| As a kind of nonionic surface-active agent, sugar ester (sugar-fatty acid ester) was commonly synthesized by the traditional chemical methods. However, these methods were limited due to complicate process and low selectivity. In recent years, great attention on the lipase-catalyzed synthesis of sugar ester has been received. It is achieved by means of esterification or transesterification catalyzed by lipase between sugar and acyl donor in organic solvent. Lipase is a kind of high efficiency and specific biocatalyst. It can catalyze the synthesis of sugar ester in non-aqueous medium.Lipase is a species of hydrolytic enzyme and is often used as hydrolysis. When condition changed, the reaction can go on in reverse direction. So in the process of synthesis, water content has to be controlled strictly to avoid reverse reaction. Water content and the nature of solvent affect the enzyme reaction evidently. In addition, other factors such as the quantity of the enzyme, the selection of acyl donor and acceptor and the ratio between them also must be considered. This paper studied with the emphasis on: (1) the effect of water content of tert-amyl alcohol and butanone as solvent, respectively; (2) when the solvent selected as butanone, the optimal water content in the system; (3) the effect of fatty acid with different numbers of carbon as acyl donor and fructose, sucrose, glucose as acyl acceptors; (4) the ratio between acyl donor and acceptors. The optimized conditions are as fllows: fructose 0.09g, palmitic acid 0.192g (the mole ratio is 1:1.5), butanone 10mL, lipase 0.1g and 4A molecular sieve 0.85g /10mL butanone. When the reaction time up to 46h, the ultimate concentration of production reaches 43.6g·L-1, and the conversion of fructose is 97.5%, which is higher than that from other researchers in abroad achieves in different conditions (their better results show that under decompression, the higher conversion is 93%, and the concentration of ultimate production is less than 30 g·L-1). The conversion of palmitic acid s 88%. After used 10 times, the enzyme activities of Novozym435 only reduce 19%.Study on ultrasound-promoted lipase-catalyzed reaction was reported in the world in recent years. However, experts have different ideas. Based on the optimized conditions of the synthesis, this paper studied the effect of different intensity ultrasound on the lipase-catalyzed reaction. Our result shows that ultrasound plays an important role in lipase-catalyzed reaction. Low energy ultrasound can decreases the reaction time when getting the same yield, increases the reaction rate, and enhances the concentration of production. When 10kHz, 0.16W-m'2, 20kHz, 9W-m'2 and 40kHz, lW-m"2 are selected .is ultrasonic parameters, the overall concentration of production vs. the reaction time appears the exponential addition form. In addition, the reaction time reduces 1/3 with ultrasound operation. What's more, when the frequency is 10 kHz and sound intensity is about 0.16W-m"2, the concentration of ester is twice more than that without ultrasonic irradiation. However, high energy ultrasound is not beneficial to vhe reaction. In the same condition, the concentration of production appears downtrend. |
PDF Full Text Request