Oldenburg, Germany


Oldenburg, Germany
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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 | Year: 2015

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.

Wallek T.,University of Graz | Rarey J.,DDBST GmbH | Rarey J.,University of KwaZulu - Natal | Rarey J.,Carl von Ossietzky University | And 3 more authors.
Industrial and Engineering Chemistry Research | Year: 2013

Common group-contribution and corresponding-state models for the estimation of normal boiling points, vapor pressures, liquid densities, and dynamic viscosities are reviewed in view of their application to fatty acid methyl esters, related fatty acids and triglycerides. Because of the limited representation of measured data for triglycerides, three previously published group-contribution models for normal boiling points, vapor pressures, and dynamic viscosities are extended through the introduction of a new group, representing the backbone structure common to all triglycerides and improving the performance of these models significantly. Conclusions are drawn in view of further refinement of the group-contribution approach for application to complex branched molecules. © 2013 American Chemical Society.

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 | Year: 2014

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.

Schmid B.,DDBST GmbH | Schedemann A.,DDBST GmbH | Gmehling J.,DDBST GmbH | Gmehling J.,Carl von Ossietzky University
Industrial and Engineering Chemistry Research | Year: 2014

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.

Ince E.,Istanbul University | Lalikoglu M.,Istanbul University | Constantinescu D.,DDBST GmbH
Journal of Chemical and Engineering Data | Year: 2014

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.

Schmid B.,DDBST GmbH | Gmehling J.,DDBST GmbH | Gmehling J.,University of Oldenburg
Fluid Phase Equilibria | Year: 2016

For the development and design of industrial processes the reliable knowledge of thermophysical properties, in particular phase equilibria is most important. Assuming that 1000 components are of technical interest, vapor-liquid equilibrium data for approximately 500,000 binary systems are needed to fit all required binary interaction parameters. Due to the fact that the measurement of all needed properties is nearly impossible, the process engineer depends on factual data banks. Besides the different phase equilibria, the Dortmund Data Bank as worldwide largest factual data bank for thermophysical properties contains nearly all worldwide available pure component, excess and transport properties. Although more than 66,300 binary VLE data sets for non-electrolyte systems are currently stored in the DDB, in total up to now VLE data for only 13,540 different binary systems are available. The reason is that some systems are very popular and were measured very often, e.g. ammonia – water, ethanol-water and so on. When the 1000 most important components are considered, VLE data for only 8635 binary systems are available. This means for only 1.73% of the systems the required binary interaction parameters can be fitted. Since the assumption of ideal behavior for the missing binary systems can be very erroneous and measurements are very time consuming, predictive group contribution models can be successfully applied to estimate the missing thermophysical properties. To cover sub- and supercritical conditions, group contribution equations of state have to be applied. They automatically take into account both phases and can be used up to high pressures and supercritical conditions. This allows for example the calculation of phase envelopes. Furthermore, the introduction of Henry coefficients for gaseous compounds is not required. At the same time, enthalpies, heat capacities, densities and so on can be predicted. Today the most sophisticated group contribution equation of state is the volume translated Peng-Robinson group contribution equation of state VTPR. In this paper, typical applications of VTPR for process development are shown and new parameters for 24 additional group combinations are given. © 2016 Elsevier B.V.

Constantinescu D.,DDBST GmbH | Gmehling J.,DDBST GmbH | Gmehling J.,University of Oldenburg
Journal of Chemical and Engineering Data | Year: 2016

For process development and simulation, the group contribution concept can be successfully applied for the estimation of the missing pure component and mixture properties. This concept has the great advantage that only a limited number of group interaction parameters is required. With the support of a company consortium founded 1996 at the University of Oldenburg, the group contribution model modified UNIFAC (Dortmund) for the prediction of phase equilibria and excess properties has been continuously revised and extended. Within the consortium the number of available group interaction parameters has been doubled. At the same time, the reliability of the results was greatly improved, and the range of applicability was extended to ionic liquids, polyethers, and so forth, and systems for which no experimental data are available, e.g., reactive systems. In this paper the group interaction parameters for the sulfur groups sulfones, sulfides, and disulfides are given. Furthermore, the current status of the consortium developments is discussed. © 2016 American Chemical Society.

Gmehling J.,University of Oldenburg | Gmehling J.,DDBST GmbH | Constantinescu D.,DDBST GmbH | Schmid B.,DDBST GmbH
Annual Review of Chemical and Biomolecular Engineering | Year: 2015

The development and design of chemical processes are carried out by solving the balance equations of a mathematical model for sections of or the whole chemical plant with the help of process simulators. For process simulation, besides kinetic data for the chemical reaction, various pure component and mixture properties are required. Because of the great importance of separation processes for a chemical plant in particular, a reliable knowledge of the phase equilibrium behavior is required. The phase equilibrium behavior can be calculated with the help of modern equations of state or gE-models using only binary parameters. But unfortunately, only a very small part of the experimental data for fitting the required binary model parameters is available, so very often these models cannot be applied directly. To solve this problem, powerful predictive thermodynamic models have been developed. Group contribution methods allow the prediction of the required phase equilibrium data using only a limited number of group interaction parameters. A prerequisite for fitting the required group interaction parameters is a comprehensive database. That is why for the development of powerful group contribution methods almost all published pure component properties, phase equilibrium data, excess properties, etc., were stored in computerized form in the Dortmund Data Bank. In this review, the present status, weaknesses, advantages and disadvantages, possible applications, and typical results of the different group contribution methods for the calculation of phase equilibria are presented. © 2015 by Annual Reviews. All rights reserved.

Gmehling J.,University of Oldenburg | Gmehling J.,DDBST GmbH | Schedemann A.,University of Oldenburg | Schedemann A.,DDBST GmbH
Industrial and Engineering Chemistry Research | Year: 2014

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.

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