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A compact Raman probe for rapid reaction monitoring in micro reactors

A compact Raman probe for rapid reaction monitoring in micro reactors. Sergey Mozharov 1 , Alison Nordon 1 , John Girkin 2 , and David Littlejohn 1. 1 WestCHEM/Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL ;

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A compact Raman probe for rapid reaction monitoring in micro reactors

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  1. A compact Raman probe for rapid reaction monitoring in micro reactors Sergey Mozharov1, Alison Nordon1, John Girkin2, and David Littlejohn1 1 WestCHEM/Department of Pure and Applied Chemistry and CPACT, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL; 2Department of Physics, University of Durham, South Road, Durham DH1 3LE E-mail: sergey.mozharov@strath.ac.uk 06 May 2009, APACT’09

  2. Outline • Process control in micro reactors • Why Raman spectroscopy? • Characteristics of our Raman setup • The probe’s performance on monitoring esterification reactions • Conclusions

  3. Process control in micro reactors products out reagents in 1. At-line analysis of the collected solution • Any analytical method can be used • Accurate and precise results • Slow data acquisition • Long response times • Not helpful in understanding the processes taking place in the micro channels

  4. Process Control in micro reactors 2. In-line analysis of the effluent solution with an integrated probe • Electrochemical methods • MIR absorption (ATR probe) • Refractometry • Limited control • Physical integration of the sensor is required products out reagents in

  5. Process Control in micro reactors 3. Non-invasive analysis at any point of the microchannel products out reagents in

  6. Raman scattering Distinct spectral features High spatial resolution Very convenient • Objectives of this research: • Design a compact Raman probe with: • high sensitivity • sufficient spatial resolution • Study its capabilities and performance for microfluidic process control at high data acquisition rates

  7. Microfluidic chip Excitation fibre Beamsplitter Aspheric lens Collection fibre Raman probe designed for micro channels

  8. Spatial resolution and glass interference

  9. Background features (toluene spectra) Green line – 150ummicro reactor channel Blue line – 1cm quartzAR-coated cuvette Background fromthe fibre Background frommicro reactor glass Full spectrum from the micro channel

  10. Flow rate 0.1+0.1 μl/min Mixing in micro reactors Flow rate 20+20 μl/min

  11. Inter-diffusion profiles. Viscosity effect

  12. Inter-diffusion profiles. Flow rate effect

  13. Esterification reaction monitoring Reagent 1 Products Reagent 2 Reagent 1 – acetic anhydride(Ac2O) with 3% vol. of H2SO4 Reagent 2 – ethanol (EtOH) or butanol (BuOH) EtOH + Ac2O = EtOAc + AcOH BuOH + Ac2O = BuOAc + AcOH

  14. Calibration graphs Reagent 1 Products Reagent 2 Channel № 33 1. Plot calibration graphs and evaluate their usefulness for predicting reaction conversions from Raman data. Calibration mixtures consist of EtOAc (or BuOAc) and Ac2O

  15. Typical derivative spectra Raman signal (derivatised) Raman shift, cm-1 Raman shift, cm-1

  16. Calibration graphs

  17. Varied flow rates Reagent 1 Products Reagent 2 Channel № 33 2. Take Raman spectra from a fixed point at varied flow rates (equimolar reagent ratio).

  18. Varied flow rates - BuOH 15 : 16 9 : 9.6 6 : 6.4 3 : 3.2 1.5 : 1.6

  19. 12 : 20 9 : 15 5.8 : 9.7 3 : 5 1.2 : 2 Varied flow rates - EtOH

  20. Varied probe position Reagent 1 Products Reagent 2 Channels: 9, 11, 13,… , 31, 33 3. Take Raman spectra from different points on the micro chip at a fixed flow regime (EtOH – 3:5 μl/min, BuOH – 3:3.2 μl/min)

  21. Calculated yield - EtOAc 9 11 13 15 17 19 21 23 25 27 29 31 33

  22. Calculated yield - BuOAc 9 11 13 15 17 19 21 23 25 27 29 31 33

  23. “Steady” Flow at 20:2 μl/min 15 : 16 9 : 9.6 6 : 6.4 3 : 3.2 1.5 : 1.6 Unsteady flow phenomena • Clearly non-random behaviour: • Anti-correlating fluctuationsof reagents’ and products’ peaks • Decreasing frequency with decreasing flow rate • Not observed with non-reacting liquids

  24. Conclusions • 1. An efficient low-cost Raman probe has been developed for monitoring microfluidic processes. • 2. It demonstrated good performance in: • diffusion profile control; • rapid composition and conversion monitoring; • revealing high frequency unsteady flow phenomena.

  25. Future work • Study flow instability, rheological and geometry factors • Study other reactions • Look for suitable data analysis techniques which take into account unwanted phenomena (peak shift and shape change, background fluctuation, fluorescence, thermal lensing) • Design a more compact dedicated system • Collaboration!

  26. Acknowledgements • Jenifer Mains (SIPBS) • Untzizu Elejalde, Paul Hynd & Lisa Muir (IoP) • Paul Dallin (Clairet Scientific) • Robert Stokes • Scottish Funding Council • University of Strathclyde • CPACT

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