S. Jarudilokkul et al., The hydrodynamics of a Graesser ("raining bucket") contactor with a reverse micellar phase, BIOTECH PR, 16(6), 2000, pp. 1071-1078
A variety of contactor types have been assessed for the liquid-liquid extra
ction of proteins using reversed micelles; however, many of these contactor
s suffer from drawbacks such as emulsion formation and poor mass transfer p
erformance. In this study, a small (1.25 L) Graesser "raining bucket" conta
ctor was assessed for use with this system since it has the potential to am
eliorate many of these problems. The aim of the work was to evaluate the hy
drodynamics of the contactor in order to use this information for future wo
rk on mass transfer performance. Hydrodynamic characteristics such as the a
xial mixing coefficient were determined by residence time distribution stud
ies using a tracer injection method. The effect of rotor speed and flow rat
e of each phase on axial mixing was investigated, and as a result of its un
usual structure, i.e., falling/rising sheet, the interfacial mass transfer
area in the Graesser was determined by image analysis. It was found that ro
tor speed had more influence on the axial mixing coefficient in the aqueous
phase than in the reverse micellar phase. The axial mixing coefficient in
each phase increased by increasing the flow rate of the same phase. The ima
ges obtained in a dropping cell showed that under the conditions of this st
udy (3 rpm, 22 degreesC), the bucket pours one phase through the other in t
he form of a curtain or sheet. A new image technique was developed to deter
mine the interfacial area of both phases, and it was found that the specifi
c area was 8.6 m(2)/m(3), which was higher than in a spray column but consi
derably lower than in a RDC or a Graesser run at high rotational speed (50
rpm) without the addition of a surfactant.