The thermal decomposition of lignin is not well characterized and leads to formation of undesirable products that requires substantial upgrading. The simplest model compound that can be employed to investigate the weak phenolic-carbon linkage in lignin is anisole (C6H5OCH3). The initial decomposition of anisole leads to phenoxy and methyl radical. Phenoxy being a resonantly stabilized radical, its reactivity is low and hence undergoes recombination with methyl, leading to ortho/para-methylcyclohexadienone isomers (o/p-MecyHDOE) as well as anisole. These isomers have very weak C-H bonds (~65 kcal/mol) compared to ~96 kcal/mol bond of the methyl C–H in anisole. Hence, the abstraction reaction from these isomers is favored. Two sets of anisole thermal decomposition data were collected at conditions that closely resemble fast pyrolysis (T=525-650°C, t ~0.8s, and P~0.8 atm) using a tubular flow reactor. In the first case, 0.75mol % anisole was diluted in N2; in the second case, 5% of the N2 buffer gas was replaced by H2. A mechanism that included rate constants obtained from CBS-QB3 calculations led to significant improvements in predictions of the observed product distributions.

Abstraction from weak C-H Bond of ortho/para-methylcyclohexadienone isomers critical in improving product distribution in anisole pyrolysis

249th National Meeting (2015)

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