Drop size distribution for liquid-liquid dispersions produced by rotor-stator mixers.

摘要

High shear mixers are broadly employed in chemical processes to produce liquid-liquid dispersions. Despite widespread use of these mixers, there is almost no basis to theoretically predict or experimentally assess their performance. Scale-up is often by trial and error causing higher processing costs and slower production rate. These problems provide the motivation to study the effect of physical properties and device geometry on drop size distribution (DSD) for liquid-liquid dispersion in these devices.; In anticipation of various ranges of drop size, three measurement techniques were employed. These are a dynamic light scattering, a high magnification video probe, and a video microscope system. For DSD measurements, interlaced Fibonacci series are used to characterize bin sizes. A simulated random sampling program was developed to estimate errors of this classification.; The main part of this dissertation is composed of two important fundamental studies. The first is the continuation of preliminary work done by Francis (1999) to consider the effect of continuous phase viscosity on the DSD in inviscid dispersed phase systems by dispersing chlorobenzene in different aqueous glycerol solutions. The second study focuses on the effect of dispersed phase viscosity and interfacial tension on the DSD. To systematically vary these parameters, silicone oils of various viscosity grades are dispersed in methanol, water, and methanol/water solutions.; To provide insight into the physics of drop breakage in mixers, mechanistic models are compared with the experimental results. Based on a constant power number, drop breakage could be controlled by inertial subrange eddies and sub-Kolmogorov inertial stresses. The plots of mean drop size versus fluid input power are presented to confirm this finding. DSDs of both fundamental studies (except 500 mPa-s silicone oil dispersions) are log-normally distributed in volume.; The final part of the dissertation considers on the application of the aforementioned techniques and fundamental studies to the production of aqueous polyurethane (PU) dispersions. To understand the influence of functional chemistry and mechanical parameters, dispersions of both non-neutralized and fully neutralized PU have been produced in batch rotor-stator mixers. The results show that DSDs are bimodal in number and independent of mechanical agitation. The functional chemistry of PU greatly affects the resulting DSD.