Deactivation in catalytic hydrodemetallation I. Model compound kinetic studies

Abstract

Model compound hydrodemetallation (HDM) studies are used to examine the effect of accumulating metal-sulfide deposits on catalyst deactivation in a clean reactant system. Experiments are carried out in a catalyst-slurry batch reactor, using a sulfided CoMo/Al 2O 3 catalyst and a low-promoter alumina carrier. The model compounds are nickel etioporphyrin (Ni-EP) and vanadyl etioporphyrin (VO-EP). Standard experimental conditions are 320°C, 4.8 MPa total pressure, and 14 kPa hydrogen sulfide. Ni-EP HDM studies carried out with the sulfided CoMo/Al 2O 3 catalyst operating in the kinetic regime show that, contrary to expectations, the catalyst does not deactivate significantly as it accumulates nickel-sulfide deposits to levels as high as 100 wt% Ni. Ni-EP HDM studies carried out with a low-promoter alumina carrier show that the carrier has a low level of catalytic activity, and neither deactivates nor acquires catalytic activity as nickel-sulfide deposits accumulate to 25 wt% Ni. The relative activity for the two catalysts matches the relative promoter loadings. VO-EP HDM studies carried out under diffusion-limited conditions with the CoMo/Al 2O 3 catalyst show that it deactivates steadily as vanadium-sulfide deposits accumulate. Both the reactivity and the apparent effective diffusivity of VO-EP on the sulfided catalyst are significantly lower than those of Ni-EP.