From agricultural waste to value: Integrated chemo and biocatalytic biorefinery processes to produce 2-furoic acid

• Microwave-assisted chemical dehydration of rice husk into furfural in biphasic system. • Selective oxidation of bio-based furfural to furoic acid by immobilized CALB under mild conditions. • Recyclability of CALB was performed for the synthesis of furoic acid. • Sequential chemo-enzymatic approach was developed for valorization of rice husk into furoic acid. The integration of biocatalysis in biorefineries can lead to synergies for raw material valorization. Enzymes must perform efficient and selective reactions when using crude effluents (to avoid costly downstream units). Herein, this is showcased with the synthesis of 2-furoic acid, starting from rice husk (agricultural waste), via a sequential organic-acid catalyzed pretreatment – to afford xylose and cellulose and lignin –, followed by the microwave-assisted acidic xylose dehydration to furfural, in situ extraction in ethyl acetate, and the final biocatalytic selective oxidation of furfural to 2-furoic acid (2-FA). To validate the concept, a xylose-rich hydrolysate (∼ 15 g xylose L −1 ) obtained from rice husk (RH) was used, achieving a furfural yield of 70 % in a biphasic system (water – ethyl acetate). The obtained furfural extracted in the ethyl acetate was subsequently oxidized to 2-furoic acid via an organic peroxide reaction mediated by Candida antarctica lipase B (CALB), with an overall yield of 90 %, and, with a yield of 41.72 % based on the initial xylose in biomass. Notably, 20 mg/mL CALB could tolerate up to 400 mM of furfural under optimum conditions of 40 °C, 48 h. The recyclability of the biocatalyst was investigated, enabling an efficient reuse of four consecutive cycles.