Abstract: Reducing sugars can be derived from biomass via hydrolysis process. A two-step hydrolysis with supercritical/subcritical water were applied for rice straw hydrolysis. The effects of key factors as the ratio of liquid phase to solid phase, reaction temperature and time on the yield of reducing sugars were evaluated. The relationship of rice straw liquefaction rate vs. ratio of liquid phase to solid phase were investigated. Rice-straw were hydrolyzed using a two-step hydrolysis process with subcritical water combined with supercritical water and one-step supercritical water hydrolysis process respectively. The maximum yield of reducing sugars was about 21% at 190℃ for 40 min when the ratio of liquid phase to solid phase of the substrates was 100:1,while treating the rice straw using the two-step process. Meanwhile, the same yield of reducing sugars were obtained when the ratio of liquid phase to solid phase of the substrates was reduced from 100:1 to 40:1 at 190℃ for only 20 min. The residues of the rice straw from the two-step process were hydrolyzed at 380℃ for 20 s; the maximum yield of reducing sugars was about 57%. Under the same conditions, the maximum yield of reducing sugars was about 32% by one-step supercritical water hydrolysis. The total yield of reducing sugars by two-step method was 45%. Thirteen percentage points was increased compared with the yield obtained by one-step method.

Key words: biomass, rice straw, supercritical/subcritical water, hydrolysis, reducing sugars