Understanding catalyst deactivation in an industrial green hydrotreater and its correlation with catalyst composition

Abstract

Understanding and mitigating catalyst deactivation is crucial for enhancing the efficiency of hydrodeoxygenation (HDO) processes in the production of biofuels. In this study sulfided metal catalysts, NiMo/Al₂O₃, NiMo/SiO₂-Al₂O₃, and NiW/Al₂O₃ along with bare supports (Al₂O₃, SiO₂-Al₂O₃, and zeolite Y) were placed in a refinery green hydrotreating unit. Potassium, phosphorus and sodium were identified as major poisons. The HDO activity of spent catalysts was assessed in a lab-scale batch reactor at 58 bar H₂ and 325 °C for deoxygenation of oleic acid. The results highlighted that the active metals, particularly NiW, had a more pronounced tendency to attract poisons compared to the supports. However, with bare supports, coking was more significant and simultaneously less poisons were trapped, which could be due to blocking of the pores with coke. In the presence of these poisons there was a significant decline in oxygenate conversion compared with fresh catalysts, with a gradual reduction in activity for both decarbonation and direct-HDO products. Solvent washing treatments with DMSO and water were employed in an attempt to recover the activity of the spent catalysts, by partially removing the poisons. However, through these treatments, the activity of the NiMo/Al₂O₃ catalyst could not be restored.