Zeolite‐Assisted Lignin‐First Fractionation of Lignocellulose: Overcoming Lignin Recondensation through Shape‐Selective Catalysis

• Published in: ChemSusChem Vol. 13; no. 17; pp. 4528 - 4536
• Main Authors: Subbotina, Elena, Velty, Alexandra, Samec, Joseph S. M., Corma, Avelino
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 07.09.2020
• Subjects: Alcohols; Aldehydes; biomass; Bonding strength; Carbohydrates; Catalysis; Chemical reactions; Cleavage; depolymerization; Fractionation; Green & Sustainable Science & Technology; heterogeneous catalysis; Lignin; Lignocellulose; Monomers; Pore size; Porosity; Pulping; Reagents; Zeolites; biomass; lignin; zeolites; depolymerization; heterogeneous catalysis
• ISSN: 1864-5631; 1864-564X; 1864-564X
• DOI: 10.1002/cssc.202000330

Organosolv pulping releases reactive monomers from both lignin and hemicellulose by the cleavage of weak C−O bonds. These monomers recombine to form undesired polymers through the formation of recalcitrant C−C bonds. Different strategies have been developed to prevent this process by stabilizing the reactive monomers (i.e., lignin‐first approaches). To date, all reported approaches rely on the addition of capping agents or metal‐catalyzed stabilization reactions, which usually require high pressures of hydrogen gas. Herein, a metal‐ and additive‐free approach is reported that uses zeolites as acid catalysts to convert the reactive monomers into more stable derivatives under organosolv pulping conditions. Experiments with model lignin compounds showed that the recondensation of aldehydes and allylic alcohols produced by the cleavage of β‐O‐4′ bonds was efficiently inhibited by the use of protonic β zeolite. By applying a zeolite with a preferred pore size, the bimolecular reactions of reactive monomers were effectively inhibited, resulting in stable and valuable monophenolics. The developed methodology was further extended to birch wood to yield monophenolic compounds and value‐added products from carbohydrates. +1 is not allowed: A new zeolite‐assisted version of lignin‐first approach is developed. The undesirable recondensation reactions between monomers are inhibited via pore‐size constraint of the catalyst. Importantly, lignin and carbohydrates are converted into value‐added products in a single process. The developed method is an additive‐ and transition metal‐free. The presented work contains extensive model studies as well as studies of the reactivity of birch wood.