Obtaining value-added hydrocarbons by catalytic pyrolysis of waste tires using acid catalysts based in supported heteropolyacids

OSORIO-VARGAS, PAULA; ILEANA DANIELA LICK; CONSUELO ALVAREZ-GALVAN; LUIS R PIZZIO; ARTEAGA-PÉREZ, LUIS E; CASELLA, MÓNICA L

CABA

Congreso; WCCE11-11th World congress of Chemical Engineering. XXX Interamerican Congress of Chemical Engineering ? IACCHE; 2023

Approximately one billion waste tires are generated annually worldwide. Catalytic pyrolysis of this residue is a promising alternative for recycling, fuel recovery, and even obtaining higher economic value products. Here, catalysts based on heteropolyacids (HPA) supported on TiO2 (H3PW12O40/TiO2) were evaluated to yield a pyrolytic liquid enriched in aromatic compounds such as BTX and p-cymene. The nature and content of the acid sites were determined through FT-IR spectra of adsorbed pyridine. In these spectra, six bands were detected; the signals at 1545 and 1635 cm-1 were associated with protonate pyridine bonded to Brønsted acid sites (BAS), while those found at 1445, 1575, and 1610 cm-1 were ascribed to pyridine coordinately bonded to the Lewis acid sites (LAS). Then, the acid site content was calculated using the vibration bands at 1445 cm-1 for LAS and 1545 cm-1 for BAS. Activity experiments were carried out in TGA-FTIR equipment and a fixed bed reactor (12 mm ID stainless steel tubular reactor) between 400 and 600 °C under 100 mL min− 1 constant nitrogen flow rate. The gaseous products were condensed at the exit of the reactor, and the composition of pyrolytic oils was determined by QP2010SE Shimadzu GC/MS. TGA measurements confirmed the catalyst's stability at working temperatures. The primary compounds of waste tire pyrolysis were D,L-limonene, and isoprene. In contrast, catalysts favored the formation of target compounds compared with the uncatalyzed reaction. TGA-FTIR studies confirmed the presence of aromatic compounds through bands observed between 1500 and 1600 cm−1, usually ascribed to the C=C stretching, mainly on catalysts with higher content of HPA ( > 15%). Moreover, pyrolysis reactions performed in a fixed bed showed that the higher the HPA content, the greater the favoring of the cracking reactions. Catalysts with low TPA loading (< 5%) promoted the formation of p-cymene by secondary reactions on D,L-limonene, while intermediate concentrations (between 15 and 30%) favored aromatization reactions leading to BTX. p-Cymene is mainly formed through isomerization reactions of aliphatic terpene driving to its isomers, terpinolene and α- and γ-terpinene, whose subsequent dehydrogenation gives rise to these aromatic terpenes. On the other hand, the C-C bond breaking of the D,L-limonene ring in the β-position could contribute to BTX formation, as described in [1]. The acidity results indicated a direct correlation between acidic properties and catalytic activity. A higher BAS/LAS ratio, related to a higher HPA content, favored the cracking and aromatization reactions leading to BTX. On the contrary, a lower BAS/LAS ratio coming mainly from the support promoted to a greater extent isomerization reactions leading to p-cymene.