Dechlorination during pyrolysis of plastics: Effect of municipal plastic waste composition

In order to close the loop in chemical recycling via pyrolysis, products must meet strict limits for halogen content to be used in conventional petrochemical processes. By integrating dechlorination as an integral part of pyrolysis, results show that the efficiency of dechlorination, both via stepwise pyrolysis and dechlorination agents, is significantly decreased in the presence of PET or cellulose in the feedstock. Product analysis showed that Cl reacts with formed oxygenated substances, some of which remain in the reactor during the 1st step at 350 °C and subsequently pass into the final liquid product. This increases the requirements for applied dechlorinating agents during the 2nd pyrolysis step. Novel agents have to therefore cope with a wide range of chlorinated hydrocarbons. By combining acidic β-zeolite with alkali hydrotalcite in a 1:1 ratio, a synergic effect towards dechlorination was observed, increasing individual efficiency by about 12% and 6%, respectively. Combining stepwise pyrolysis, which removed 38% of Cl on average, with the mentioned mixture of agents, 95% efficiency and 12.2 ± 1.2 ppm of Cl were obtained in the final liquid product. Such a level of dechlorination may be sufficient, considering that the pyrolysis liquid will be diluted in conventional petrochemical feedstocks.