Opportunities and barriers for producing high quality fuels from the pyrolysis of scrap tires

The 7·106 t of waste tires that are generated yearly represent for a potential source of fuels considering its composition, rich in C and H, and its chemical features. Waste tires can be recycled through several processes aiming for either material, energy, or chemical product recovery. In this work we review the current status of these valorization pathways, with a particular focus on pyrolysis, its main products and their characteristics. Despite the extended reviews on the pyrolysis of tires, scarce material is available regarding the possibilities that scrap tires pyrolysis oil (STPO) offers and its limitations. STPO is both the most economically and energetically attractive product, and its composition (as obtained by different authors) is analyzed in this work, finding that the main barriers to solve for its direct implementation are (i) high sulfur content, (ii) high content of aromatics and (iii) high proportion of heavy molecules (>350 °C). From an industrial perspective, a sequential 2-stage hydrotreating-hydrocracking strategy has been proposed for STPO upgrading in order to simultaneously overcoming all these limitations and produce high quality fuels.