%0 Journal Article
%T Modeling of Catalytic Hydrodemetallation L'hydrom¨¦tallation catalytique
%A Wei J.
%J Oil & Gas Science and Technology
%D 2006
%I Institut Fran?ais du P¨¦trole
%R 10.2516/ogst:1991026
%X 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. L'extraction des compos¨¦s organo-m¨¦talliques du vanadium et du nickel par hydrotraitement constitue une ¨¦tape importante de la purification et de l'am¨¦lioration du fuel-oil et des r¨¦sidus. Contrairement aux ¨¦l¨¦ments soufre, azote et oxyg¨¨ne qui sont transform¨¦s en gaz au cours de l'hydrotraitement, le vanadium et le nickel se d¨¦posent sur les catalyseurs et au bout d'un certain temps les d¨¦sactivent. Le m¨¦canisme de la d¨¦sactivation a ¨¦t¨¦ expliqu¨¦ par le fait qu'il se produit une obstruction des sites actifs du catalyseur et un blocage des voies de diffusion. Dans l'¨¦tude d'un catalyseur le but recherch¨¦ est de concevoir une structure qui absorbe autant de m¨¦tal que possible sans ¨ºtre bloqu¨¦e. Des exp¨¦riences r¨¦centes ont r¨¦v¨¦l¨¦ que ces sulfures m¨¦talliques ne se d¨¦posent pas en couches uniformes et continues, et le mode qui pr¨¦vaut est celui de larges cristallites discontinus dont le diam¨¨tre peut atteindre plusieurs centaines d'Angstr ms. La majeure partie de la surface des catalyseurs utilis¨¦s ne pr¨¦sente pas de d¨¦p ts de m¨¦tal. Une bonne repr¨¦sentation de ce mode de d¨¦position est donn¨¦e par le mod¨¨le de la sph¨¨re al¨¦atoire (Random Sphere) et de l'aiguille al¨¦atoire (Random Needie). Par cons¨¦quent, il vaut mieux avoir quelques grands cristallites que des couches uniformes continues.
%U http://dx.doi.org/10.2516/ogst:1991026