Abstract
Problem statement: Though efficient in terms of reaction yield and time, the chemical approach to synthesizing alkyl ester has drawback such as difficulties in the recovery of glycerol and the need for removal of salt residue. On the other hand, biocatalyst allow for synthesis of specific alkyl esters and easy recovery of glycerol. However, the solvent-free alcoholysis, does not give high conversion. The same problem was also found when ethyl or methyl acetate was used as acyl acceptors. Approach: Lipase catalyzed transesterification of oil and dialkyl carbonate was predicted to give higher conversion in solvent free reaction system. Results: Alkyl esters were synthesized enzymatically to overcome the problems associated with chemical processes. In this study, dialkyl carbonates were used as an alkyl donor for the production of alkyl ester. Nine commercial lipases were tested for their suitability for the reaction system. Among the lipase tested, Novozym 435 was chosen for optimization study because of their higher activity. In a solvent-free reaction system, the ester formation using dialkyl carbonate was 6 times higher than using ethanol and methanol. The effect of various reaction parameters such as temperature, amount of enzyme, organic solvent and structure of substrates were studied to determine optimal condition. The optimal conditions of ester formation were reaction temperature at 60°C, reaction time at 8 h, enzyme amount of 10% (w/w of oil) and 0.2% wt added water. Conclusion: Solvent-free lipase catalyzed transesterification of palm kernel oil and dialkyl carbonates gave higher conversion of ester compared to the reaction using short chain alcohol as an alkyl donors.
Highlights
Nowadays, dialkyl carbonate has been attracting wide attention as an environmentally benign chemical raw material (Ono, 1997)
Esterification reaction: Screening experiments with lipases were conducted at 10% lipase by weight of triglycerides, with isohexane or dialkyl carbonate as a solvent
Preliminary experiments were carried out with nine commercial lipases for alkyl ester synthesis to identify the most suitable lipases enzymes for subsequence esterification reaction
Summary
Dialkyl carbonate has been attracting wide attention as an environmentally benign chemical raw material (Ono, 1997). It can be used as alkylating and alkylcarbonylating agents in place of dialkyl sulphate, alkyl halides and phosgene. The use of dialkyl carbonates as alkylating agent has been thoroughly studied using various catalysts and conditions and appears to be the reagent of choice for the methylation of phenols (Gryglewicz et al, 2003). Interest in organic synthesis using dialkyl carbonate has increased, but not much information on enzymatic synthesis of alkyl esters with dialkyl carbonates has been reported. Transesterification of fatty acids with dialkyl carbonates to produce ester has been reported by
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