Modelling RDM catalysts deactivation by metal sulfides deposits: An original approach supported by HREM investigations and pilot tests results

Heterogeneous RDM catalysts function as sinks for trace metals which would otherwise irreversibly poison downstream refining catalysts. Since the early seventies, a number of RDM catalysts deactivation models have been proposed, featuring an ever increased sophistication degree, maybe following the spilling over of low cost computer power into laboratories. With these models no attempts were made to preview or determine a very important property of a RDM catalyst: its Ultimate Storage Capacity (USC). The authors shall define this property as the mass x of metals relative to the unit mass of fresh catalyst, accumulated in a pellet till the catalysts residual activity becomes zero, provided the pellet has always functioned in the true chemical regime for HDM. Equation 1 relates the USC to measurable properties: x = ({Omega}:{rho}{sub MS}.{epsilon}{sub 0}.y/{rho}{sub C}). In Equation 1, {epsilon}{sub 0} is the catalysts initial porosity, {rho}{sub C} its initial grain density, {rho}{sub MS} the deposited metal sulfides true density, y their metal content, and {Omega} the fraction of {epsilon}{sub 0} occupied by the solid deposits in the occluded catalyst. For the perfect RDM catalyst, {Omega} = 1, but in the general case {Omega} > 1: the geometric structure of the fresh catalyst pores system,more » for instance the frequency of occurrence of bottlenecked pores, will determine the value of {Omega}. To their knowledge, no direct measurement technique of {Omega} has been reported up to now, although such a technique would be, in their opinion, quite essential for assessing the ability of a given porous material to become a good RDM catalyst support. In this paper, they propose a method to determine the {Omega} value of a RDM catalyst through a rapid RDM aging test.« less