Pyrolysis is the optimal approach to treat waste plastics from municipal solid waste. However, the inferior quality of waste plastic pyrolysis oil (WPPO) limits its further application and requires refining. The deactivation mechanism of Ni-based catalyst in the hydrotreating process of WPPO was investigated. The accelerated deactivation experiment of catalyst was performed with model oil containing different impurities, and results indicated that the deactivation of catalyst was related to chlorides, nitrides, and sulfides in WPPO. By changing the concentration of chloride, the interactions between the three impurities were studied. Combined with the characterization results of fresh and spent catalysts, chloride was the direct cause of the deactivation of the catalyst. Chlorine atoms in chlorides were converted into HCl gas in hydrotreating, which reacted with Ni active sites, resulting in the sintering of the average Ni particle size from 52.62 nm to 139.63 nm, and the loss of Ni active components by 3–8 wt%, especially inhibiting the hydrodesulfurization activity of the catalyst. In addition, HCl reacted with NH₃ (byproduct of nitride hydrogenation) to generate NH₄Cl. The high concentration of HCl in the reaction system increased the crystallization temperature of NH₄Cl from 210 °C to 294 °C, which led to the crystallization of ammonium salts in the catalyst bed. NH₄Cl crystals adsorbed on the catalyst surface, resulting in a decrease in specific surface area and pore volume, and an increase in the average pore diameter of the catalyst, which was the main reason for the rapid deactivation of the catalyst. This stduy provides a theoretical basis for the development of hydrotreating catalyst for WPPO with high activity, adjustable selectivity and anti-deactivation.

The morphology of catalyst in SEM images (A, B) and Ni particles in TEM images (C, D).

Bencheng Wu

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