(143c) Development of a Coupled CFD – DEM Simulation Method for a Tablet Coating Process

Tablets are the most common form of drug administration and they are often coated to mask the API’s taste, to add protection functionality, to provide a modified release of an active pharmaceutical ingredient (API), to add a second API (active coating) or to provide differentiation through coloring. Especially, with respect to active coating, ensuring content uniformity - and thus coating uniformity - is a challenging task. Consequently, intra-tablet and inter-tablet coating variability are critical quality attributes.

Simulation of the tablet coating process can help to understand the underlying principles of the tablet coating process more deeply. This includes the tablet movement inside the tablet coater including mixing inside the tablet drum, the tablet surface velocity as well as the residence time inside the spray zone (or other zones inside the tablet coater) and the cycle time between two distinct spray zone visits and can calculate coating variability from this data.

Mechanistic models are developed to help find the optimal process conditions in regards to the heat and mass transfer as well as the drying mechanics during the tablet coating process [1]. These models can help to optimize an existing coating process. But to test new processes in silico more sophisticated simulation tools are necessary. Over the last couple of years CFD-DEM simulation has become more complex [2]. DEM nowadays allows the realistic simulation of industrial scale applications [3] as well as incorporating realistic particles shapes. Tablet coating is an attractive application of this modelling approach due to the reasonable number of tablets and the necessity to incorporate both fluid and tablet motion to adequate capture process performance.

In this work a model to realistically simulate biconvex tablets will be coupled to a CFD simulation. The momentum exchange will be done via a drag model that includes the non sphericity of the tablets as well as corrections for the changing void fractions surrounding the tablets. We will also show a method to include the heat and mass transfer in the CFD-DEM simulations. The proposed models will be verified and validated against existing theoretical models as well experimental results.

References:

[1] D. Niblett, S. Porter, G. Reynolds, T. Morgan, J. Greenamoyer, R. Hach, S. Sido, K. Karan, and I. Gabbott, “Development and evaluation of a dimensionless mechanistic pan coating model for the prediction of coated tablet appearance,” Int. J. Pharm., vol. 528, no. 1–2, pp. 180–201, 2017.

[2] D. Jajcevic, E. Siegmann, C. Radeke, and J. G. Khinast, “Large-scale CFD–DEM simulations of fluidized granular systems,” Chem. Eng. Sci., vol. 98, pp. 298–310, Jul. 2013.

[3] P. Boehling, G. Toschkoff, K. Knop, P. Kleinebudde, S. Just, A. Funke, H. Rehbaum, and J. G. Khinast, “Analysis of large-scale tablet coating : Modeling , simulation and experiments,” Eur. J. Pharm. Sci., vol. 90, pp. 14–24, 2016.