Enzymatic transesterification reaction temperature

The transesterification reaction can be catalyzed by enzymes, the most common being the lipase. The reaction takes place at normal pressure and temperatures 50 to 55 °C with low energy consumption. The yield of methanolysis depends on several factors as temperature, pH, type of micro-organism producing the enzyme, the use of cosolvents, etc. However, low yields in methyl esters and very long reaction times make the enzymatic processes not competitive enough at this time [9, 11, 17]. 

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. 

Loupy and co-workers [68] have studied the effectiveness of microwave irradiation in increasing the enzymatic affinity and selectivity of supported lipases in esterification and transesterification reactions under dry media conditions (see Scheme 37). The esterification and transesterifications of racemic 1-phenylethanol 64 were studied in a temperature range of 70-100 °C. The lipases considered were the Pseudomonas cepacia lipase (LP) and Candida Antarctica lipase (SP-435). The initial rates and enantiomeric ratios E were significantly enhanced under microwave irradiation. Even so, in cases where classical conditions showed poor reaction, complete conversion could be achieved with increased reactivity under microwave conditions. This was largely attributed to the exclusion of the volatile by-products from the equilibrium. More importantly, the supported enzymes showed good stability and could be reused three more times in the reactions under study without loss of activity. 

The chemo-enzymatic synthesis of polyurethanes has been reported through the inter-esterification of castor oil and linseed oil at ambient temperature, using lipase as a catalyst and foUowed by treatment of the inter-esterified product with TDI. In the first step, partial esters are prepared by transesterification of soybean and linseed oils with n-butanol in the presence of lipozyme (a lipase) as the catalyst. The partial esters are then reacted with different diisocyanates to obtain a series of polyurethanes. The reaction of polyhydroxy compounds (transesterification reaction between different compositions of castor oil and glycolysed poly(ethylene terephthalate)) with diisocyanates offers a polyurethane network for new insulating coating applications. ... 

Lipase-catalyzed ring-opening polymerization of lactones was carried out over a wide temperature range of between 40 and 120 °C. The reaction temperature of higher than 80 °C was greater than that used in the conventional enzymatic reactions. It has been reported that imder relatively dry conditions, enzymes, such as lipases, proteases, and esterases, were catalytically active at temperatures around 90-120 °C [3-5]. Turner et al. demonstrated that lipase actually catalyzed the transesterification of octadecanol with palmityl stearate at 130 °C using lipase CA [6]. 

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. 

Enzymatic transesterification is generally performed at a lower temperature than the chemical reaction to prevent loss of Upase activity. Lipases from different sources show varying optimum temperature in the range of 20—70°C for their activity. Moderate temperature requirements by lipase-catalyzed transesterification make this process less energy-intensive. An increase in temperature increases the enzyme activity up to optimum temperature, beyond which denaturation of enzyme occurs, thereby decreasing its activity. With the increase in reaction temperature, initial reaction rate also increases, thus reducing the time taken for conversion. However, because of the enzyme denaturation beyond optimum temperature, conversion efficiency decreases. 

The deciding factor for optimum temperature of the Upase-catalyzed reaction includes immobilization, stabUity of Upase, alcohol to oil molar ratio and the type of solvent. In the continuous process, temperature is the key operational factor (Fjerbaek et al., 2009). In conclusion, the optimum temperature for the enzymatic transesterification process results fiom the interaction between the operational stability of the Upase and the rate of transesterification reaction (Gog et al., 2012). 

The conventional copolymerization pathways to PDMS and PET copolymers are paved with difficulties due to both physical incompatibility and chemical convertibility issues with regard to the catalysts and temperatures used for esterification and transesterification reactions [22]. In particular, the strong acids typically used in esterification or transesterification reactions will break the siloxane bonds Si-O-Si unless great care is taken. In order to address this problem, a facile enzymatic synthesis of silicone aromatic polyester (SAPE) and silicone aromatic polyamide (SAPA) in toluene under mild reaction conditions has been reported [26, 27], as shown in Schemes 2.4 and 2.5. 

The dimethyl ester of adipic acid, rather than adipic acid, was used as a transesterification substrate. Reaction rate studies had shown that the transesterification would be much faster than the esterification reaction. It was considered that the rate of attack on the oxazolidine ring by methanol would be slower than the rate of attack by water and that the ring opening would not be catalysed by the enzyme, whereas the rate of the transesterification would be increased significantly, particularly at the low temperature of the enzymatic esterification. 

Finally, enzymatic procedures may be used to produce concentrates of n-3 fatty acids. Depending on the type of enzyme, reaction time, temperature, and the concentration of the reactants and enzyme, it is possible to produce concentrates in different forms, e.g., as free fatty acids or as acylglycerols. Thus, processes such as transesterification, aci-dolysis, alcoholysis, and hydrolysis, as well as esterification of fatty acids with alcohols or glycerol, may be employed. 

In terms of CO2 as a reaction medium, a novel one-step process involving supercritical CO2 and enzymahc hydrolysis of cellulose has been shown to produce a 100% glucose yield [47]. However, to maintain the high pressure and temperature (160 bar and 50 °C) means the technology may have limited viability for industrial production, but it is an ideal technology for specialty products and possibly for other applications. For example, butyl butyrate can be synthesized via enzymatic esterification and transesterification using a lipase, Novozym 435, under supercritical CO2 conditions. Butyl butyrate is a component of pineapple flavor used by... 

CAL-B-conjugated MOFs showed no loss of enantioselectivity and activity in transesterification of ( )-l-phenylethanol with vinyl acetate at room temperature. The authors speculated that the enhanced rate acceleration of 3D MOF compared with ID and 2D MOFs could be explained by confined spaces nearby the surface-anchored enzymes for substrates to contact enzymes more efficiently. In addition, the Am groups of IRMOF-3 presumably help to maintain the optimum pH for the enzymatic reaction. 

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