(167f) Breakage of Needle Shaped Crystals under Compaction

Many chemical products, e.g. pharmaceutical substances have the form of crystals with a large aspect ratio (needle-shaped particles). During unit operations such as pressure filtration, mechanically agitated vacuum drying, or conveying, these particles often undergo uncontrolled changes in particle size distribution (PSD) due to fragmentation. In order to understand and eventually predict the effect of each unit operation on PSD, two types of information must be known: (i) the stress and shear conditions within the process equipment of interest, and (ii) breakage rate of particles of interest under well-defined stress and shear conditions.

The objective of the present work is to investigate the latter by means of computer simulations using the discrete element method (DEM). Elongated particles with a chosen aspect ratio have been created by linking individual spherical discrete elements by bonds with a large elongational stiffness and given values of bending stiffness and ultimate bending strength. A randomly packed layer of these particles has been formed and gradually compressed between two infinite parallel solid walls. The particle size distribution as function of the compaction ratio and the bending strength has been recorded.

A computational parametric study with respect to the initial particle size distribution, inter-particle friction, and ultimate bending strength of the particles has been performed and compared with experimental data for the breakage of alumina extrudates.