Optimal operating conditions and equilibrium characteristics for rice bran oil extraction

Abstract

Rice bran is the cuticle between the paddy husk and the rice grain and is obtained as a byproduct in rice processing. The bran contains 15-20 wt% oil and approximately 95% is extractable. Rice bran oil is a very important source of oil, both as an edible oil and non-edible oil. The oil has high medicinal value, due to presence of anti-oxidants, anti-cancer agents, cholesterol reducing agents, skin improving agents, anti-dandruff and anti-itching agents. The oil can also be used for production of soap, surfactants, cosmetic formulations, emulsifiers, textile auxiliaries, synthetic rubber products etc. Experiments were conducted using soxhelt apparatus and the pilot plant scale leaching unit, to extract rice bran oil by solvent extraction, for various brands of rice bran available in Sri Lanka. The key factors controlling the extraction and optimal operating conditions have been identified. Methods of bran pre-treatment, extraction temperature, extraction time, pellet size and FFA content are the factors affecting oil extraction. Analysis of FFA content in the extracted oil shows that steaming is the most effective method of bran pre-treatment. Bran obtained from parboiled paddy has a higher yield of rice bran oil compared to the raw rice bran despite the oil is darker in colour. Comparison of extraction results by various pretreatment methods shows an enhancement of oil extractability due to steaming. Pelletization of bran provides easy percolation and avoids channeling of the solvent and contamination of the oil from fine solids. Equilibrium data shows no preferential adsorption of oil or solvent to the inert bran and approximately constant solid/solvent ratios in the underflow streams. This data can be used in design calculations of solid liquid extraction equipment.