line data. However, universal functional (UNIFAC) and modified UNIFAC methods were used as well to predict the phase equilibrium in the system specified from experimental data using the interaction parameters between CH3, OCOO, COOH, and H2O functional groups. Distribution coefficients and separation factors were assessed for the immiscibility region. © 2014 American Chemical Society. Source

Bilde M.,University of Aarhus | Barsanti K.,Portland State University | Booth M.,University of Manchester | Cappa C.D.,University of California at Davis | And 34 more authors.
Chemical Reviews

There are a number of techniques that can be used that differ in terms of whether they fundamentally probe the equilibrium and the temperature range over which they can be applied. The series of homologous, straight-chain dicarboxylic acids have received much attention over the past decade given their atmospheric relevance, commercial availability, and low saturation vapor pressures, thus making them ideal test compounds. Uncertainties in the solid-state saturation vapor pressures obtained from individual methodologies are typically on the order of 50-100%, but the differences between saturation vapor pressures obtained with different methods are approximately 1-4 orders of magnitude, with the spread tending to increase as the saturation vapor pressure decreases. Some of the dicarboxylic acids can exist with multiple solid-state structures that have distinct saturation vapor pressures. Furthermore, the samples on which measurements are performed may actually exist as amorphous subcooled liquids rather than solid crystalline compounds, again with consequences for the measured saturation vapor pressures, since the subcooled liquid phase will have a higher saturation vapor pressure than the crystalline solid phase. Compounds with equilibrium vapor pressures in this range will exhibit the greatest sensitivities in terms of their gas to particle partitioning to uncertainties in their saturation vapor pressures, with consequent impacts on the ability of explicit and semiexplicit chemical models to simulate secondary organic aerosol formation. Source

Gmehling J.,University of Oldenburg | Gmehling J.,DDBST GmbH | Schedemann A.,University of Oldenburg | Schedemann A.,DDBST GmbH
Industrial and Engineering Chemistry Research

A sophisticated software package for the selection of the most suitable solvents or solvent mixtures for liquid-liquid extraction was developed. For the selection in particular, phase equilibrium information such as selectivity, capacity, etc. was used. For the determination of these properties, besides group contribution methods, such as UNIFAC or modified UNIFAC (Do) and the group contribution equations of state PSRK or VTPR, experimental data collected and updated in the Dortmund Data Bank (DDB) can be applied. For the final selection, pure component and mixture properties such as the surface tension, density, flash point, viscosity, etc. are accessible via DDB also. The applicability of the program package was demonstrated by means of various extraction processes of industrial importance. © 2014 American Chemical Society. Source

Moller B.,University of KwaZulu - Natal | Moller B.,Sasol Limited | Rarey J.,University of KwaZulu - Natal | Rarey J.,DDBST GmbH | And 2 more authors.
Fluid Phase Equilibria

Infinite dilution activity coefficients play a vital role in modeling of phase and chemical equilibrium behavior. From the dependence of the limiting activity coefficient of a solute on the solvent, important properties like liquid and solid solubility in these solvents can be deduced. Although a large amount of experimental information is available in the open literature as well as from thermophysical data banks such as the Dortmund Data Bank (DDB), the behavior of high boiling solutes in low boiling solvents is often not known, partly due to difficulties in experimental determination.A method for the extrapolation of infinite dilution activity coefficients and thus the liquid and solid solubility of any solute in different solvents within one solvent family is under development. Results of a method applicable to any solute in a large variety of different saturated hydrocarbon compounds are presented in this paper. In this method, the activity coefficient is assumed to consist of a combinatorial and residual contribution. In the case of alkane solvents, only this combinatorial contribution changes when going from one solvent to another. Several well known combinatorial expressions were evaluated and were found to produce poor extrapolations in many instances. Quite surprisingly, free-volume combinatorial expressions performed best even for some of the rather low molecular weight compounds used in this test.A new empirically modified free-volume expression is proposed which allows for accurate extrapolation. Additional activity coefficient data have been determined via GLC (gas-liquid chromatography) to validate the method. In most cases extrapolations were within 10% of the experimental findings and safely within or close to the scatter of literature data. The method allows for example the safe estimation of the infinite dilution behavior as well as liquid and solid solubility of high boiling components in hydrocarbons from data for high boiling solvents usually determined easily by gas-liquid chromatography. Additionally, the newly developed combinatorial expression for infinite dilution data should be able to greatly improve other predictive mixture models, e.g. UNIFAC, mod. UNIFAC and COSMO-RS type models in the cases when large molecules in low molecular weight solvents are considered. This was verified for a larger number of experimental limiting activity coefficient data from literature. © 2013 Elsevier B.V. Source

Schmid B.,DDBST GmbH | Schedemann A.,DDBST GmbH | Gmehling J.,DDBST GmbH | Gmehling J.,Carl von Ossietzky University
Industrial and Engineering Chemistry Research

Today development, design, and optimization of the various processes is carried out with the help of process simulators. The reliability of the results mainly depends on the quality of the thermodynamic model and the model parameters used. While gE models can be applied for calculation of the phase equilibrium behavior of multicomponent systems using only binary experimental data, group contribution methods like UNIFAC or modified UNIFAC Dortmund allow prediction of the required thermophysical properties using only a limited number of group interaction parameters. For systems containing supercritical components equations of state like Soave-Redlich-Kwong or Peng-Robinson or group contribution equations of state (GCEOS) like the predictive Soave-Redlich-Kwong (PSRK) or the volume-translated Peng-Robinson group contribution equations of state (VTPR) can be applied. In different papers it was already shown that VTPR is a very powerful thermodynamic model. In this paper new group interaction parameters for 192 group combinations are presented, so that the actual matrix now contains group interaction parameters for 252 group combinations. In this paper predicted results of the VTPR group contribution equation of state are compared with the results obtained using modified UNIFAC Dortmund or the PSRK method. © 2014 American Chemical Society. Source

Discover hidden collaborations