R. Vander Wal, A. Sengupta, E. Musselman, K. Zeller, G. Skoptsov
Penn State University,
Keywords: nanographene, plasma, characterization, methane, hydrogen, fossil, spectroscopy microwave
Summary:1. Optical Diagnostics for Advanced CTL and and GTL Processes H Quest Vanguard is developing broad-spectrum microwave plasma processes targeting conversion of hydrocarbon feedstocks such as coal and natural gas to value-added materials, chemicals and fuels. Optical diagnostics are central to reaction characterization and hold particular value for species identification and temperature determination. Observed intensity ratios or spectra band shapes can yield temperature by Boltzman analysis using spectral constants. Moreover, optical emission serves to identify reactive species and intermediates, albeit indirectly inferred by the observation of their electronically excited counterparts, e.g. CH* radicals and the atomic hydrogen Balmer lines at 656.2 nm and 486.1 nm. For example, the presence of key atomic or diatomic radicals can support postulates of electron impact dissociation, and radical mediated bond insertion or radical capping reactions and provide mechanistic insights from the temperatures associated with the different degrees of freedom – electronic, vibrational, such as from the C2* Swan band emission. 2. Material Characterization for CH4 to H2 Microwave (MW) activated natural gas decomposition for H2 generation produces no CO2 and requires zero process water, in contrast to the present industrial process – steam reforming. Notably it opens a path for renewable energy storage by coupling electrical energy into chemical bond energy – with H2 being particularly versatile as fuel or chemical precursor. Moreover MW activated natural gas decomposition does not require a carbon as catalyst but rather produces carbon. Therein MW driven decomposition of methane achieves green hydrogen production and production of value-added carbon materials. Initial assessment of these carbon materials requires characterization by microscopic and spectroscopic techniques. Illustrative examples of carbon products by high-resolution transmission electron microscopy (HRTEM), Raman and X-ray diffraction will be shown. Complementary thermo-gravimetric analyses assess the oxidative reactivity of the carbon products. Optical diagnostics such as multi-wavelength pyrometry relate these material characteristics to reactor conditions and can be applied for process control. 3. Chemical Analyses Microwave (MW) processing of carbon feedstocks for aromatic compounds and tars from biochars and coals does not produce CO2 and requires zero process water, in contrast to the traditional process – via coke ovens. Aromatics and tars are valued chemicals and feedstocks for advanced composites – sought for light weighting transportation vehicles and accompanying energy savings. The MW process produces fast heating resulting in flash devolatilization and pyrolysis followed by fast quenching, preserving the primary pyrolysis products and volatiles’ molecular structure. Within the MW generated Ar plasma the entrained carbon undergoes rapid pyrolysis. Multi-wavelength pyrometry of the carbon in the MW reaction zone yields a temperature of ~ 1200 K. Gas-chromatography mass spectrometry analyses of the process with coal as the hydrocarbon feedstock indicate stabilization of the aromatic pyrolysis products due to immediate quenching under inert atmosphere with hydrogenation or methylation in reactive atmospheres containing H2 or CH4 respectively. Optical emission spectroscopy identifies atomic and radical species participating in these reactions.