(87g) Further Studies on Optimization of Agitation in Suspension Polymerizers

Suspension polymerization is a common process for making products such as PVC. Droplets of monomer are dispersed in water in the presence of a surfactant and once the desired droplet size is achieved an initiator is added to start the reaction. The size of the polymer particles produced is governed by the size of the monomer droplets formed at the start of the process.

As the reaction proceeds, coagulum is formed which can coat the impellers and vessel walls or form large masses which can damage the agitator if they impact the blades or shaft. The formation of coagulum can be minimized by using an impeller that generates a high flow but, at the same time, it must provide sufficient shear to generate the desired monomer droplets.

Droplet sizes in stabilized liquid-liquid dispersions have been measured to identify which impellers can be characterized as “high or low shear”. The droplet sizes are correlated in terms of the kinetic energy dissipation rate (KEDR) in the impellers’ trailing vortices (see Grenville et al., Chem. Engg., Aug 2017). The measured relationship between the impellers’ characteristics is used to validate prediction of the trailing vortex KEDR made with large-eddy simulation computational fluid dynamics.

A case study on retrofitting in a suspension polymerization reactor will be presented.