Abstract
Milling is an important step in pharmaceutical manufacturing as it not only determines the final formulation of the drug product, but also influences the bioavailability and dissolution rate of the active pharmaceutical ingredient (API). In this respect, the air jet mill (AJM) is most commonly used in the pharmaceutical industry as it is a non-contaminating and non-degrading self-classifying process capable of delivering narrow particle size distributions (PSD). Keeping the principles of Quality by Design in mind, the Critical Process Parameters (CPPs) of the AJM have been identified to be the pressures at the grinding nozzles, and the feed rate which affect the PSD, surface charge and the morphology of the product (i.e. the Critical Material Attributes (CMAs)). For the purpose of this research, the PSD is considered to be the only relevant CMA. A population balance based model is proposed to simulate the dynamics milling operation by utilizing the concept of breakage functions. This model agrees qualitatively with experimental observations of the air jet mill unit present at Janssen Pharmaceutica but further steps for model validation need to be carried out.
Highlights
The air jet mill (AJM) is one of the most common equipments used to micronize active pharmaceutical ingredients (API) in the pharmaceutical industry
Relatively few studies can be found in the literature which deal with modelling or control of the air jet mills, especially for organic compounds
Some other studies have been aimed at modelling the air jet mill using Markovian theory [4], or steady state population balance model [5], these are not directed towards control
Summary
Where, mi is the mass of the particles in size class i within the milling chamber. The total mass holdup inside the chamber is given by . Fin,i is the particle size distribution of the feed (% in size class i), is the solid feed rate to the mill, is the total production rate of the mill, and fout,i is the particle size distribution of the output. The solid feed rate and the particle size distribution of the feed are known, while the output particle size distribution is measured. The hold-up inside the mill and the product output rate, cannot be measured directly leading to identifiability issues as will be discussed later
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