Raman Spectra of Formic Acid Gasification Products in Subcritical and Supercritical Water
Formic acid gasification was carried out in a continuous supercritical water reactor at temperatures from 300°C to 430°C, residence times between 4 s and 65 s, a constant pressure of 25 MPa, and a constant initial formic acid concentration of 3.6 wt%. Raman spectra of the reaction products in the reactor effluent stream were collected for each experimental condition. The intent is to use this Raman data to characterize reaction pathways and reaction rates of formic acid decomposition in subcritical and supercritical water. To do this, each Raman spectra can be used to calculate the molar concentration of each reaction product, which in this case includes hydrogen, carbon monoxide, carbon dioxide, and residual formic acid. All spectra were collected at 25 MPa and 20°C. Spectra were collected using a Raman flowcell from MarqMetrix (Seattle, WA) which includes a high-resolution fiber-optic Raman laser, and an optical cell with a sapphire ball lens, which allows for focusing the Raman laser into the effluent stream and collecting Raman spectra along the same axis in the backscatter configuration. The Raman laser used has an excitation wavelength of 785 nm, and was operated at 300 mW. For each experimental condition, five spectra were collected and averaged, with each spectra using a 20 s integration time. This was to minimize measurement noise. The "dark" signal was subtracted automatically with the MarqMetrix data collection software, and the fluorescent background signal was subtracted using a semi-manual MATLAB routine, which is included with this dataset. Spectra were normalized to the height of the prominent sapphire peak, to correct for any optical effects.