Mechanism research on hydrogen production from catalytic pyrolysis of waste tire rubber

Waste tires are currently disposed of through various approaches such as landfill and incineration, which not only causes environmental pollution, but also lead to the wastage of resources. As an important type of solid waste, tire rubber has a high carbon-to-hydrogen ratio, which makes it a good material for hydrogen production from pyrolysis. In this study, molecular dynamics simulations combined with experimental methods are used to explore the mechanism of hydrogen production from the catalytic pyrolysis (CP) of waste tire rubber (WTR) over Ni, ZSM-5 and Ni/ZSM-5. The simulation results show that the three catalysts potentially promote the release of hydrogen radicals from monomers and facilitate attack by H· radicals to generate hydrogen. Compared with ZSM-5 and Ni, the Ni/ZSM-5 catalyst exerts better catalytic effects, leading to higher contents of produced H2 and hydrocarbons. In the low-temperature stage, the long chain cracks into monomer compounds, which mainly include isoprene, styrene, and 1,3-butadiene. Meanwhile, in the high-temperature stage, free radicals attack monomers to generate small molecules. The main gas products from the catalytic pyrolysis of waste tire rubber are hydrogen, methane, and ethylene. The use of all three catalysts leads to a low final catalytic pyrolysis temperature, high catalytic pyrolysis rate, and excellent catalytic effect. This work aims to provide a deeper understanding of the reaction thermodynamics and kinetics for the formation mechanisms of gaseous products, primarily hydrogen.