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|Title: ||Evolution of particle size distribution in suspension polymerisation reactions|
|Authors: ||Jahanzad, Fatemeh|
|Issue Date: ||2004|
|Publisher: ||© Fatemeh Jahanzad|
|Abstract: ||Suspension polymerisation processes are commercially important for the production of
polymer beads having wide applications. Polymers produced by suspension
polymerisation can be directly used for particular applications such as chromatographic
separations and ion-exchange resins. Particle Size Distribution (PSD) may appreciably
influence the performance of the final product. Therefore, the evolution of PSD is a
major concern in the design of a suspension polymerisation process.
In this research, methyl methacrylate (MMA) has been used as a model monomer. A
comparative study of MMA suspension polymerisation and MMNwater dispersion was
carried out, for the first time, to elaborate the evolution of mean particle size and
distribution. Polyvinyl alcohol (PVA) and Lauroyl Peroxide (LPO) have been used as
stabiliser and initiator, respectively. Polymerisation experiments were carried out using
a 1-litre jacketed glass reactor equipped with a turbine impeller and a condenser. The
stabiliser, initiator and chain transfer concentrations, inhibitor concentration and type,
reaction temperature, impeller speed, and monomer hold up were used as variables. A
mathematical model was developed to predict the kinetics of polymerisation as well as
the evolution of PSD by population balance modelling. The experimental results were
compared with the model predictions.
From the comprehensive experimental results, the characteristic intervals of a typical
suspension polymerisation were realised as:
1) Transition stage during which PSD narrows dramatically and drop size decreases
exponentially due to higher rate of drop break up in comparison with drop coalescence
. _ until a steady state is reached. The importance, and even the existence, of the transition
stage have been totally ignored in the literature. The results indicate that increasing the
impeller speed, and PV A concentration will lead to a shorter transition period. Also
increasing the rate of reaction, via increasing initiator concentration, and reaction
temperature will shorten this period.
2) Quasi steady-state stage during which the rate of drop break up and drop coalescence
are almost balanced leading to a steady-state drop size and distribution. The occurrence
of this stage is conditional. Low impeller speed and PV A concentration may remove the
quasi steady-state stage completely and drops may start growing considerably after a
sharp decrease in size during the transition stage.
3) Growth stage during which the rate of drop break up considerably falls below the
rate of drop coalescence due to the viscosity build up in drops leading to drop
enlargement and PSD broadening. Results show that the onset of the growth stage may
not be fixed and it depends on the balance of the forces acting on drops. The onset of
the growth stage in terms of time was advanced with decreasing stirring speed and PV A
concentration and increasing monomer hold up. Under a static steady state, which is
formed when a high concentration of PV A is used, there is almost no growth.
4) Identification stage during which a solid-liquid suspension is attained and the PSD
and mean particle size remain unchanged afterwards. The onset of this stage appears to
be fairly constant for different formulations.
The developed model could fairly predict the rate of polymerisation. It was also capable
of predicting the evolution of particle size average and distribution qualitatively in the
course of polymerisation. The results can be used as a guideline for the control of
particle size and distribution in suspension polymerisation reactors. A more quantitative
exploitation of the model has been left for a future research.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University|
|Appears in Collections:||PhD Theses (Chemical Engineering)|
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