Contribute by : Anuj Narang – The control of mass and heat transfer is crucial in polymerization reactors to obtain particular polymer grades as well as high yields. Bulk polymerizations or polycondensations can be quite complex, especially during the final stage. The reason is the rheological behavior at continuously rising viscosity. At such high viscosities, barriers to heat and mass transfer determine the yield, molecular weight distribution and, thus, product quality.
Especially for the production of polyesters the selection of a suitable mixing system is very important. Together with the rheological complexity, water and glycol has to be removed continuously by evaporation through the liquid surface to move the chemical equilibrium towards the desired polyester product.
Today, still very often simple helical type impellers are used inside spherical or conical shaped reactors. As a major disadvantage, they show significant formation of dead zones together with incomplete axial mixing as soon as viscosities rise.
The reason for the success of the EKATO high-viscous polyester impeller is that it has been designed for optimum heat transfer as well as quick blending in a high-viscous regime. Together with this, it shows an axial flow pattern in the laminar regime, providing a frequent renewal of the liquid surface. As a consequence, the best mixing conditions for a quick and efficient water or glycol removal are established.