Dynamic Fluid Saturation Method for Hydrocarbons Thermodynamics’ Properties Determination

Low solubility compounds suffer from lack of data, leading to an impoverishment in thermodynamic parameters such as Gibbs free energy (ΔG), enthalpy of dissolution (ΔH), entropy (ΔS), infinite dilution coefficient (γ^∞) and isobaric heat capacity (C_p) of utmost practical importance for industrial optimization processes. Dynamic fluid method is a novel technique for low solubility (expressed as molar fraction χ) determination based on the saturation of a specific heated fluid passing through a saturation cell. The heated components are kept inside a chromatographic oven maintained at a constant temperature to within ± 0.05°C by means of a PID temperature controller. A regular stream of fluid, using a constant flow pump, passes through the saturation cell packed with an inert stationary phase (Gaz chrom R 60/80) pre-coated with the organic compound. The solute transported by the fluid is subsequently trapped in a specific extraction column (inverse phase). The organic compound is removed by back flushing using the appropriate solvent in order to dissolve and carry out the totality. A low flow of fluid through the generator column is to be set to avoid safely the formation of colloidal dispersion, to increase the contact time and to keep small pressure drops across the generator/extractor column. The gas chromatography coupled to mass spectrometer detector is used in order to quantify the solute. The validation of this apparatus was achieved by comparison of our values with the ones extracted from previous papers using the static method to determine aqueous solubility of the ethylbenzene, and a precision of our solubility measurements was established to be better than 0.2%. In continuous, aqueous solubility and thermodynamics properties of perfluorocarbons compounds were determined in the range of temperature from 273 K to 333 K. Considering the contribution of chromatographic, calibration and other operational errors, the combined measurement uncertainty (standard deviation) was established to be less than 3%.