Plasma-Assisted Chemical-Looping Combustion: Low-Temperature Methane and Ethylene Oxidation with Nickel Oxide

Abstract

The chemical reaction network of low-temperature plasma-assisted oxidation of methane (CH4) and ethylene (C2H4) with nickel oxide (NiO) was investigated in a heated plasma reactor through time-dependent species measurements by electron–ionization molecular beam mass spectrometry (EI-MBMS). Methane (ethylene) oxidation by NiO was explored in temperature ranges from 300–700 °C (300–500 °C) and 300–800 °C (300–600 °C) for the plasma and nonplasma conditions. Significant enhancement of methane oxidation was observed with plasma between 400 and 500 °C, where no oxidation was observed under nonplasma conditions. For the oxidation of methane at higher temperatures, three different oxidation stages were observed: (I) a period of complete oxidation, (II) a period of incomplete CO oxidation, and (III) a period of carbon buildup. For the C2H4 experiments, and unlike the CH4 experiments, the plasma resulted in a significant amount of new intermediate oxygenated species, such as CH2O, CH3OH, C2H4O, and C2H6O. Carbon deposits were observed under both methane and ethylene conditions and verified by X-ray photoelectron spectroscopy (XPS). ReaxFF (reactive force field) simulations were performed for the oxidation of CH4 and C2H4 in a nonplasma environment. The simulated intermediates and products largely agree with the species measured in the experiments, though the predicted intermediate oxygenated species such as CH2O and C2H6O were not observed in experiments under nonplasma conditions. A reaction pathway analysis for CH4 and C2H4 reacting with NiO was created based on the observed species from the MBMS spectra along with ReaxFF simulations.

Combustion in a Sustainable World: From Molecules to Processes

“…As a model compound, guaiacol was studied in the presence of ammonia over HZSM-5 catalyst by online photoionization mass spectrometry to detect intermediates and products and to derive a mechanism for the process; the experiments were complemented by density functional theory calculations . The low-temperature oxidation of methane and ethylene with nickel oxide was studied by Burger et al in a plasma-assisted chemical looping combustion process . They analyzed the reactive atmosphere by electron ionization molecular-beam mass spectrometry to obtain time-resolved species profiles .…”

“…The plasma was found to significantly improve the oxidation, and additional species were observed during ethylene oxidation with plasma activation . While ReaxFF simulations provided support for the development of a plausible oxidation model under nonplasma conditions, detailed mechanisms for the plasma-assisted process remain to be developed . Raj et al investigated the Claus process, which is used to recover sulfur from H 2 S-rich gases in natural gas processing plants .…”

“…45 The low-temperature oxidation of methane and ethylene with nickel oxide was studied by Burger et al in a plasma-assisted chemical looping combustion process. 46 They analyzed the reactive atmosphere by electron ionization molecular-beam mass spectrometry to obtain time-resolved species profiles. 46 The plasma was found to significantly improve the oxidation, and additional species were observed during ethylene oxidation with plasma activation.…”

“…46 They analyzed the reactive atmosphere by electron ionization molecular-beam mass spectrometry to obtain time-resolved species profiles. 46 The plasma was found to significantly improve the oxidation, and additional species were observed during ethylene oxidation with plasma activation. 46 While ReaxFF simulations provided support for the development of a plausible oxidation model under nonplasma conditions, detailed mechanisms for the plasma-assisted process remain to be developed.…”

“…46 While ReaxFF simulations provided support for the development of a plausible oxidation model under nonplasma conditions, detailed mechanisms for the plasma-assisted process remain to be developed. 46 Raj et al investigated the Claus process, which is used to recover sulfur from H 2 S-rich gases in natural gas processing plants. 47 Catalyst poisoning by aromatic contaminants must be avoided, and therefore small aromatics such as benzene, toluene, xylene, and others should be oxidized in the Claus furnace upstream of the catalyst.…”