The 6th International Conference on Biomass Energy (ICBE2018)

305 / 2018-07-31 10:27:47

Fractionating Wheat Straw via Phosphoric Acid plus Hydrogen Peroxide (PHP) Pretreatment and Structural Elucidation of the Derived Lignin

Plenary track > B. Biomass Polygeneration

A cost-effective pretreatment process to fractionate lignocellulose biomass is the key to unlocking an integrated multi-product biorefinery. This work reports a facile technique route to fractionating wheat straw biomass into its three usable forms (i.e., cellulose, oligosaccharides and lignin) via combining phosphoric acid and hydrogen peroxide (PHP) as a pretreatment solvent. In particular, this work elucidated the properties and structure of the derived lignin. Results show that 39.7 g cellulose-rich fraction, 4.7 g oligosaccharides and 4.5 g lignin could be harvested from 100g wheat straw (dry basis) at mild conditions (50 °C). The resultant cellulose-rich fraction was highly accessible for hydrolytic enzymes (96.3% glucose conversion, in 24 h). The obtained PHP lignins were characterized by high purity (> 99.0%), rather low molecular weight (Mw < 1436 g mol-1) and abundant with carboxylic acid functional groups, showing tremendous prospects for further value-added applications. When the chemical structures of PHP lignins were elucidated using prevalent techniques of 31P, 13C and 2D-HSQC NMR, their degree of condensation was quite limited, and extensive ring-opening oxidations occurred on their aromatic substructures during PHP pretreatment. It was proposed that the synergistic effect between biomass deconstruction of phosphoric acid and strong oxidation induced by hydrogen peroxide under acidic conditions were responsible for the efficient lignocellulose fractionation. While HO+ or HO· derived from hydrogen peroxide was responsible for the efficient catalysis of ring-opening reactions on lignin aromatics. This work showed the technical feasibility and mechanistic insights of PHP fractionation towards building a multi-product lignocellulose biorefinery.