Design and development of a new static mixing bioreactor for enzymatic bioprocess: Application in biodiesel production

Mass transfer efficiency plays an important role in enzymatic biological processes, especially for non-aqueous biocatalytic processes. In these processes, low interphase mass transfer rates result in relatively long reaction residence time in traditional batch reactors. Therefore, the design and development of new bioreactors is crucial. In this study, a novel static mixing bioreactor was designed and applied to enzymatically catalyzed biodiesel production, which is a typical interfacial reaction system. In order to achieve good mixing effect and low pressure drop, the structure of bioreactor, including unit configuration, aspect ratio and rotation angle was designed and optimized by computational fluid dynamics. The realizable k-epsilon model was used, it was proved to be grid independent with 833678 hexahedral unstructured grids that were adopted to improve the structure for material mixing. After modification of the reactor, the final optimized structure is an R-R configuration with an aspect ratio of 1.5 and a rotation angle of 150°. Based on the above improved bioreactor, the process conditions for enzymatic production of biodiesel were optimized. The optimized reaction conditions were as follows: the length of the static mixer was 30 cm, the material flow rate was 1.77 m/s, the reaction temperature was 40 °C, the amount of methanol added was 3 times, and molar ratio of 3.4 alcohol to oil and 10% lipase dose were used. Under the optimal conditions, the yield of biodiesel in 1.5 h could reach 81.28%, and it could still be above 70% after 12 times of repeated use of lipase. Under the same reaction conditions, the reaction time for the static mixer to reach the same conversion rate (81.28%) was 1/3 of that of the stirred reactor, confirming the excellent mass transfer performance of the static mixer bioreactor.