Conversão térmica e catalítica do polietileno tereftalato para obtenção de hidrocarbonetos e insumos químicos sustentáveis

Abstract

Polyethylene terephthalate (PET) is one of the main polymers used for packaging liquids for human consumption, and its volume of use is responsible for large amounts of plastic waste disposed of in the environment. In this work the use of pyrolysis was evaluated as a process for the depolymerization of PET, carried out at 550 oC, with the variation of the internal atmosphere of the reactor, between inert (N2) and reactive (H2), temperature variation of the second furnace of the reactor, varying its temperatures in 350, 450 and 550 °C and an exploratory study of the influence of inorganic additives (Na2SO4, MgSO4, SiO2, Al2O3, Na2CO3, CaCO3) in a thermocatalytic process in-situ. Additionally the quality improvement of the final product was evaluated by the treatment of the pyrolysis vapors by exsitu catalysis with the reactor operating in Tandem mode. Hierarchical Beta zeolite (H-Beta), MgZn-O and H-Beta doped with 20% bimetallic oxide (β-20% MgZn-O) were employed. The highest yield of pyrolytic liquid (56%) was obtained under atmosphere of H2 and process temperature of 550 °C, presenting as main constituent aromatic hydrocarbons, especially benzene, with formation of 15% of coke. In this condition was evaluated the addition of salts and oxides in the insitu form, which favored a greater formation of coke and reduction in the yield of pyrolytic liquid. Among the additives studied, Na2CO3 was most promising considering that it favored the production of a pyrolytic liquid with a lower concentration of PET-derived acids and a higher aromatic hydrocarbon content, especially when a Na2CO3 proportion of 30% was used. In the ex-situ catalytic processes, the catalysts promoted a reduction in the pyrolytic liquid yield, however, the oil presented a better quality for presenting lower contents of carboxylic acids and a higher concentration of aromatic hydrocarbons, especially for benzene, which had an increase of up to 500% in relation to the non-catalytic system. The present work also demonstrated the potential for a conversion of PET to benzoic acid of 11.65%, which could globally produce 8.4 thousand tons of benzoic acid per day, and could be directed to industrial applications.