The effect of hydrotreating on the pyrolysis oil composition by GC-MS

Abstract

The processing of waste tires is a significant challenge. The pyrolysis of waste tires offers a sustainable pathway to produce fuel, addressing both waste management and energy recovery challenges. However, due to the content of a large amount of unsaturated, aromatic hydrocarbons, and sulfur compounds, their direct use as fuel is not possible. Catalysts based on Pd, Pt, and other metals are commonly used for the hydrotreating of pyrolysis oil for the production of alternative transportation fuels. The effect of hydrotreating with commercial Pt/Al2O3 and NiMo/Al2O3 catalysts on the chemical composition of tire pyrolysis oil was analyzed by GC-MS following a developed extraction sample preparation procedure. Pyrolysis of the tire was conducted at 500 °C in a nitrogen atmosphere. The catalytic hydrotreating was evaluated with a 250 mL reactor at 250–350 °C and at 6.5 MPa hydrogen pressure. The hexane solution of pyrolysis oil was sequentially extracted with water, dimethyl sulfoxide and then treated with oleum to separate complex pyrolysis oil into water-soluble compounds, polycyclic aromatic hydrocarbons, and saturated hydrocarbons (naphthenes and alkanes). It was found that unsaturated hydrocarbons and water-soluble compounds were effectively removed from pyrolysis oil using hydrotreating with a NiMo/Al2O3 catalyst, demonstrating superior performance compared to the Pt/Al2O3 catalyst, which showed only partial removal. Moreover, it was demonstrated that NiMo/Al2O3 is a more efficient catalyst for the hydrotreating of pyrolysis oil to reduce toxic PAHs, as well as sulfur, nitrogen, and oxygen content from pyrolysis oil. Compared to conventional Urals crude, TPO possesses a higher proportion of valuable gasoline and diesel fractions but is also contaminated with significantly more sulfur, nitrogen, and aromatic compounds. Although hydrotreating produced a diesel fraction meeting key fuel specifications (e.g., heating value, flash point, density), its residual PAH (0.200 wt%) and sulfur (0.0432 wt%) content still exceeds commercial diesel standards.