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 degrees C) and its fraction s separated by ion-exchange chromatography was investigated using hot-stage microscopy. The initial time of mesophase formation and its growth rate we re measured for each fraction. The results showed that the amphoteric fract ion was the most prone to coke formation, followed by the basic and acidic fractions. Mesophase formation for the neutral and aromatic fractions was d elayed, and its growth rate was considerably slower. The relative order of coking propensity of the fractions is amphoteres > bases > Hamaca resid > a cids > neutrals > aromatics. Although the Hamaca resid contained high conce ntrations of aromatic and neutral components with a relatively lower coking propensity, its coking propensity was much more similar to that of the aci dic and basic fractions, which were less abundant in the resid. This propen sity shows that the interactions among the individual components were not p roportional to their concentrations in the feed and that the amphoteric fra ction may have had a larger influence on coke formation relative to the oth er components. It was further observed that under the reaction conditions e mployed, the amphoteric fraction had high viscosity, did not develop a dist inct 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 feasibi lity of selective removal of problematic components in the feedstocks prior to processing.