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 N-2 and CO2 led to a preliminary mechanistic understanding of the formation and relationship of light hydrocarbons (C1-4), aromatic derivatives, and polycyclic aromatic hydrocarbons (PAT-Is), 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 degrees C in N-2 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 coil and petroleum-derived fuels. However, the formation of PAT-Is in a CO2 atmosphere was decreased considerably (i.e., similar to 50%) by the enhanced thermal cracking behavior, and the ultimate fates of these species were determined by different pathways in CO2 and N-2 atmospheres. Consequently, this work has provided a new approach to mitigate PAHs by utilizing CO2 as a reaction medium in thermochemical processes.
