Mass Transfer in Emulsion Polymerization: High Solids Content Latex and Mixing Effects

The impact of different agitator configurations used during the emulsion polymerization of vinylidene fluoride (VDF) is studied with the goal of achieving a solids content of 55 wt% while minimizing particle coagulation and maintaining low levels of surfactant. The design and number of impellers, their spacing and the agitation speed are shown to have a strong influence on the transfer of gaseous monomer to the aqueous phase, and thus the rate of polymerization. Increasing the number of impellers on the central shaft, and decreasing the spacing of the impellers close to the latex surface has a strong influence on the ability to incorporate gaseous monomer, so the solids content and the latex level in the reactor increased. Furthermore, it is found that changes in the agitation rate during the reaction is necessary at high solids content to avoid destabilizing the particles in view of the low surfactant concentrations used. Agitation in emulsion polymerization is often treated as a secondary consideration. However, when one is dealing with gaseous sparingly soluble monomers, agitation becomes critical. This study shows that the slightest changes to the design of an agitation system can have a significant impact on the performance of the reactor. image