Modeling of Catalytic Hydrodemetallation

Abstract

\n The removal of organo-metallic compounds of vanadium and nickel by hydrotreating is an important step in the cleaning and upgrading of fuel oil and resids. Unlike the elements of sulfur, nitrogen and oxygen, which are converted to gases in the hydrotreatment, vanadium and nickel are deposited on the catalysts and deactivate them after a period of time on stream. The mechanism of deactivation was theorized to take place by covering active catalyst sites and by blocking diffusion paths. A goal of catalyst design is to make a structure that would absorb as much metal as possible without being blocked. Recent experiments have shown that these metal sulfides do not deposit in continuous and uniform layers, and the prevailing mode is that of discrete large crystallites of up to several hundred Angstroms in diameter. Most of the surface of the aged catalyst appears no to be covered by metal deposits. This mode of deposition has been modeled successfully by a Random Sphere and a Random Needle Model. This implication on design and operation is that it is better to have few large crystallites than to have continuous uniform layers.\n