Esterification of glycerol and ibuprofen in solventless media catalyzed by free CALB: Kinetic modelling

• Ibuprofen solubility in glycerol grows exponentially with temperature.
• Stable nanoemulsions glycerol–ibuprofen are obtained.
• Activity is a hyperbolic function of stirrer speed, water content and enzyme and ibuprofen concentrations.
• Kinetic modelling suggests that ibuprofen reacts in the glycerol phase.
• High thermal stability exists till 80 °C, probably due to interfacial enzyme immobilization.

The enzymatic reaction of ibuprofen and glycerol in solventless media without and with the optimum content in water to obtain ibuprofen monoester is studied, selecting an adequate kinetic model for both cases. Preliminary runs led to fixing concentration of lipase CALB-L at 2 g L−1 and stirring speed at 720 rpm, and showed that a 10% water content enhances both initial rate of reaction and final yield to the monoester. For further comparison of hydrated and non-hydrated systems, kinetic runs were performed at several ibuprofen initial concentrations (20–100 g L−1) and temperatures (50–80 °C). In all cases, the formation of an emulsion was observed and analyzed by focused beam reflectance measurement (FBRM), dynamic light scattering (DLS) and turbidimetry. Considering kinetic and thermodynamical data, several phenomenological kinetic models were proposed and fitted to all the available data, using physical and statistical criteria to select the best ones. In both cases, the chosen model was a reversible Michaelis–Menten model of pseudo-first order with respect to the concentration of ibuprofen with no inhibition caused either by substrates or products. Kinetic constants showed that water addition resulted in mass transfer enhancement.

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