abstract
Wax precipitation is one of the most important flow assurance problems. The adequate characterization of the content and composition of the waxes present in the oil is one of the major obstacles in dealing with this issue. In this work, two different methods for the extraction of waxes from different crude oils are compared. The methods used differ significantly with regard to the separation of waxes from asphalthenes. Further purification of paraffins for characterization was carried out using sequential elution chromatography. The n-paraffin distribution determined by gas chromatography along with wax melting temperature and total n-paraffin content determined by differential scanning calorimetry show remarkable differences in the waxes depending upon the precipitation method used. The separation carried out by method 1 allows for heavier n-alkanes to be retained but with a higher content of impurities, as revealed by their lower melting points and n-paraffin content. Method 2 provides a better purification of the waxes but at a cost of losing some of the heavier n-paraffins. The waxes recovered are shown to be macrocrystalline waxes, with H/C ratios above 2 and average molecular weights between 450 and 530. (1)H nuclear magnetic resonance (NMR) analyses show a very low content of aromatic hydrogen, indicating the good separation achieved by the sequential chromatographic method used to isolate waxes, while the (13)C NMR results indicate the structure of the waxes to be mainly formed by straight chains with methyl branches.
keywords
NUCLEAR-MAGNETIC-RESONANCE; CLOUD POINT MEASUREMENT; DISTILLATE FRACTIONS; SYNTHETIC MIXTURES; PARAFFIN WAXES; NEW-MODEL; PRECIPITATION; TEMPERATURE; PETROLEUM; SPECTROSCOPY
subject category
Energy & Fuels; Engineering
authors
Espada, JJ; Coutinho, JAP; Pena, JL
our authors
acknowledgements
The authors thank Repsol for providing the crude oil samples and the financial support through the research project