Continuous Polyolefin Cracking on an HZSM-5 Zeolite Catalyst in a Conical Spouted Bed Reactor

The effect of operating conditions on product yields and compositions has been studied in the catalytic cracking of polyolefins (high- and low-density polyethylene and polypropylene) in a conical spouted bed reactor. The catalyst has been prepared by agglomerating an HZSM-5 zeolite (SiO2/Al2O3 = 30) with bentonite and alumina. The study has been carried out in continuous mode, in the 450-570 degrees C range, with polyolefin flow rates between 1 and 2 g min(-1) and feeding up to 1 kg of polyolefin into a 30 g catalyst bed. The result is an excellent performance of the reactor-catalyst pairing for continuous catalytic pyrolysis, given that the yields obtained in the pyrolysis of high-density polyethylene at 500 degrees C without defluidization problems and very low catalyst deactivation are as follows: 60 wt % C-2-C-4 olefins, 15 wt % nonaromatic C-5-C-11 hydrocarbons, 10 wt % single-ring aromatics, and 14 wt % C-4 alkanes. Only small differences are observed in the pyrolysis of the different polyolefins.