(546d) Analysis of Mass Transfer in a Three-Phase Taylor-Couette Reactors: Implications for Mixing in Fermentation

Designing novel bioreactors has recently garnered significant attention as a cutting-edge topic in biomanufacturing. The utilization of Taylor vortex flow, generated in the annular region between a rotating inner cylinder and a stationary concentric outer cylinder, has attracted increasing interest for its application in multiphase reaction and separation processes. In our study, we focus on applying Taylor vortex flow to achieve simultaneous fermentation and in situ product recovery, which alleviates product inhibition on growth, enhance productivity, and increase genetic stability of the culture. To effectively implement this concept, a deeper understanding of mass transfer between three phases (including two immiscible liquids and gas phase) is crucial. In this study, we designed experiments using a semi-batch liquid-liquid-gas Taylor vortex device to ferment a fatty-alcohol producing strain with a continuous gas feed to investigate volumetric mass transfer coefficients (k_La). Fatty alcohols are commonly used as emollients, thickeners, and surfactants in various industries. Dodecane is often added into the fermentation medium to simultaneously extract the relatively toxic fatty alcohols from the broth. The results indicate that, for gas-liquid mass transfer, k_La increases with the rotation speed of the inner cylinder (corresponding to azimuthal Reynolds number). However, beyond a critical value, further increases in rotation speed have minimal impacts. Moreover, increases in gas flow rate in the range of 60 and 250ml/min significantly enhance k_La at fixed azimuthal Reynolds numbers. In contrast, for liquid-liquid mass transfer between the aqueous phase (fermentation medium) and the organic phase (dodecane), higher azimuthal Reynolds numbers in the range of 13611 and 27222 were found to enhance interphase mass transfer at fixed gas flow rates. Additionally, increasing the gas flow rate was observed to enhance the liquid-liquid mixing rate, resulting in higher k_La between the aqueous and organic phases. In the context of bioreactors, oxygen mass transfer from air to fermentation broth plays a critical role in balancing biomass accumulation and metabolic functions closely relevant to product synthesis. By optimizing k_La through manipulation of gas flow rate and cylinder rotation speed in a Taylor vortex bioreactor, we are able to improve the availability of oxygen in the fermentation media, balance metabolic activities and therefore enhance overall productivity.