Hydrodynamics and oxygen transfer behaviour of water in diesel microemulsions in a draft tube airlift bioreactor

Abstract

Determinations of pertinent hydrodynamic and mass transfer parameters were carried out inside draft tube internal loop airlift bioreactor (DTAB) containing water in diesel (W/D) microemulsions with water to diesel volume ratio ( φ) in the range 2.5–40%. For comparative purposes, data for diesel and water was also obtained. Increase in φ of the microemulsion systems up to 40% or increase in the amount of surfactant used to make the microemulsions resulted in a decrease in the values of ɛ g and k L a, which was attributed to the increase in the viscosity of the microemulsions. This viscosity was found to be a more suitable correlating parameter than φ. Increase in the value of φ of the W/D microemulsion resulted in a decrease in the values of liquid velocity ( v L ) for u gr up to 0.032 m/s. At higher gas velocities, similar v L values were obtained for all the microemulsions. On the other hand, increase in φ of the W/D microemulsion resulted in increase in both the circulation time and mixing time values obtained inside the DTAB, although the difference was more pronounced at lower values of u gr. Suitable empirical correlations relating ɛ g , k L a, v L , circulation time and mixing time to riser superficial gas velocity ( u gr) and kinematic viscosity were presented. The downcomer holdup data for diesel and W/D microemulsions was related to the riser holdup data using a single correlation.