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Cationic Polymerization in Rotating Packed Bed Reactor: Experimental and Modeling

Jian-Feng Chen, Hua Gao, Hai-Kui Zou, Guang-Wen Chu, Lei Zhang, Lei Shao, and Yang Xiang

Key Lab for Nanomaterials, Ministry of Education, Research Center of Ministry of Education for High Gravity Engineering and Technology, Beijing University of Chemical Technology, Beijing 100029, P.R. China

Yi-Xian Wu

State Key Lab of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, P.R. China

DOI 10.1002/aic.11911

Published online December 30, 2009 in Wiley InterScience (

On the basis of analysis of key engineering factors predominating in cationic poly- merization, butyl rubber (IIR) as an example was synthesized by cationic polymeriza- tion in the high-gravity environment generated by a rotating packed bed (RPB) reactor. The influence of the rotating speed, packing thickness, and polymerization temperature on the number average molecular weight (Mn) of IIR was studied. The op- timum experimental conditions were determined as rotating speed of 1200 r min 1, packing thickness of 40 mm and polymerization temperature of 173 K, where IIR with Mn of 289,000 and unimodal molecular weight distribution of 1.99 was obtained. According to the experimental results and elementary reactions, a model for the pre- diction of Mn was developed, and the validity of the model was confirmed by the fact that most of the predicted Mns agreed well with the experimental data with a deviation within 10%. VC 2009 American Institute of Chemical Engineers AIChE J, 56: 1053–1062, 2010 Keywords: cationic polymerization, butyl rubber, rotating packed bed, modeling, number average molecular weight


The past decade has seen a rapid development and wide application of cationic polymerization for the synthesis of a wide variety of novel materials with potential commercial interest, such as polyisobutylene, polybutenes, butyl rubber (IIR), etc.1–12

The rate constants of propagation (kp) in the cationic poly- merization vary considerably, e.g., kp’s from 103 to 109 L mol 1 s 1 have been reported for isobutylene polymeriza- tion.13,14 It is proposed that the discrepancy in kp reported for various cationic polymerizations is due to different mechanistic interpretations and assumptions.15 Two general methods, diffu- sion clock (DC) and ionic species concentration methods, are

Correspondence concerning this article should be addressed to J.-F. Chen at and Y.-X. Wu at

VC 2009 American Institute of Chemical Engineers

typically used to determine the propagation rate constants in

cationic polymerization of vinyl monomers. Both of the meth-

ods give similar values of kp (kp 1⁄4 104–105 L mol 1 s 1) for

the polymerization of some substituted styrenes, while consid-

erable higher values of kp (kp 1⁄4 109 L mol 1 s 1) are obtained

by DC method in the case of styrene and isobutylene.16–18 De-

spite large variation with some monomers, it is generally

accepted that the rate constants of propagation in the cationic

polymerization of alkenes are similar for most systems with kp

1⁄4 105 ` 1 L mol 1 s 1.16,19 Therefore, the cationic polymeriza-

tion features an extremely rapid intrinsic reaction rate with

apparent reaction rate affected significantly by micromixing.20– 24

Micromixing is the final stage of turbulent mixing and consists of the viscous-convective deformation of fluid ele- ments, followed by molecular diffusion. It is believed that micromixing plays a very important role in chemical indus- try when the time scale of the chemical reaction involved is

AIChE Journal April 2010

Vol. 56, No. 4 1053

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