Aqueous redox flow batteries (RFBs) as grid-scale energy storage devices hold great potential to accomodate the rising demand for intermittent renewable energy sources. A significant parameter that enhances the sustainability of RFBs is selecting the appropriate redox species. In this study, we investigated the application of lignosulfonate as a redox species for the negolyte of aqueous RFBs because lignosulfonate is a low-cost, abundant, highly water-soluble material with a high phenol content. To overcome the intrinsic electrochemically irreversible nature of lignosulfonate, herein, oxidative depolymerization was employed to modify the chemical structure in a weakly alkaline media. The modified lignosulfonate exhibited improved electrochemical activity, as indicated by cyclic voltammetry, with distinct redox peaks that correspond to lignin-derived monomers, such as vanillin and 4-hydroxybenzaldehyde. The modified lignosulfonate, as negolyte, paired with ferrocyanide in the counterpart in a lab-based single RFB cell. The RFB utilizing 50 g L⁻¹ modified lignosulfonate showed 80.6 % capacity retention over 50 cycles and nearly 1.5 times higher discharge capacity than the RFB using non-modified lignosulfonate. By increasing the concentration of modified lignosulfonate up to 200 g L⁻¹, the discharge capacity increased threefold; however, the capacity retention dropped to 60 %. This study presents an opportunity to utilize bio-based electrolytes in building novel, cost-effective, and sustainable RFBs.

In the past decades, substantial research efforts have been directed towards increasing the availability of renewable and recycled raw materials. Lignin, one of the most abundant natural polymers, constitutes a vast, renewable, and largely untapped source of aromatic structures. In addition, it is one of the most abundant renewable sources of carbon. Despite the countless research projects aimed at valorizing kraft lignin, the largest source of industrial lignin, relatively few commercial kraft lignin products have emerged. Simultaneously, lignosulfonates represent a commercially successful range of products with a steady and growing global market. This paper reviews the current outlook of technical lignin research, including common misunderstandings, and discusses various factors that have hampered the use of lignin as a renewable source of materials and chemicals.

This study explores paired electrolysis, leveraging the oxygen reduction reaction (ORR) and industry-relevant lignosulfonate oxidation to enhance sustainable electrochemical processes. The anode reaction is driven by the direct oxidation of lignosulfonate, an abundant biopolymer derived from sulfite pulping, on bare graphite electrodes, eliminating the need for costly catalysts. This process occurs in a membrane electrolyzer, where the cathode catalyst dictates ORR selectivity: a carbon paper cathode modified by the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) favors hydrogen peroxide formation via a 2-electron pathway, while a platinum-modified carbon paper cathode facilitates full oxygen reduction to water via a 4-electron pathway. When applying a cell voltage of 0.7 V (a geometrical current density of 0.04 mA cm^–2), the air-saturated catholyte had an 8-fold decrease in dissolved oxygen, which corresponded to 68% faradaic efficiency and an electrical energy consumption of 0.0233 W hour l^–1. Removing the low molecular weight lignosulfonate (<3.5 kDa) via dialysis minimizes membrane crossover but also reduces oxygen consumption rates. The oxidation process preserves the lignosulfonate backbone while enriching its quinone content, offering a novel, energy-efficient approach to biomass valorization. By integrating lignosulfonate oxidation with ORR, this work presents a cost-effective and sustainable alternative to conventional anodic processes, with potential applications in green hydrogen peroxide production and biobased electrochemical systems.

Brownstock washing, a critical process in cleansing kraft pulp, removes dissolved lignin residues from the pulp after it has passed through the cooking digester. It plays a significant role in kraft pulp mills by enhancing economic efficiency and environmental sustainability. Improved washing efficiency leads to better pulp quality and more effective recovery of cooking chemicals. Our study aimed to better understand the impact of different chemical compositions in washing liquors on washing performance. We tested a range of washing liquors, including neutral solutions (deionized water, 1M NaCl, 3M NaCl, 1M Na2SO4) and alkaline solutions (tap water, washing liquor composed of 0.35M NaOH and 1M Na2SO4, and white liquor with 50 g[OH]/l and 8.77 g[HS]/l). These liquors were evaluated for their efficacy in maximizing lignin extraction. Our findings suggest that salt solutions generally reduce washing efficiency. Deionized water and white liquor proved to be the most efficient washing agents, while high-concentration salts and those with high ionic strength negatively impacted washing efficiency. This suggests that brownstock washing may not be operating at its full potential.

Lignin nanoparticles (LNPs) are gaining increasing interest for applications in various fields, where the particle homogeneity, morphology, and surface properties are critical for performance. In this study, lignin obtained via kraft process from spruce and eucalyptus was employed as precursor for the fabrication of lignin nanoparticles with tunable physicochemical properties. Linear ester groups with varying chain lengths were introduced to systematically investigate the effects of the hydrophobic moiety distribution on lignin nanoparticle formation via solvent-shifting self-assembly. Results demonstrated that esterification-induced structural changes altered the balance of key noncovalent interactions (hydrogen bonding, π–π stacking, and hydrophobic interactions), which collectively governed the self-assembly process, with longer ester chains promoting compact particles with hydrophobic surfaces. By directly linking molecular-level modification of lignin to alterations in the inter- and intramolecular interactions driving the self-assembly of nanoparticles, this study provides a mechanistic framework for the rational design of lignin nanoparticles through controlled chemical modification, thereby expanding their application flexibility.

In the manufacturing of cellulose derivatives, improving cellulose accessibility is essential for achieving a high product quality. In this study, endoglucanase enzyme treatment was applied prior to the cationization reaction to enhance the accessibility of hydroxyl groups for the production of cationized dialdehyde cellulose (CDAC). A range of enzyme dosages (0.09–45.00 ECU/g) was tested, and their effects on the swelling behavior and surface charge density of the final product were evaluated. The surface charge density of the ultimate cellulosic derivative confirmed its cationization and was proven to enhance the charge density of cationized dialdehyde cellulose (35% increase) compared to untreated pulp with enzyme. Additionally, the modified cellulose exhibited a significantly higher swelling capacity than regular pulps. These findings suggest that enzymatic pretreatment can enhance fiber reactivity and support a more sustainable and efficient production of cellulose-based derivatives, offering a promising potential for commercial applications.

The role of sodium sulfate was considered relative to pulp washing liquors and its impact on the reattachment of lignin to pulp fibers during the brownstock washing process. The dissolution of lignin during washing and its potential redeposition onto the pulp fibers is influenced by various factors. Three distinct types of pulp-unbleached, bleached, and cotton linters-were used to explore these effects. The washing experiments were conducted using industrial wash liquor and were repeated further with the addition of sodium sulfate. The resulting products of the washing process, including the liquor discharge and the washed pulp, were thoroughly evaluated. Analytical techniques, such as UV measurements of lignin content in the liquor discharge and characterization of the pulp, were employed to assess the outcomes. The findings reveal that the addition of sodium sulfate to the washing liquor resulted in an increase in its conductivity and ionic strength. Moreover, it was observed that lignin reattachment to pulp fibers was noticeably greater when washing was performed with sodium sulfate addition. Among the pulps studied, unbleached kraft pulp exhibited the highest degree of lignin reattachment, followed by bleached kraft pulp, with cotton linters showing the least.

This work has focused on oxygen's role in the delignification process within the context of pulp production. We have investigated the role of oxygen in a complex set of chemical reactions taking place during this process, including both oxidative and non-oxidative reactions. This study explores the impact of pH changes during the oxygen delignification process and the characteristics of the resulting pulps. Additionally, this research examines the effect of oxygen, by comparing conventional oxygen delignification with trials using air and nitrogen. Industrial softwood kraft pulps with a kappa number of 35 were subjected to delignification for 20-120 min under alkaline conditions. The resulting pulps were assessed for kappa number, intrinsic viscosity, fiber charge, and ISO brightness. An important observation from this research is the reduction in lignin molecular weight upon exposure to oxygen and air, suggesting depolymerization reactions facilitated by oxygen species, whereas nitrogen exposure results in less pronounced changes. This finding underscores the impact of oxygen in altering lignin structure, thus informing the selectivity and effectiveness of the delignification process.

Lignin, a bio-originated polymer, is being explored as an alternative to nonrenewable fossil resources. It is obtained from biomass during pulping and is mostly burned for energy. In most kraft pulp lines, residual lignin in the pulp is oxidized and solubilized during an oxygen delignification step. This study proposes an isolation method for lignin solubilized during oxygen delignification, which we refer to as "oxlignin", and explores its structural characteristics and properties. The study found acid precipitation to be an effective method for partially isolating oxlignin from the oxygen delignification step. Various analytical methods were employed, including UV-vis absorption analysis, 31P NMR spectroscopy, FT-IR spectroscopy, SEC, and TGA. In addition, the solubility of the lignin was studied in four different solvents and compared to the commercial kraft lignins. The study found that oxlignin is a promising substitute for lignosulfonates in certain applications due to its hydrophilicity and high solubility in water, methanol, and ethanol. Compared to kraft lignins, oxlignin has a lower phenolic group content but higher carboxylic acid content.

Glucuronoxylan is the main hemicellulose in the secondary cell wall of angiosperms. Elucidating its molecular structure provides a basis for more accurate plant cell wall models and the utilization of xylan in biorefinery processes. Here, we investigated the spacing of acetyl, glucuronopyranosyl and galactopyranosyl substitutions on Eucalyptus glucuronoxylan using sequential extraction combined with enzymatic hydrolysis and mass spectrometry. We found that the acetyl groups are preferentially spaced with an even pattern and that consecutive acetylation is present as a minor motif. Distinct odd and even patterns of glucuronidation with tight and sparse spacing were observed. Furthermore, the occurrence of consecutive glucuronidation is reported, which adds to the growing body of evidence that this motif is not only present in gymnosperms but also in angiosperms. In addition, the presence of terminal galactopyranosyl units, which can be released by β-galactosidase, altered the digestibility of the glucuronoxylan by GH30 and GH10 xylanase and appeared to be clustered within the polymeric backbone. These findings increase our understanding of the complex structure of glucuronoxylans and its effect on the extractability and biological degradation of Eucalyptus wood.