Process Analysis and Spectroscopy Group
Head: Prof. Dr.-Ing. Johannes Kiefer

The accurate determination of thermodynamic parameters and physicochemical properties in a process forms the basis for sustainable design and efficient operation of an overall system. The Process Analysis and Spectroscopy Group develops experimental techniques for measuring the parameters of interest in order to enable the fundamental characterization of a given process or system. The ultimate aim is to understand the phenomena at the molecular scale and to unravel their relationships with the macroscopic behavior of a material or process. For this purpose, optical and spectroscopic methods are developed utilizing the interactions of light and matter. Such methods facilitate non-contact measurements with high spatial and temporal resolution. The parameters of interest include the temperature and the chemical composition. Moreover, our methods allow a detailed analysis of the molecular structure and molecular interactions, and hence a comprehensive characterization of a process or material. We develop methods for and apply them to any kind of system in the areas of process engineering, chemistry and the life sciences. The following list of projects gives an overview of our activities.

Monitoring of Process Fluids

• Monitoring the electro-chemical oxidation of methanol in a direct alcohol fuel cell
  • Online measurement of fuel concentration
  • Determination of Faradaic efficiency
  • Investigation of fuel loss phenomena
• Monitoring of a distillation column
  • Measurement of product quality / chemical composition
  • Comparison of variable operation strategies

[1] F.M. Zehentbauer, E.J. Bain, J. Kiefer, "Multiple parameter monitoring in a direct methanol fuel cell", Measurement Science and Technology 23, 045602, 6 pp (2012).

[2] H.C. Struthers, F.M. Zehentbauer, E. Ono-Sorhue, J. Kiefer, "Chemical composition monitoring in a batch distillation process using Raman spectroscopy", Industrial & Engineering Chemistry Research 50, 12824-12830 (2011).

Fig: Schematic experimental setup for fuel cell monitoring

Characterization of Membrane

• Determination of porosity maps
  • Bulk porosity across the thickness of membrane
  • Surface porosity in a thin layer
• Investigation of molecular adsorption mechanisms at membrane surface

[3] J. Kiefer, N.H. Rasul, P.K. Gosh, E. von Lieres, "Surface and bulk porosity mapping of polymer membranes using infrared spectroscopy", Journal of Membrane Science 452, 152-156 (2014).

Fig: Surface porosity distribution of a polymer membrane

Food, Pharmaceutical and Biochemical Systems

• Investigation of emulsions
  • Determination of the chemical composition
  • Investigation of molecular stabilization mechanisms
• Development of Raman spectroscopy methods with reduced / suppressed fluorescence interference
  • Shifted-Excitation Raman Difference Spectroscopy (SERDS)
  • Polarization approaches
• Development of analytical methods for chiral molecules and optically active samples

[4] J. Kiefer, K. Noack, A. Leipertz, "Background suppression for Raman analysis of pharmaceutically active compounds in fluorescing media", American Pharmaceutical Review 16, 32-35 (2013).

[5] J. Kiefer, M. Kaspereit, "Determination of the Raman depolarization ratio in optically active samples", Analytical Methods 5, 797-800 (2013).

Fig: Shifted-Excitation Raman Difference Spectroscopy (SERDS) using a broadband light source

Molecular Interactions in Ionic Liquids and Organic Solvents

• Investigation of molecular interactions such as hydrogen bonds
  • Between ions in an ionic liquid (IL)
  • Between organic solvents and ILs
  • Between different organic solvents
• Investigation of structure-property relationships *Prediction of macroscopic properties from chemical structure

[6] M. Namboodiri, M.M. Kazemi, T.Z. Khan, A. Materny, J. Kiefer, "Ultrafast vibrational dynamics and energy transfer in imidazolium ionic liquids", Journal of the American Chemical Society 136, 6136-6141 (2014).

[7] K. Noack, A. Leipertz, J. Kiefer, "Molecular interactions and macroscopic effects in binary mixtures of an imidazolium ionic liquid with water, methanol, and ethanol", Journal of Molecular Structure 1018, 45-53 (2012).

Fig: Molecular configuration in a binary mixture of an IL and acetone

Combustion Systems

• Development of non-contact methods for flames
  • Laser-induced Fluorescence (LIF) for visualization of combustion intermediate species, e.g. CH and HCO radicals
  • Laser-induced Breakdown Spectroscopy (LIBS) for determination of the local fuel-air ratio and the temperature
• Methods for characterizing fuel blends and automotive mixture formation processes
  • Determination of the chemical composition of multi-component fuels
  • Investigation of fuel evaporation

[8] S. Corsetti, F.M. Zehentbauer, D. McGloin, J. Kiefer, "Characterization of gasoline/ethanol blends by infrared and excess infrared spectroscopy", Fuel 141, 136-142 (2015).

[9] B. Zhou, J. Kiefer, J. Zetterberg, Z.S. Li, M. Aldèn, "Strategy for PLIF single-shot HCO imaging in turbulent hydrocarbon flames", Combustion and Flame 161, 1566-1574 (2014).

Light emitting diodes (LEDs) for spectroscopy

• Development of low-cost sensors
  • LEDs as alternative light sources and surrogates for lasers
• Exploitation of the spectral properties of commercial LEDs
  • LEDs as tunable light sources
  • LEDs as multi-color light sources

[10] M.A. Schmidt, J. Kiefer, "Polarization-resolved high-resolution Raman spectroscopy with a light-emitting diode", Journal of Raman Spectroscopy 44, 1625-1627 (2013).

[11] R. Adami, J. Kiefer, "Light-emitting diode based shifted-excitation Raman difference spectroscopy (LED-SERDS)", Analyst 138, 6258-6261 (2013).

[12] J. Kiefer, "Instantaneous shifted-excitation Raman difference spectroscopy (iSERDS)", Journal of Raman Spectroscopy 45, 980-983 (2014).

Fig: Comparison of Raman spectra recorded with an LED and laser