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231-W017.pdf

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International Journal of Chemical Engineering and Applications, Vol. 3, No. 6, December 2012 Kinetics Modeling of Free-Radical Polymerization on

Spinning Disk Reactor

Safoora Sajad, Mitra Ahmadi, and Mohammad Reza Moghbeli



Abstract—Spinning disk reactor (SDR) technology reportedly achieves significant enhancements in free radical polymerization rates. The effect on those rates has been attributed to the unique hydrodynamic environment experienced by the reacting polymer films. The rotating surface of SDR promotes extension of the polymer chains, which prevents the propagating chains from terminating through bimolecular reactions. In this work, a numerical simulation is applied to investigate how reduced rates of termination would affect time conversion behavior of free radical initiated styrene polymerization. Comparisons have been made between model predictions and SDR experimental results. The closeness of predicted and experimental results indicates strong evidence that the hydrodynamic regime created on the surface of a SDR can lead to reduced rates of bimolecular termination.

Index Terms—Polystyrene polymerization, spinning disk reactor, termination rate constant

I. INTRODUCTION

The spinning disk reactor (SDR) technology proposes an alternative approach through a step change in manufacturing several operations, most notably with respect to the ability to cope with very fast chemical reactions such as polymerization, crystallization, and competing fast chemical reactions. The technology creates highly sheared thin liquid films which feature superior heat/mass transfer properties. The short diffusion and conduction path length achievable by the very thin films creates the basis for the very high transport rates within the film.

SDR technology has been successfully used for a range of procedures including free-radical and cationic polymerization processes [3] and organic catalytic reactions [7].

The improved product quality including high selectivity and narrow crystal size/molecular weight distributions observed in these processes, are directly influenced by the micromixing intensity in the process liquid. However, so far no comprehensive study of micromixing in SDR thin films has been performed. Here, we study the hydrodynamic conditions for which the SDR film gives the best micromixing efficiency and evaluate its micromixing performance in comparison to other reactor systems. It is assumed that the centrifugal forces and divergent nature of the reacting film on the spinning disc provide conditions which minimize the termination of the macro radicals,

Manuscript received September 15, 2012; revised November 26, 2012.

Mitra Ahmadi is with the Department of Chemical Engineering, Payame Noor University (e-mail: mi_ahmadi2003@yahoo.com).

resulting in great increments in the polymerization rate. The experimental data in this study are derived from a previous research carried out by Moghbeli and collaborators [5]. Experimentally, the bulk free-radical polymerization of styrene was carried out on a disc surface at 70oC with 2, 2- azobi- sisobutyronitrile (AIBN) as the initiator.

II. MODEL FORMULATION

Production, consumption, and diffusion in the mass balance equation don’t have important role in the total equation due to constant total mass. Therefore mass fraction can be shown as following equation:

TABLE I: KINETICS CONSTANT FOR POLYSTYRENE WITH AIBN AS AN INITIATOR [6].

(Ur A)r (Ur A)rdr (UzS)z (UzS)zdz  (U A) (U A) acc.

L K P 0  m o l e . m i n 

8

6.12810 exp 

7068RT

L K t 0  m o l e . m i n 

10

7.5510 exp 

1677RT

K min1 d

16

1210 exp 

 30714.02 RT

Cal  R  m o l e . K 

1.987

   d

With extension of Taylor series, the Equation 1 changes

to following equation:

(UrA)r dr(UzS)z dz r z

If we suppose to ρ is constant the above equation will be convertedto:

U U 1U U

rr z0 (3)

(U W) (rddzdr) d 

m  t t

(1)

(2)

r r r  z

The continuity equation of mole fraction in cylindrical

coordinates is formulated as:

Ci Ci 1 Ci Ci

t (Ur r U r  Uz z )

(4)

r2 2

Equation 4 can be simplified with some assumptions such

1  D 

C

(r i)

1 2C i

2C  i

iM r r 

z2 

DOI: 10.7763/IJCEA.2012.V3.231

413

r 

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 Supercritical Fluid Extraction 231-W017.pdf Page 001
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