(501b) An Aggregated Understanding of Alkaline Hydrogen Peroxide (AHP) Conversion of Biomass Hemicelluloses to Organic Acids
Hemicellulose represents up to 30% of biomass dry weight been the second most abundant non-food carbohydrate only next to cellulose. However, due to its lower degree of polymerization and crystallinity compared to cellulose, hemicelluloses are much more susceptible to degradation during chemical and thermal treatment. The ensuing degradation products have little value and can even be detrimental for subsequent fermentation and downstream processing. Designing a pretreatment chemistry to guide hemicellulose degradation toward the formation of useful products is of significant interest. We recently demonstrated that hemicellulose can be converted to carboxylic acids by AHP treatment, especially in the presence of a metal catalyst. This provides a potential and appealing pathway for the conversion of hemicellulose to high value compounds. However, a detailed understanding of the mechanisms involved in metal catalyzed AHP reactions with hemicellulose and the effects of metal catalysts on reaction kinetic and yields have not been studied before.
This study investigated the interaction of peroxide reactive species with hemicellulose, its role on the conversion to carboxylic acids, and describes the role of metal catalysts on the generation of beneficial reactive species for hemicellulose conversion. Due to the complexity of the process, the first approach was to identify key peroxide derived reactive species responsible for conversion using model hemicellulose compounds (i.e. glucomannan and xylan). The metal catalyst interaction with reactive species was investigated to improve the efficiency of hemicellulose conversion using both metal ions and organometallic complexes. Finally, we develop a deeper understanding of the reaction mechanism and reaction kinetics using a simplistic model that describes three main reaction pathways taking place during conversion. From these studies, we have been able to describe the effect of metal ions, organometallic complexes and single reagents on AHP. We believe that the incorporation of hemicellulose-to-carboxylic acids as an additional product without the need of additional steps during biomass pretreatment could be determinant into inclining the balance toward a successful biorefinery industry.