Kinetic study on free lipase NS81006-catalyzed biodiesel production from soybean oil

• The kinetic of free lipase NS81006 catalyzed biodiesel production was studied.
• Both esterification after hydrolysis and direct methanolysis can form biodiesel.
• The competitive inhibitory effect of methanol also exists.
• The dominant reaction pathway for biodiesel production is direct methanolysis.

In recent years, free lipase has been regarded as a promising biocatalyst for biodiesel production due to its cost efficiency and faster reaction rate. Free lipase NS81006 has been demonstrated to be capable of efficiently catalyzing the methanolysis of soybean oils and further kinetic study is of great significant to reveal the related mechanism of free lipase catalysis. In this paper, the kinetic models based on Ping-Pong Bi Bi mechanism were proposed in lipase-mediated alcoholysis process for biodiesel production. The whole model was calculated from separate reaction blocks including hydrolysis, esterification and transesterification, and Matlab was used to estimate the kinetic constants by fitting experimental data of the conversion of soybean oil. It was found that in the process of NS81006-catalyzed methanolysis of soybean oil, the hydrolysis followed by esterification as well as the methanolysis would occur simultaneously. The inhibitory effect of methanol on free lipase could also be observed from the relative high inhibition constant of methanol compared with other equilibrium constants. Moreover, as it can be seen from the simulated results, the enzymatic rate constants for direct transesterification are much greater than those for hydrolysis, indicating that transesterification is a more dominant reaction pathway for the free lipase NS81006 mediated biodiesel production.

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