Decoupling the efficiency of pre-prepared versus directly mixed alumina nanofluids for ultrasonic-assisted vanadium and nickel removal from heavy crude oil

Abstract

Heavy crude oils contain elevated concentrations of vanadium and nickel, which severely impair refining efficiency, accelerate catalyst deactivation, and increase environmental burdens during petroleum processing. Although nanoparticle-assisted and ultrasonic-based demetallization methods have been widely reported, the influence of nanofluid preparation route on metal removal efficiency has not been systematically isolated or quantified. This study presents a direct and controlled comparison between two alumina-based treatment routes for ultrasonic-assisted demetallization of East Baghdad heavy crude oil: a pre-prepared alumina nanofluid and a directly mixed nanoparticle–kerosene–surfactant system. Both systems were evaluated under identical ultrasonic conditions (40 kHz, 60 min) across a temperature range of 20–75 °C, enabling independent assessment of preparation methodology effects. The pre-prepared alumina nanofluid exhibited markedly superior demetallization performance, achieving vanadium and nickel removal efficiencies of 92% and 85%, respectively, compared with 83% and 72% obtained using the directly mixed system. This improvement is attributed to the formation of a stable and uniformly dispersed nanofluid, which ensures sustained accessibility of γ-Al₂O₃ active sites and enhances adsorption of metal–porphyrin complexes under ultrasonic cavitation. Comprehensive physicochemical characterization using TEM, XRD, TGA, AFM, and BET analyses confirmed that the pre-preparation route preserves nanoparticle structural integrity while maximizing surface activity and mesoporosity. The principal novelty of this work is the experimental demonstration that nanofluid preparation route, rather than nanoparticle chemistry alone, constitutes a governing parameter in heavy crude oil demetallization efficiency. By decoupling formulation effects from operational conditions, this study establishes a design principle for sustainable nanofluid-based upgrading systems.