Diffusion in Liquids with Dissolved Gases by Dynamic Light Scattering Experiments, Equilibrium Molecular Dynamics Simulations, and Prediction Models

Abstract

The aim of this thesis is the characterization of diffusive mass transport in liquids with dissolved gas through analysis of structure-property relationships in a variety of fluid systems. For this, systematically selected binary mixtures of a liquid solvent with a dissolved gas close to infinite dilution have been investigated by dynamic light scattering experiments and molecular dynamics simulations. Within this thesis, details on analyzing the molecular structure of the fluid using simulation results as well as improvements to molecular force fields are given. The evaluation of results is performed over 89 different mixture combinations of a liquid with a dissolved gas, totaling 451 diffusivities. The 17 liquid solvents can be classified as linear, branched, or cyclic alkanes, linear alcohols, an acid, an ester, or an ionic liquid and the 11 different gases vary in terms of molecular weight, size, shape, and polarity. A simple, predictive engineering model is presented, which is empirically developed based on these 451 experimental diffusivity results and requires only the solvent dynamic viscosity and density, the temperature, and the molar mass and core volume of both mixture components. A group contribution method is presented which is used to calculate the molar core volume. The average absolute relative deviation between prediction and experimental results is less than 20%. The model is additionally evaluated against 314 diffusivities from the literature for binary mixtures close to infinite dilution of one component and the average absolute relative deviation is 24%. This positive evaluation includes data for gaseous mixtures, suggesting that the model reflects a realistic behavior, since it is able to perform beyond the scope of its development.