Production of reducing sugars from lignocellulosic kikuyu grass residues by hydrolysis using subcritical water in batch and semibatch reactors
A subcritical hydrolysis of Kikuyu grass lignocellulose residues was carried out in batch and semi batch mode operations. Experiments assessed the effect of temperature (250-300 °C), mass ratio (6:1-30:1), pressure (1 490-3 190 psi), and water flow rate (3-9 ml/min) in reducing sugars (RS) yield. Reducing sugar production was measured by means of the DNS method, and efficiency was calculated as the ratio between the mass of produced reducing sugars and the total mass of the residue fed to the reactor. A maximum RS of 9.7% was measured in batch hydrolysis experiments at 300 °C, 30:1 mass ratio and 3 190 psi, whereas 22% accumulated RS yield was obtained in semi batch experiments at 300 °C, 2 000 psi and 9 ml/min. The lower yield was attributed to the extended reaction time in batch experiments in comparison to semi batch experiments, in which the reaction time is not only shorter but also the hydrolysis products are continuously removed from the reactor. Analysis of Variance of data for batch experiments showed only the interaction between temperature and mass ratio to be significant, whereas the pressure had no significant effect. A notorious decrease in pH was measured with increasing reaction times due to the formation of acidic degradation products. The results showed the feasibility of producing reducing sugars from lignocellulosic residues available in large amounts and currently discarded without any utilization through subcritical hydrolysis.