The majority of PVC resin production nowadays is using suspension polymerization method. In a typical suspension polymerization, a known quantity of demineralized water is charged into a pressure vessel and other polymerization ingredients such as initiator, buffer and protective colloid are added. The vessel is then sealed and evacuated and vinyl chloride (VCM) is introduced into the vessel. Protective colloid action and agitation on the reaction mixture promote the formation of micro-droplets of VCM in water.
The vessel is heated up to the polymerization temperature, activating the initiator which starts the polymerization reaction. Once the polymerization effectively starts, heat is evolved. This heat is removed by cooling water in the vessel jacket. Polymerization reaction usually runs up to a VCM to PVC conversion of more than 75%, when there is no more free VCM phase remains.
At the end of polymerization reaction, PVC slurry (PVC resin particles in water) is discharged out of the reaction vessel and the remaining unreacted VCM is stripped from the PVC slurry in a highly effective stripping column. The slurry is then centrifuged to separate most of the water, resulting in PVC resin which still contains small amount of water, which is then introduced into the dryer to give dry PVC resin ready to be delivered to customers.