Non invasive process probe for inline Raman monitoring through optical inspection glasses

Raman spectroscopy features some significant advantages against existing spectroscopic techniques. Amongst them are higher chemical sensitivities compared to NIR and a relatively low detection range for water molecules, in contrast to MIR spectroscopy. In process installations, compared to all spectroscopic techniques Raman plays only a minor role. Main challenges for process integration are long-term stability of the available measurement systems, high installation costs of so-called immersion probes and the addition of measurement points to existing plant layouts in piping and vessels. After the implementation of probes, a technical clearance that consists of an acceptance and pressure test has to be carried out by external certification authorities. A practical alternative is demonstrated by a robust probe concept, which enables beam propagation through large aperture optics. Therefore, focal lengths exceeding 25 mm allow real-time measurement of samples from the outside of piping filled with analytes through optical windows in production plants. The potential of this new measurement option is tested exemplarily by the detection of ethanol through optical windows of various thicknesses. A quantitative real-time monitoring of a mixture of propylene carbonate in water through an inspection glass PN 16 was tested in a pilot plant scale. The presented Raman probe has a high potential for the use in industrial plants, as it allows a simple, cost-efficient and contact-free adaption to existing measurement points in process analytic technology and features a long service life.