| Thermochemical conversion methods, like pyrolysis and gasification, applied to biomass yield a complex slate of light gases, condensable vapors and refractory aromatic tars. The goal of gasification is to maximize the conversion of biomass to syngas (CO and H2), while minimizing the aromatic tar (benzene, naphthalene, etc). Biomass has a complex structure of primarily three biopolymers: cellulose, hemicellulose, and lignin. Design of facilities for conversion of biomass to useful fuels and chemicals is impeded by a lack of fundamental knowledge concerning the detailed reactions and the kinetic parameters that govern the process. To address this problem I have approached it from two perspectives. First, a "bottom up" approach was performed by studying the detailed reaction mechanisms of molecules that model important chemical structures in lignin using a hyperthermal nozzle (up to 1350 °C, 30-100 mus) with detection by time-of-flight mass spectrometry and matrix-isolation infrared spectroscopy. The second, "top down", study was employed using a laminar entrained flow reactor (LEFR) to pyrolyze solid biomass samples over a range of temperatures (300-950 °C) and residence times (0.2-0.8 s) with detection by molecular beam mass spectrometry (MBMS). The first study showed conclusively the most important reaction pathways of the lignin model compounds, and how those pathways lead to tar precursor molecules. The biomass pyrolysis study revealed, in great molecular detail, the evolution of the troublesome tar. Combining the results from the two studies enabled a detailed reaction mechanism for biomass to be postulated. This will serve as the foundation for a reactor-independent biomass conversion mechanism that will, hopefully, aid in the design of facilities that produce clean syngas at a reduced cost. |
