Project Motivation and Objectives

1. Spectroscopic Techniques for In-Situ Characterization of Biomass Pyrolysis Processes Samuel Burt, Chloe Dedic, Joseph Miller, and Terrence MeyerDepartment of Mechanical Engineering, Iowa Sate University Guaiacol Results and Discussion Materials Project Motivation and Objectives • Gain knowledge about the condensation of the vapors given off by biomass pyrolysis • Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy • Laser-Induced Fluorescence • Two Photon Fluorescence • Conclude whether improvements can be made to pyrolysis techniques • Lower cost of upgrading bio-oil • Lessen human contact with phenols • Ethanol/ Methanol CARS • Discernibility of ethanol and methanol OH peaks indicates that the same could be possible for various phenols • Ti:Sapphire Femtosecond Laser (Solstice, Spectra-Physics) • 100 fs pump, stokes pulses • Operates at 1 kHz, 2.5 µJ/pulse • Fundamental Frequency of 798 nm • Probe pulse tuned from 530-735 nm Methanol Phenol • Schematic based on the work of Teixeira, Mooney, Kruger, Williams, Suszynski, Schmidt, Schmidt, and Dauenhauer at Iowa State University, 2011 Ethanol • Nd:YAG (Spectra-Physics) • Excites at 266 nm • 10 mJ/pulse, 10 Hz • Intensified CCD Camera • Shows presence of fluorescence • Used in concert with 1.26 m spectrometer, which identifies wavelength of fluorescence • Guaiacol CARS • No vapor phase data available from phenols • Distinct guaiacol peaks in CH stretch region Results and Discussion • Ultraviolet/Visible Spectra Differences in wavelength to be used in identifying specific compounds in pyrolysis vapors Experimental Methods 266 nm • Coherent Anti-Stokes Raman Scattering (CARS) Spectroscopy • Four Wave Mixing Process • Energy difference between pump and stokes beams excites molecule to higher vibrational/rotational state • CARS signal = signature of specific compound • Ultraviolet/Visible Spectroscopy • Beer’s Law: I/Io = 10-abc • . Conclusions • Remarks • We acquired vapor-phase CARS results on methanol, ethanol, and acetone. We believe that we occasionally saw flashes of phenols in their trials, but our technique could not obtain a consistent enough flow of phenol vapor to obtain data. • We acquired condensed-phase CARS results on methanol, ethanol, acetone, and guaiacol. • We viewed 2-methoxy-4-vinylphenol with the intensified CCD camera via fluorescence. The next step in this process is to direct the fluorescence into a spectrometer so we can determine the wavelength. a = 1293 M-1cm-1 • Wavelengths of maximum absorption equal those of Laser-Induced Fluorescence/Two Photon Fluorescence • Laser-Induced Fluorescence • Excites a molecule to higher electronic state, which then fluoresces down at a specific wavelength • Viewed with spectrometer and/or high speed camera • Two-Photon Fluorescence • Uses ultrafast laser to view samples with high resolution Members of our lab are currently designing a high-temperature, heated flow cell to analyze CARS signal up to six inches above a sample. • Laser-Induced Fluorescence • Two-photon fluorescence from condensed phase guaiacol on the right shows high resolution of this technique compared with single photon on the left. Methanol, ethanol, and a few varieties of phenols were used as model compounds for this experiment. Phenols are crucial in the condensation of pyrolysis vapors, and methanol and ethanol have similar properties with phenols, while being easier to use in some cases. Intensified CCD camera shows 2-methoxy-4-vinylphenol fluorescing in a cloud above a cuvette. Energy-Level Diagram for vibrational CARS (VCARS)