(64e) Molecular Structure of Heavy Oil Revealed - 2: The Effect of Severe Hydroprocessing

Previous studies on the effect of hydroconversion on asphaltene molecules have shown that severe hydroconversion results in the following changes in molecular structure: a decrease in the average molecular weight, an increase in aromaticity, a decrease in sulphur and oxygen level, and a reduction in the average length of alkyl side chains. It has also been found that converted asphaltenes are less soluble in conventional solvents. In this presentation we will discuss the effect of severe hydroprocessing using two samples (feed and product asphaltenes) from a commercial unit. The molecular information derived from this AFM/STM study illustrates the wide variety of molecules present in the asphaltene fraction. Apart from some isolated unusual molecules, e.g. one consisting of 17 substituted aromatic rings, the observed molecules fall in the expected MW range. Some of the main differences between feed and product asphaltenes will be discussed. The most striking difference is that the product asphaltenes have a more bulky (3-D) nature, which probably explains the fact that their tendency to flocculate is significantly lower than in the case of the feed asphaltenes (the feed asphaltenes form larger aggregates).