Kinetic Modeling of the Hydrotreating and Hydrocracking Stages for Upgrading Scrap Tires Pyrolysis Oil (STPO) toward High-Quality Fuels

The upgrading of scrap tires pyrolysis oil (STPO) has been studied in order to produce high-quality alternative fuels, conceived as the second and third stage of an industrially orientated valorization pathway for tires: pyrolysis, hydrotreating, and hydrocracking. The experiments have been carried out in a fixed-bed reactor under the following experimental conditions: (i) for hydrotreating: NiMo/Al₂O₃ catalyst; time on stream (TOS), 0-8 h; 300-375 °C; 65 bar; H₂:oil ratio, 1000 (v/v); space time, 0-0.5 g_cat h g_feed^-1; and (ii) for hydrocracking: PtPd/SiO₂-Al₂O₃ catalyst; TOS, 0-6 h; 440-500 °C; 65 bar; space time, 0-0.28 g_cat h g_feed^-1; H₂:oil ratio, 1000 (v/v). From the results, lump-based kinetic models have been established for both stages, considering the reactions of (i) hydrodesulfurization (HDS), (ii) hydrocracking (HC), and (iii) hydrodearomatization (HDA) in each one of them. Catalyst deactivation is insignificant in the hydrotreating stage but important for the hydrocracking stage. Therefore, deactivation has been considered in the corresponding kinetic equations. The computed deactivation constants have allowed for quantifying the contribution of each lump/composition fraction to coke formation.