The present contribution provides experimental data for the liquid viscosity and surface tension of n-alkane based model systems at temperatures up to 573 K. The fundamental advantage of the used surface light scattering (SLS) method lies in its application in thermodynamic equilibrium without calibration in a contactless way. The investigated systems comprise the pure fluids n-dodecane (n-C 12 H 26 ) and n-octacosane (n-C 28 H 58 ), their binary mixture at a n-C 12 H 26 mole fraction of about 0.3, and the commercially available hydrocarbon wax SX-70 representing a multicomponent mixture of n-alkanes with a broad chain length distribution. For the first time, it could be demonstrated that the SLS method can simultaneously access the liquid viscosity and surface tension of such medium-to long-chained n-alkane systems close to saturation conditions over a broad temperature range from 323 to 573 K. Typical measurement uncertainties of 2% based on a coverage factor k = 2, i.e., a level of confidence of more than 95%, were obtained. Over the entire temperature range, a simple polynomial equation for the dynamic viscosity and a modified van der Waals equation for the surface tension represent the measured data of the pure and binary systems well. The present investigations improve the data situation for hydrocarbon systems in the high-temperature range where no measurement results exist in literature.

In this study, we demonstrate the ability of polarization-difference Raman spectroscopy (PDRS) to detect dissolved free water molecules in a n-octacosane (n-CH) liquid-rich phase, and thus to determine its solubility, at temperatures and pressures relevant to the Fischer-Tropsch synthesis. Our results for the pure alkane reveal thermal decomposition above a temperature of 500 K as well as an increase of gauche conformers of the alkane chains with an increase in temperature. For binary homogeneous mixtures, raw spectra obtained from two different polarization scattering geometries did not show a relevant signal in the OH stretching frequency range. In contrast, isotropic spectra obtained from the PDRS technique reveal a narrow and tiny peak associated with the dangling OH bonds. Over the complete range of temperatures and pressures, no signature of hydrogen-bonded water molecules was observed in the isotropic Raman scattering intensities. A thorough investigation covering a large range of temperatures and pressures using PDRS signals showed that the higher the fraction of gauche conformers of hydrocarbon, the higher the solubility of water. The proportion of gauche and trans conformers was found to be water-concentration-independent, and the intensity of the OH-dangling peak increased linearly with increasing the vapor partial pressure of water. Therefore, we established a relation between a relevant intensity ratio and the concentration of water obtained from SAFT calculations. Contrary to the results from relevant literature, the calibration factor was found to be temperature-independent between 424 and 572 K. The isotropic Raman scattering intensities are corrected in order to provide a better representation of the vibrational density of states. The influence of correction of the isotropic scattering intensities on the solubility measurements as well as on the analysis of the molecular arrangement is discussed.

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The transport properties of wax and water mixtures under confinement and particularly inside catalyst nanopores is a topic of significant interest for the petrochemical industry. These mixtures are the products of the Gas-To-Liquids (GTL) process through the Fischer−Tropsch (FT) route, which experienced an increasing number of commercially viable applications over the past decades. Under reaction conditions, water is produced in high concentrations, leading to phase segregation inside the catalyst nanopores and water-assisted sintering of catalytic nanoparticles, reducing catalyst lifetime and increasing GTL operational cost. It is thus important to understand the wax−water liquid−liquid equilibrium (LLE) at reaction conditions, as it determines the maximum allowable amount of water in the FT wax. Furthermore, elucidating the phase behavior of wax−water mixture inside the nanopores, by explicit incorporation of wall effects, is essential in revealing the role of confinement on mixture phase behavior. The present study focuses on simulating the phase behavior of the n-octacosane (n-C 28 )−water mixture inside TiO 2 nanopores. Molecular Dynamics (MD) simulations with realistic molecular models were employed, highlighting the importance of confinement on the mixture transport properties, particularly in the excess water regime. Even though phase segregated mixtures retain their structural properties compared to their bulk counterparts, significant deviations arise in terms of density profiles inside the nanopore. Water molecules organize into two discrete layers on the TiO 2 surface, shielding n-C 28 from the nanopore walls. Octacosane's self-diffusion is not influenced by confinement; water on the other hand is severely hindered by the TiO 2 nanopore surface, with its diffusivity bearing a strong dependence on the distance from the nanopore center.

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