Optimal immobilization conditions of lipase from Candida Rugosa for biodiesel production

Abstract

Biodiesel or fatty acid methyl ester is a non-toxic, biodegradable and renewable energy source. Recently, biodiesel can be produced by lipase catalyzed transesterification and become more attractive since the by product, glycerol can be easily recovered and the purification process for biodiesel is simpler. Candida rugosa lipase (CRL) is one of the most frequently used enzymes. However, the cost of enzyme remains a barrier. To reduce the cost, CRL were immobilized on 7 types of hydrophobic supports and Sepabeads EC-OD was finally selected. Afterwards, various optimal conditions for the immobilization of CRL on Sepabeads EC-OD were investigated. The results were as follows; pH 6, 500 mM ionic strength, 8 mg/ml enzyme loading at 30 ℃ for 30 min and t-butanol as the adjuvant. The immobilized lipase was later applied for the catalysis of transesterification between palm oil and methanol. The optimal transesterification by the immobilized CRL on Sepabeads EC-OD were investigated. The results were as follows; 6-step addition mode of methanol, 3 to 1 molar ratio of methanol to palm oil, 30% enzyme loading by oil weight and 5% water content (v/w of oil) for 12 hours at 40℃. Then, 6 from 9 types of non-edible and waste plant oils were selected from standard physical properties to be used as the substrates for the production of biodiesel by transesterification catalyzed by 2 commercial immobilized lipase and CRL on SepabeadsEC-OD in comparison. The results showed that seed oils of 3 species; papaya, rambutan and physic nuts could be highly converted to biodiesel in comparable yield when the reactions were catalyzed by all 3 types of enzymes (approximately 80 %). Finally, the enzymes were tested for reusability in both transesterification and hydrolysis. For the biodiesel production, the activity considerably decreased after the 2nd-3rd cycle. In contrast, the relative hydrolytic activities of the immobilized lipase could be well maintained over ten repeated cycles. Overall results indicate that the obtained immobilized CRL on SepabeadsEC-OD can catalyze the transesterification for the production of biodiesel as efficiently as the commercial enzymes.