(42c) Effect of Milling Media on Kinetics of Stirred Media Milling Process - in-Line Monitoring of Particle Size and Population

Hubert, M., Bristol-Myers Squibb Company
Redman, T. P., METTLER TOLEDO AutoChem

Milling is an important unit operation in the field of processing technology. It plays a significant role in a wide range of industries including the pharmaceutical, cement, catalyst, chemical, mining and other industries. Various types of milling systems are used in R&D and manufacturing. Proper selection of the milling system is dependent on many factors including particles properties, bulk properties, operational conditions, environmental issues, experience and others.

This study concerns the widely used stirred media milling system. A batch stirred media mill of volume 0.5 L with recirculation loop was used in this study. The effects of milling media material, size and loading on the milled product have been investigated. All of these parameters are critically important in designing a robust process: the modulus of elasticity of the milling media is linked to breakage mechanism; the size and size distribution of the milling media influences the kinetics of the milling process as well as the span of size distribution of the milled product; and loading of the milling media also affects both the kinetics and the breakage mechanism.

In order to understand and control the milling process one has to rely either on theory or measurements or their combination. Unfortunately, the milling theory is not robust enough to allow quick and reliable prediction of particle dimensions of the milled product. So, the only way to reliably control the milling process is through measurements of the milled material. There are, however, many different techniques and approaches regarding measuring the milling process. Our goal is to measure the size distribution of the milled product, in-process and in real-time, without the need for sampling or dilution.

FBRM (Focused Beam Reflectance Measurement) was used for real-time measurement of particle dimensions in a real process environment. Milling was carried out in a stirred media mill. The FBRM probe was installed directly in a product recirculation loop and used to monitor kinetics of the milling process as well as to determine the process endpoint.


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