Raman-Spectroscopy for Measuring Chemical Reactions in Micro Reactors

Micro heat exchangers, micro mixers and micro reactors have gained importance in chemical, pharmaceutical and life sciences applications. Due to the large surface to volume ratio these devices provide efficient mass and heat transfer. This results in greater selectivity and higher yield for chemical reactions. The Institute for Micro Process Engineering is working on the development, manufacturing, and testing of micro channel devices mainly manufactured of stainless steel, where channel widths and depths lie in the range of 0.2 mm. In order to obtain a better understanding of the physical and chemical processes within such components and to optimize these devices it is necessary to get a look into these micro channels during a mixing process or a chemical reaction. For this purpose laser Raman spectroscopy can be applied. This method is very selective for individual chemical compounds and allows a spatial resolution better than 0.01 mm. Figure 1 shows the experimental setup. The light of an air cooled cw argon ion laser is focused by a microscope objective into a micro channel, measuring the Raman bands over its cross section at several distances from the mixing point. A spectrograph with a CCD-array detects the Raman light, which consists of lines that are characteristic for the chemical compounds flowing through the micro channels and can therefore be used to calculate their concentrations.