Solid-liquid suspension flow is often involved in the production of pharmaceuticals and fine chemicals. In these fields, working with continuous small-scale equipment in order to save costs and resources is of increasing interest. Therefore, it is also important to enable process control for small-scale apparatus, which requires the development of new concepts to observe and control crystallization processes in minichannel equipment. The particles and crystals should be detected and measured with as low impact as possible because contact between process medium and the sensors can often lead to the incrustation of the sensor, disturb the particle size and shape, or contaminate the system.
For the observation of crystallizing processes in minichannel crystallizers, a non-invasive, temperature-controlled flow-cell is designed in this work. In particular, this flow cell has been designed to examine crystals in a fluorinated ethylene propylene (FEP) tube with an inner diameter of 1.6 mm. Crystals can be investigated using a standard optical camera and microscope. An image processing routine enables the evaluation of crystal size. This is crucial for the assessment of the process and crystal size distribution, which is often a quality criterion in the crystallization process.
The contribution will show how the flow-cell for two-phase flow is constructed and the evaluation routine is implemented. Based on experimental data, the applicability of the equipment and the evaluation method are described.