Two-liquid Systems Research Articles

Aqueous-organic membrane bioreactors part II. Breakthrough pressure measurement

The effect of membrane type—structure and wettability—on the operation of two-phase, aqueous-organic, membrane bioreactors has been studied. The influence of surfactants on membrane wettability is reported. A simple, but highly sensitive, technique for the measurement of breakthrough pressures is described. Experimental measurements of the variation in break through pressures as the concentration of tenside in the system was changed are reported. On the basis of the results from these measurements it is concluded that: (i) hydrophilic and, highly retentive, amphiphilic ultrafiltration membranes may be used to operate two-phase bioreactors, (ii) amphiphilic microfiltration membranes should never be used in such reactors and (iii) PTFE membranes would always be a poor choice for use in such devices because they always have a low breakthrough resistance in two-liquid systems—breakthrough pressures as low as 100 mbar were observed for the system ethyl laurate-water-PTFE, which contains no surface-active component. It is shown that these results are in general agreement with rules of thumb for the selection of membranes, presented earlier. The influence of membrane history on its wetting behavior—due to effects such as polymer surface restructuring—is highlighted. The limits on the utility of simple breakthrough pressure tests in determining suitable membranes, for use in two-phase bioreactors, owing to possible complications resulting from the exact mechanism of enzyme action is pointed out.

Droplet Breakup and Distribution in Stirred Immiscible Two-Liquid Systems

Droplet Breakup and Distribution in Stirred Immiscible Two-Liquid Systems

EXPERIMENTAL STUDIES OF MASS TRANSFER RATE IN THE DISPERSED PHASE AND MOVING BEHAVIOR FOR SINGLE OSCILLATING DROPS IN LIQUID-LIQUID SYSTEMS

Mass transfer rate in the dispersed phase was measured on single drops falling or rising with oscillation of oblate-prolate type through stationary liquid fields. The two-liquid systems used were water and aqueous glycerine solution drops in benzene and in carbon tetrachloride, and water drops in toluene. The iodine was used as the solute which transferred from the drops to the organic solvents. The moving behavior of the oscillating water drops during mass transfer was investigated in regard to frequencies, amplitudes and terminal velocities of the drops by use of a high-speed cine camera. Experimental dispersed-phase Sherwood number is correlated with the dispersed-phase Schmidt number and the modified Reynolds number which is defined by use of diameter, frequency and kinetic viscosity of the dispersed phase. The extraction efficiency obtained is also compared with the model of Angelo et al., and it is found that the experimental results were explained satisfactorily by use of their model. An empirical equation for the critical drop diameter of the oscillation onset is also obtained.