Polycyclic Aromatic Hydrocarbon (PAH) formation in thermal degradation of Styrene Butadiene Copolymer (SBR)

This study has been initiated to quantify the release of the Polycyclic Aromatic Hydrocarbon (PAH) species from Styrene· Butadiene Copolymer (SBR) during gasification. The identification and quantification has been detennined experimentally using Gas Chromatography/ Mass Spectroscopy (GC/ MS) coupled to a Thenno-Gravimetric Analysis (TGA) unit. SBR samples were pyrolysed in a TGA unit in a Nz atmosphere. The identities and absolute concentrations of over 32 major and minor species have been established, including a large number of aromatics, substituted aromatics, and PAHs. The light hydrocarbon species also have been detennined simultaneously and identified as Hz, C2Hz, CHt, CzH6, and C4H 10 with lower concentrations of other hydrocarbon gases. Significant amounts of ethyl benzene, toluene, and styrene were observed between 330°C and 500°C. The largest PAH detected was the family of (molecular weight 302), benzo[ghi]perylene with peak concentrations reaching 0.19 ppmv. The effluent species detected suggest that fonnation of PAH's occurs either through hydrocarbon addition reactions or benzene ring re-combination reactions. In itself gas phase release of benzene molecules or radicals, thus facilitating the PAH production route. Preliminary calculations done using MOPAC provided some insight into the energy required to break the benzene ligand bond from the butadiene structure. The measurements supply infonnation on the identities and levels of hazardous air pollutants, and provide useful new data for the development and validation of detailed reaction mechanisms describing their origin and fate. INTRODUCTION The disposal of used automobile tires has caused many environmental and economic problems. In the US, 750 million to 2 billion used tires have been stockpiled, which are increasing at a rate of 280 million per year[l]. Around 2,600,000 metric tons of used tire were produced in the European Union in 200 1. A low percentage is re-capped or reused for reduced-quality rubber but around 80% of these tires are accumulated in dumps, posing hazards such as disease and accidental fires and adversely impacting the environment[2]. Tire disposal requires special solid waste management because of their particular properties. addition, the chemical structure of SBR lends The durability and strength of tires make their 79 Copyright © 2006 by ASME