Particle Shape Characterisation via Image Analysis: from Laboratory Studies to In-process Measurements Using an in Situ Particle Viewer System

Abstract

A recent evaluation of a new in situ particle viewer (ISPV) system for the examination of particle shape and its subsequent development during crystal growth is presented. Precharacterization studies using conventional and hot-stage microscopy reveal that the ISPV probe system together with a commercial image analysis software is capable of generating representative high-quality images which can be processed and analysed. ISPV studies of the batch crystallization of L-glutamic acid in a 20-L reactor are shown to be able to characterise effectively crystallization and polymorphic phase transformation processes, revealing potential applications in both small-and large-scale reactor systems. Some improvements to the probe, such as increasing the resolution and reducing the encrustation using thermal coating, are suggested.

Comparison of external bulk video imaging with focused beam reflectance measurement and ultra-violet visible spectroscopy for metastable zone identification in food and pharmaceutical crystallization processes

“…In comparison to in-situ video microscopy (Qu et al, 2006;Kempkes et al, 2008;Li et al, 2008), external on-line imaging (Calderon De Anda et al, 2005;Larsen et al, 2007) and flow-through cell based imaging techniques (Eggers et al, 2009) the BVI may not be suited to monitor particle size characteristics accurately as the image resolution is low and the depth of field is large. This latter aspect makes difficult the calibration of the number of pixels associated to a certain particle size (as the determined particle size is influenced by the distance from the imaging device), however the methodology provides a low-cost and robust metastable zone determination approach.…”

Measurement, modelling, and closed-loop control of crystal shape distribution: Literature review and future perspectives

“…However, for on-line monitoring, optimisation and control of shape and size distributions in a crystalliser, it is essential to accurately and efficiently obtain 3D crystal information of the whole crystal population and the associated properties. Of the many techniques [1,[41][42][43][44][45][46][47][48][49][50][51] for the imaging and reconstruction of 3D objects, optical imaging and image analysis techniques proved to be the most promising ones for 2D shape measurements [1,17,19,23,24,26,29,30,32,34,37,39,[52][53][54], and the techniques that are likely the most suitable ones for obtaining 3D crystal shape, hence growth rate of each crystal face, have made some advances in recent years [1, 45-50, 55, 56]. This is a very active research area with huge challenges and opportunities to innovatively develop process instrument and/or process probes and the associated image processing and shape reconstruction software for the real-time monitoring, optimisation and control of particulate processes.…”

“…Louhi-Kultanen and co-workers [31,32] studied batch cooling crystallisation of sulfathiazole using an ATR-FTIR spectroscopy and image analysis simultaneously. Kramer and coworkers also conducted research using a prototype imaging probe, ISPV, which was also used at Leeds for the examination of particle shape and its subsequent development during crystal growth [52]. Srinivasan and co-workers [34] applied the PVM imaging probe and developed statistical monitoring graphs using the information from image analysis including multivariate image analysis [33].…”

“…This system can provide flexible arrangement among camera, light and particles in order to obtain high quality images, however, it may take a long time to tune the optic arrangement for the best configuration because the camera must focus on a small volume of slurry near the inner wall with light guide pointing at the same volume with proper illumination intensity. In contrast, imaging probe [29,30,39,52,64] can overcome these disadvantages but the feature of flexible arrangement will lose and currently the system cannot be applied to small size reactors (say 0.1litre) due to the smallest size of the probe available. The probe may only be used for short periods due to the high temperature of slurry in reactors or continuously cooling of the probe is required.…”

Crystallisation Route Map

“…The comparisons of power number, discharge flow number, secondary circulation flow number and pumping efficiency at three different scales suggest that the scale up with the selected laboratory vessels has little effect on the macro mixing performance for optimisation of the configuration and operating conditions of an industrial scale reactor. Further details about the experimental and modelling investigations of process scale-up can be found in the literature, such as [28,32,[45][46][47][48][49].…”