Comparison of processing characteristics of Mayan and Wilmington heavy residues: 2. Characterization of vanadium and nickel complexes in acid-base-neutral fractions

Abstract

Wilmington 538 °C + and Mayan 496 °C + crude oil residues were hydrotreated at four temperature levels. The products from hydrotreating were gases and condensates in the overhead and heavy liquids and (at high temperatures) solids in the reactor. The heavy liquids were separated into acid-base-neutral (ABN) fractions by a unique nonaqueous ion exchange technique developed at NIPER. The analyses of the condensates, the characterization of the ABN fractions, and the changes in composition of the heavy liquid products caused by hydrotreating is reported elsewhere 1. Nickel and vanadium complexes in the feeds, whole heavy liquid and ABN fractions were characterized by determining the total metal content, the porphyrinic metal content and the molecular weight distribution of the metal complexes by size exclusion chromatography/inductively coupled plasma. For both crudes, the metal complexes spanned a wide range of chemical behaviour and molecular weight. The resistance of the various classes of metal complexes to hydrodemetallization varied enormously and depended on the chemical type more than the hydrotreating temperature. Both nickel and vanadyl porphyrins were found to appear, in certain ABN fractions, in greater amounts after hydrotreating than before, thus suggesting that the presence of selected porphyrins may be masked by intermolecular interactions and/or attached functionalities and thus they are not detected as porphyrins by visible spectrometry.