Efficient microwave-assisted production of furanics and hydrochar from bamboo (Phyllostachys nigra “Boryana”) in a biphasic reaction system: effect of inorganic salts

Abstract

In this study, a microwave-assisted process was developed for the production of 5-hydroxymethylfurfural (HMF), furfural, and hydrochar from bamboo (Phyllostachys nigra “Boryana”) in a biphasic reaction system. The system consisted of an acidified aqueous phase and methyl isobutyl ketone (MIBK) as the organic phase and enabled the instantaneous extraction of HMF and furfural in the organic phase. In this way, unwanted side and rehydration reactions are avoided. The aim of the study was to maximize HMF and furfural yields from bamboo in short reaction times. Building on previous studies, an HCl concentration of 0.13 M was used to ensure the simultaneous conversion of cellulose and xylan to HMF and furfural, respectively. To shorten the reaction time considerably, higher reaction temperatures were applied in this study (200–240°C). The use of microwave irradiation allowed very short reaction rates for maximum HMF and furfural production. Yields of 21 wt% HMF, 13 wt% furfural, and 39.5 wt% hydrochar were achieved using bamboo culm particles and by applying 0.13 M HCl (10 wt% NaCl) and 220°C with a reaction time of 2 min. The results show that the required reaction time to reach a maximum HMF and furfural yield was not significantly influenced by the particle size (< 200μm–2 mm). The effect of NaCl in the production of HMF and furfural was assessed. It was clear that the addition of NaCl increased the maximum HMF yield but also enhanced the unwanted rehydration reaction to levulinic acid. Results indicated that NaCl could be absorbed on the surface of the hydrochar.