Modelling fluidized bed polymerization reactors

Why it matters

Gas-phase polymerization of propylene in fluidized beds is one of the most widely used commercial routes to polypropylene. Output is often limited by how fast heat can be removed from the bed, and product quality depends on the particle size distribution as well as on polymer properties. Reliable models are needed to understand, scale and operate these reactors.

The problem

Earlier models tended to predict either polymer properties or particle size distribution, not both. Condensed-mode operation, where a condensing agent is fed to remove more heat and raise production capacity, adds vapour-liquid equilibrium and phase distribution to an already coupled system. Underneath sits the hydrodynamics of the bed itself, which CFD models must be validated against before they can be trusted.

What we do

1. Couple reaction and particle size. Combine a mixing-cell model and detailed polymerization kinetics with a population balance for particle size distribution, to simulate multi-monomer, multi-site Ziegler-Natta reactors.
2. Model condensed mode. Add vapour-liquid equilibrium calculations to see how condensate fraction, temperature and monomer partial pressure affect performance, and compare predictions with available plant data.
3. Test the hydrodynamics. Run experiments in rectangular beds with a central jet, using glass and polypropylene particles, and compare them with Eulerian-Eulerian CFD.

Approach

The reactor-scale models are dynamic and built to be general, so the same framework serves different kinetics and operating strategies. The experiments use digital image analysis and wall pressure fluctuations to characterise time-averaged and dynamic bed behaviour. This work formed part of Ranjeet Utikar’s PhD research at IIT Bombay and was carried out with colleagues at the National Chemical Laboratory in Pune.

Outputs

• A computational model for predicting particle size distribution and performance of fluidized bed polypropylene reactor
• Single jet fluidized beds: Experiments and CFD simulations with glass and polypropylene particles
• Modeling of a Fluidized Bed Propylene Polymerization Reactor Operated in Condensed Mode

Collaborators

National Chemical Laboratory (Pune) and the Indian Institute of Technology Bombay.

Contact

For collaboration or student projects in polymerization reactor modelling, contact the SMILE lab.