Thomas Reschke


Modelling and design of aqueous two-phase systems.


Area: downstream processing
Project Start: 1.04.2010
Supervisor(s): Prof. Dr. Andrzej Górak, Prof. Dr. Gabriele Sadowski
University: Dortmund


Thomas successfully defended his thesis in July 2014 and is an alumnus of the CLIB-GC. He now works for a multinational corporation.

During his studies, Thomas won, together with his colleague Christoph Held, the Syngenta Challenge at the Thermodynamics Conference 2013 in Manchester, UK. They managed to model the phase equilibrium of benzoic acid and water, using one set of parameters to model the liquid-liquid, liquid-solid and liquid-gaseous equilibria.

About the Project


Aqueous two-phase systems show an enormous potential for the application as high capacity unit operation for the downstream processing of valuable biomolecules. One crucial step in process development is the knowledge of the partitioning of the phase forming components, as well as the bio-products in these complex systems. To decrease the amount of necessary experiments for process development, a reliable thermodynamic model has to be available. Within this work, the ePC-SAFT equation of state is applied to model the partitioning behaviour of the phase forming components with respect to process relevant parameters such as temperature, system pH, phase forming components and co-solutes used.


The industrial production of valuable biomolecules, such as proteins, is an emerging field of e.g. the red biotechnology in both, academia and industry. For the downstream processing of these products, often time and energy intensive unit operations, such as chromatography are used on lab as well as on industrial scale. This leads to high production costs, of which 80% can be ascribed to the downstream processing. First investigated in 1956 by Albertson [1], aqueous two-phase systems (ATPS) were shown to have an enormous potential for the extraction of these biomolecules. In general ATPS show a high biocompatibility and are cheap in comparison to chromatographic methods.

The most examined ATPS consist of a hydrophilic polymer and a salt or two hydrophilic polymers serving as phase-forming components. Beside polymers and salts, there are various other solutes, including (poly-)alcohols, ionic liquids, and polyelectrolytes forming ATPS in various combinations. As the database for most of these combinations is scarce, one aim of this project is the development of a high-throughput method to investigate novel ATPS. For the application of ATPS on biomolecules it has been shown that the partitioning of proteins in the two aqueous phases can be influenced by process parameters, such as the systems pH, temperature, polymer molecular weight, and tie-line length. However, the tie-line length itself depends on most of the above mentioned parameters, leading to highly complex dependencies for extraction processes and a high experimental effort.

To overcome this effort process models are applied to determine the influence of the process parameters on the biomolecules partitioning. These models are typically supported by empirical or thermodynamic models to determine the phase compositions. Empirical models offer a simple approach to determine single tie-lines but the amount of necessary parameters increase tremendously with each considered system parameter. The use of thermodynamic models is beneficial as it allows for predictive modeling for changing system conditions without adjusting additional parameters. Furthermore a thermodynamic approach allows for a better understanding of the phase behaviour and the transfer to experimentally undetermined systems.

Within this work the ePC-SAFT [2,3] equation of state (EoS) is used for the calculation of ATPS phase equilibria. Calculations of an ATPS consisting of water, polyethylene glycol (PEG) and Na2SO4 show, that the model is able to calculate the liquid-liquid equilibrium of two aqueous phases. By calculating the densities of both phases, the location of the polymer-rich and salt-rich phase can be determined. The calculated top phase contains a high amount of PEG and a small amount of salt, whereas the bottom phase contains a high amount of salt and almost no PEG. These characteristics are in good accordance with the available experimental data. [4]


[1] P.-A. Albertson "Partition of cell particles and macromolecules" John Wiley & Sons, 3rd Edition, 1986 [2] J. Gross, G. Sadowski "Perturbed-Chain SAFT: An Equation of State Based on a Perturbation Theory for Chain Molecules" Ind. Eng. Chem. Res. 40 (2001) 1244–1260. [3] L.F. Cameretti, G. Sadowski, J.M. Mollerup "Modeling of aqueous electrolyte solutions with perturbed-chain statistical association fluid theory" Ind. Eng. Chem. Res. 44 (2005) 3355–3362; Ind. Eng. Chem. Res. 44 (2005) 8944.

[4] S. Hammer, A. Pfennig, M. Stumpf "Liquid-Liquid and Vapor-Liquid Equilibria in Water + Poly(ethylene glycol) + Sodium Sulfate"J. Chem. Eng. Data 1994, 39, 409-413


Reschke T., Naeem S., Sadowski G. (2012)- "Osmotic Coefficients of aqueous weak electrolyte solutions" J. Phys. Chem. B, 2012, 116 (25), 7479-7491

C. Held, T. Reschke, R. Müller, W. Kunz, and G. Sadowski, Measuring and modeling aqueous electrolyte/amino-acid solutions with ePC-SAFT, The Journal of Chemical Thermodynamics, vol. 68, pp. 1-12, 2014

T. Reschke, C. Brandenbusch, and G. Sadowski, Modeling aqueous two-phase systems: I. Polyethylene glycol and inorganic salts as ATPS former, Fluid Phase Equilibria, vol. 368, pp. 91-103, 2014

T. Reschke, C. Brandenbusch, and G. Sadowski, Modeling aqueous two-phase systems: II. Inorganic salts and polyether homo- and copolymers as ATPS former, Fluid Phase Equilibria, vol. 375, pp. 306-315, 2014


Project description
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