ZnCl2 Enhanced Acid Hydrolysis of Pretreated Corncob for Glucose Production: Kinetics, Thermodynamics and Optimization Analysis

Abstract

The biomass of agricultural wastes as a source of fermentable sugars for biofuels production will address the food security and environmental preservation issues. These wastes are rich in lignocellulosic materials which can be hydrolyzed into fermentable sugars. However, low sugar yield and high energy consumption are some of the challenges faced in the process of hydrolization. This study investigated the low-cost corncob substrate for glucose production by dilute sulphuric acid hydrolysis in the presence of ZnCl2 at temperatures below 100°C after pretreatment with 10% NaOH.Time dependent hydrolysis data were analyzed by Saeman model, and thermodynamic parameters were obtained using Erying and Arrhenius equations while Box-Behnken model (Design Expert 6.0 version) was used for experimental design. As the substrate concentration increased from 50 mg/L to 150 mg/L, glucose yield increased from 10.4 mg/g to 14.6 mg/g for pretreated corncob while an increase from 3.4 mg/g to 8.6 mg/g was noted for untreated corncob. The hydrolysis rate constant was two orders of magnitude higher than the degradation rate constant. Thermodynamic parameters revealed endothermic process with positive Gibb’s free energy of hydrolysis having average values of 84.76 kJ/mol and 79.87 kJ/mol for pretreated and untreated samples respectively. The optimum yield from the model was found to be 177.44 mg/g with 3.94% H2SO4 and 0.43 mol/L ZnCl2 for 200 g/L compared with optimum yield of 46.37 mg/g obtainable without ZnCl2. The results of this study showed that the alkaline pretreatment of corncob increased the accessibility of cellulose from the solid fraction and increased glucose production.