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Characterization of molecular diffusion in liquids with dissolved gases

Subject Area Technical Thermodynamics
Term from 2015 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 279736335
 
Final Report Year 2023

Final Report Abstract

Molecular mass diffusion was characterized in binary mixtures of a liquid with a dissolved gas over a wide range of thermodynamic states by applying dynamic light scattering (DLS) and equilibrium molecular dynamics (EMD) simulations for the determination and prediction of the Fick diffusion coefficient D11. DLS contributed to a reliable database where results were used as validation for EMD simulations, which, in turn, provide insight into the fluid structure and support the interpretation of D11 values. D11 predicted with EMD simulations close to infinite dilution of the gas or over a wide composition range agreed well with the DLS results in nearly all cases. Correct modelling of the interactions between solute and solvent represented by the thermodynamic factor was shown to be crucial for the accurate prediction of D11. In the second funding period, the chosen systems included extended ranges of molecular characteristics like molar mass, size, and polarity of gases as well as chain length, branching, oxygenation, and degree of hydrogenation of liquids. The 89 mixtures studied provided a sound database for developing an improved prediction model for D11 close to infinite dilution of the dissolved gas, where newly identified relations between fluid properties and diffusivities were considered. For 765 D11 data from this work and literature spanning seven orders of magnitude, the average absolute relative deviation of predicted from experimental data is 21%.

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