(264c) Modeling the Breakage of Crystalline Materials in Air Jet Mills

Air jet mills are important tools in the size reduction processing of pharmaceutical powders. The benefits of the air jet mill to the pharmaceutical industry are its sanitary design (no moving parts or media) and ability to produce narrow particle size distributions (PSDs). Due to the high-value nature of active pharmaceutical ingredients (APIs), a trial-and-error approach to obtain optimal milling conditions would not be cost-effective.

A novel PBE (population balance equation)-aided approach was proposed for modeling the continuous milling of a spiral jet mill. It involves: (a) use of inexpensive, readily available excipient powders to predict mill-related model parameters; and (b) use of micro-identation or micro-milling to measure the material-dependent properties of the high value APIs (with only small quantities being consumed). The model requires PSD of the feed and mill operating conditions (grinding pressure, feed pressure, and feed rate) to predict the product PSD of brittle crystalline materials. The advantage of this approach is that it can be utilized to describe many self-classifying mills. In order to obtain optimal milling conditions for a new mill, mill-dependent model parameters can be obtained from inexpensive excipient powders. Quick material characterization experiments can be made with limited powder consumption on expensive powders to determine powder-dependent mill parameters.