Production of reducing sugars from bean dregs waste by hydrolysis in subcritical water

Reducing sugar, as a biomass energy precursor, can be further transformed to fuel alcohol in a fermentation process by means of micro-organisms or yeast. This study investigated the production of reducing sugars from bean dregs waste by hydrolysis in subcritical water. It was investigated that the effect of reaction temperature, reaction time and CO2 on reducing sugar yield. The optimum hydrolysis technology conditions were obtained. The addition of carbon dioxide led to an increase in reducing sugar yield. The highest yield of total reducing sugars is 65.7% at 300 °C and 360 s. Kinetics was conducted in a temperature range of 260-300 °C. Since the reaction kinetics in sub-critical water is very complicated, a simplified kinetic model to describe the hydrolysis of bean dregs wastes is proposed. The differential equations resulting from the model were fit to experimental data to obtain kinetic rate constants. By means of the Arrhenius plot, the activation energy as well as the pre-exponential factor was determined. A good agreement between the simplified model and the experimental data was obtained. The kinetic parameters provided useful information for understanding the hydrolysis reaction of bean dregs waste. Based on the results, this method could become an efficient method for biomass wastes liquefaction, producing valuable reducing sugars.