Vinyl chloride drop behaviour in suspension polymerisation reactors
The suspension polymerisation of vinyl chloride is the main industrial process used for the production of PVC. One of the key operations in this process is liquid-liquid agitation. The stability of the dispersion formed by such a system depends upon a number of parameters that have to be controlled. The present study clarifies drop behaviour in dispersion of vinyl chloride monomer, using poly(vinyl alcohol) stabilisers, before and during polymerisation. In order to carry out our experiments, a11. capacity pressurised reactor system connected to an external microscopic optical cell was designed along with a reflux system. Parameters affecting the initial VCM dispersion, prior to suspension polymerisation, such as residence time, agitation speed, volume fraction and type and concentration of suspending agent have been studied in some details and a correlation relating the Sauter mean diameter (D32) to the vessel geometry, the volume fraction and the Weber number has been proposed. Studies of drop coalescence using a tracer ( dye ) under different experimental conditions showed that the rate of coalescence between non-polymerising VCM droplets was relatively slow, proportional to the agitator speed and decreased by increasing PVA concentration. The PVA adsorption on VCM droplets during both dispersion and polymerisation was also studied. It was found that during polymerisation the rate of adsorption was relatively high at the early stages. The individual mechanisms of the droplets formation and subsequent droplet agglomeration processes in suspension polymerisation were also investigated. It was found that the method of addition of initiator was very important as it affects the morphology as well as the conversion of the final product. The influence of the condenser operation in the suspension polymerisation of vinyl chloride and its effects on the mechanism of droplet formation were also studied and the fate of monomer droplets returning from the condenser were investigated. The external morphology of the final PVC particles was studied using scanning electron microscopy (SEM) technique.