Ethyl levulinate, produced through esterification of levulinic acid, is a ketoester with various applications. Synthesis of ethyl levulinate was carried out in solvent-free system using immobilized Candida antarctica lipase B (Novozym 435) as the biocatalyst for the reaction. Response surface methodology (RSM) with a four-factor-five-level central composite rotatable design (CCRD) was employed to study and optimize the reaction conditions in the synthesis of levulinate ester. The effect of four main reaction parameters including time, temperature, ethanol/levulinic acid molar ratio and amount of enzyme on the synthesis of ester were analyzed. A quadratic polynomial model was fitted to the data with an R2 of 0.8993. Model validation experiments show good correspondence between actual and predicted values. A high conversion yield (96.2%) was obtained at the optimum conditions of 51.4 °C, 41.9 min, 292.3 mg enzyme amount and 1.1:1 alcohol:acid molar ratio.
Most substrate for esterification has the inherent problem of low miscibility which requires addition of solvents into the reaction media. In this contribution, we would like to present an alternative and feasible option for an efficient solvent-free synthesis of menthyl butyrate using a novel thermostable crude T1 lipase. We investigated the effects of incubation time, temperature, enzyme loading and substrate molar ratio and determined the optimum conditions. The high conversion of menthyl butyrate catalyzed by crude T1 lipase in a solvent-free system is greatly affected by temperature and time of the reaction media. The highest yield of menthyl butyrate was 99.3% under optimized conditions of 60 °C, incubation time of 13.15 h, 2.53 mg, 0.43% (w/w) enzyme to substrate ratio and at molar ratio of butyric anhydride/menthol 2.7:1. Hence, the investigation revealed that the thermostable crude T1 lipase successfully catalyzed the high-yield production of menthyl butyrate in a solvent-free system. The finding suggests that the crude T1 lipase was a promising alternative to overcome shortcomings associated with solvent-assisted enzymatic reactions.
Enzymatic synthesis of xylitol fatty acid ester was performed in hexane using Novozym 435 (immobilized Candida antarctica lipase on macroporous resin). Taguchi method based on three levels, six variables L27 orthogonal array robust design was implemented to optimize experimental conditions. The effects of reaction parameters including reaction time (7-24 h), enzyme amount (0.05-0.3 g), temperature (30-60 °C), amount of molecular sieve (1-4 g), substrate molar ratio (0.3-1) and xylitol concentration (0.005-0.015 g/ml) on the percentage yield of sugar ester were investigated. The optimum conditions derived via Taguchi method were: reaction time 7 h, temperature 60 °C, amount of enzyme 0.12 g, amount of molecular sieve 2.5 g, substrate molar ratio 1 and xylitol concentration 0.015 g/ml. The actual experimental yield was 96.10% under optimum condition, which compared well to the maximum predicted value of 96.27%.
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