Scale-up of a suspension-like polymerization process for the microencapsulation of phase change materials

Microcapsules of polystyrene with a high level of encapsulated paraffin wax and a narrow size distribution were prepared by a suspension-like polymerization process. The scale-up of this microencapsulation process was carried out by designing a pilot plant that was geometrically proportional to that used on the laboratory scale with the aim of preparing microcapsules with a similar particle size and with the same phase change material (PCM) content as those obtained in the laboratory. In order to verify the effectiveness of the scale-up procedure, a number of experiments on the pilot plant were carried out using the optimal formulation found on the laboratory scale. Only slight differences in mean particle size and encapsulated paraffin content were observed between the two scales at higher stirring rates. The experimental values were fitted to the theoretical expression for the average dissipation rate as a function of the mean particle size. This showed that the classical nonintermittent Kolmogoroff theory is applicable on the laboratory scale, whereas in the pilot plant a large intermittence took place, thus limiting the scale-up to higher stirring rates at which an equal average dissipation rate in both scales led to the same mean particle size. The final results indicated that the assumptions made during the scale-up process were correct.