Thermal reactions of aromatic hydrocarbons in the pyrolysis of ethane and propane

The influence of aromatics on the pyrolysis of ethane and propane was studied using benzene, toluene, α-methylnaphthalene and anthracene as model compounds. The experiments were performed in a tubular flow reactor at ordinary pressure, temperatures of 700-850°C, residence times between 0.1-1s and low concentration of aromatics (1-6%mole). Aromatic hydrocarbons inhibited the pyrolysis rate of ethane and propane and the following order of inhibitory effect which decreases with the increase of temperature was found: toluene > α-methylnaphthalene > benzene > anthracene. The C1-C4 composition of the effluent was only slightly influenced by the presence of aromatics, which were found to suffer an appreciable transformation to alkylated derivatives, depending on their structure and despite their thermal stability when highly diluted with N2 at the same temperatures. The transformation of the aromatic hydrocarbons was explained by the interference of the main chain propagators (·H, ·CH3, ·C2H3, ·C2H5) with the aromatic and benzyl type radicals. Benzene has only a small contribution to soot formation, a phenomenon which however was found to increase when alkylaromatic and polycyclic hydrocarbons are present in the feed.