Investigation of the thermal behavior and interaction of Venezuelan heavy oil fractions obtained by ion-exchange chromatography

The coking propensity of Hamaca heavy oil (+510 °C) and its fractions separated by ion-exchange chromatography was investigated using hot-stage microscopy. The initial time of mesophase formation and its growth rate were measured for each fraction. The results showed that the amphoteric fraction was the most prone to coke formation, followed by the basic and acidic fractions. Mesophase formation for the neutral and aromatic fractions was delayed, and its growth rate was considerably slower. The relative order of coking propensity of the fractions is amphoteres>bases>Hamaca resid>acids>neutrals>aromatics. Although the Hamaca resid contained high concentrations of aromatic and neutral components with a relatively lower coking propensity, its coking propensity was much more similar to that of the acidic and basic fractions, which were less abundant in the resid. This propensity shows that the interactions among the individual components were not proportional to their concentrations in the feed and that the amphoteric fraction may have had a larger influence on coke formation relative to the other components. It was further observed that under the reaction conditions employed, the amphoteric fraction had high viscosity, did not develop a distinct mesophase stage, and formed fine-grained mosaic coke over a very short period of time. The results of this work may be used to assess the feasibility of selective removal of problematic components in the feedstocks prior to processing.