Effect of catalyst deactivation and reaction time on hydrocracking heavy hydrocarbon liquids

The activity and fouling behavior of a commercial NiMo/Al₂O₃ catalyst has been studied during the hydrocracking of a coal extract at short reaction times. The catalyst was precoated with a carbonaceous deposit beforehand in order to study the interaction between a coated catalyst and fresh feed. The conversion of the heavier fraction (boiling point above 450 °C) of the feed steadily increased with time. However, the progression in the amount of carbonaceous deposits on the coated catalyst was not uniform. A large initial deposition was observed when the catalyst and fresh feed were placed in contact. This initial deposition was reversible, and within the first 10 min of reaction, much of the deposit redissolved into the liquid phase with increasing reaction times. This bulk exchange of material between the deposits and the solution appears to be a mechanism which would help explain the sustained level of catalytic activity despite the large carbonaceous deposition. A "harder" more permanent deposit layer built up more gradually as reaction time increased.