A thermodynamic model for organic and aqueous tablet film coating

A tablet film-coating model for aqueous- and/or organic-based systems is shown to predict exhaust stream conditions thereby facilitating process optimization and scale-up. This coating model uses the First Law of Thermodynamics and conservation of mass principles to complete a material-energy balance on the coating unit operation for a closed, non-isolated system. Heat loss from the coating pan is incorporated into the model through a parameter called a heat loss factor (HLF) that is directly related to the heat transfer coefficient and pan surface area. For a mixed organic-aqueous coating formulation, the outlet air temperature and humidity are most notably affected by the coating composition and the inlet drying air temperature, which controls the evaporative cooling rate. The coating solution temperature and inlet air relative humidity do not significantly influence the exhaust air temperature, Tair,out. The HLF was determined to be 24 to 62 cal/min degrees C for the LDCS-20 to HCT-30, 360 cal/min degrees C for the HCT-60, 0 cal/min degrees C for the HC-130L and 945 to 1322 cal/min degrees C for the Accela-Cota-48 to Compulab-36 coating pans. This model successfully predicts Tair,out within 3 degrees C for a given coating pan, and within 6 degrees C scaling up from one to 220 kg pans for both organic- and aqueous-based coatings. The model is also useful for probing process and formulation variable sensitivity critical to establishing process robustness.