Ozone oxidation pretreatment of softwood kraft lignin: An effective and environmentally friendly approach to enhance fast pyrolysis product selectivity

To enhance the efficiency and environmentally friendliness of the pyrolysis of lignin, we investigated the effects of ozone oxidation pretreatment on the softwood lignin structure and pyrolysis product distribution during the pyrolysis process. Fundamental characteristic analysis shows that the structure of lignin after pretreatment changed compared with that of the original lignin. The lignin side chain hydroxyl was oxidized to carbonyl or carboxyl, enhancing the depolymerization of lignin. 2D HSQC NMR analysis reveals that pretreatment mainly interrupted unstable chemical bonds like ether linkage of lignin. In order to determine the effect of pretreatment on pyrolysis, the pyrolysis experiment was performed on raw and pretreated lignin separately. Results showed that the pretreatment improves the yield of bio-oil from lignin pyrolysis. Furthermore, the relative content of phydroxyphenyl type phenols derived from lignin pyrolysis is positively correlated with the oxidation degree. Thus, the pretreatment has great potential in improving aromatic production during pyrolysis of lignin, and could selectively transform lignin to high value-added platform compounds.