Catalytic Hydrodemetalation of Heavy Oils

Abstract

In the past two decades, residuum hydrotreating has become a very important refining process. Designed originally to reduce the sulfur in heavy fuel oils, it has also been used in a variety of schemes for converting heavy oils into more valuable transportation fuels. Chevron Research Company offers for license the Chevron Residuum Hydrotreating Process which contains the best features of the processes developed independently by the Chevron and Gulf research organizations before their two parent companies merged in 1985. Since residuum feedstocks contain organometallic impurities, studies of the hydrodemetalation reaction were instrumental in the successful development of the catalysts used in this process. This reaction has the unique feature that it is a heterogeneous catalytic rection in which the organometallic reactant leaves an easily identifiable deposit on the catalyst surface at the precise place where the reaction occurred. Chevron Research has developed catalysts and processes which remove the common trace metals present in crude oil residua–nickel, vanadium, and iron. Demetalation kinetics have been measured over a variety of catalysts in order to generate more effective catalysts. Spent catalysts have been analyzed by micro-probe techniques to try to understand the long-range effects of metals deposition on reactor pressure drop buildup and catalyst deactivation. Pore diffusion theory has been used to help correlate the data and improve the scale-up operation. This paper reviews these developments and points out the importance of catalyst porosity, size, and shape on catalyst activity and life. Factors which can contribute to a pressure drop buildup in a fixed bed reactor are also covered.