Organic Removal from Spent Ni–Mo–V Hydroprocessing Catalysts: Mechanisms, Treatment Routes, and Process Integration—A Critical Review

Spent Ni–Mo–V-bearing hydroprocessing catalysts from heavy-oil refineries commonly contain free petroleum, adsorbed heavy hydrocarbons, carbonaceous coke, and sulfur- and nitrogen-bearing compounds. These distinct contaminant fractions create operational and environmental constraints before metal recovery, yet published removal efficiencies often rely on incompatible definitions and analytical bases. This critical review evaluates physical separation, solvent and surfactant washing, thermal desorption, pyrolysis, controlled oxidation, and hybrid treatment as pretreatment routes for subsequent hydrometallurgical or pyrometallurgical recovery rather than catalytic regeneration. A feed-specific mechanism–technology matrix, common mass-balance indicators, and a process-integration framework are proposed. Evidence suggests that solvent cleaning can target mobile oil without fully eliminating refractory coke, whereas staged thermal processing can access more strongly retained fractions at the expense of energy demand, emissions control, and phase changes. A reported mass-loss percentage cannot be equated automatically with oil removal, and concentration-based metal enrichment cannot establish quantitative metal retention. Future comparative work should quantify oil, coke, total carbon, sulfur species, metal losses, solvent closure, energy demand, emissions, and downstream metallurgy on consistent feed bases. The most defensible industrial choice is a staged, contaminant-specific pretreatment selected against explicit feed-quality requirements, rather than universal maximization of organic removal.