Laboratory of Engineering Thermodynamics (LTD)

Assistant Professorship Electrolyte Thermodynamics and Molecular Simulation

Electrolyte solutions play an important role in many topics relevant for the future, such as energy, mobility and raw material supply. Knowing and understanding the behavior of electrolyte solutions is important for making further progress in these fields. This particular importance of electrolyte solutions results from their special properties, which are caused by the freely moving particles that carry charges - the ions. The presence of the ions, however, leads to a complex thermodynamic behavior: strong and long-ranged intermolecular interactions occur between ions and solvent molecules, leading to a considerable structuring of the solution. Therefore, the description of the properties of electrolyte solutions is more complex than that of systems without ions and requires tailor-made approaches.

The group 'Electrolyte Thermodynamics and Molecular Simulation' employs a plethora of methods and works across scales to study the behavior of electrolyte solutions, model their properties, and develop and carry out system- and process-level simulations. We measure a wide range of fluid properties and phase equilibria, using a variety of analytical methods. We work on all classes of thermodynamic models in use today, from phenomenological approaches to modern equations of state and atomistic models. A special focus is devoted to molecular modeling and simulation. The model development also features the use of advanced methods of multicriteria optimization. We develop scale-bridging simulation techniques for systems and processes and use these methods for analysis and optimization. In all of this, experiment, modeling and simulation are not independent of each other, but always go hand in hand.




Assistant Professorship Electrolyte Thermodynamics and Molecular Simulation
JP Dr.-Ing. Maximilian Kohns

Research Topics

  • Experimental Determination of Properties of Electrolyte Solutions
  • Modeling of Electrolyte Solutions
  • Molecular Modeling and Simulation of Polar Fluids and Electrolyte Solutions
  • Multicriteria Optimization
  • Chemical Processes
  • Electrochemical Systems

Selected Projects

Thermodynamics of the All-Vanadium-Redox-Flow-Battery

Redox flow batteries (RFB) are a promising approach to electrochemical energy storage. In RFB, two different electrolyte solutions kept in individual storage tanks are fed to an electrochemical cell in which reversible redox reactions take place. RFB can thus be considered to be a hybrid technology between a battery and a fuel cell. Nowadays, the most widely used RFB is the all-vanadium RFB (AVRFB), in which the two half cells contain aqueous solutions of sulfuric acid solutions and vanadium species in various oxidation states. The physical chemistry of these solutions is complex and comparatively few material properties of these solutions are available in the literature. We investigate the properties of these solutions as well as the thermodynamics of the AVRFB. We perform fluid property measurements as well as measurements of the open circuit voltage of a lab cell. This information will be used to improve existing modeling approaches for AVRFB and to use these models for optimization.

Elucidation of droplet microexplosions in nanoparticle synthesis in spray flames

Spray flame synthesis is a versatile process for the production of nanoparticles. In this process, an organic electrolyte solution of a metal salt is atomized in a nozzle, the solvent ignites on a pilot flame and finally, oxide nanoparticles are formed. It is known that the quality of the obtained nanoparticles is related to the occurrence of cascades of microexplosions of the spray droplets. However, the causes and mechanisms of these microexplosions are largely unknown so far. Within the framework of the DFG Priority Program 1980, we are investigating possible causes for these microexplosions by carrying out simulations of the coupled heat and mass transfer during the evaporation of individual spray droplets in a hot atmosphere. The plethora of fluid properties and phase equilibria of the organic electrolyte solutions required for these simulations are determined experimentally and models are developed for these properties.

Molecular Modeling and Simulation of Electrolyte Solutions

The characteristic behavior of electrolyte solutions is largely caused by the strong electrostatic interactions between ions and solvent molecules. The development of molecular models for electrolytes directly addresses this level. This atomistic detail makes it possible to capture the structure of the solution inherently correctly; for which other types of models usually only achieve a rough approximation despite investing great efforts into this. Molecular models therefore allow reliable predictions of thermal, caloric as well as structural properties of electrolyte solutions. This model depth, however, also requires the use of suitable and efficient simulation methods. We are therefore not only developing new molecular models for electrolyte solutions, but also new simulation methods. Currently, we are e.g. investigating the structure-property relationships of highly concentrated electrolyte solutions as well as the dielectric properties of polar fluids.

Process Simulations of the Extraction of Valuable Products from Water Streams

Securing the availability of critical raw materials is crucial for the development of technologies relevant for the future. In this, aspects of sustainability play a major role. The focus should lie on both the exploitation of new sustainable sources and on the recovery of valuable materials at the end of a product's lifetime. Using existing thermodynamic models for aqueous multicomponent electrolyte solutions, we perform process simulations of precipitation sequences of aqueous electrolyte solutions. Such simulations have already been used to consider precipitating salts in the evaporation of seawater. Currently, we are focusing on the recovery of the critical raw material phosphorus from municipal wastewater. The developed models and programs can be used not only to analyze existing concepts, but also to design and optimize new approaches.

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