Added-Value Chemicals from Lignin Oxidation

Abstract

Lignin is the second most abundant component, next to cellulose, in lignocellulosic biomass. Large amounts of this polymer are produced annually in the pulp and paper industries as a coproduct from the cooking process—most of it burned as fuel for energy. Strategies regarding lignin valorization have attracted significant attention over the recent decades due to lignin’s aromatic structure. Oxidative depolymerization allows converting lignin into added-value compounds, as phenolic monomers and/or dicarboxylic acids, which could be an excellent alternative to aromatic petrochemicals. However, the major challenge is to enhance the reactivity and selectivity of the lignin structure towards depolymerization and prevent condensation reactions. This review includes a comprehensive overview of the main contributions of lignin valorization through oxidative depolymerization to produce added-value compounds (vanillin and syringaldehyde) that have been developed over the recent decades in the LSRE group. An evaluation of the valuable products obtained from oxidation in an alkaline medium with oxygen of lignins and liquors from different sources and delignification processes is also provided. A review of C4 dicarboxylic acids obtained from lignin oxidation is also included, emphasizing catalytic conversion by O2 or H2O2 oxidation.

Microwave-Assisted Lignin Wet Peroxide Oxidation to C4 Dicarboxylic Acids

“…As the IAT is a softwood lignin (high percentage of G units), the available sites at the C 5 position allow an easy condensation during the extraction process, which corroborates the high degree of condensation comparatively with the Table 3. Assignments and Quantification of Structures/Linkages and Functional Groups, Identified by 13 Industrial & Engineering Chemistry Research other two lignins (hardwood lignins). This fact is also associated with the β-O-4 content, given that this bond is mainly cleaved in the extraction process.…”

“…IAT and EOL characterization had been reported in previous works. 35,41 Quantitative 13 C NMR characterization was carried out for IAT and EKL lignins. Quantitative 13 C NMR analysis for EOL lignin was previously reported by Costa et al 41 Ashes were quantified by incinerating 0.5 g of lignin at 600 °C until a constant mass was achieved.…”

“…35,41 Quantitative 13 C NMR characterization was carried out for IAT and EKL lignins. Quantitative 13 C NMR analysis for EOL lignin was previously reported by Costa et al 41 Ashes were quantified by incinerating 0.5 g of lignin at 600 °C until a constant mass was achieved. Carbohydrates content was determined by performing an acid methanolysis of the lignin.…”

Efficient cell factories for the production of N‐methylated amino acids and for methanol‐based amino acid production

“…In this respect it has to be noted that methanol initially is oxidized to formaldehyde and there are other sources of formaldehyde that may be used as substrates for fermentation. However, formaldehyde has to be liberated from these, for example, by degradation of formaldehyde oligomers such as trioxymethylene and hexamethylenetetramine (Kaszycki and Koloczek, 2002) or by demethylation of vanillin and other methylated aromatic compounds that are present in lignin (Wendisch et al ., 2018a; Costa et al ., 2021). Albeit attractive, this is clearly unchartered terrain and it is questionable whether these compounds will be available at reasonable cost and quantities.…”

Scavengome of an Antioxidant

“…The last class, i.e., chemical related to biomimetic (C), differs from class B only in the anhydrous organic solvent medium, which may still provide relevant models of oxidative processes within biological membranes. In some cases, we also classify oxidative conditions using biologically less relevant pH values into class C. In the model systems class B and C, three subgroups can be distinguished: (a) oxygen atom donors (H2O2, t-BuOOH, O2 in alkaline media) (Costa et al, 2021;Wenz et al, 2019) (b) electron donors (e.g. NaIO4, K3Fe(CN)6, Ru 3+ , Cu 2+ , Fe 2+ /Fe 3+ , Au 3+ ) (Galletti et al, 2018;Pradhan et al, 2020;Wu et al, 2021;Yang et al, 2016) (c) agents that mimic the nitrating capacity of peroxynitrite (eg.…”