Typical features of E-PVC processes

Residual VCM is removed by stripping the polymer suspension or latex. This section includes unstripped suspension/latex storage tank(s). Usually the stripping uses the effects of steam, nitrogen, vacuum (alone or in combination), and temperature. The process can be performed in 

The stripping of latex must be operated in such a way that the latex remains stable, and neither coagulates nor flocculates. The latex is sensitive to temperature, to agitation and to time. 

The VCM content of PVC suspension after stripping is normally very low. In the case of latex, stripping is more difficult and the residual VCM content depends on a variety of parameters, for instance emulsifier content and type, latex particle size, latex stability, the recipe and the requirements of resin end properties. When steam is used for stripping, the overhead steam containing recovered VCM is condensed. The condensate can be returned to the stripping system, or can be transferred to the water stripper of the effluent treatment or other sections of the process, in order to recover contained VCM and thus to prevent VCM emissions from this effluent. In all cases, the non-condensed overhead gas containing stripped VCM is collected in a recovery unit. 

The spray drying causes the agglomeration of the latex particles into secondary particles with a mean particle size of approximately 30 micrometres. These may be subsequently broken down by the use of a mechanical grinding process, to recover some or all of the original latex particle size distribution. 

Drying conditions have a profound impact on particle morphology and can be used to produce either paste or general emulsion polymers from the same reactor product. In the spray dryer, the latex particles of approximately 0.5 pm in size stick together into secondary particles with a mean diameter of approximately 30 pm. 

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