(752f) Mixture Homogeneity Measurements in a Vertical Bladed Mixer Using Tracer Particles

Vertically bladed mixers are widely used in various solids-handling industries such as cosmetics and food and pharmaceutical manufacturing. While regulatory bodies such as the Food and Drug Administration (FDA) have strongly encouraged inline and online Process Analysis Tools (PATs) [1], traditional mixture homogeneity measurements are performed only at specific stages in the mixing process. Additionally, these methods may suffer from drawbacks due to sample extraction requirements (invasive methods) or measurement restrictions to free surfaces (noninvasive methods). In this study, mixture homogeneity is continuously measured in a bench scale vertically bladed mixer fitted with two 45^o blades. Wood particles are mixed with plastic particles of varying densities, and a single wood particle is tagged with a stainless steel insert to allow X-ray radiographic particle tracking in a projected X-ray image. The tagged particle’s projected location in the mixer vessel is tracked over a sufficient time period to provide the local particle distribution of all similar particles.

Mixture homogeneity values are quantified by developing a standard deviation based mixing index, a grid-independent location based mixing index [2], and the Gini coefficient [3], utilizing the tracer particle location distribution. Mixing values thus obtained are calculated continuously and demonstrate the potential for real time mixing measurements using only a few tracer particles. The effect of particle density ratio on mixing is reported and the relative differences in the sensitivity of the mixing indices to changes in mixture homogeneity are compared.

References

[1] Guidance for industry, PAT-A framework for innovative pharmaceutical development, manufacturing and quality assurance, Food and Drug Administration, Rockville, MD, 2004.

[2] M.S. Siraj, S. Radl, B.J. Glasser, J.G. Khinast, Effect of blade angle and particle size on powder mixing performance in a rectangular box, Powder Technol. 211 (2011) 100–113.

[3] A. Sen, J. Foster, On Economic Inequality, Clarendon Press Oxford, 1997.