Synthesis of sulfonated magnetic nano-catalyst using rice husk ash for corncob hydrolysis: kinetic and thermodynamic study

Abstract

This study developed a magnetic solid acid catalyst for corncob hydrolysis. The core, Fe3O4 nanoparticle of the catalyst, was prepared using the co-precipitation method, which was supported by SiO2 nanoparticles prepared from rice husk ash. The Fe3O4/C–SiO2 was modified to produce a solid acid catalyst via the sulfonation method. Properties of Fe3O4/C and the sulfonated catalyst were assessed using FTIR, SEM, EDS, XRD, XPS, and VSM. Pretreated corncob was hydrolyzed at 80, 90, and 100 oC under a solid-to-liquid ratio of 1:10, using sulfonated Fe3O4/C for 100 min. Results showed that sulfonated Fe3O4/C–SiO2 contained HSO3 group indicating the success of the sulfonation process. The catalyst possessed a porous surface with a surface area of 72 m2/g and a total acid density of 0.96 mmol/g. The hydrolysis rate of corncob increased with reaction time and temperature, with the highest total reducing sugar observed at 90 °C. Batch data obtained from the corncob hydrolysis using a solid catalyst can be described by Saeman’s and integral first-order reaction models, establishing that cellulose hydrolysis is a first-order reaction. The activation energy for glucose formation was 12.33 and 42.4 kJ/mol for Saeman’s and first-order reaction models, respectively. Thermodynamic parameters; ∆H, ∆S, and ∆G revealed that the hydrolysis process was thermodynamically favoured, and the glucose formation was more stable relative to the degradation products. Sulfonated Fe3O4/C–SiO2 showed sustained activity after being reused four times.