Mathematical modelling in batch emulsion polymerization

Abstract

Emulsion polymerisation, suspension polymerisation and the dispersion processes of styrene in water have been carried out at 50°C in a stainless steel, stirred batch reactor of 3.63 dam capacity. The reactor was fitted with a temperature control facility and could be operated with or without internal baffles. A mathematical model covering stages I,II and III of emulsion polymerisation has been proposed and its predictions have been compared with experimental data. Classical models do not present satisfactory predictions for the case of low soap concentrations or for the case of high impeller speed at low or intermediate soap concentrations. The model presented here overcomes this problem by taking into account the amount of soap adsorbed onto the dispersed monomer droplet interface. An existing relationship between monomer droplet size, impeller speed and impeller diameter for an unbaffled vessel and a new relationship for a baffled vessel were incorporated into the model. During stage III the increase in monomer particle viscosity reduces the translational mobility of the radicals with the result that the reaction rate increases dramatically(the gel-effect). Analogous behaviour in suspension polymerisation of styrene has been investigated and a relationship between the termination rate constant and the level of monomer conversion has been developed. This relationship is incorporated into the model for emulsion polymerisation. The predictions of the current model incorporating the soap adsorption and the gel effect amendments are in good agreement with experimental data for emulsion polymerisation of styrene at 50°C across the whole of the conversion.