Evaluation of the effects of process parameters on granule mean size in a conical high shear granulator using response surface methodology

Response surface methodology was used to investigate the effects of operating parameters such as impeller speed, binder mass and granulation time on the average size of granules produced in a lab scale conical high shear granulator. Two quadratic models were proposed to express granule mean size as a function of impeller speed and binder mass as well as impeller speed and granulation time. It was found out that in the studied domain, the influence of each parameter on granule size differs from one another. While increasing binder mass at constant quantity of powder increased the average size linearly, increasing impeller speed changed the mean size in accordance with quadratic trend. The granule average size was proportional to granulation time and there was an interaction between impeller speed and granulation time. It was also shown that the granule mean size is related to maximum pore saturation (Smax) and Stokes deformation number (Stdef) of granules. Although the equation describes this relationship is applicable in the studied domain, it serves to address using dimensionless groups not only to specify growth regime or breakage probability, but also to determine the granule average size for coalescence or breakage (attrition) dominant regimes.