Abstract
A styrene polymerization in a lab-scale CSTR equipped with a pitched blade turbine impeller was simulated using the computational fluid dynamics (CFD) approach. The impeller motion was integrated in the geometry using the multiple reference frame (MRF) technique. The presence of non-linear source term and the highly coupled nature of transport equations of the polymerization, made the convergence difficult to achieve. The effects of the impeller speed, the input-output locations and the residence time on the polymerization in the CSTR were investigated. The CFD simulation shows that good mixing remained limited to the impeller region. Regions far from the impeller remained unmixed due to high viscosity of the polymer mass. The path lines of the particles, released at the inlet, were also generated to analyze the reaction progress as the chemicals travel throughout the reactor. The monomer conversion computed using the CFD model was compared to data reported in the literature. Conversion predicted using the CFD model is in good agreement with that obtained from the CSTR model at low residence time. However, the CFD predicted coversions were higher than those calculated from the CSTR model, at high residence time. It was found that the input-output locations had significant effect on the conversion and the homogeneity in the CSTR.
Highlights
Despite the importance of CSTR in polymerization area, the Computational Fluid Dynamics (CFD) approach has not been exploited yet, to extract the details about the non-homogeneity in the CSTR. It can be concluded from the above discussion that there is a strong need to identify the effect of mixing on the CSTR polymerization, using the CFD approach
The CFD model development for styrene polymerization in a CSTR is divided into four sections, namely: 1. Geometry creation 2
Computational Fluid Dynamics (CFD) technique was exploited to investigate the effect of mixing on the polymerization of styrene in a lab scale CSTR
Summary
Chain polymerization reaction consists of three main steps, namely initiation, propagation and termination. Sometimes due to viscosity rise during the polymerization, termination reactions becomes diffusion controlled and freezes in extreme conditions, leading to the well-known Gel effect. This effect may be due to poor micro mixing on molecular level and may end up in reactor instability. Micro-mixing affects both propagation and termination reaction rates. These effects are usually considered in the formulation of the two reaction rate constants in which diffusion control takes over and auto-acceleration polymerization become function of conversion. Macro-mixing cannot be treated the same way and need different approach.
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