Characterization of the Solid Residue and the Liquid Extract Separated by Propane-Induced Crude Oil Fractionation

Abstract

Following a previously reported experimental procedure, a heavy petroleum sample was fractionated by mixing a predefined volume of oil with liquid propane above its saturation pressure at different propane/oil ratios. The separated fractions, considered two mutually saturated liquid phases in equilibrium at p and T separation conditions, were denominated solid residue and liquid extract and were characterized by chemical and spectroscopic methods including elemental compositional and SARA analyses, FTIR, and NMR. The results show that the amount yielded or produced increases for the solid residue and decreases for the liquid extract as the propane/oil ratio increases and that the four SARA components are present in both fractions, independently of the propane/oil ratio used in the fractionation process. The data also indicate that polar components are present in the liquid extract even at the highest dilutions that correspond to rather low solubility parameters. Complementary results show that after the flocculation process and the subsequent liberation of propane, the solid residue and the liquid extract were easily recombined with minimal losses by remixing both fractions. Physical and chemical analysis indicated that the recombined and the original oil presented similar characteristics in terms of API gravity, SARA, elemental composition, FTIR, and NMR, but substantial differences in their rheological behavior. The similarity between original and recombined oil is also evidenced by 1H DOSY NMR that shows that sets of aggregates are present in the spectra for both oil samples.

Diffusion‐Ordered Spectroscopy (DOSY) as a Powerful NMR Method to Investigate Molecular Mobilities and Intermolecular Interactions in Complex Oil Mixtures

“…In Figure 1, all IR spectra show two significant vibration absorption bands, besides the bands of C−H stretching modes (aromatic ῡ Φ‐H in 3100–3000 cm −1 and alkyl ῡ C‐H in 3000–2800 cm −1 ) and alkyl C−H bending modes (alkyl δ C‐H with two peaks around 1459 and 1376 cm −1 ) [28] . One band is associated with the C=O stretching vibration ( ῡ C=O peaked at ~1700 cm −1 ) of carbonyl groups, typically from carboxylic acid groups, in line with the high TAN of Heavy Crude.…”