Droplet stabilization in high holdup fraction suspension polymerization reactors

This paper presents a study on the evolution of the drop size of a methyl m ethacrylate suspension in an aqueous agitated medium in the absence and in the presence of polymerization reaction. The influence of the impeller spee d, of the fraction of monomer and of the surfactant concentration on the Sa uter diameter has been determined for the non-reactive system and a correla tion between the diameter and these parameters has been established. The ev olution of the Sauter mean diameter has been explained by the mean of the v ariation of the interfacial tension of the system. In the case where a reac tion occurs, the properties of the organic phase evolve, that may modify th e equilibrium between coalescence and breakage. Consequently, the surfactan t concentration has to be higher than without reaction. If this concentrati on is sufficient, the bead size remains nearly constant during all the reac tion. It is defined by the initial properties of the binary system and by t he hydrodynamic operating conditions. If the concentration is too low, the bead diameter increases during the reaction especially in the gel effect zo ne. The final size depends not only on the hydrodynamic factors, but also o n the kinetic parameters. Moreover, the hydrolysis ratio of the surfactant has an effect on the bead size due to the quantity adsorbed on the organic surface. (C) 1998 Elsevier Science Ltd. All rights reserved.