(600b) Catalytic Conversion of Lignin in Ionic Liquids Via Catalysis and Biocatalysis

Authors: 
Shi, J. - Presenter, University of Kentucky
Das, L., University of Kentucky
Stevens, J., University of Kentucky
Liu, E., University of Kentucky
Lignin makes up 20-30% of the plant biomass and is the most abundant aromatic polymers in nature. Converting lignin into high-value chemicals adds revenues for a biorefinery thus improves the economic viability of biofuel production. Ionic liquids (ILs) have received increasing interest because of their potentials in fractionating and pretreating lignocellulosic biomass. Given the unique properties of aqueous ILs that provide for lignin solubility and biocompatibility to enzymes and microbes, we foresee a great opportunity to develop a new strategy for lignin extraction and depolymerization via catalysis and biocatalysis in aqueous ILs. The stability and activity of commercial fungal and plant laccases and a recombinant bacterial laccase were evaluated in difference concentration of ILs. Results suggest that certain ILs were fully compatible with laccases; while some appeared as non-competitive inhibitors. Immobilization of laccase on solid matrix, i.e. membrane surface helped to retain the enzyme activity and overcome the inhibition effects. We also explored catalytic oxidation route in ILs by screening a range of metal catalysts and oxidizing agents. Molecular weight distribution of lignin fraction was followed using gel permeation chromatography while the oxidation products such as vanillic acid, syringaldehyde, and syringic acid were identified and quantified using a GC-MS. Cleavage of the lignin structures was further investigated by NMR to understand the plausible oxidation mechanisms. Results from this study provide insights into the oxidative degradation pathway of lignin in the presence of IL and the selectivity of catalyst towards product formation. In situ lignin conversion in IL will also help to tackle the challenges associated with IL recycle and recovery.