Characterization of lignins from Populus alba L. generated as by-products in different transformation processes: Kraft pulping, organosolv and acid hydrolysis

Evaluation of lignin-enriched side-streams from different biomass conversion processes as thickeners in bio-lubricant formulations

“…Moreover, a predominance of bands assigned to S units was observed for eucalypt AHL, SEL and EKL lignins (Fig. 1a, b, and c), similarly to other lignins derived from hardwoods [5,6,35,40,41], with bands at 1327-1324 cm −1 (ring breathing) and 831-829 cm −1 (out of plane C-H bending vibration). On the contrary, pine kraft lignin (PKL) spectrum (Fig.…”

“…This fact is especially relevant among lignin molecules present in solid residues during hydrothermal processes, as the AHL and SEL lignin fractions studied herein. Contrary, the main reaction produced in the lignin solubilized during kraft pulping is the alkaline hydrolysis of β-O-4′ alkyl-aryl ether bonds, yielding a more important reduction in molecular weight [32,41]. Finally, it must be noticed that hydrolysis lignins were not completely soluble in the alkali solution used as eluent, the highmolecular-weight fraction, probably containing LCCs complexes, being presumably the one that was not completely solubilized [54].…”

“…The main 2D NMR signals are listed in Table S1 (in the Supporting information), whereas Table S2 (in the Supporting information) displays 1 HNMRand 13 C NMR signals. All signals were assigned according to those previously described in the literature [4][5][6]21,[40][41][42][43][44][45][46][47].…”

Obtaining Fermentable Sugars from a Highly Productive Elm Clone Using Different Pretreatments

“…In addition, the external catalyst (sulfuric acid) used together with ethanol in organosolv pretreatment also promotes the lignin depolymerization and solubilization [45]. The delignification degree (49%) observed for Ademuz elm clone at the highest severity, i.e., 60 min, 180 • C, 30% ethanol, and 1% H 2 SO 4 is quite similar to the values observed by Martín-Sampedro et al [43] and Jiménez-López et al [40] for white poplar (46%) and black locust (50%) at the same pretreatment conditions. These values are higher compared to lignin extraction (27-42%) reported in different elm wood materials subjected to similar organosolv pretreatment parameters but with major ethanol concentration (75% v/v) [46,47].…”

“…Previous studies have also shown the ability of acid hydrolysis pretreatment to extract lignin from different hardwoods, which is produced by the lignin fragmentation and solubilization due to the aryl-ether linkages breakdown [42]. At the highest severity of acid hydrolysis pretreatment, a delignification of 39.2% was found for Ademuz elm clone, whereas at similar conditions (i.e., 60 min, 180 • C, 3% H 2 SO 4 ) Martín-Sampedro et al [43] reported a slightly higher delignification degree (43%) with white poplar, and Jiménez-López et al [40] described lower lignin extraction (33%) with black locust. Ibarra et al [33] obtained lower values for lignin extraction (3-11%) when different poplar clones were exposed to acid hydrolysis at similar pretreatment conditions but lower temperature (i.e., 130 • C).…”