Prediction of mixtures in computer-aided molecular and process design

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The goal of an integrated molecular and process design is to find the optimal processing materials together with the optimal process configuration. Examples for processing materials that significantly influence the performance of the process but do not appear in feed or product streams are the working fluids in heat pumps, refrigerants, and solvents in processes like gas adsorption. To be able to optimize the molecules in such processes, predictive models for thermodynamic properties are required that are applicable to the entire molecular design space. In this project, two modelling approaches, homosegmented and heterosegmented group contribution methods, are compared and enhanced with their applicability to mixtures specifically. In homosegmented group contribution methods, the challenge that is addressed is the prediction of binary interaction coefficients needed to accurately predict the thermodynamic behaviour of mixtures. Heterosegmented group contribution methods promise a better description of mixtures as the heterogeneity of molecules is resolved on a finer level. The challenge here is the formulation of an optimization problem that minimizes an objective function for the discrete molecules.To identify advantages of both modelling approaches, they will be used to find optimal mixed working fluids for an organic Rankine cycle. A particularly interesting research question in this context is, whether the heterosegmented approach can identify isomers as optimal structures, that the homosegmented approach can not distinguish. The better performing approach will then be applied to the optimization of emerging processes in energy and chemical engineering.For a consistent model for bulk and interfacial properties, the project also includes a working package on the application of the heterosegmented group contribution approach to density functional theory. Integrated molecular and process design for processes in which interfaces are important (e.g., adsorption heat pumps or chillers) is less developed and therefore this work package aims to contribute to the groundwork required in future optimization applications.Overall, this project has the goal to improve the thermodynamic foundations of integrated molecular and process optimizations for fluid mixtures with the aspiration to help identifying more efficient and thus more sustainable process solutions.