Refining of Ethanol Biorefinery Residues to Isolate Value Added Lignins

The isolation of lignin coproducts from the residual solids of a hardwood based biocatalytic bioethanol process was examined, using extraction methods based on aqueous alkali or aqueous ethanol. This work focused on understanding how the structural features of raw lignin in the process residue influenced the refined lignin isolation yields, in addition to polymeric and structural characteristics. On the basis of this approach, the extraction based lignin refining could be optimized. Mild extraction conditions allowed for recovery of approximately 40 wt % of the lignin present in the starting material. This yield could be increased to about 76 wt %, by the application of base or acid catalyzed reactive extraction conditions liberating the bonded insoluble fractions of the residue. All isolated lignin products were characterized in terms of their functional groups, molecular weights and thermal properties. The lignins from mild alkali and ethanol extractions showed similarities in their chemical profiles. In contrast, the reactive extractions and degradative aqueous treatments produced structurally different lignins. As expected, the molecular weight and the thermal properties of the isolated lignins were affected by the isolation process and these differences are rationalized. (Figure Presented).