Valuable petrochemicals, petroleum fractions, and sulfur compounds in oils derived from waste tyre pyrolysis using five commercial zeolites as catalysts: impact of zeolite properties

Valuable petrochemicals such as benzene, toluene, and xylenes have been observed in waste tyre-derived oils, indicating that waste tyre exhibits its potential to be used for an alternative source for sustainably producing petrochemicals. However, without a catalyst, such chemicals cannot be produced in a high amount. Sulfur compounds causing environmental problems and the low quality of oils were also found in tyre-derived oils. In waste tyre pyrolysis, zeolites that have been used very often to improve the quality of oil are HZSM-5 and HY, owing to their cracking and single-ring aromatics-producing abilities. Some other zeolites have been also employed occasionally, but the effects of zeolite properties on the hydrocarbon species and sulfur compounds in oils have not been explained clearly. The objective of this work was therefore to investigate the effects of zeolite properties, that are, acidity/basicity, pore channel structure, pore size, and Si/Al ratio on hydrocarbon species in pyrolysis products, especially valuable C6–C8 petrochemicals and sulfur compounds. The oils were analyzed using SIMDIST-GC for petroleum fractions and using a GC × GC–TOF/MS for valuable petrochemicals and sulfur-containing compounds. The analysis of the results from using five zeolites indicated that, for high production of valuable C6–C8 petrochemicals from waste tyre pyrolysis, a catalyst must (a) possess acid sites, rather than basic ones, that have high enough strength for cracking, which can result in high production of naphtha fraction and (b) have a complex channel structure with a large enough pore size (at least ~7 Å) that allows molecules to stay inside at a long contact time. In addition, high acid strength is more preferred to high acid density for high production of valuable C6–C8 petrochemicals, but high acid density is more preferred for production of oil with low sulfur content.