Molar Refractivity and Oxygen Solubility

Abstract

This study dealt with two experimental topics. One topic evaluated the relationship between molar refractivity and the experimentally measurable parameters refractive index, density and molar mass. The other topic dealt with an experimental method to determine oxygen solubility in hydrocarbons. The objective of the molar refractivity study was to determine which of the different equations that correlate molar refractivity, refractive index, density, and molar mass better express the empirical data. Molar refractivity is a temperature invariant property, therefore, the best correlation would be the one in which the calculated molar refractivity is least temperature-dependent. To evaluate these correlations, high precision, and accurate temperature-dependent data for refractive index (0.000001 readability), and density (0.000001 g/cm3 readability) of pure components were measured. The data were collected for different groups of reagents, namely: alkanes, alkenes, alkynes, cyclic compounds, alkyl aromatics, 1-alcohols, carboxylic acids and sulfur compounds of different compound classes. For each model compound, the measurements were performed nine times for each temperature condition. Measurements were obtained at five different temperatures when possible, depending on the boiling and melting point of the sample. Once the data were collected, it was found that the molar refractivity calculated with the correlation by Eykman (R_M= ((n^2-1)/(n+0.4))∙M/ρ) was the least temperature-dependent. The Eykman correlation performed best for all of the model compounds, except propionic acid and butyric acid. The average first derivative (dn/dρ) of refractive index with respect to density of alkanes (0.598 ± 0.003), alkenes, (0.604 ± 0.002), and alkynes (0.587 ± 0.005) were roughly the same as the value of 0.6 reported in literature for hydrocarbons. For the selected 1-alcohols and carboxylic acids, the dn/dρ increases with the increase of the carbon chain length and the decrease of the polarity, due to the presence of oxygen, which suggested that the dn/dρ could be used to track changes in chemical composition. In sulfur-containing compounds dn/dρ appeared to depend more on the hydrocarbon nature than in the position of the sulfur. On the other hand, for the study of dissolved oxygen in hydrocarbons, the goal was to find or develop an experimental method to determine oxygen solubility in hydrocarbons, and to use the experimental measurement to calculate Henry’s constant. The first method involved oxygen determination by titration, but could not be successfully adapted for use with hydrocarbons. The second method determined oxygen concentration from the pressure difference resulting from oxygen dissolving in the liquid hydrocarbon. Results from this method compared favorably with measurements reported in the literature.