Coking propensity and reactive radical evolution during thermal reaction of heavy residue and SARA fractions at 250-400?C

In this study, the coking propensity and reactive radical evolution of heavy residue and SARA fractions at 250-400 degrees C were studied to gain an insight into the coke induction process. The interactions among fractions for thermal coking were discussed. Results showed that residue started to form coke (i.e. toluene-insoluble at room temperature) at 350 degrees C for longer times while resins and asphaltenes have already extensively produced coke at 250 degrees C with no coke induction period. This indicates that the coke induction depends on the solubility gap of reactant and coke. The coking process can be fitted with the second-order and autocatalytic kinetics for residue while second-order kinetics for heavy fractions with initial coke precursor amount varying with temperature. Asphaltenes are the sole fraction that generated reactive radicals at 250 degrees C and responsible for the radicals of thermal residue. The explosion of reactive radicals began when the temperature exceeded 350 degrees C and became steady as the thermal reaction proceeded. The coke at low temperatures mainly originated from the molecules aggregation with faint radical emergence while that at high temperatures is strongly correlated with the radical evolution. The maltene subfractions could suppress the coking of asphaltenes possibly because of the physical solvation and chemical hydrogen donating behavior to cap reactive radicals. It can serve as the intrinsic im-munity for coke inhibition of heavy residue during thermal partial upgrading.

Automated summary

This study investigates the coking propensity and radical evolution of heavy residue and SARA fractions at different temperatures to understand the coke induction process. Results show that residue starts to form coke at higher temperatures while resins and asphaltenes produce coke at lower temperatures without an induction period. The solubility gap between reactant and coke influences the coke induction. The coking process can be described by different kinetics for residue and heavy fractions, while asphaltenes generate reactive radicals and contribute to the radical evolution. Maltene subfractions can inhibit the coking of asphaltenes by solvation and hydrogen donation behavior.