Kinetics of Reducing Sugar Formation from Coconut Husk by Subcritical Water Hydrolysis

Coconut husk hydrolysis using subcritical water (SCW) with N₂ as pressurizing gas was carried out in a batch reactor at temperature of 150 °C-190 °C, at pressure of 60-100 bar and the reaction time from 20-60 min. The effect of SCW pretreatment could reduce lignin and produced reducing sugars. The highest TRS (total reducing sugar) yield was 0,4904 at 170 °C, 80 bar, and the reaction time of 20 min. Reducing sugars concentration increased when temperatures rised from 150 to 170 °C. However, reducing sugar concentration decreased at temperature above 170 °C. The decrease of reducing sugar was due to degradation of reducing sugars into its degradation products. A first-order reaction model was determined to describe the reaction rate constant of the formation of reducing sugar and its degradation products. Kinetic parameters were obtained by fitting the proposed equation with the experimental data. The reaction rate constant increased when temperature increased from 150 to 170 °C, but then decreased when the temperature increased above 170 °C. Activation energy was also determined based on the Arrhenius equation.