Production of vanillin from lignin: The relationship between beta-O-4 linkages and vanillin yield

Lignin is the renewable source of aromatics in nature, and the conversion of lignin into vanillin is very attractive. However, the vanillin yield is closely related to the resource of lignin and its isolation process, and relatively low yield of vanillin is always obtained from lignin. In order to improve the vanillin yield from lignin, in this work, the relationship between lignin linkages and vanillin yield was explored. Five lignins (kraft lignin, alkali lignin, lignosulfonate, and two enzymatic lignins) and various lignin model compounds (monomers, dimers, and polymers) were characterized by NMR spectroscopy and oxidized to prepare vanillin. Results indicated that the interunit linkages of the lignin had a significant influence on the vanillin yield. The more beta-O-4 linkages in lignin, the higher yield of corresponding aldehydes was obtained. It is believed that the vanillin yield can be significantly improved by using lignins with high content of beta-O-4 linkages.