Discrete Element Modeling (DEM) for Mixing of Cohesive Solids

The vast majority (>70%) of pharmaceutical products produced are solid oral dosages. These products are made through the processing and mixing of granular solids. (Jivraj et al., 2000; Huang et al., 2015) Mixing is generally treated as an individual unit operation where combinations of granular excipients, lubricants and active pharmaceutical ingredients are blended into a single product. Mixture homogeneity is then critical to ensure product quality and it is for this reason that the mixing of granular solids is of particular interest to the pharmaceutical industry. Discrete Element Modeling (DEM) was used to study cohesive granular solids mixing in a rotary kiln. The goal was to develop a quantitative relationship between particle properties (e.g. surface energy, particle density, and particle size) and simulated mixing behavior. Mixing behavior was quantified using the axial dispersion and variance decay rate constant coefficients. The results indicate cohesive forces (i.e., surface energy) are negatively correlated with the axial dispersion and variance decay rate constant coefficients. Furthermore, the relationship between relative standard deviation decay constant and axial dispersion coefficient are found to be linear for a system with constant fill level, cylinder dimensions, and angular velocity, and independent of particle size, bulk density, and surface energy.

Huang Z. et al. Flow and Bulk Density Enhancements Of Pharmaceutical Powders Using a Conical Screen Mill: A Continuous Dry Coating Device. Chemical Engineering Science, 2015. 125: p. 209-224.

Jivraj, Mira, et al. Review: An Overview Of The Different Excipients Useful For The Direct Compression Of Tablets. Pharmaceutical Science and Technology, 2000. 3: p. 58-63.