In chemical engineering physical properties of both homogeneous phases and interfaces play an important role in the design and optimization of apparatuses. The goal of interafacial thermodynamics is to provide these properties for application, to understand the fundamentals of processes in unit operations, and to improve their description. Its methods, e.g. molecular thermodynamics, allow investigation of processes on different time and length scales.

These investigations are conducted in close interplay between experiment, theory and simulation. A special emphasis is put on the following questions:

• What influence do interfacial properties have on transport processes in chemical engineering operations? How can this influence be modelled?
• How can established methods of interfacial thermodynamics be extended to more complex mixtures, in which e.g. an orientation of components at interfaces occur?
• How can structural properties of interfaces be measured?

Assitant Professor Interfacial Thermodynamics
JP Dr.-Ing. Kai Langenbach

Research topics:

• Modelling and prediction of interfacial properties of complex mixtures
• Modelling of mass transport through intefaces (cf. Enrico)
• Orientation behavior of fluids in homogeneous phases and at interfaces
• Experimental investigation of mass transport through interfaces (cf. Enrico)
• Experimental investigation of interfacial properties
• Application of interfacial thermodynamics to chemical engineering unit operations

Currently different methods are used to describe effects at interfaces. These differ in the degree of detail and thereby require different computational time. These methods can be seen as differrent degrees of approximation to answer the same question. Within the ERC Adcvanced Grant Enrico, among other topics, it is tested, which detail of approximation is necessary in order to arrive at good results, or which degree of detail is the minimum for a description of mass transport through the interface. Doing this, interesting effects can occur, like the enrichment of some components at phase boundaries, whose influence on transport is investigated in the project.

The structure of simple fluids is almost exclusively dominated by repulsive interactions, e.g. that of the Lennard-Jones fluid. Because of this, a repulsive reference is often chosen to develope equations of state around. If anisotropic force fields (e.g. for water) occur, this assumption needs not be valid anymore. In the framework of Co-Oriented Fluid Functional Equation for Electrostatic interactions (COFFEE) this assumption is partially liffted thus improving the description of components with anisotropic interactions. This method is further developed at the Laboratory of Engineering Thermodynamics in order to apply it to e.g. mixtures and heterogeneous systems, i.e. systems with interfaces. This will hopefully allow a better description of complex mixtures using the methods of interfacial thermodynamics in the future.

When working with regenerative sources for the production of materials and intermediates in chemical industry, challenges occur that are rare in classical systems. E.g. of ten one of several compounds in the production are not available in pure form. This makes it impossible to experimentally determine their properties or those of their mixtures with other compounds. Using methods from molecular thermodnyamics, it is nevertheless possible to predict several properties. I this project Associating Lattice Cluster Theory (ALCT) is used to predict the liquid-liquid equilibrium in ternary sysetms. In contrast to other methods, it is possible to use available experimental information to achieve quantitative predictions, which can be validated experimentally.