Chemical Engineering and Processing, Vol.46, No.4, 334-342, 2007
Hydrodynamics and oxygen transfer behaviour of water in diesel microemulsions in a draft tube airlift bioreactor
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 (phi) in the range 2.5-40%. For comparative purposes, data for diesel and water was also obtained. Increase in phi 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 epsilon(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 phi. Increase in the value of phi 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 V 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 epsilon(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. (c) 2006 Elsevier B.V. All rights reserved.