Application of Activated Rice Husk for Adsorptive Bleaching of Groundnut Oil: Kinetic, Equilibrium and Thermodynamic Study

Abstract

Kinetic, equilibrium and, thermodynamic studies of the bleaching of crude groundnut oil at optimized conditions were carried out using activated rice husk as an adsorbent for the bleaching process. The efficiency of bleaching was estimated by measuring the absorbance using a double- beam spectrophotometer at a wavelength of 450nm. The effects of adsorbent dosage, bleaching temperature and, contact time on the bleaching efficiency were studied. A directly proportional relationship was found between dosage and contact time and the bleaching efficiency while a bell curve was discovered for temperature increase. The surface area of the rice husk increased from 150.32 to 1450.32 m2/g while the pore volume decreased from 0.15524 to 0.12844 cm3/g after activation which was determined via a Brunauer-Emmet-Teller (BET) analysis and the results further validated by the Scanning Electron Microscopy (SEM) images obtained. The kinetic data of the bleaching process were best described by the pseudo-second order kinetic model while the equilibrium adsorption isotherm analysis showed that the results from the Temkin isotherm were the most significant. The thermodynamic study revealed that the adsorptive bleaching process is feasible, spontaneous and, exothermic with a decrease in entropy. The enthalpy value also showed that the adsorption process is predominantly physisorption. This study has revealed that an effective adsorbent can be produced from rice husks under optimized process conditions.