An experimental study on the thermal decomposition of catechol

Abstract

In order to better elucidate the role of thermal decomposition products in the formation of polycyclic aromatic hydrocarbons (PAH) from complex fuels, we have performed pyrolysis experiments in a tubularflow reactor, using the model fuel catechol ( ortho -dihydroxybenzene), a, phenol-type compound representative of structural entities in biomass, coal, and wood. Catechol pyrolysis at temperatures of 700–1000°C and a residence time of 0.4 s produces a range of C 1 −C 6 products, which have been analysed by nondispersive infrared analysis and by gas chromatography with flame-ionization detection. Quantification of product yields versus temperature reveals that the major products are CO, acetylene, 1.3-butadiene, phenol, cyclopentadiene, benzene, and ethylene, minor products are methane, ethane, propyne, propadient, and propylene. CO is the highest yield catechol pyrolysis product at all temperatures. Among the hydrocarbons, 1,3-butadiene is the highest yield product at temperatures up to 800°C; above 800°C acetylene is. The structural features of catechol and the experimental product yield data—considered with the established reactions for phenol decomposition—suggest that the major products of catechol decomposition come from the following routes: (1) phenol and benzene from H displacement of OH on catechol and phenol, respectively, (2) cyclopentadiene from unimolecular decomposition of the phenoxy radical, and (3) 1,3-butadiene, acetylene, and CO from decomposition of the hydroxy-substituted phenoxy radical (but with different oxygenated C 5 intermediates). The remaining, C 1 −C 3 products appear to arise chiefly from the decomposition of key radicals such as cyclopentadienyl, propargyl, and 1,3-butadienyl. The results presented in this work, in concert with those from a complementary study of the C 7 −C 28 catechol products, provide the basis for the development of a detailed kinetic model for both pyrolytic catechol decomposition and PAH formation and growth.