Abstract:
This research investigated the preparation of hydrothermal carbon-based catalysts (HTC-SO3H) derived from defatted rice bran (DRB) and glucose for biomass conversion to 5-hydroxymethylfurfural (HMF). Firstly, the effects of hydrothermal carbonization conditions: temperature (180-250 °C) and time (1-8 h) on the yield and the chemical characteristics of the hydrothermal carbons (HTCs) were investigated. The HTCs were then sulfonated with sulfuric acid to obtain HTC-SO3H catalysts. The stability of the catalysts was evaluated based on the amount of biomass conversion products leached into the water at a specified biomass conversion condition. Since no HMF and furfural, and only small amounts of levulinic acid and formic acid, were leached from DRB derived HTC-SO3H (HTCDRB-SO3H) catalyst synthesized from the DRB derived HTC (HTCDRB) prepared at the carbonization condition of 220 °C for 3 h, this condition was suggested to be a suitable carbonization condition for the preparation. Compared with HTCDRB-SO3H, the glucose derived HTC-SO3H (HTCG-SO3H) prepared at the same condition showed the lower stability. The stability improvement of HTCG-SO3H was then studied at the longer hydrothermal carbonization time (6-24 h). While glucose derived HTCs (HTCGs) prepared at all conditions exhibited similar chemical and structural characteristics, examination of liquid fractions from hydrothermal carbonization suggested the suitable hydrothermal carbonization condition to be at 220 °C and 6 h. Sulfonated catalysts prepared at the proposed conditions were shown to promote cellulose hydrolysis and fructose dehydration with relatively high reactivity.
