Work package 5.2 - Locally resolved in-situ measurement of concentrations for isobutane oxidation using laser Raman spectroscopy
Principal Investigator: Dr. G. Rinke (KIT)
Main Scientific Goals:
By developing new experimental techniques, important contributions to an improved understanding of the interaction between hydrodynamics and chemical reactions in two-phase flows can be achieved. Laser Raman spectroscopy is used to determine the local substance concentrations at several measurement points within a Taylor. A special pulsed Nd:YAG laser is used as excitation source and Raman spectra can be measured with only one single short laser pulse (10 µs), even within a microchannel.
- Development of a Raman system with a pulsed laser
- Development of a microreactor for optical in-situ measurements for high temperature and high pressure
- In-situ monitoring of the oxidation of isobutane in microreactors
For two-phase measurements during the oxidation of isobutane, a complete Raman spectrum has to be recorded in a very short time, because the air bubbles can move fast. Therefore, a laser with short pulses is necessary. Thus, even chemical reactions with complex Raman spectra can be evaluated. However, the pulse energy has to be as high as possible to get a good signal to noise ratio and a low limit of detection. As excitation source we use a special pulsed Nd:YAG laser at 532 nm with a pulse length of 10 µm. The laser pulses are focused with a microscope objective through a 2 mm thick quartz window into a microchannel with a silicon base plate. This microreactor with optical access (fig. 1) can be used up to 80 bars and 250 °C. Fig. 2 shows the optical setup.
As first measurements with this pulsed-laser Raman system the Taylor flow of cyclohexane and air was measured within a microreactor. Fig. 3 shows the Raman spectrum of the liquid phase (cyclohexane) within this microchannel. It was measured with only one laser pulse.
Further work will examine the isobutane oxidation (typically at 50 bars and 135 °C) and monitoring isobutane and its reactions products.
Fig. 1: Microreactor for optical in-situ measurements
Fig. 2: Optical setup of the Raman system with pulsed laser
Fig. 3: Raman spectrum of cyclohexane in a Taylor flow with one laser pulse
Cooperations: WP 2.5 (HZDR)
- G. Rinke, R. Dittmeyer. In-situ measurement of concentrations for two-phase reactions using laser Raman spectroscopy, 2nd International Symposium on Multiscale Multiphase Process Engineering (MMPE), 24. - 27. 9. 2014, Hamburg
- C. Fräulin, G. Rinke, R. Dittmeyer. Characterization of a new system for space-resolved simultaneous in situ measurements of hydrocarbons and dissolved oxygen in microchannels, Microfluidics and Nanofluidics 16(1-2), 149-157 (2014)
- C. Fräulin, G. Rinke, R. Dittmeyer. In-situ Laser Raman Spectroscopy Adapted to Process Conditions for Studying Cyclohexane Oxidation, Journal of Flow Chemistry 3(3), 87-91 (2013)
Dr. G. Rinke
Karlsruher Institut für Technologie (KIT),
Institut für Mikroverfahrenstechnik
Tel.: (0721) 608 – 23556