Evaluation of OxiOrganosolv pretreated hardwood and softwood lignocelluloses as substrates for the chemoenzymatic production of 5-hydroxymethylfurfural (HMF)

Furans, such as 5-hydroxymethylfurfural (HMF), are compounds of great importance that can serve as starting materials for the synthesis of polymers. Their production from lignocellulose-derived sugar streams offers a promising alternative to fossil fuels, while enabling biomass transformation to chemicals with higher value. In the present work, the production of HMF from OxiOrganosolv pretreated beechwood and pine was assessed by integrating a three-step process of enzymatic saccharification and isomerization followed by catalytic dehydration. The use of isobutanol in the pretreatment solvent and the addition of polyoxometallates (POMs) as oxidative catalysts were evaluated. The results showed that isobutanol leads to high delignification rates for both beechwood and pine, yielding cellulose-rich pulps with high susceptibility to enzymatic hydrolysis and isomerization. A fructose production up to 51.2 and 53.4 g/g of pretreated material was achieved for beechwood and pine, respectively, corresponding to 14 and 11.3 g of HMF/g of pretreated material. Regarding the use of POMs, the commercially available phosphomolybdic acid (HPMO) and POMs modified with oxidation metals (Fe-PMO, Cu-PMO) were tested, verifying their beneficial effect to lignin depolymerization and the composition of the final pulp. Hydrolysates produced from HPMo and Cu-PMo-assisted OxiOrganosolv pretreatment were efficiently used for the production of HMF, while severe inhibition of the dehydration reaction was observed with the hydrolysates from Fe-PMo pretreated biomass due to the presence of residual metals. This is the first systematic report comparing two lignocellulosic materials subjected to different pretreatment conditions for their potential to produce fructose and, subsequently, HMF.