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 catalys t. 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 hydrogenolysi s step is proposed, and follows the concentration trace of reactants (VO-EP and VO-EPH2) very well for most reaction times. The different modeling ste ms from the different selectivity of the catalysts. Under our experimental conditions the slowest step is the terminal hydrogenolysis instead of the f irst hydrogenation, so the steps after the first hydrogenation cannot be lu mped into one step in modeling our experimental data. Thus, the whole kinet ic scheme should incorporate the tetrahydrogenated species (VO-EPH4) found in our samples. (C) 2001 Academic Press.