(348b) Characterization of High Quality Lignin Isolated From Ionic Liquid Pretreated Biomass: Residual Lignin V/s Re-Precipitated Lignin

A process based on enzymatic hydrolysis and fermentation is a promising route in converting lignocellulosic biomass to ethanol. However, the components of biomass (cellulose, hemicellulose, and lignin) are intricately bound together, thereby requiring suitable pretreatment of the substrate prior to hydrolysis. Ionic liquids (ILs) being non volatile, non-flammable and recyclable, are gaining wide recognition as green solvents for pretreating biomass. From an economic standpoint, it is necessary to facilitate the production of value-added products from all components of biomass, including lignin, given its interesting functionalities and properties owing to its complex aromatic nature. Structurally, lignin consists of three units (p-coumaryl, coniferyl and sinapyl alcohol) that are incorporated in the form of phenylpropanoids: p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) respectively, and it can be processed into a wide range of value-added products including  flame retardant materials, mixed phenolics, fibers, adhesives, fillers, surfactants, etc.

 The IL pretreatment process & strategic choice of enzymes result in almost carbohydrate-free (mostly lignin) residue after hydrolysis. In this regard, our approach not only provides high saccharification yields but also nearly pure lignin that can be processed into value-added products. This is unique in the sense that lignin is obtained as a residue rather than being dissolved and precipitated as in other current methods. An investigation of the H/G/S ratio of the residual lignin obtained can provide valuable information to assess its subsequent processability, as it assists in determining the type & number of cross-links within the lignin polymer and with other cell wall components. In view of this, our study addresses: (1) the isolation of high quality lignin from different types of IL pretreated biomass (corn stover, poplar wood and switch grass) subjected to enzymatic hydrolysis, using new generation enzyme mixtures, and (2) the characterization of recovered lignin using chromatographic, spectroscopic, and thermal methods in order to assess its usability for further processing to produce value-added products, and (3) comparison of the recovered residual lignin with IL-extracted-and-re-precipitated lignin.