Green Etherification of Fructose to 5-Ethoxymethylfurfural over Functionalized Sugar- and Agro-Biochars

The demand for sustainable materials from agricultural waste is increasing rapidly. This study investigates the development of sustainable biochar materials derived from agricultural residues, including rice husk (RBC), sawmill waste (WBC), and glucose-based sugar char (SC). A series of catalysts was prepared by pyrolysis followed by treatment with sulfuric acid for the synthesis of 5-ethoxymethylfurfural (EMF), a biofuel additive. Catalyst characterizations further revealed distinct differences in powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), pore-size analysis, NH3-TPD, and X-ray photoelectron spectroscopy (XPS), all of which contributed to the catalytic activity. Functionalized sugar biochar exhibited excellent conversion up to 99% fructose with maximum selectivity to EMF linked to surface acidity (6.0 mmol/g). Further assessment of the biochar catalyst's potential involved kinetic studies, which revealed that the etherification reaction follows pseudo-first-order behavior with an activation energy of 36.6 kJ mol−1. The hot filtration method (Sheldon's test) proved and demonstrated the need for a heterogeneous catalyst. This work highlights a green, metal-free strategy for producing high-value biofuel additives from renewable carbohydrates.