Spent hydroprocessing catalysts include, but are not limited to, nickel sulfide, vanadium sulfide, and/or molybdenum sulfide. ???Superbase??? refers to a material that can deprotonate hydrocarbons such as paraffins and olefins under reaction conditions. ???TAN??? refers to a total acid number expressed as milligrams (???mg???) of KOH per gram (???g???) of sample.