CATALYTIC PROCESSING OF HEAVY CRUDE OILS AND RESIDUALS II. DIFFUSIONAL LIMITATIONS AND DEACTIVATION PHENOMENA

In the past two decades, there has been a considerable effort directed towards the development of effective processes for upgrading heavy oil and residual feedstocks. These materials are more difficult to process than lighter feedstocks because of their large molecular size and heteroatom and metals content. Significant diffusional limitations arise because the molecular size of the constituents of these feedstocks is large relative to typical catalyst pore sizes. The high heteroatom and metals content leads to the deposition of coke and metal sulfides on the catalyst surface. These deposits decrease the intrinsic activity of the surface as well as the catalyst pore size which causes a reduction in reactant diffusion rates within the catalyst. A sound understanding of these two important phenomena is necessary for the development of effective catalysts and catalytic processes for hydrotreating these materials.

In this article, recent literature dealing with two significant problems In catalytic processing of heavy oils is reviewed. Results from Investigations of the diffusional characteristics of these materials in small pores and some of the complex problems with catalyst deactivation are discussed.