Combining laccase with Cu(salen) catalysts for oxidation of kraft lignin

The transformation of kraft lignin using laccase with Cu(salen) catalysts was studied. The effect of the laccase/MCM – to – laccase/MCM + Cu(salen)/NaY ratio on the yields of monomeric aromatic chemicals (MACs) and the molecular weight (Mw) of kraft lignin was studied. The MACs yield decreased as the ratio increased, and the vanillin yield reached its highest value when the ratio of laccase was 50 wt % at a reaction temperature of 80 °C. The formation of MACs was enhanced by using a combination of laccase with Cu(salen) catalysts, while the formation of vanillin was dominant in the process. The formation of 4-hydroxy-3,5-dimethoxy benzaldehyde, 2-methoxy phenol, 4-hydroxy-3,5- -dimethoxyphenyl ethanone, 4-hydroxy-3-methoxyphenyl ethanone, 4-hydroxy- -3,5-dimethoxy benzoic acid, 4-hydroxy benzaldehyde, and 2-methoxy-4- -vinylphenol was also found in this work. The effect of the reaction parameters on the MACs yield and the Mw of the kraft lignin was described, and the main reactions occurring in the kraft lignin were discussed.