Radicals from the Atmospheric Pressure Pyrolysis and Oxidative Pyrolysis of Hydroquinone, Catechol, and Phenol

Abstract

The burning of tobacco creates various types of free radicals that have been reported to be biologically active. Some radicals are transient but can initiate catalytic cycles that generate other free radicals. Other radicals are environmentally persistent and can exist in total particulate matter (TPM) for extended periods. In spite of their importance, little is known concerning the precursors of these radicals or under what pyrolysis/ combustion conditions they are formed. We performed studies of the formation of radicals from the gas-phase pyrolysis and oxidative pyrolysis of hydroquinone (HQ) and catechol (CT) between 750 and 1000 °C and phenol from 500 to 1000 °C. The initial electron paramagnetic resonance (EPR) spectra were complex, indicating the presence of multiple radicals. Using matrix annealing and microwave power saturation techniques, phenoxyl, cyclopentadienyl, and peroxyl radicals were identifiable, but only cyclopentadienyl radicals were stable above 750 °C.

Measuring biomass fast pyrolysis kinetics: State of the art

“…On the contrary, the conventional pyrolysis experiments of Akazawa at 600 C yielded unsaturated phenols such as vinyl phenol, propenyl, and methyl phenols as major products (Akazawa, Kojima, & Kato, 2015). Khachatryan et al (2010), Adounkpe, Khachatryan, and Dellinger (2008), and Adounkpe, Khachatryan, Dellinger, and Ghosh (2009) investigated the free-radical intermediates of fast pyrolysis of catechol, hydroquinone, and phenol. In a pyrolysis temperature range of 350-900 C, o-semiquinone radicals were dominant in the product stream up to 750 C, while cyclopentadienyl radicals were most dominant species beyond 800 C (Adounkpe et al, 2008(Adounkpe et al, , 2009).…”

“…Khachatryan et al (2010), Adounkpe, Khachatryan, and Dellinger (2008), and Adounkpe, Khachatryan, Dellinger, and Ghosh (2009) investigated the free-radical intermediates of fast pyrolysis of catechol, hydroquinone, and phenol. In a pyrolysis temperature range of 350-900 C, o-semiquinone radicals were dominant in the product stream up to 750 C, while cyclopentadienyl radicals were most dominant species beyond 800 C (Adounkpe et al, 2008(Adounkpe et al, , 2009). Scheer et al (2010Scheer et al ( , 2011Scheer et al ( , 2012 derived unimolecular decomposition schemes of phenol and methoxyphenols like anisole, ortho-, meta-and para-guaiacols, and decomposition of cyclopentadiene, methylcylopentadiene using multiplexed experiments with a hyperthermal nozzle reactor.…”

Characteristics of pine wood oxidative pyrolysis: Degradation behavior, carbon oxide production and heat properties

“…It has been manifested that pyrolysis under certain oxygen concentration could greatly improve the conversion rate of polymers [1][2][3]: cycloparaffin became easier to decompose under oxidative environment [4]. For aromatic compounds, oxygen could promote the yields of volatile products [5].…”

Stable Organic Radicals in Lignin: A Review

“…An EPR spectrum from a Burley tobacco sample was compared with a lignin sample because the pyrolysis of tobacco was similar to that of the pyrolysis of lignin (Figure A, spectrum 2) . These similarities originated from radicals formed, such as catechol, hydroquinone, and other organics, in the presence of trace quantities of oxygen . If the spectrum of tobacco (Figure , spectrum 2, black line) was subtracted from the spectrum of EPR radicals from the lignin pyrolysis (Figure , spectrum 1, red line), the resulting subtraction spectrum was obtained with an elevated g value of 2.0064 and Δ H p–p=18 G (Figure , spectrum 3, blue line).…”