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Oxidative Depolymerization of Kraft Lignin for Microbial Conversion
journal contribution
posted on 2019-06-12, 21:03 authored by Omar Y. Abdelaziz, Krithika Ravi, Fabian Mittermeier, Sebastian Meier, Anders Riisager, Gunnar Lidén, Christian P. HultebergThe valorization
of lignin is being increasingly recognized as
crucial to improve the economic viability of integrated biorefineries.
Because of its inherent heterogeneity and recalcitrance, lignin has
been treated as a waste product in the pulp and paper industry, but
new technologies are now being explored to transform lignin into a
sustainable resource and enhance its value chain. In the present study,
alkaline oxidative depolymerization was investigated as a potential
form of pretreatment to enable further biological conversion of LignoBoost
kraft lignin (LB). LB lignin oxidation reactions were studied at various
temperatures (120–200 °C) and O2 partial pressures
(3–15 bar) to identify the optimal conditions for obtaining
a biocompatible, oxidatively depolymerized lignin (ODLB) stream. The
low molecular weight compounds resulting from this treatment consisted
mainly of aromatic monomers and carboxylic acids. The highest yield
of aromatic monomers, 3 wt %, was obtained at 160 °C and 3 bar
O2. The yield of carboxylic acids increased with both increasing
temperature and O2 pressure, exceeding 13% under the harshest
conditions investigated. The growth of four aromatic-catabolizing
bacterial strains was examined on reaction product mixtures, all of
which showed growth on agar plates utilizing ODLB as the sole source
of carbon and energy. Rhodococcus opacus and Sphingobium sp. SYK-6 were found to consume most of the
aromatic monomers present in the ODLB (e.g., vanillin, vanillate,
acetovanillone, and guaiacol). The findings of this study indicate
that pretreatment by oxidative depolymerization has potential in the
biological valorization of technical lignin streams, for the production
of valuable chemicals and materials.