(617be) Integration of CFD and Polymerization for an Industrial Scale Cis-Polybutadiene Reactor

Integration
of CFD and Polymerization for an Industrial Scale Cis-polybutadiene Reactor

Chao-zhong Xu, Jia-jun
Wang, Xue-ping Gu, Lian-fang Feng

State Key Laboratory
of Chemical Engineering,
College
of Chemical & Biological Engineering, Zhejiang
University, Hangzhou P.R. China 310027

jiajunwang@zju.edu.cn

Abstract
A
major objective of polymerization reaction engineering is to understand how the
reaction mechanism, the physical transport processes, reactor configuration and
operating conditions affect the polymer properties that assessed product
quality. In
particular, cis-polybutadiene polymerization in
industrial scale reactors becomes quite complicated due to complex mechanism
and metastable
behaviors. However, computational fluid
dynamics (CFD)
is barely exploited to forecast the polymer product quality in the general modeling approach though some efforts
have been done toward a better understanding of polymerization process. Hence, modeling
polymerization by CFD,
which takes polymer quality indices into consideration, still remains very challenging
and significant.

A
CFD model coupled with polymerization kinetics was developed to investigate butadiene
solution polymerization using
three-component system (Ni, Al,
B) as catalyst and raffinate oil as solvent not previously available for a 12 m³
industrial scale reactor equipped with a double helical ribbon agitator. The integration of kinetic
model with
two catalytic active sites
and CFD model was accomplished by solving continuity, momentum, energy and
species equations simultaneously, in which the reactive source terms related to
polymerization were implemented by a user-defined function with the method of
moments. Model
validation was successfully conducted by comparing CFD results with plant data
and the developed
model was further extended to discuss the effects of operation conditions
including inlet temperature, impeller as well as inlet flowrate of solvent, and
finally shed light on the differences of reactor behaviors from ideal CSTR
model.

The
simulation indicated that the
reactor behaviors
with
double helical ribbon agitator were very similar to traditional CSTR model in
the middle and the top of the reactor, while at the inlet near the reactor bottom,
there apparently existed a deteriorated area for polymerization in the present
production process. The distinction between double helical ribbon agitator and frame
impeller mainly embodied in axial circulation capability and it seemed to be
easier to keep the uniformity of polymerization process when helical ribbon agitator
was used. It was also found when compared with inlet temperature, the
fluctuation of reactor performance was more sensitive to inlet flowrate of
solvent and therefore it was more advisable to regulate the inlet temperature for
normal operations in industrial production in most cases. The results showed the
proposed method could be served as a guidance to achieve a better control on cis-polybutadiene
production, thereby maintaining the stability of polymerization process and optimizing the quality of
products.

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