Valorization of waste plastic mixtures by pyrolysis and in-line catalytic cracking on a hierarchical HY zeolite

The pyrolysis and in-line catalytic cracking of a polyolefin mixture composed of 40% PP, 30% LDPE and 30% HDPE has been conducted on a HY zeolite catalyst. The plastics pyrolysis step has been performed in a conical spouted bed reactor at 500 °C in continuous mode, attaining a stream with 69.8% of waxes (>C 21 ) and 30.2 wt% of volatiles (<C 21 ). This stream was fed into a fixed bed reactor to assess the influence temperature and catalyst stability in the 450-550 °C range have on the evolution of product yields with time on stream and catalyst deactivation. The main fraction at 450 °C was that of non-aromatic C 5 -C 11 (45.5 wt%), but the prevailing fraction at 550 °C shifted to light olefins (C 2 -C 4 yield of 53.1 wt%). When operation time increased, the yield of these fractions and those of light alkanes (C 1 -C 4 ) and aromatics decrease at the expense of C 11+ hydrocarbons due to the decrease in catalyst activity. Samples of spent catalysts were taken from the catalytic reactor at two different axial positions subsequent to the runs at different temperatures. The results showed the catalyst in direct contact with the waxes coming from pyrolysis reactor (first half of the reactor) led to a high content of slightly structured coke, whereas that located in the second half of the reactor (close to the outlet) became more structured. This is because the stream in the second location is richer in light olefins, whose condensation is the main cause of coke formation. • Polyolefin mixture was valorized via pyrolysis and catalytic-cracking on HY zeolite. • The pyrolysis step yields a stream containing 69.8% waxes. • HY perform well for the production of gasoline-range compounds and light olefins. • Longer time on stream decreases olefins and aromatics due to catalyst deactivation. • Waxes produce a less structured coke but light olefins a more condensed one.