Reaction pathways of anthracene selective catalytic steam cracking using a NiK/Al₂O₃ catalyst

Selective catalytic steam cracking (SCSC) provides an alternative for the upgrading of polycyclic aromatic hydrocarbon (PAH) structures present in heavy oil fractions. In this process steam is used as source of hydrogen at relatively mild temperatures (in the range of 400-500°C), favouring the formation of products derived from the scission of C-C bonds of the internal ring. The opening of the central ring in PAH structures is an effective route leading to the formation of more valuable intermediates with less hydrogen consumption compared to hydrocracking. The latter proceeds mostly via external ring opening, which implies high hydrogen consumption and leads to the formation of smaller amounts of monocyclic products. A compromise between anthracene (a model compound of polyaromatic structures characteristic of high molecular weight asphaltenes) conversion and selectivity to liquid productswas obtained at 450°C using a NiK/Al₂O₃ catalyst and therefore reaction pathways at this temperature were established. SCSC of anthracene was found to occur via two simultaneous reaction pathways, leading to the formation of biphenyls products (mainly methyl biphenyl) via fluorenone as intermediate and naphthenic derived products.