MECHANISM OF COKE FORMATION FROM HYDROCRACKED ATHABASCA RESIDUUM

Coke forming tendencies of hydrocracked Athabasca residuum were studie d. The per cent toluene insolubles formed was taken as an indicator of the coke forming tendency. A coking unit and a tubing reactor were us ed for experiments under atmospheric pressure and at high pressures, r espectively. The types of toluene insolubles formed were analysed usin g optical microscopy. The paper discusses the results and correlates t he amount and type of toluene insolubles formed with the reaction cond itions. At the lowest and highest severity conditions studied, the tol uene insolubles formed were predominantly isotropic and anisotropic, r espectively. Reaction temperature and time were found to be dominant f actors in producing toluene insolubles; of all the variables studied, the reaction temperature was the most important. The optical texture o f toluene insolubles produced in the laboratory was compared to that f rom Syncrude's commercial plant. Anisotropic particles are proposed to be formed by homogeneous nucleation and from the conversion of isotro pic to anisotropic particles.