Selective pyrolysis of waste tire rubber for limonene production

The present study proposes a promising strategy for selective pyrolysis of waste tire rubber particles into high-value limonene under the dual action of chemical pretreatments and basic Ca x Mg 1-x Al oxides. The experimental results demonstrate that chemical pretreatments of rubber particles significantly enhance limonene selectivity in pyrolysis products while effectively suppressing the generation of sulfur-containing compounds. Among the various pretreatments, the rubber particles pretreated with 1 wt.% sulfuric acid exhibits optimal performance, which achieves a relative limonene content as high as 35%. The introduction of Ca 0.3 Mg 0.7 Al substantially promotes the selective production of limonene that gives a maximum relative content of 46% in pyrolysis oils. Kinetic analysis confirms that the application of as-prepared Ca 0.3 Mg 0.7 Al greatly lowered the average activation energy from 245.8 kJ/mol to 217.5 kJ/mol for waste tire rubber particles pyrolysis. Moreover, the plausible reaction pathway for waste tire rubber particles pyrolysis under the action of chemical pretreatments and composite metal oxides was proposed. This study, through experiments under ideal laboratory conditions, clarifies the core mechanism of the synergistic regulation of limonene selectivity by chemical pretreatments and basic Ca x Mg 1-x Al oxides, and provides basic research support and technical development directions for the subsequent targeted conversion of industrial-scale waste tire rubber into high-value limonene-rich pyrolysis oils.