Vanadium and nickel deposition on FCC catalyst: Influence of residual catalyst acidity on catalytic products

The alteration of catalytic activity and selectivity of the cracking catalyst by porphyrinic metallic elements present in heavy crude oil fractions is a subject that requires serious attention. In this study, the effects of the two most deleterious of the metals (vanadium and nickel) and how they shift the product selectivity of the catalytic cracking are discussed, with a key focus on the catalytic behavior of the residual acidity consequent upon metal deactivation. Increasing loadings of vanadium and nickel were deposited on the FCC catalyst and subjected to a simulated FCC regeneration unit conditions. It is found that at loadings greater than 0.3 wt%, vanadium is 4-5 times as destructive as nickel on the crystalline structure of the catalyst. Catalytic evaluation results revealed correlations between residual surface acidity, catalyst activity and amount of coke formed on the catalyst at a constant catalyst-to-oil ratio (CTO). This result is in slight contrast with the widely reported enhanced coking activity of vanadium on FCC catalyst consequent upon dehydrogenation reaction. An alternative coke formation pathway based on the residual catalyst acidity is advanced for the observed coking behavior of high vanadium laden catalyst. In addition, a vanadium control measure relying on the acid-base chemistry and hydrothermal stability of a mixed-metal oxide is demonstrated as an effective method to limit the mobility of vanadium into the framework of the catalyst, the action that initiates vanadium deleterious effects. This study is expected to renew interest in the research on the coking behavior of metal poison catalysts.