Improvement in the production of aromatics from pyrolysis of plastic waste over Ga-modified ZSM-5 catalyst under C1-gas environment

Abstract

This study explores, for the first time, the influence of various C1 gases, such as methane (CH₄), carbon dioxide (CO₂), and biogas (CH₄ + CO₂), on catalytic pyrolysis of plastic waste (polypropylene) to evaluate their potential in producing aromatic hydrocarbons. Also, this study used the 0.5 wt%, 1 wt%, 3 wt%, and 5 wt% Ga-modified ZSM-5 catalyst and its reduction-oxidation processed catalysts owing to their promising catalytic properties. According to the results, the highest yield (39.5 wt%) of BTEX (benzene, toluene, xylene, and ethylbenzene) was achieved under CH₄ over RO-GHZ(1) catalyst among all tested conditions. The reduction-oxidation process not only promotes a significant reduction of the Ga-size but also induces its diffusion inside the pore, compared to GHZ(1). This leads to the formation of highly active GaO⁺ ionic species, balancing the Lewis/Brönsted ratio, thereby accelerating the aromatization reaction. The effect of Ga loading on the RO-GHZ catalyst was also evaluated systematically, which showed a negative impact on the BTEX yield owing to the lowering in the concentration of active GaO⁺ species. A detailed catalyst characterization supports the experimental results well.