Computational Fluid Dynamics Study of a High -Impact Polystyrene Polymerization Reactor

I.L. GAMBA; D.A. ESTENOZ; N.M. NIGRO

2011-01-01/2011-12-01

Ingeniería Química

Qca.,Petroqca.y Carboqca.-Petroquimica

The use of computational fluid dynamics (CFD) to model a pilot plant horizontal plug-flow reactor (HPFR) for the production of  high-impact polystyrene (HIPS) leads to the main objective of this technical report that was to evaluate the effect of the fluid-dynamics (FD) and kinetic phenomena on the performance of the reactor, obtaining not only global variables, such as conversion and species concentrations, but molecular structure characteristics of the final product. The polymerization reaction model was developed using the method of moments. The purpose of using this method was to reduce and convert the thousands of polymerization steps into a conventional reaction scheme that has a manageable size. The model included six steps: initiator decomposition, thermal initiation, chemical initiation, propagation, chain transfer to monomer, and termination by combination. The coupling of the chemistry modeling with the simulation of the flow field were done by incorporating the polymerization reaction kinetics into the CFD by standard user-defined functions (UDFs) coded in C language. The UDF code was written for the reaction source terms linked to the species transport model coded in the CFD program. The approach consisted in solving conservation equations for chemical species. The model predicted the local mass fraction of each species by means of the resolution of a convection-diffusion equation for every species. Finally, the influence of initiator concentrations and inlet temperatures on monomer conversion and polydispersity is discussed. A sensitivity analyses is used to understand the impact of chemical kinetics on monomer conversion.