Oxidative depolymerization potential of biorefinery lignin obtained by ionic liquid pretreatment and subsequent enzymatic saccharification of eucalyptus

This study compared the oxidative depolymerization potential between ionic liquid (IL)-pretreated/enzyme lignin, diluted acid (DA)-pretreated/enzyme lignin, and soda lignin of eucalyptus, by means of alkaline nitrobenzene or cupric oxide (CuO) oxidation which depolymerize lignin into phenolic aldehydes such as vanillin and syringaldehyde. Here, the IL-pretreated/enzyme lignin was prepared by 1-ethyl-3-methylimidazolium acetate pretreatment and subsequent enzymatic saccharification. Upon the oxidative depolymerization of lignin sample by alkaline nitrobenzene oxidation, total yield of vanillin and syringaldehyde was 36.6% for untreated control eucalyptus. In contrast, the yield was enhanced upto 48.0% for IL-pretreated/enzyme lignin. As for the soda lignin prepared by alkali cooking, the yield was 29.0%. As for the DA-pretreated/enzyme lignin prepared by DA pretreatment and subsequent enzymatic saccharification, the yield was 39.5%. Therefore, it was found that the IL-pretreated/enzyme lignin showed the highest yield of phenolic aldehydes (vanillin and syringaldehyde) via alkaline oxidation, namely, highest oxidative depolymerization potential among the lignin tested.