Experimental investigation of thermal decomposition of dihydroxybenzene isomers: Catechol, hydroquinone, and resorcinol

Abstract

In this study, dihydroxybenzene isomers such as catechol, resorcinol, and hydroquinone were used as models of volatiles from solid fuels to better elucidate the mechanism of the thermochemical conversion of solid fuels. These isomers were pyrolyzed in a two-stage tubular reactor with a residence time up to 3.6 s and temperature ranging from 650 to 950 °C. In total, 51 products were identified by online gas chromatography. The product distribution from the pyrolysis of the three isomers was quite different. p-Benzoquinone was the primary product obtained from the pyrolysis of hydroquinone, while o-benzoquinone and m-benzoquinone were not detected from the pyrolysis of catechol and resorcinol, respectively. CO was the major final product formed from catechol, resorcinol, and hydroquinone, with maximum yields of 27.3 wt%, 19.4 wt%, and 20.0 wt%, respectively, whereas CO 2 (15.5 wt%) generated from resorcinol was significantly higher than those generated from hydroquinone (1.0 wt%) and catechol (0.8 wt%) at 950 °C and 0.3 s. Considering the mass selectivity of C 1-C 5 light hydrocarbons, the possible reaction pathways leading to CO and CO 2 were analyzed to describe the pyrolysis of catechol, resorcinol, and hydroquinone. Catechol mainly afforded CO and C 4 hydrocarbons by H-migration and ring-opening reactions. Hydroquinone mainly generated CO, C 2 , and C 4 hydrocarbons, with the initial step being the formation of p-benzoquinone. During the pyrolysis of resorcinol, competition reactions occurred for the formation of CO and CO 2 with the production of C 1-C 5 hydrocarbons at a nearly equal mass selectivity. Compared with catechol and hydroquinone, resorcinol produced significantly more C 5 hydrocarbons, which suggested the intramolecular combination of aldehyde radical and ketone radical for explaining the large amount of CO 2 formed from the pyrolysis of resorcinol.

Metamorphic meta isomer: carbon dioxide and ketenes are formed via retro-Diels–Alder reactions in the decomposition of meta-benzenediol

“…Here resorcinol showed a 15-fold increase in decarboxylation compared to the other two isomers. 19 C5H6 can further decompose to yield either C5H5 radicals and hydrogen or to acetylene (m/z 26) and propyne/allene (m/z 40). Cyclopentadienyl (C5H5) dissociates to propargyl (C3H3, m/z 39) and acetylene, as summarized in R4: 37,57 The C5H6 ms-TPES changes significantly with pyrolysis temperature and is analysed in detail below.…”

“…Yang et al employed a two-stage tubular reactor coupled with GC/MS detection to study the decomposition of benzenediols, and observed a 15-fold increase in CO2 production for resorcinol (RES) compared to the other two isomers. 19 They also reported a computed biradical driven reaction mechanism for the formation of CO2. However, their kinetics calculations suggested that decarboxylation is not feasible, at odds with their experimental data.…”

Measuring biomass fast pyrolysis kinetics: State of the art

“…The micropyrolyzer reactors are usually coupled with gas chromatography (GC) techniques like GC-MS, GC-TOF-MS (time-of-flight mass spectrometer), or GC-FID ( Figure 2; Choi, Lee, Proano-Aviles, Lindstrom, Johnston, & Brown, 2017;Ronsse et al, 2012). U-shaped two-stage tubular reactors, separated by quartz wool, have been reported by Norinaga et al (Kousoku, Norinaga, & Miura, 2014;Norinaga et al, 2013;Qi et al, 2017;Yang et al, 2013;Yang, Appari, Kudo, Hayashi, & Norinaga, 2015;Yang, Furutani, Kudo, Hayashi, & Norinaga, 2016) for intrinsic gas-phase pyrolysis kinetic studies of cellulose and lignin model compound such as catechol, resorcinol, and hydroquinone pyrolysis. Pyroprobe reactors consist of a horizontal tubular reactor, wherein the sample is introduced using a quartz sample holder.…”

Isomer-dependent catalytic pyrolysis mechanism of the lignin model compounds catechol, resorcinol and hydroquinone

“…The p -benzoquinone product was only observed for hydroquinone ( p -benzenediol), while resorcinol ( m -benzenediol) produced significantly more CO 2 and C 5 hydrocarbons than the other two isomers. 17 Based on computations, a biradical reaction pathway was proposed. 18 By using in situ photoelectron photoion coincidence (PEPICO) methods, we found compelling spectroscopic evidence ( vide infra ) that the resorcinol decomposition mechanism is dominated by a retro-Diels–Alder reaction to produce CO 2 and C 5 H 6 isomers (R1) instead or it leads to two highly reactive ketenes species (R1).…”