Monitoring crystal breakage in wet milling processes using inline imaging and chord length distribution measurements

TL;DR

This paper investigates inline imaging and chord length distribution measurements to monitor crystal breakage during wet milling, aiming to improve control of particle size and shape in crystallisation processes.

Contribution

It evaluates the strengths and limitations of existing tools for estimating particle size and shape, demonstrating their complementary use in process monitoring.

Findings

CLD tool outperforms imaging in certain conditions

Imaging provides detailed shape information

Combined tools enable better process control

Abstract

The success of the various secondary operations involved in the production of particulate products depends on the production of particles with a desired size and shape from a previous primary operation such as crystallisation. This is because these properties of size and shape affect the behaviour of the particles in the secondary processes. The size and the shape of the particles are very sensitive to the conditions of the crystallisation processes, and so control of these processes is essential. This control requires the development of software tools that can effectively and efficiently process the sensor data captured in situ. However, these tools have various strengths and limitations depending on the process conditions and the nature of the particles. In this work, we employ wet milling of crystalline particles as a case study of a process which produces effects typical to crystallisation processes. We study some of the strengths and limitations of our previously introduced tools for estimating the particle size distribution (PSD) and the aspect ratio from chord length distribution (CLD) and imaging data. We find situations where the CLD tool works better than the imaging tool and vice versa. However, in general both tools complement each other, and can therefore be employed in a suitable multi-objective optimisation approach to estimate PSD and aspect ratio.