27 Jun 2014

Can we improve the monitoring of product temperature by combining an infrared camera with a freeze dryer?

Infrared image of the primary drying step of cheese slurry, where unexpectedly large temperature
Infrared image of the primary drying step of cheese slurry, where unexpectedly large temperature differences are present. This kind of information can only be obtained using the new coupling described in this work.
© EU 2014

Freeze drying is widely employed in, e.g., the pharmaceutical and food industries as in the case of instant coffee. It is also a technique used at the JRC-IRMM to dry reference materials. This scientific article describes an innovative process analysis tool to monitor freeze-drying processes.

Freeze-drying is an excellent way of gently drying thermally sensitive materials and preserving thermally labile compounds. By combining an infrared (IR) camera (for temperature measurements) with a process-scale freeze dryer, it was possible to monitor several different modes of freeze-drying in real-time with superior thermal and spatial resolution in comparison to existing technologies. The published work is the first report of its kind, combining an IR-camera and a freeze dryer. The technique has significant potential for further developments both with respect to process monitoring and for providing a better understanding of freeze drying processes.

When used for reference material processing, the removal of water dramatically improves long term stability of biological materials. Currently a few temperature (Pt-100) probes are directly placed in the materials that are undergoing drying for monitoring of product temperature. This parameter is linked to the progress of drying and is therefore an important monitoring parameter together with shelf temperatures and pressure in the drying chamber. The shelves in the freeze-drying chamber are plates in which the cooling/heating medium is flowing. When materials are placed on these shelves cooling and heating takes place by changing the temperature of the cooling medium. The Pt-100 probes provide only a very limited spatial resolution since only 8 of such probes of approximately 2 mm diameter can be placed over six shelves with a 6.5 m2 shelf area. The new combination with the IR-camera makes contact-free monitoring of one full tray or 150 vials with 30000-measurement points possible. As a result a movie/video of the drying process from -40 °C to +25 °C was obtained with surprising findings which already suggest further experiments.

Read more in: H. Emteborg et al., Infrared thermography for monitoring of freeze-drying processes: instrumental developments and preliminary results, J. Pharm. Sci. (2014) 103:2088–97, doi:10.1002/jps.24017

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