Kinetics of Vanadyl Etioporphyrin Hydrodemetallization

The kinetics of hydrodemetallization (HDM) of vanadyl etioporphyrin (VO-EP) has been studied in a batch autoclave at 543 K and 5 MPa of total pressure, with white oil as solvent and presulfiding CoMo/Al2O3 (TK 710) as catalyst. The most widely accepted kinetic model comprised of only dihydrogenated intermediate (VO-EPH2) does not fit our experimental data. A new model with two reversible hydrogenation steps and a lumped irreversible hydrogenolysis step is proposed, and follows the concentration trace of reactants (VO-EP and VO-EPH2) very well for most reaction times. The different modeling stems from the different selectivity of the catalysts. Under our experimental conditions the slowest step is the terminal hydrogenolysis instead of the first hydrogenation, so the steps after the first hydrogenation cannot be lumped into one step in modeling our experimental data. Thus, the whole kinetic scheme should incorporate the tetrahydrogenated species (VO-EPH4) found in our samples.