Lignins Isolated via Catalyst-free Organosolv Pulping from Miscanthus x giganteus, M. sinensis, M. robustus and M. nagara: A Comparative Study

Abstract

As a low-input crop, Miscanthus offers numerous advantages that, in addition to agricultural applications, permits its exploitation for energy, fuel, and material production. Depending on the Miscanthus genotype, season, and harvest time as well as plant component (leaf versus stem), correlations between structure and properties of the corresponding isolated lignins differ. Here, a comparative study is presented between lignins isolated from M. x giganteus, M. sinensis, M. robustus and M. nagara using a catalyst-free organosolv pulping process. The lignins from different plant constituents are also compared regarding their similarities and differences regarding monolignol ratio and important linkages. Results showed that the plant genotype has the weakest influence on monolignol content and interunit linkages. In contrast, structural differences are more significant among lignins of different harvest time and/or season. Analyses were performed using fast and simple methods such as nuclear magnetic resonance (NMR) spectroscopy. Data was assigned to four different linkages (A: b-O-4 linkage, B: phenylcoumaran, C: resinol, D: b-unsaturated ester). In conclusion, A content is particularly high in leaf-derived lignins at just under 70 % and significantly lower in stem and mixture lignins at around 60 % and almost 65 %. The second most common linkage pattern is D in all isolated lignins, the proportion of which is also strongly dependent on the crop portion. Both stem and mixture lignins, have a relatively high share of approximately 20 % or more (maximum is M. sinensis Sin2 with over 30 %). In the leaf-derived lignins, the proportions are significantly lower on averageStem samples should be chosen highest possible lignin content is desired, specifically from the M. x giganteus genotype which revealed lignin contents up to 27 %.

Hydrogenation and Hydrogenolysis with Ruthenium Catalysts and Application to Biomass Conversion

“…Lignin is a randomly linked polymer (Figure 8) comprising phenolic p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) moieties (see also Figure 9) that are linked via ether linkages (ß-O-4', α-O-4', 4-O-5'), biphenyl (5-5'), resinol ( ß-ß'), and other condensed linkages (ß-5′, ß-1′) as well as dibenzodioxocin, and phenylcoumaran linkages [109,127]. The complex structure of lignin is the result of the biosynthetic pathway that involves oxidation of phenolic precursors to radicals followed by radical coupling that leads to stepwise build-up of lignin structure [128].…”

“…Chemical structure of important biomass fractions, lignin (left), cellulose with 1,4-glycosidic linkages and selected hydrogen bonds (right, top) and the common molecular motif of hemicellulose (right, bottom). For the structure of lignin, the characteristic aromatic p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) moieties as well as aromatic ether linkages (-O-), dibenzodioxocin, biphenyl, resinol, and phenylcoumaran linkages[109,127] were marked.…”