Sensors for the chemical industry

Measuring systems based on attenuated total reflection (ATR) in the near- (NIR) and mid-(MIR) infrared are used in many laboratory analytical systems to determine the chemical composition of liquid samples. Since the interaction of the sample with the optical radiation happens very close to the surface of the ATR crystal (in the range of a few micrometers), surface contamination must be avoided. In the lab, this is usually not a problem, because the planar ATR crystals are easily cleaned manually before they come into contact with the sample and measurements are typically performed quickly.

Hollow cylinder geometry allows automated in-process cleaning

In industrial processes, cleaning has to be automated and easyly integrated into the process workflow. This results in entirely new requirements for the design of ATR sensors. Besides a high pressure and temperature stability of the ATR measuring system in processes, the crystal surface of the ATR must be designed to be easily accessible in cleaning processes. Edges or cavities, which are difficult to clean, should therefore be avoided. Here, cylinder-shaped main bodies are advantageous because they do not contain inaccessible corners and can be retracted into separate cleaning chambers, e.g. via O-ring seals.

© Fraunhofer IPM
Robust ATR spectrometers for use in industrial environments: To ensure easy cleaning of the ATR crystals, Fraunhofer IPM relies on a hollow cylinder geometry for the construction of ATR spectrometers. Clean crystal surfaces are necessary to ensure an undisturbed mass transfer on the surface of the ATR element.

A process-compatible ATR sensor for isocyanate production

In the publicly funded, industry-led joint project »ZYRAT«, Fraunhofer IPM is developing a novel, particularly robust ATR process sensor with an ATR element of hollow cylindrical shape. Regardless of the practical advantages in terms of cleaning a cylindrical process sensor, the typical performance parameters of an ATR sensor (sensitivity, selectivity and stability) should remain unaffected. The goal is a process sensor for industrial plant and process monitoring during the production of isocyanates in the chemical industry. The functional model of such a sensor was successfully tested with substitutes in a laboratory environment. Application tests with isocyanates are planned for the next months.

Part of this work was funded within the framework of the BMBF call for tenders »Digital Optics« in the joint project »ZYRAT« (13N14188).