Pervaporation aided enzymatic production of glycerol monostearate in organic solvents

In this paper the enzymatic manufacture of glycerol monostearate was studied in high polar organic solvents. Water produced during the reaction has a disadvantageous effect on the reaction rate and enzyme activity. This byproduct water was removed and the water content was kept constant using a pervaporation unit which could be integrated on-line with the reaction system. The best yield (90%) after 6 h reaction time was achieved at 408C, at seven-fold glycerol excess using dioxane as solvent. The enzymatic esterification reaction could be described by the Random Bi Á Bi mechanism. A mathematical model have been estimated and experimentally verified by a set of experiments with varying and constant water contents. The experiments both in batch and integrated system (esterification Á pervaporation) could be described with good accuracy by the proposed model.

Fig. 3. Comparison of experimental data with calculated profiles for molar ratio 1:7 (solvent Á dioxane). reaction rate than the calculated ones. For initial water content equal 0.50% (w/w) (Fig. 4) the experimental data gives higher data than predicted from the model. These results may suggest that initial water concentration equal 0.50% (w/w) is close to the optimal value of enzyme activity. Literature reports indicate that at very low initial water content the enzyme is not sufficiently hydrated and shows poor catalytic activity, but at high values the thermodenaturation of the enzyme may occur [17]. According to The results presented that kinetic model of enzymatic esterification of stearic acid and glycerol (in the presence of acetone as solvent) based on Random Bi Á Bi mechanism is in good agreement with experimental data for different molar ratios (acid Á glycerol 1:3, 1:5, and 1:7). The similar experiments were performed for esterification process with dioxane as a solvent. As can be seen in Fig. 3, model with the same kinetic constants can be applied. The experiments in integration system esterification Á pervaporation can also be described with good accuracy by the proposed model. The effect of initial water content in the reaction substrate can be analyzed, too. The highest reaction rate values were obtained for initial water content equal 0.50% (w/w) (Fig. 4). It may suggest that this initial water content is close to the optimal enzyme activity. Similar conclusions are given in literature reports [19,20]. Using the optimal initial water content in the reaction mixture for integrated system esterification Á pervaporation higher reaction rate can be expected than without pervaporation process. Nomenclature Fig. 4. Comparison of experimental data with calculated profiles * initial water content 0.50% (w/w) (solvent Á dioxane).