Effect of CV-ZSM-5, Ni-ZSM-5 and FA-ZSM-5 catalysts for selective aromatic formation from pyrolytic vapors of rubber wastes

- Rubber waste was catalytically pyrolyzed using HZSM-5 catalysts.
- The aromatic selectivity was in the order of CV-HZSM5 > Ni-HZSM-5 > FA-HZSM5.
- High catalyst content enhanced the aromatic formation with decreasing the non-aromatics.
- The rubber:catalyst ratio of 1:5 showed the optimum result for maximizing aromatic selectivity (80.8-95.9%).
- HZSM-5 catalysts enhanced greatly MAHs selectivity, especially BTX.

A large and increasing amount of polymeric wastes, including plastic, rubber and tyres, are produced each year causing increasing disposal and environmental problems. The recycling of these wastes is an alternative way to solve the problem of polymeric waste management. Thermal/catalytic degradation (pyrolysis) of these wastes is of interest for liquid fuel production. In this work, rubber waste collected from the bicycle brake industry was used as the feedstock for pyrolysis for liquid fuel production. Three HZSM-5 zeolites, synthesized from the conventional hydrothermal method (CV-HZSM-5), Ni loaded HZSM-5 (Ni-HZSM-5) and HZSM-5 derived from fly ash (FA-HZSM-5), were examined for their catalytic performance in the fast pyrolysis of rubber waste using analytical gas chromatography-mass spectrometry. The pyrolysis was performed at 500 °C with different rubber: catalyst weight ratios (1:1, 1:5 and 1:10). Increasing the catalyst content remarkably enhanced the formation of aromatic hydrocarbons and decreased the non-aromatic fractions drastically, and was optimal at a rubber: catalyst ratio of 1:5 yielding 80.8-95.9% aromatic and 2.8-18.7% aliphatic hydrocarbon products and only approximately 2% oxygenates and nitrogenates. The aromatic selectivity of the catalysts was ranked in the order of CV-HZSM5 > Ni-HZSM-5 > FA-HZSM5. Overall, the three HZSM-5 catalysts showed a superior catalytic performance for upgrading pyrolytic vapours from rubber wastes in terms of enhancing the aromatic production, especially benzene, toluene and xylene compounds.