Oxidation Of Lignosulfonates Research Articles

Mild and efficient approach to aromatic backbone cleavage using copper-lignosulfonate/hydrogen peroxide system

This study investigates the dual role of copper ions in catalysis and complexation during the oxidation of lignosulfonates with hydrogen peroxide (H2O2) under alkaline conditions. The presence of copper ions reduces partial oxidation by 86 % compared to H2O2 treatment alone, enhancing overall conversion efficiency to 63 % under increased oxidative conditions. Analyses reveal that copper-lignosulfonate complexes facilitate redox cycling and hydroxyl radical generation through interactions with H2O2, confirming copper’s dual functions. This mechanism mitigates the hindrance of sulfonic groups on hydroperoxide anions, leading to lignosulfonate degradation into dicarboxylic acids. These findings provide novel insights into the copper-lignosulfonate/H2O2 system, expanding the understanding of oxidative degradation mechanisms beyond traditional Fenton-like reactions. Furthermore, this system offers a simplified and efficient alternative for industrial applications, particularly in integration with the sulfite pretreatment process of woody biomass for producing valuable co-products.

High-Throughput Screening Assay for Laccase Engineering toward Lignosulfonate Valorization.

Lignin valorization is a pending issue for the integrated conversion of lignocellulose in consumer goods. Lignosulfonates (LS) are the main technical lignins commercialized today. However, their molecular weight should be enlarged to meet application requirements as additives or dispersing agents. Oxidation of lignosulfonates with fungal oxidoreductases, such as laccases, can increase the molecular weight of lignosulfonates by the cross-linking of lignin phenols. To advance in this direction, we describe here the development of a high-throughput screening (HTS) assay for the directed evolution of laccases, with lignosulfonate as substrate and the Folin–Ciocalteau reagent (FCR), to detect the decrease in phenolic content produced upon polymerization of lignosulfonate by the enzyme. Once the reaction conditions were adjusted to the 96-well-plate format, the enzyme for validating the assay was selected from a battery of high-redox-potential laccase variants functionally expressed in S. cerevisiae (the preferred host for the directed evolution of fungal oxidoreductases). The colorimetric response (absorbance at 760 nm) correlated with laccase activity secreted by the yeast. The HTS assay was reproducible (coefficient of variation (CV) = 15%) and sensitive enough to detect subtle differences in activity among yeast clones expressing a laccase mutant library obtained by error-prone PCR (epPCR). The method is therefore feasible for screening thousands of clones during the precise engineering of laccases toward valorization of lignosulfonates.

Effect of oxidative treatment on the colloid-chemical properties of lignosulfonates

The effect of oxidative treatment on colloid-chemical properties of lignosulfonates was studied. Oxidation of lignosulfonates (403–423 K, \(P_{O_2 } \) = 0.2–0.8 MPa, 0.5–1 h) is accompanied by a decrease in the content of hydroxy groups and by an increase in the content of carbonyl groups in oxidation products. Under severe oxidation conditions (423–433 K, \(P_{O_2 } \) = 0.8 MPa, 3 h), lignosulfonates undergo chemical degradation with the formation of lower carboxy derivatives. The oxidized lignosulfonates exhibit lower performance, compared to the initial samples, in wetting and dispersion of sphalerite and elemental sulfur.

New catalytic processes for a sustainable chemistry of cellulose production from wood biomass

The present paper describes the results of studies directed to novel catalytic processes design for the environmentally friendly production of cellulose. The new delignification catalyst which is produced by chemical interaction of elemental sulfur with hydrazine in superbase medium was used for the improvement of efficiency and ecological purity of the conventional pulping process. This catalyst reduces the concentration of polysulfides in pulping liquor and the yield of side sulfur-containing compounds (by 1.5 times). The processes of wood delignification with sulfur-free reagents based on catalytic pulping with acetic acid and hydrogen peroxide and on the delignification of steam-activated wood with NaOH or Na2CO3 solutions have prospects for the environmentally benign production of cellulose. The new catalytic process of vanillin production by oxidation of lignosulfonates with molecular oxygen was described.

Fine Chemicals from Lignosulfonates. 1. Synthesis of Vanillin by Oxidation of Lignosulfonates

The oxidation of lignosulfonates (LS) to vanillin by persulphate, oxygen, and a variety of catalytic systems has been investigated. Cobalt and copper catalysts appeared to be the most effective in the oxidation by oxygen. An investigation where multivariate mathematical and statistical design and modelling have been used for the process optimisation has led to the development of a multivariate mathematical model which describes the oxidation process with high predictive capacity. By using this model, an increase of the vanillin yield from 4.1% of the current procedure to 7.2% is obtained, this corresponding to 75% relative improvement of the yield.