Experiments and numerical modeling to estimate the coating variability in a pan coater

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The purpose of this work is to investigate the effect of the coating process parameters on coating performance and coating variability, and hence determine the optimal operating conditions. Coating of particles is done to mask the unpleasant taste or odor of the drug, to control the bioavailability of the API, and to increase shelf-life. The coating solution is sprayed in specific locations of the granular bed and coating uniformity is achieved by interparticle collisions and overall mixing behavior in the coater. Thus, good understanding of particle flow and granular mixing in a pan coater is vital to optimize the process parameters to reduce coating variability. Coating experiments are performed at previously determined optimal mixing conditions using Lactose nonpareils. The coating fluid (aqueous solution of Opadry II) is sprayed intermittently at different flow rates and concentration. Vernier Caliper is used to measure the change in diameter and the coating of the particles. Moreover, DEM based numerical modeling of spray coating is also performed for same operational parameter set and spray characteristic (center and the radius of the spray zone) used in the experiments. DEM simulation provides the residence time distribution of all the particles passing through the spray zone. The coating variability in the experiments is estimated at different pan and spray variables. The coating variability decreases with the increase inpan tilt, coating time and an optimum speed. The spray characteristics does not seem to have much effect on the variability although better coating is observed under better mixing conditions of high tilt and pan speed for the same spray parameters. The mass distribution of coated particles is quantified in the numerical model by the total number of particles passing through the spray zone and also by the frequency distribution of the residence time of the coated particles. It is observed that the simulations are in good agreement with the experiments for the effect of orientation (tilt) of the pan coater on coating variability. However simulations over predicted the effect of speed as compared to the experiments to reach the minimum coating variability. In the current study, the experimental setup did not reflect the typical bead coating setup used in the industry; rather depict a simplified setup to validate the numerical model.

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