Enzymatic transesterification reaction water content

The inline measurement of the water vapour pressure makes it possible to monitor its progress in the course of the reaction. The water vapour pressure does not stay constant but slowly decreases until a very low value is reached. In the absence of the enzyme however no such decrease was detected (Figure 6). We believe that the enzymatically catalyzed hydrolysis of isopropenyl acetate is responsible for this decrease in water content. The hydrolysis occurs as a parallel reaction to the transesterification of isopropenyl acetate to menthyl acetate. It is not yet clear how significant the contribution of this parallel reaction to the overall decrease in (transesterification)reactivity is. If we assume that the rate constants for the hydrolytic reaction are of the same order of magnitude as those for the transesterification such a parallel reaction would lead to a significant decrease in the rate of transesterification as the water activity rises. At low water activities the hydrolytic reaction might be responsible for the observed decrease in reactivity. Very likely however the accumulation of water around the enzyme... 

Abstract Biodiesel is a fatly acid alkyl ester that can be derived fiom any v etable oil or animal fat via the process of transesterification. It is a renewable, biodegradable, and nontoxic fuel. In this paper, we have evaluated the efficacy of a transesterification process for rapeseed oil with methanol in the presence of an enzyme and tert-butanol, which is added to ameliorate the negative effects associated with excess methanol. The application of Novozym 435 was determined to catalyze the tiansesterification process, and a conversion of 76.1% was achieved under selected conditions (reaction temperature 40 °C, methanol/oil molar ratio 3 1, 5% (w/w) Novozym 435 based on the oil weight, water content 1% (w/w), and reaction time of 24h). It has also been determined that rapeseed oil can be converted to fatty acid methyl ester using this system, and the results of this study contribute to the body of basic data relevant to the development of continuous enzymatic processes. 

The transesterifications of divinyl adipate with glucose in DMF catalyzed by alkaline protease from Bacillus subtilis at various water contents were examined. The enzymatic reaction by the Bacillus protease was carried out in the presence of more than 2% water and maximum reaction rate was observed at a water content of 20%. It seems that the protease activity in DMF can be recovered by the addition of water (Figure 14 B). 

There are many factors affecting enzymatic transesterification (Fjerbaek et al, 2009 Robles-Medina et al, 2009). Among the key factors are type, stability and reusability of hpase, type of the acceptor alcohol, substrate ratios, quality of feedstocks, reaction temperature, water activity and/or water content. 

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