CHARACTERIZATION OF THE INITIAL WEATHERING OF PETROLEUM HYDROCARBONS BY FTIR SPECTROSCOPY AND SUPERCRITICAL FLUID CHROMATOGRAPHY

ABSTRACT Chemical changes resulting from the weathering processes of oils have been investigated on a bench scale weathering apparatus. A multicomponent oil simulating crude oil was developed for this purpose. Hydrocarbon concentrations resulting from evaporation and dissolution were measured using Fourier transform infrared (FTIR) spectroscopy and interpreted by a computer program (CIRCOM), which uses the method of principal components regression for multicomponent quantitative analysis. This method could be fast and accurate for quantitative assessments of changes in chemical and physical properties of an oil. However, this study outlines only the chemical measurements of saturated and aromatic hydrocarbon composition. Experiments were also undertaken to study weathering processes on oil droplets. In this technique single droplets of crude oil were suspended in water, the trends of dissolution were studied, and the behavior of the remaining heavy fraction assessed by FTIR spectroscopy and capillary column supercritical fluid chromatography (SFC). SFC was used to identify compounds, especially high molecular weight alkanes, and their changes in concentration with time in suspension in water. The results show that the main changes in the composition of oil droplets in stagnant waters are loss of low molecular weight material and differential loss of high boiling n-alkanes compared to their isoprenoid counterparts. FTIR spectroscopy and SFC proved powerful techniques for detecting minimal weathering processes, including oxidation, dissolution, and microbial degradation.