Elucidating radical-mediated pyrolysis behaviors of preoxidized lignins

Unlocking the potential of phenolated kraft lignin as a versatile feed additive

Lignin, a renewable natural antioxidant and bacteriostat, holds promise as a versatile, cost-effective feed additive. However, traditional industrial lignin faces limitations, including low reactivity, poor uniformity, and unstable properties, necessitating chemical modification. Complex modification methods pose economic and toxicity challenges, so this study adopted a relatively simple alkali-catalyzed phenolization approach, using phenol, catechol, and pyrogallol to modify kraft lignin, and characterized the resulting products using various techniques. Subsequently, their antioxidant, antibacterial, adsorption properties for heavy metal ions and mycotoxins, growth-promoting properties, and antiviral abilities were assessed. The phenolation process led to lignin depolymerization and a notable increase in phenolic hydroxyl content, particularly in pyrogallol-phenolated lignin (Py-L), rising from 3.08 to 4.68 mmol/g. These modified lignins exhibited enhanced antioxidant activity, with over 99 % inhibition against E. coli and S. aureus, and remarkable adsorption capacities for heavy metal ions and mycotoxins. Importantly, Py-L improved the growth performance of mice and reduced influenza mortality. Furthermore, density functional theory calculations elucidated the mechanism behind the enhanced antioxidant properties. This study presents a promising avenue for developing versatile feed additives to address challenges related to animal feed antioxidant supplementation, bacterial control, and growth promotion.

Radical footprinting and regularity revealing during the pyrolysis of technical lignins

Revealing radical-mediated reactions is conducive to illustrate lignin pyrolysis and achieve subsequent regulation. Three technical lignins (hot-water-extracted lignin, kraft lignin, and soda lignin) were selected in this study and pyrolyzed from 400 °C to 700 °C, and their pyrolysis radicals in both chars and bio-oils were monitored with the electron paramagnetic resonance spectrometer. Results showed that spin concentrations of char radicals had a volcanic trend against the pyrolysis temperature, and reached the maximum values at 550-600 °C. However, the contents of bio-oil radicals were low during pyrolysis at low and medium temperature, but their spin concentrations exploded abruptly over 600-650 °C. Meanwhile, the bio-oil yields were found to drop after 550-600 °C, and the three inflection temperatures for char radicals, bio-oil radicals, and bio-oil yields were perfectly matched. These findings systematically elucidated the radical regularity in technical lignin pyrolysis and fundamentally contributed to the development of radical-mediated lignin pyrolysis mechanisms.

The enrichment of sugars and phenols from fast pyrolysis of bamboo via ethanol-Fenton pretreatment

The high-purity compounds (e.g., sugars and phenols) are important raw materials and chemicals, which can be produced by biomass pyrolysis. However, the direct biomass pyrolysis produces complex compounds and thus inhibiting its large-scale utilization. To increase the yield and enrichment of sugars and phenols, a green coupling process based on ethanol-Fenton pretreatment combined with fast pyrolysis is firstly proposed. The bamboo was effectively separated into the ethanol-Fenton pretreated bamboo (EF-bamboo), lignin-rich fractions, and hemicellulose-degradation intermixtures with the massive removal of inorganic metals via this process. Compared with the fast pyrolysis of raw bamboo, the levoglucosan yield of EF-bamboo increased 5.4 times and the enrichment of sugars improved from 7.6% to 59.7%. Similarly, the yield of monophenols from lignin-rich fractions increased around 0.6 times and the enrichment of monophenols increased from 25.7% to 63.5%. This work provides a green and efficient route to produce high-yield and high-enrichment sugars and phenols.