4.2.1 Cellulose and Lignin Composition in Biomass

Great variability in lignocellulosic biomass feedstocks is observed in wood or non­wood plants: differences in fiber dimensions, lignin, and cellulose content across different species [22]. Enzymatic hydrolysis of 1,100 natural Populus trichocarpa trees resulted in a wide range of sugar yields that depended on the lignin content and the ratio of syringyl and guaiacyl units in lignin. Among the 1,100 samples, the lignin content ranged from 15.7 to 27.9 wt%, while the syringyl-to-guaiacyl unit ratio ranged from 1.0 to 3.0 [23]. Even in the same plant, differences were observed between the mature sections at the base and the younger sections at the top [24].

Due to this great diversity of chemical composition and the complex structure of native biomass, effective methods for the dissolution or hydrolysis of purified

Aromatic products

Fig. 4.1 Generalized chemical structure of lignin and schematic for its conversion into monomeric aromatic products. Reactions which cleave aryl-ethers and aryl-alkyl linkages would enable conversion of lignin into valuable aromatic chemicals. Reprinted from [28], copyright (2011), with permission from Elsevier cellulose or glucose oligomers can fail to translate to native biomass. In lignin, each type of linkages in the constituting monolignols provides a possible pathway for biomass delignification (Fig. 4.1) [25-28]. Developing a unique IL pretreat­ment that would be suitable for multiple feedstocks represents a tremendous challenge.