STEADY-STATE DROP-SIZE DISTRIBUTIONS IN HIGH HOLDUP FRACTION DISPERSION-SYSTEMS

Macroscopic phenomena in suspension polymerization reactors are extrem ely complex, and breakage and coalescence of polymerizing monomer drop lets are not well understood, especially for high dispersed-phase volu me fractions. Depending on the agitation, concentration and type of su rface-active agent the droplet size call exhibit a U shape variation w ith respect to the impeller speed. This behavior has been confirmed ex perimentally and theoretically as the balance between breakage and coa lescence rates of monomer drops. Both processes are related to the dro p surface energy, which is proportional to the interfacial tension and its variation with time. In this study die most comprehensive models describing breakage and coalescence processes in a dispersion system w ere incorporated into a generalized numerical algorithm to predict the steady-state drop-size distributions in a high holdup (50%) liquid-li quid dispersion system. To assess the effectiveness of the theoretical model in simulating drop-size distributions in high holdup dispersion systems, experiments were carried out with a model system of 50% n-bu tyl chloride in water in the presence of a surface-active agent, poly( vinyl alcohol), at different concentrations and agitation rates. The t heoretical model can predict reasonably well the drop-size distributio n for all experimental conditions A systematic theoretical and experim ental investigation elucidates the relationships between the changing structure of PVA molecules at the monomer/water interface and their ef fects on breakage and coalescence frequencies at different agitation t imes and rates.