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Over wide temperature and pressure ranges, the molecular dynamics simulation is performed to study the mass transfer of six n-alkanes from n-C5H12 to n-C10H22 in CO2 at infinite dilution by calculating the diffusion coefficients, which have not yet been measured by experiment. Meanwhile, the structural properties of these systems are explored. It is found that under different temperature and pressure conditions, the variation trends of the radial distribution functions of n-alkanes are quite different, while the variation trends of the average coordination number of n-alkanes can be divided into three types. The radius of gyration and the solvent accessible surface area are both affected by temperature and carbon chain length, but their variation trends are different, and it could explain the abnormal variation trends of the radial distribution functions and the average coordination number. [ABSTRACT FROM AUTHOR]

The diffusion coefficients of 14 n-alkanes (ranging from methane to n-tetradecane) in liquid and supercritical methanol at infinite dilution (at a pressure of 10.5 MPa and at temperatures of 299 K and 515 K) were deduced via molecular dynamics simulations. Values for the radial distribution function, coordination number, and number of hydrogen bonds were then calculated to explore the local structure of each fluid. The flexibility of the n-alkane (as characterized by the computed dihedral distribution, end-to-end distance, and radius of gyration) was found to be a major influence and hydrogen bonding to be a minor influence on the local structure. Hydrogen bonding reduces the flexibility of the n-alkane, whereas increasing the temperature enhances its flexibility, with temperature having a greater effect than hydrogen bonding on flexibility. [ABSTRACT FROM AUTHOR]

Self-diffusion and structural properties of n-alkanes have been studied by molecular dynamics simulation in the temperature range between the melting pressure curve and 600 K at pressures up to 300 MPa. The simulated results of lower n-alkanes are in good agreement with the existing experimental data, and support the reliability of results of the simulations of self-diffusion coefficients obtained at the extreme conditions. We predict the self-diffusion coefficients for methane, ethane, propane and n-butane at the similar reduced temperatures and pressures to draw a comparison between them. Then the correlation between self-diffusion and structural properties are further investigated by calculating the coordination numbers. Moreover, we define four distances and their corresponding relative deviations to characterize the flexibility of long-chain n-alkanes. The simulated results show that the self-diffusion of n-alkane molecules is mainly affected by the close packing, and the flexibility has a strong impact on the self-diffusion of longer n-alkane molecules. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Intradiffusion coefficients of acetylacetone (AcAc) andmethanol/ethanol/1-propanol/1-butanolwere measured in binary liquid mixtures over the whole concentrationrange at 303.15 K by the 1H diffusion-order spectroscopy(DOSY) nuclear magnetic resonance (NMR) method based pulse field gradient(PFG). The solvent effect on the enol-keto tautomeric equilibriumas well as differences in intradiffusion coefficients (D) between two tautomers were also studied. The experimental resultsshow that from methanol to 1-butanol, the differences in Dbetween the enol and keto tautomer vary from 5 % to 26 % at differentconcentrations of AcAc. The densities and viscosities of binary liquidmixtures of AcAc with the above four alkanols have also been determinedat 303.15 K and employed to calculate the excess molar volumes anddeviations in viscosity over the entire range of mole fractions. Isothermsof VEas a function of mole fraction ofAcAc show positive deviations in methanol and ethanol but negativedeviations in 1-propanol and 1-butanol, whereas all isotherms of Δηas a function of mole fraction of AcAc record negative deviations.The VEand Δη are fitted toa Redich–Kister type equation. The measured results are interpretedin terms of molecular interactions in the solutions. [ABSTRACT FROM AUTHOR]