Thorsten Schnabel

Molecular Modeling of Hydrogen Bonding Fluids: Formic Acid and Ethanol + R227ea

Currently, molecular modeling and simulation gains importance for the prediction of thermophysical properties of pure fluids and mixtures, both in research and industry. This is due to several reasons: Firstly, the predictive power of molecular models allows for results with technically interesting accuracies over wide range of state points and makes it superior to classical methods. Secondly, a given molecular model provides access to the full variety of thermophysical properties, such as thermal, caloric, transport or phase equilibrium data. Finally, through the advent of cheaply available powerful computing infrastructure, reasonable execution times for molecular simulations can be achieved. Molecular modeling and simulation are based on statistical thermodynamics which links the intermolecular interactions to the macroscopic thermophysical properties. This sound physical background also supports the increasing acceptance compared to phenomenological modeling.

Molecular Modeling of Hydrogen Bonding Fluids: Vapor-Liquid Coexistence and Interfacial Properties

A major challenge for molecular modeling consists in optimizing the unlike interaction potentials. A broad study on fluid mixtures [1] recently showed that among the variety of combination rules that were proposed in the past, none is clearly superior. In many cases, all are suboptimal when accurate predictions of properties like the mixture vapor pressure are needed. The well known Lorentz-Berthelot rule performs quite well and can be used as a starting point. If more accurate results are required, it is often advisable to adjust the dispersive interaction energy parameter which leads to very favorable results [1,2,3,4,5].

Molecular Modeling of Hydrogen Bonding Fluids: Monomethylamine, Dimethylamine, and Water Revised

In chemical engineering, the knowledge on thermopysical properties of pure fluids and mixtures is important for the design and optimization of processes. As the experimental data base is often narrow, methods are required that predict thermophysical properties quantitatively. Usually, equations of state or G models are used for that purpose. They are known as excellent correlation tools, but they lack in predictive power and hold only little promise for further improvement. Molecular modeling and simulation is an alternative approach for pure fluids and mixtures with excellent predictive power, a high potential for further development and various applications for technical problems. Especially for hydrogen bonding and associating fluids, phenomenological models have a poor description of thermophysical properties compared to molecular modeling. However, simulations of fluids forming hydrogen bonds are computationally quite expensive. The reason for that lies in the resolution of hydrogen bonds which involves the occurrence of very strong intermolecular forces and the formation of clusters.