(2012) Environmental Science and Technology_Utilizing carbon dioxide as a reaction medium to mitigate production of polycyclic aromatic hydrocarbons from the thermal decomposition of styrene butadiene rubber

Kwon E.E., Yi H., Castaldi M.J.

() Environmental Science and Technology ISSN: 0013936X Vol.46 Issue.19 Article No. DOI: 10.1021/es301933p

The CO₂ cofeed impact on the pyrolysis of styrene butadiene rubber (SBR) was investigated using thermogravimetric analysis (TGA) coupled to online gas chromatography/mass spectroscopy (GC/MS). The direct comparison of the chemical species evolved from the thermal degradation of SBR in N₂ and CO₂ led to a preliminary mechanistic understanding of the formation and relationship of light hydrocarbons (C_1-4), aromatic derivatives, and polycyclic aromatic hydrocarbons (PAHs), clarifying the role of CO₂ in the thermal degradation of SBR. The identification and quantification of over 50 major and minor chemical species from hydrogen and benzo[ghi]perylene were carried out experimentally in the temperature regime between 300 and 500 °C in N₂ and CO₂. The significant amounts of benzene derivatives from the direct bond dissociation of the backbone of SBR, induced by thermal degradation, provided favorable conditions for PAHs by the gas-phase addition reaction at a relatively low temperature compared to that with conventional fuels such as coal and petroleum-derived fuels. However, the formation of PAHs in a CO₂ atmosphere was decreased considerably (i.e., ∼50%) by the enhanced thermal cracking behavior, and the ultimate fates of these species were determined by different pathways in CO₂ and N₂ atmospheres. Consequently, this work has provided a new approach to mitigate PAHs by utilizing CO₂ as a reaction medium in thermochemical processes. © 2012 American Chemical Society.