(714a) Prediction of Flowability of MethocelTM Direct Compression Grades Using a Limiting Flow Rate Calculation
AIChE Annual Meeting
Thursday, November 17, 2016 - 12:30pm to 12:48pm
The evaluation of flowability of fine powders is often addressed by standard flow testers. The flow functions from shear testers, discharge rate through cones, orifice plates or a compaction ratio are used as descriptors of the flowability of powders. However, these testers can fail to address the discharge characteristics from a hopper at commercial scale to predict the actual discharge rate of a fine powder, because they do not consider the effects of interstitial air pressure.
This paper discusses the discharge rate of fine powders from a hopper using permeability, compressibility, and shear testing in combination with the calculation of the limiting discharge rate using Johansonâ??s approach . The predictive concept for powder discharge rate using the limiting flow rate calculation is correlated with experimental discharge rates from a model hopper. The use of permeability and bulk density was found to be the most important powder descriptors to predict discharge rates of fine powders. Based on the calculation of the limiting flow rate, predictive correlations were developed based on permeability and bulk density.
The impact of flowability of a material on tableting was evaluated experimentally with a Piccola bilayer press. It was found that the standard deviations of tablet weight, compaction force and radial tensile strength can be described as a function of flowability. With increasing flowability, variation in all three metrics was significantly reduced. Thus, the characterization of powder flowability can be applied to understand how variation in the tableting process might be reduced.
 Johanson, J. R., â??Two-Phase Flow Effects in Solids Processing and Handling,â? Chemical Engineering, pp. 77â??86 (Jan. 1, 1979).