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Projekt Druckansicht

Thermophysikalische Eigenschaften von langkettigen Kohlenwasserstoffen, Alkoholen und deren Gemischen mit gelösten Gasen

Fachliche Zuordnung Technische Thermodynamik
Thermodynamik und Kinetik sowie Eigenschaften der Phasen und Gefüge von Werkstoffen
Förderung Förderung von 2018 bis 2022
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 392447067
 
Erstellungsjahr 2022

Zusammenfassung der Projektergebnisse

In the research project, a systematic characterization of long-chained hydrocarbons, alcohols, and their mixtures with and without dissolved gases has been carried out by the investigation of their liquid dynamic viscosity ηL and interfacial tension σ by surface light scattering (SLS) and equilibrium molecular dynamics (EMD) simulations up to a temperature T = 573 K in macroscopic thermodynamic equilibrium. By systematically varying the molecular characteristics of the solvent, i.e. the carbon chain length, branching, hydroxylation, and degree of hydrogenation, and of the solute, i.e. size, weight, and polarity, a fundamental understanding of how these molecular features influence the aforementioned macroscopic properties could be achieved. For this, the SLS technique and EMD simulations were further developed to be applicable to systems consisting of liquids with dissolved gases over a wide range of T up to 573 K and pressures p up to 7 MPa. In addition, the liquid density ρL was determined with a vibrating-tube densimeter for the pure solvents, binary liquid mixtures, and some binary mixtures containing dissolved gases. ηL and σ could be determined by SLS with typical expanded uncertainties (coverage factor k = 2) of (2.2 and 2.0)%. In the case of EMD simulations, commonly applied FFs from the literature were tested, which stimulated a further development of promising FFs for their enhanced performance at high T. In a first step addressing 15 pure solvents, the experimental investigations of ρL, ηL, and σ allowed to develop T-dependent correlations, which could be used for the validation of the EMD simulations.P1,P3,P4 Here, the newly developed FFs, which incorporate a T-dependent modification of the Lennard-Jones energy parameter, could significantly improve the predictions of the thermophysical properties, especially at elevated T. Compared to the experimental results, an overestimation of ηL and σ by around (20 and 10)% and an underestimation of ρL by around 1.5% was found. In a next step, corresponding investigations were extended to four different binary liquid mixtures. Here, EMD simulations, could be used to connect the behavior of σ with the enrichment of molecules at the vapor-liquid phase boundary. Based on the experimental results and the findings from EMD simulations, empirical correlations representing ρL, ηL, and σ of the mixtures as function of T and the composition could be developed. For binary mixtures consisting of the aforementioned solvents and a dissolved gas, the low experimental uncertainties for the ηL and σ results determined by SLS allowed to resolve the influence of the solvent and solute characteristics on the properties. In contrast to the addition of the small and weakly soluble H2 and He to the solvents, which do not affect ηL and σ at p up to 7 MPa, reduced values for both properties on the order of (20-50)% were found in the case of more soluble gases, e.g., CH4 and CO2. The molecular characteristics of the solvent were found to strongly influence the thermophysical properties of mixtures consisting of a polar solvent and polar solute and were usually small in mixtures based on alkanes. Finally, ternary mixtures consisting of liquids and dissolved gases with either two solvents or solutes were characterized by determining ηL and σ via SLS and EMD simulations. The experimental and simulation results have shown that the relative change in both properties by dissolving a gas is usually independent of the solvent composition in mixtures consisting of two solvents with one dissolved gas. In general, the influence of the dissolved gas of the properties of the ternary mixtures can often be estimated with the help of the underlying binary sub-systems. On the basis of the experimental results from this work, prediction models from the literature for ηL and σ were evaluated. While simple mixing rules based on the pure component properties are able to predict ηL and σ of binary liquid mixtures within about 5%, they cannot be directly applied to mixtures containing dissolved gases. This is due to the fact that ηL and σ for the pure solutes often only exist at thermodynamic states far away from those investigated here. In this context, the extended hard-sphere theory model and the parachor model of Macleod & Sugden were found to be best suited for the prediction of ηL and σ of mixtures containing dissolved gases. Using the aforementioned models, ηL and σ of mixtures containing dissolved gases can be predicted with average absolute relative deviations of about (4 and 7)%. The present project could contribute to a fundamental understanding about ηL and σ of longchained hydrocarbons, alcohols, and their mixtures with dissolved gases. The combination of SLS and EMD simulations has shown to be a powerful tool, not only for the determination of the aforementioned properties, but also for the development of structure-property relationships. The collaboration with the working group of Prof. Wu in Xi’an has proven to be invaluable for the outcome of this project and has led to further collaborations exceeding the contents of this project.

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