Simultaneous production of 5-hydroxymethylfurfural and furfural from bamboo (Phyllostachys nigra “Boryana”) in a biphasic reaction system

Abstract

In this study, the microwave-assisted hydrolysis of bamboo (Phyllostachys nigra “Boryana”) to 5-hydroxymethylfurfural (HMF) and furfural in a dilute acid (H2O) / methyl isobutyl ketone (MIBK) biphasic system is investigated. Building on previous studies using model components cellulose and xylan, main emphasis in this study is given to the effect of particle size on the reaction rates that are involved in the conversion of bamboo particles by incorporating solid-liquid interactions into the reaction kinetics. Conversion yields of 37% HMF and 35% furfural from bamboo culm and 35% HMF and 34% furfural from bamboo leaves (based on cellulose and xylan content) were achieved, applying 0.13 M HCl and 177 °C under microwave (MW) heating. The results showed that the required reaction time to reach a maximum HMF and furfural yield increased significantly with increasing particle size. For particles having a diameter <2.5 mm, the reaction rates follow first-order homogeneous kinetics, whereas for particles ≥2.5 mm, the reaction kinetics follow the shrinking core model. The chemical reaction (i.e., hydrolysis) at the surface of the unreacted particle core was shown to be the rate limiting step. The reaction rate constants for the hydrolysis of cellulose and xylose decreased with increasing particle size. Moreover, for bamboo culm particles with a particle size of 5 mm, the hydrolysis reaction rate constant decreased by a factor 10 compared to 1–1.5 mm particles.