Abstract
Lignin valorisation towards added-value products has become a relevant topic to consolidate a future circular bioeconomy. In this context lignin oxidation to C4 dicarboxylic acids (C4-DCA) by catalytic wet peroxide oxidation is emerging as a value-added strategy, supported by the extensive use of these building blocks in several industrial fields. In this work, lignins from different sources and processes (Indulin AT, Lignol, alkali and E. globulus kraft lignins) were oxidised using H2O2 and titanium silicalite-1 catalyst (TS-1) under different operating conditions (temperature, pH, time, H2O2, and TS-1 load). Indulin AT was the lignin leading to the highest succinic acid yield (11.3 wt%), and TS-1 catalyst enhanced its production four times over the non-catalysed reaction. Malic acid was also produced at high yields, especially for Lignol lignin. The other lignins (E. globulus kraft, and alkali lignins) also produced these C4 acids but at lower yields. The catalyst remained stable at the used experimental conditions, and showed potential to be reused for several cycles without being deactivated. Overall, the catalytic conversion of lignin to C4-DCA can help to guide the pathway to renewable chemicals production.
Highlights
Lignin is obtained as a by-product in pulp mills, where it is burned in the recovery boiler to produce energy and heat
Four different lignins were studied: alkali lignin (ALK), commer cialised by Aldrich; Indulin AT (IAT), commercialised by MeadWestvaco Corporation, USA; a lignin isolated from an industrial black liquor obtained from a Portuguese Eucalyptus globulus kraft pulping mill (The Navigator Company, Portugal) (EKL); and a lignin produced by an ethanol organosolv process from Eucalyptus globulus (EOL), supplied by Lignol Innovations, Canada
Lignin catalytic peroxide oxidation using titanium silicalite-1 catalyst (TS-1) catalyst proved that C4-dicarboxylic acids (DCA) could be obtained at attractive yields
Summary
Lignin is obtained as a by-product in pulp mills, where it is burned in the recovery boiler to produce energy and heat. This step is usually considered a bottleneck in pulp production (Ahmad et al, 2020; Mathias, 1993). Units are linked by β-O-4 (50–65 %), 5− 5’ (4–10 %), α-O-5 (4–8 %), and α-O-5′ (6–8 %) linkages, among others (Rodrigues Pinto et al, 2011) These structural differences introduce challenges for the depolymerisa tion and upgrading of the recalcitrant lignin matrix. Cooking methods focused on high-quality cellulose, such as kraft, sulfite, and alkaline processes, use harsh conditions to achieve their objective, causing strong modifications in the lignin structure (Sun et al, 2018).
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call