Biorefinery processes for the valorization of Miscanthus polysaccharides: from constituent sugars to platform chemicals

A biorefinery scheme was proposed for manufacturing platform chemicals (furfural, denoted F, and 5-hydroxymethylfurfural, denoted HMF) from Miscanthus polysaccharides (including hemicelluloses and cellulose). The feedstock was first subjected to hydrothermal processing, which caused an extensive hemicellulose solubilization, yielding solids enriched in cellulose and aqueous solutions rich in saccharides. The acidic processing of the aqueous solutions in the presence of methyl isobutyl ketone (MIBK), which acted as an extracting agent, led to the formation and the in situ separation of F from pentoses at high molar yields (up to 78%). Moreover, HMF and levulinic acid were obtained from the hexoses released from the feedstock. The cellulose-enriched solids from hydrothermal processing were used as a substrate for HMF manufacture, employing a combination of enzymatic and chemical treatments. The enzymatic hydrolysis yielded glucose (in concentration up to 59 g /L), which was enzymatically isomerized into fructose in the presence of sodium tetraborate at yields up to 80%. Acidic treatments of the resulting reaction media at low temperature (134 °C) in the presence of H₂SO₄ enabled the formation of HMF at yields about 49%. Under the assayed conditions, glucose remained practically unaltered, facilitating its reutilization in the isomerization stage.