(431a) Study of Flow and Mixing in High Shear Mixers Using Numerical Techniques

A variety of blending equipment is available for use in the pharmaceutical industry, such as V-blenders, double-cone blenders, and continuous mixers. Ribbon and ploughshare mixers are a high shear type, where the action of one or more blades produces convective motion in the granular bed. Their names reflect their respective blade designs – helical ribbon type in one and plough shaped in the other. These are often found to be suitable for mixing highly cohesive materials such as active pharmaceutical ingredients (APIs). During the blending process, ribbon blenders are generally observed to create a lesser degree of size-segregation compared to tumbling blenders. They are, however, prone to having dead zones and the high shear can cause over-lubrication problems in case a lubricant like magnesium stearate is used.  This study focuses on a large scale discrete element method (DEM) based simulation of the effect of process parameters on blending performance of these two blenders. The effects of fill level, loading order of cohesive/finer material (API or lubricant) relative to the excipient, and blade speed are investigated. The nature of powders is simulated using slump tests and DEM simulation parameters are fine-tuned to simulate material flow behavior. Multi-core/multi-processor parallel computing is used to scale the DEM simulations to more realistic number of particles. The findings are compared with available experimental data [1,2]. The results show the applicability of such mechanistic models can be extended further up from small lab-scale equipment to pilot-scale and above.

[1] Laurent B.F.C and Cleary P.W. Comparative study by PEPT and DEM for flow and mixing in a ploughshare mixer. Powder Technology, 228 (2012) 171-186.

[2]Muzzio, F.J., Llusa M., Goodridge C.L., Duong N., Shen E. Evaluating the mixing performance of a ribbon blender. Powder Technology, 186 (2008) 247-254.