## 2 Lignocellulose Feedstock Biorefineries  
### First- and Second-Generation LCF Biorefineries  
For the first-generation biorefineries, sugar and starch crops were used (i.e., sweet corn, sugar cane) [7; 8; 9; 10; 11; 12]; there was then a change in feedstocks in the so-called second-generation biorefinery--potential biomasses for these new refineries include grasses cultivated in arid conditions, agroforestry residues, and any kind of crop waste (Figure 2) [13; 14; 15; 16]. Statistics show that 170 million metric tons of lignocellulosic is produced annually, while no more than 5% of these LCF components are exploited, mainly due to a significant recalcitrance caused by the lignin [17]. Biorefining is an important option to carry out innovative vaporization of lignocellulosic materials, which has triggered intense research on how to convert lignins into target chemicals and fuels. LCF sources for biorefinery use include soft and hard wood, lignocellulosic-rich grasses, and agroforestry waste. The market for bio-based products is expected to increase to \(\copyright\) million by 2030 (average annual growth rate of 4%) [13]. Figure 1: Sustainable polymers from polysaccharides and agricultural waste. Reproduced with permission from [5], Springer Nature, 2019. According to a recently reported market study, until 2023 an annual growth rate of 2% is predicted for the global lignin market, resulting in an increase of the total market size from $800,500,000 in 2017 to $904,500,000 in 2023 [18; 19]. Among the most interesting products generated from lignocellulosic biomasses are biofuel and bioethanol. Here, we focus the isolation and application of lignins obtained from LCF biomasses. Lignin is mainly studied as a polyol-substitute for polyurethane and resin production, but also as an electrode material for sustainable electrochemical energy storage [20]. Lignocellulosic biomasses are rather resistant to enzymatic and chemical hydrolysis and therefore require harsh reaction conditions (i.e., strong acids or bases). LCF pretreatment and pulping results in the separation of cellulose/hemicellulose and lignin. Depending on the pulping process, the macromolecular lignin is partially degraded. In their review articles, [PERSON] et al. and [PERSON] et al. discussed lignin depolymerization strategies (catalyzed reductive and oxidative cleavage, respectively) and correlated mechanisms in order to produce lignin oligomeric fragments, such as phenol derivatives, to be used for further polymerization [21; 22]. In general, the detailed 3D lignin structure (monoligenol ratio and linkages) depends on a number of different parameters: the biomass source and crop genotype/phenotype, due to different biosynthesis pathways (i.e., soft and hard wood, grasses), and the pulping process (e.g., kraft, steam explosion, organosolv). Figure 3 shows the most common lignin linkages formed during biosynthesis, some of which having been elucidated within the last five years [23; 24]. Table 1 shows average values for monolignol linkages found for hard/soft wood and grasses [25; 26; 27]. These structural differences are rather difficult to specify by conventional analytical methods using data univariate processing, due to signal overlapping in spectral data. [PERSON] et al. studied the ratio of biphenyl fragments (5-5' linkages) of different biomasses (six softwoods and 15 hardwoods) [28]. A focus of lignin-derived materials includes novel bio-based polymers, such as polyurethane [29; 30; 31; 32; 33; 34], as coatings and/or foams for construction applications. In addition, the bioactivity of lignins is widely studied, including antioxidant, antiviral, and antimicrobial activity [35; 36; 37; 38]. In order to obtain valuable oligomer fragments, the macromolecular lignin structure is depolymerized using various strategies, including oxidative and reductive depolymerization via homo  
Figure 2: Schematic diagram shows the differences between lignocellulosic feedstocks from the first and second generations: sources, valorization processes, and end products.