CFD Modeling for High Impact Polystyrene Process Improvement

I.L. GAMBA

Montreal

Encuentro; TOTAL VI Meeting Montreal 2012; 2012

TOTAL Petrochemicals USA

High impact polystyrene (HIPS) is a rubber toughened polymer, a special class of material prepared by blending a high modulus, glassy polymer with a soft, rubber component. In HIPS, rubber is added to polystyrene to improve its toughness when impacted. HIPS is a commodity plastic with a total United States production of all polystyrene resins at almost 3 million pounds per year. This versatile product can be found in many compositions and structures, that offer an exceptional range of final properties for applications in automotive, furniture (office machines and supplies), houseware (electronics and appliance housings), computer, packaging (disposable cups and lids), toys. The final product is a two-phase system where rubber is dispersed throughout a polystyrene matrix as discrete particles. These particles have a unique morphology characterized by spherical rubber particles filled with polystyrene occlusions. Final polymer properties are largely determined by its morphology and molecular structure. Improvement of the HIPS production process is sought to better meet quality product requirements as well as to reduce cost. As far as complex and intricate physical phenomena are concerned, how and what precisely happens in the polymerization reactors remains uncertain. By integrating each chemical and physical phenomenon, novel approaches based on Computational Fluid Dynamics (CFD) can help in improving the understanding of the process that leads to rubber particle formation, which is critical in controlling HIPS properties. An extensive literature search shows that CFD has been used only to study the hydrodynamics of the reactors in isothermal condition and without polymerization. Nevertheless, a CFD model can integrate fluid dynamics together with kinetics of polymerization, energy and mass balances, exothermicity, reactor cooling, etc into the simulation of an industrial reactor. Therefore it could bring insight in the influence of hydrodynamics on the product quality. The main objective of this project is to develop a CFD model for the continuous prepolymerization reactor integrating hydrodynamics together with kinetic phenomena that could help to better understand what happens inside the reactor. The ultimate goal of the model would be to help in determining the appropriate operating conditions to obtain an a priori-specified-characteristics product.