Utilizing Carbon Dioxide as a Reaction Medium to Mitigate Production of Polycyclic Aromatic Hydrocarbons from the Thermal Decomposition of Styrene Butadiene Rubber

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.