(116l) Experimentally Validated Numerical Modeling Study of Mixing in a Coating Pan

Coating of particles is done in the pharmaceutical industry, to mask the unpleasant taste or odor of the drug, to control the bioavailability of the drug, to protect the tablet from the environment (increase shelf-life), and sometimes to improve tablet appearance. During coating, the coating solution is sprayed at discrete locations on the cascading region of the granular bed, and only the liquid jet directly coats a small fraction of tablets. The distribution of the coating solution from these locations to the remainder of the bed occurs through mixing. Thus, the knowledge of particle flow and mixing in a pan coater is thus critical to optimize the design and operation of such equipment. Mixing is an important but poorly understood aspect of coating of pharmaceutical preparations (esp. tablets). Experimental and computational methods are developed to perform quantitative examination of mixing patterns and mixing rates in rotating coating pan. White and red non-pareils of 6-7 mesh size loaded in the ellipsoid pan coater to check the effect of initial loading (side-side and front-back), fill level, orientation of the vessel and the vessel speed on granular mixing. Video-imaging, MATLAB and discrete pocket samplers are used to quantify the mixing and to finally estimate the optimal operating condition. DEM (Discrete element method) based numerical model was also developed to study the effect of granular mixing in a coating pan. Digitally recorded mixing states from experiments are used to fine tune the model. In both the experiments and simulation, we observed slower axial dispersion than radial convection when the axis of rotation of the mixer is horizontal (no tilt). However, tilt enhances axial mixing, and faster axial mixing is seen for higher tilt angles from the horizontal. The speed of the rotating vessel has no prominent effect on the rate of mixing in a coating pan, as observed in experiments and simulations. Moreover, fill level has no significant effect on the rate of mixing. Finally effect of vessel speed on coating is simulated modeling the coating of the particles passing through prescribed spray location on the cascading zone. Higher vessel speed enhances granular coating for moderate filling and tilted orientation of the coater.