Bleaching of Palm Oil by Activated Local Bentonite and Kaolin Clay from Afashio, Edo-Nigeria

Abstract

The bleaching potential of Afashio kaolin (AFK), from Edo state in Nigeria, for removal of pigments from palm oil was investigated in comparison with that of local bentonite (BN). Both AFK and BN were activated by acid treatment. Batch experiments were conducted to study the effects of adsorbent dosage (2 – 8 %), contact time (0 – 1.5 hr) and temperature (60 – 90^oC) on pigment adsorption. Four adsorption isotherms were used to model the equilibrium data for both adsorbents (AFK and BN), namely Langmuir, Freundlich, Sips and Redlich-Peterson models. The Sips model provides the best correlation and adsorption occurred in monolayer. Kinetic adsorption data were analyzed using the pseudo-first order, pseudo-second order, and intraparticle diffusion models. The regression results showed that the adsorption kinetics was more accurately represented by the pseudo-first order kinetic model. Intraparticle diffusion studies reveals that pore diffusion is the controlling mechanism. Thermodynamic parameters, ?G, ?H and ?S, were calculated as a function of both temperature and adsorbent dosage. The values of enthalpy change were positive and greater than 40 kJ/mol in all cases, indicating that the bleaching process is endothermic and chemisorption in nature. The results suggest that AFK could be employed as low-cost alternative for removal of pigments from vegetable oil though BN is better.

Keywords: Afashio kaolin, bentonite, bleaching, equilibrium isotherms, kinetic models