Sluge Formation During Heavy Oil Conversion

Abstract

Sludge formation during visbreaking, or the catalytic hydro-conversion of residual sets limits on the amounts of these feed-stocks converted into more useful products. Large amounts of sludge form at high conversions in these refinery processes, and it fouls downstream units. It is generally believed that sludge forms because the asphaltenes flocculate during processing. The exact mechanism is not known, however. The asphaltenes may become less soluble, or they may become less well solubilized, or both during processing. Although it is known that the amount of sludge formed depends on the feed-stock, or crude source, it has not been possible to link feedstock properties to the tendency to form sludge during processing in a reliable manner. In this work we develop “single molecule” representations of the asphaltenes (heptane insolubles) and resins (pentane insolubles/ heptane solubles) from several crude sources based on the elemental composition, and parameters determined by C13 NMR and proton NMR. The amount of sludge formed in laboratory tests can be correlated to three feed-stock parameters: the amount of polynuclear aromaticity in the asphaltenes, the degree of alkyl-subsitution on the polynuclear core in the single molecule representation of the asphaltenes, and the number of “asphaltene molecules” to “resin molecules”.