Quantitative Investigation of Free Radicals in Bio-Oil and their Potential Role in Condensed-Phase Polymerization

We report on the quantitative analysis of free radicals in bio-oils produced from pyrolysis of cellulose, organosolv lignin, and corn stover by EPR spectroscopy. Also, we investigated their potential role in condensed-phase polymerization. Bio-oils produced from lignin and cellulose show clear evidence of homolytic cleavage reactions during pyrolysis that produce free radicals. The concentration of free radicals in lignin bio-oil was 7.5x10(20)sping(-1), which was 375 and 138times higher than free-radical concentrations in bio-oil from cellulose and corn stover. Pyrolytic lignin had the highest concentration in free radicals, which could be a combination of carbon-centered (benzyl radicals) and oxygen-centered (phenoxy radicals) organic species because they are delocalized in a system. Free-radical concentrations did not change during accelerated aging tests despite increases in molecular weight of bio-oils, suggesting that free radicals in condensed bio-oils are stable.