(578a) CFD Model of Suspension Polymerization in Mixed Reactors

The properties of polymer produced by suspension polymerization (SP) are determined the particle size distribution (PSD) of dispersed polymer particles. We aimed our effort at filling the gap in description of the SP in industrial reactors. 

SP process starts with dispersed droplets of monomer in the water phase. In case of bead SP, the reaction changes monomer droplets into a mixture of polymer and monomer. During the polymerization the droplet viscosity increases in orders of magnitude which strongly influences the rates of the agglomeration and breakage. In well-mixed experimental vessels the PSD is determined by particle breakage due to the homogeneity of the flow field. On the other hand, industrial reactors have large settling zones, where agglomeration of particles takes place.

Mixed vessel CFD model was coupled with population balance equations (PBE) of dispersed phase. The polymerization kinetics model provided the evolution of average polymer chain length and subsequently the viscosity of the dispersed phase. The simulations predicted PSD of the dispersed phase and it’s dependency on the geometry of the vessel, mixing frequency and viscosity evolution during the polymerization. Since the polymerization and the fluid mixing have different time scales, a fully coupled CFD + PBE model describing the whole polymerization is computationally unfeasible. Steady state simulations were carried out following the viscosity evolution. Agglomeration and breakage kernels were adopted form literature [1, 2] and the closure problem of PBE was overcome by Quadrature Method of Moments (QMOM) [3].

This approach determines the significance of the variable viscosity on the PSD. Such an approach can be used for optimization of mixing conditions in large industrially used reactors.

Used literature:

1.         Kotoulas, C. and C. Kiparissides, A generalized population balance model for the prediction of particle size distribution in suspension polymerization reactors. Chemical Engineering Science, 2006. 61(2): p. 332-346.

2.         Laakkonen, M., V. Alopaeus, and J. Aittamaa, Validation of bubble breakage, coalescence and mass transfer models for gas-liquid dispersion in agitated vessel. Chemical Engineering Science, 2006. 61(1): p. 218-228.

3.         Petitti, M., et al., Bubble Size Distribution Modeling in Stirred Gas-Liquid Reactors with QMOM Augmented by a New Correction Algorithm. Aiche Journal, 2010. 56(1): p. 36-53.