Oxidative degradation of lignin for producing monophenolic compounds

Oxidative degradation of lignin for producing monophenolic compounds was carried out under microwave irradiation, with H2O2, CuO and Fe2(SO4)3 as the oxidants. The results indicated that the yield of monophenolic compounds and degradation rate of lignin feed reach 11.86% and 90.88%, respectively, under the relatively benign conditions of 180°C. Oxidative degradation of lignin with H2O2 as a single oxidant gives a high degradation rate but a lower yield of monophenolic compounds, due to the aromatic ring opening reaction; however, Cu2+ present in the oxidant system is able to promote the cleavage of side chain and ether bond, whereas Fe3+ to enhance the oxidation ability of H2O2, which are then conducive to improving the yield of monophenolic compounds. A moderate increase of degradation temperature and reaction time are favorable for improving the yield of monophenolic compounds. Owing to the coexistence of lignin degradation and recondensation of degraded fragments, the prevention of degraded lignin from recondensation turns to be a key issue to achieve a high yield of monophenolic compounds.