Studies on Coking of Residual Oils (Part 4): Behavior of Sulfur in Kuwait Vacuum Residual Oil during Coking Reaction

A pyridine-soluble matter in a synthetic coal, obtained from Kuwait vacuum residual oil by a coking reaction, has been subjected to a further coking reaction. This stepwise coking reaction was carried out three times. Coking reactions of asphaltene and maltene separated from the residual oil have also been carried out at 430°C for 0.5, 3 and 5 hours. It has become apparent that, in an initial step of the coking reaction, high molecular weight compounds of high sulfur content preferentially form a pyridine-insoluble matter, and it has been proposed that, in a later step, the coking reaction proceeds with cleavage of C-S bonds of thiophene type compounds, resulting in partial desulfurization of the pyridine-insoluble matter. A microscopic observation and an electron probe analysis have made it clear that sulfur is distributed homogeneously over various kinds of textures of the synthetic coal.