Deacidification effects of rice hull-based adsorbents as affected by thermal and acid treatment

Rice hull ash (RHA) was evaluated as a source of adsorbent for edible oil processing, especially its application in reducing free fatty acid (FFA). RHA300, RHA400, RHA500, RHA600, RHA700, RHA800 and RHA900 were prepared by burning rice hulls at 300, 400, 500, 600, 700, 800 and 900 °C, respectively. Increased pyrolysis temperature resulted in an increase in pH (increased alkalinity) of RHAs from 9.53 to 9.98. RHA500 was the most effective in reducing residual FFA, followed by RHA400 and RHA300. About 30-46% reduction of FFA was observed in degummed soybean oil and more than 80% reduction in degummed oil-hexane miscella at 5 g/100 g oil of RHA500. On heating of the ash greater than 500 °C the loss of adsorptive capacity for FFA was shown in case of RHA800 and RHA900. RHA500 reduced about 50% FFA of commercial vegetable oils such as olive oil and corn oil. There was no significant adsorptive difference between the kinds of fatty acids dissolved in isooctane. Acid activation for RHA500acid did not improve the FFA adsorption relative to nonactivated RHA500.