Influence of roasting on the structure and leaching behavior of spent residue hydrotreating catalysts

Abstract

Residue hydrotreating is a critical process in petroleum refining. The spent catalysts typically contain Ni (Co) and Mo (W) as active metals and accumulated Ni and V from processed residues during the operation. Substantial amounts of spent residue hydrotreating catalysts (sRHCs) are generated, which pose severe environmental threats and require proper treatment. After roasting, sRHCs can be further utilized efficiently, such as metal leaching and recovery. Herein, two typical sRHCs, spent hydrodesulfurization and hydrodemetallization catalysts, were selected to investigate the phase transformations and structural changes during roasting. It was found that roasting at 600 °C promoted crystal growth and the formation of composite oxides through solid-state reactions compared to roasting at 430 °C, which hindered the leaching of Ni and Fe in H₂SO₄ and NaOH. However, the elevated oxidation states of V induced by high-temperature roasting facilitated V leaching, while aggregated deposited metals improved the leaching of Mo and Al. The spent hydrodemetallization catalysts predominantly formed Ni/Fe–V–O composite oxides, VO₂ and metal sulfates during roasting, whereas the spent hydrodesulfurization catalysts tended to generate Ni–Mo–O composite oxides and V₂O₅. In addition, the influence of the phase structures of the roasted sRHC on their leaching efficiency in H₂SO₄, water, and NaOH solutions was studied. Fe₂O₃ and VO₂ exhibited a superior leaching performance in H₂SO₄, MoO₃, metal sulfates, NiMoO₄, and AlVO₄ demonstrated a higher leaching efficiency in NaOH, and V₂O₅ possessed good leaching efficiency in both H₂SO₄ and NaOH.