Hydrodynamics and gas-liquid mass transfer in an oscillatory flow reactor: influence of liquid properties

Abstract

Liquid properties, such as, surface tension and viscosity are important parameters as they control gas-liquid mass transfer in bioprocesses. An oscillatory flow reactor provided with smooth periodic constrictions (OFR-SPC) was considered to evaluate its potential for mass transfer performance in non-pure gas-liquid systems. The effect of surface tension and viscosity on the volumetric (kLa) and liquid-side mass transfer coefficients (kL), interfacial area, (a), gas holdup (G) and bubbles dynamics were investigated under different operational conditions (oscillation amplitude (x0) and frequency (f) and superficial gas velocity (ug)). Two liquid phases, ethanol and sucrose aqueous solutions covering a range of surface tension and viscosity values were used. For the bubble size distribution (BSD) measurements an image analysis technique was used. A Design of Experiment (DoE) methodology was implemented in this work to establish the relation of x0, f, ug, surface tension and viscosity with kLa. According to the results, changes in the liquid properties and operational conditions showed marked effects on bubbles size and mass transfer. However, surface tension and viscosity had no significant influence on G, contrary to the reported for common contactors, where G increased in the presence of ethanol and decreased at moderate/high viscosities. Moreover, it was found that increasing the oscillatory movement notably improved kL, and kLa (2 to 6-fold), either in ethanol or sucrose solutions, compared to common reactors, even with moderate power consumption (~105 W m-3). This improvement resulted from the bubbles breakage, which originates bubbles with small and approximately the same size (homogeneous regime) enhancing a, instead, lower oscillations resulted in large bubbles (heterogeneous regime). The results demonstrate that the OFR-SPC can ensure outstanding mass transfer rates, with potential and feasibility for use in gas-liquid bioprocesses, where mass transfer and liquid properties are important.