Nonsevere furfural production using ultrasonicated oil palm fronds and aqueous choline chloride-oxalic acid

Furfural is a versatile platform chemical that can be employed to produce green fuel and chemical intermediates. In this study, oil palm fronds were first subjected to ultrasonic pretreatment using an ultrasonic probe in water, which was followed by reaction in an aqueous choline chloride-oxalic acid (16.4 wt% H₂O) deep eutectic solvent. The focus of this study was to investigate whether the duration and amplitude of ultrasonic pretreatment improve the furfural yield from oil palm fronds. Mechanoacoustic and sonochemical effects induced by ultrasound waves disrupted the lignin carbohydrate complex in biomass, which increased the hemicellulose availability in the oil palm fronds for furfural production in the subsequent aqueous choline chloride-oxalic acid reaction. By employing ultrasonic pretreatment at 80 % amplitude for 3 min and then an aqueous choline chloride-oxalic acid reaction at 120 °C for 60 min, a furfural yield of 56.5 % was obtained. Characterization studies (e.g., Fourier transform infrared spectroscopy, Brunauer-Emmet-Teller, X-ray diffraction, and field emission scanning electron microscopy) on the oil palm fronds yielded insights into the reaction. Additionally, the reacted oil palm frond residues had a high glucan content, which could be considered a valuable byproduct.