Characterization and Modification of Biomass Pyrolysis Chars for Environmental Applications
Smith, Matthew William
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Abstract: In this project the deconvolution of Raman, X-ray Photoelectron, and Nuclear Magnetic Resonance spectra of chars are examined. To support this work, spectra calculated for a wide variety of polyaromatic structures have been examined using density functional theory. Based on these results a new fitting and interpretation procedure for Raman spectra of chars has been proposed. This method identities out of plane deformation, 5 membered ring systems, 7+ membered ring systems and heteroatom inclusions, in addition to monitoring the cluster size of aromatic domains. A modified deconvolution procedure has also been proposed for XPS spectra. This method utilizes sequential deconvolution of the O 1s and C 1s spectra. In this method the C 1s deconvolution is constrained by the results of the O 1s spectrum, using the maximum and minimum bonds of for carbon-oxygen bonds based on theoretical groupings. A new quantitative 13C multiple cross-polarization NMR technique was successfully applied to pyrolysis chars. Coupled with a REDOR type dephasing series this method was used to estimate the cluster size and number of atoms at each distance in a series of cellulose chars. This method provided results consistent with far more time intensive direct polarization studies. The methods developed have been applied to three thermoseries of chars from primary biomass constituents; cellulose; hemicellulose (xylan); and lignin (milled wood lignin). The results of these studies, in combination with bulk chemical and morphological tests identified fundamental differences, and basic similarities, in the pyrolysis behavior of each compound. Each sample was found to move on a generally ordering trajectory with temperature until 600 oC when out of plane deformations became significant for each material between 600 and 700oC. Ring cluster size was found to increase slowly until 600 oC and then increased significantly. Finally the effects of ozone on two dissimilar chars, from Douglas fir wood and bark, were examined. These results show dramatically more intense reactions with bark char, though the content of acid groups increased for both materials. Our studies also identified a strong correlation between reactor temperature and lactone group formation.