plots the effects of reaction temperature and time on oligomeric sugar formation under various reaction-temperature (100–140 °C) and reaction-time (1–3 h) conditions. With increasing reaction temperature, the sugar yields decreased, which indicated that oligomeric sugars hydrolyzed to mono-sugars by passing time at higher temperature.
Fig. 3(E) plots the effects of reaction temperature and time on 5-HMF formation. At low temperatures, which are to say, until 120 °C, the 5-HMF yield linearly increased, and at 130 °C, it was consistently maintained after 2 h. At 140 °C, the 5-HMF concentration slightly decreased with passing reaction time; at the same temperature after 2 and 3h, it was lower than at 130 °C. These results indicated that the 5-HMF produced from the sugars had been further converted into LA and formic acid by hydration