Highly Efficient Lignin Depolymerization via Effective Inhibition of Condensation during Polyoxometalate-Mediated Oxidation
journal contributionposted on 18.06.2019, 00:00 by Weisheng Yang, Xu Du, Wei Liu, Andrew W. Tricker, Hongqi Dai, Yulin Deng
Any type of content formally published in an academic journal, usually following a peer-review process.
Depolymerization of lignin to low-molecular-weight products plays a vital role in upgrading of lignin into high-value chemicals. One of the problems of lignin depolymerization is the recondensation of the lignin fragments through positive α carbon (Cα+) coupled with electron-rich lignin aromatic rings during the depolymerization process. Many pretreatment methods have been proposed to efficiently inhibit the recondensation by blocking active Cα–OH groups, but barely a few oxidative methods were reported for the following lignin depolymerization. Herein, we reported an effective lignin depolymerization process in which the active Cα–OH groups were first converted to stable CαO by TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and then depolymerized by oxidation of polyoxometalate (POM) under relatively mild conditions (150 °C, 10 bar O2). The POM is an intermediate oxidation agent that was completely regenerated during the lignin depolymerization process. Under 150 °C and 10 bar O2 for 6 h, 74.5 wt % lignin was converted to DCM-extractable low-molecular-weight compounds (average molecular weight of 363 Da), yielding 19.4 wt % aromatic monomers (based on total lignin mass). The novel oxidative depolymerization method reported here is more effective than common oxidative depolymerization methods reported in the literature.