The hydrodynamics of a Graesser ("raining bucket") contactor with a reverse micellar phase

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.