Modeling of Suspension Vinyl Chloride Polymerization: From Kinetics to Particle Size Distribution and PVC Grain Morphology

Abstract

A comprehensive multiscale, multiphase modeling approach is developed to describe the dynamic evolution of polymerization rate, average molecular weight, and morphological properties of poly(vinyl chloride) (PVC) produced in batch suspension polymerization reactors. Dynamic evolution of the molecular (molecular weight distribution, long chain branching, short chain branching, terminal double bonds) and morphological (particle size distribution, grain porosity) properties of PVC can be calculated from the numerical solution of the proposed integrated model. In particular, polymer molecular properties are determined by employing a detailed kinetic mechanism that describes the free-radical polymerization of vinyl chloride monomer in both monomer- and polymer-rich phases. The initial monomer droplet size distribution and final polymer particle size distribution depend on the type and concentration of the surface-active agents, the quality of agitation (reactor geometry, impeller type, power input, etc.) and the physical properties (density, viscosity, interfacial tension, etc.) of the continuous and dispersed phases. A dynamic discretized particle population balance equation (PBE) is numerically solved to calculate the dynamic evolution of the particle size distribution of the produced PVC in a batch suspension reactor. Furthermore, the primary particle size distribution inside the polymerizing monomer droplets, which affects the porosity of the final PVC grains, is determined from the solution of a PBE governing the nucleation, growth, and aggregation of primary particles inside the polymerizing monomer droplets. Theoretical model predictions are compared successfully with a comprehensive series of experimental data on polymerization kinetics, particle size distribution, and PVC grain morphology.