Chemical process of multiphase system in lignin-biochar co-pyrolysis for enhanced phenol recovery

Carbon materials prepared by biomass pyrolysis have been studied for conversion of lignin into phenols. In this study, the control mechanism of free radicals on phenolic products selectivity was studied using guaiacol as a model chemical. The results showed that gaseous radicals or carbon-centered radicals of carbon materials could promote phenols formation through different mechanisms. In gas-phase system, the selectivity of phenols was mainly controlled by methyl radicals which led to a theoretical selectivity of phenols lower than 50%. In the heterogeneous system, methyl radicals and phenolic radicals were easily and rapidly adsorbed on the carbon edge sites. The o-hydroxyphenoxy radical was the key intermediate and was firstly absorbed on the carbon center radical sites where phenols produced at the same position after undergoing desorption and hydrogenation. In conclusion, the present study concluded that conversion of lignin to phenols can proceed rapidly as long as there are carbon-centered radicals distributed at zigzag edge on the carbon surface.