The Reactivity of Free Radicals in Biomass Char Studied by EPR Spectroscopy

In this review, the features of electron paramagnetic resonance (EPR) spectra of biomass chars prepared from single biopolymers (cellulose, pectin, lignin, etc.) to complex plant materials (tobacco) are summarized, and the interaction of biomass chars with air, O2 and/or H2O as detected by EPR is critically examined. The effects of inorganic components are emphasized for understanding the creation and annihilation of free radicals in biomass chars in the presence of O2 or air. While the EPR spectra can be difficult to interpret, the interactions observed reflect fundamental processes occurring in biomass chars during pyrolysis and combustion that may affect the chemical composition of biomass conversion products as well as cigarette emission.