Selecting oxygen source for partial oxidation of methane to methanol using microwave plasmas

Emission Spectroscopic Studies of Plasma-Induced NO Decomposition and Water Splitting

“…Plasma methods have been extensively used in materials processing and the abatement of air pollutants such as halogenated hydrocarbons, NO x , and SO x . − Other plasma research areas include ozone formation, ammonia synthesis, and activation of CH 4 , H 2 O, and CO 2 . − Many types of plasmas, such as radio frequency (rf), microwave (MW), direct current (dc), and alternating current (ac) plasmas, have been used for these purposes. Virtually any reaction may be initiated by plasmas; however, the applications of plasmas are often limited by such factors as low output due to operation at low pressures as in the case of rf/MW plasmas.…”

Tailoring Vibrational Excitation Pathways for High-Yield Oxidation of Methane to Methanol

“…These results indicate that rising methanol levels within the reactor shifts the reaction kinetics, causing methanol overoxidation to CO 2 to surpass methanol production (time/τ 99% conversion > 0.05, Figure C). In other words, previous studies that report high methanol selectivity and low conversion (generally with thermal catalysis − ) or low methanol selectivity and high conversion (generally with plasmas ,,− ) can be related based on the residence time of reactants and the energetics of reactant excitations in plasmas.…”

“…Comparison between nonequilibrium DMtM and steam methane reforming (SMR) + Fischer–Tropsch (FT) process. (A) Comparison of the process yields and energy efficiency (η, Materials and Methods, and eq ) for DMtM conversion. ,,− ,, Selective vibrational excitations and active methanol removal can break the selectivity–conversion limit and enable scalable process yields. To get a conservative estimate and generalize the definition for specific energy input (SEI) for all compositions used across the literature, the entire plasma-deposited energy is assumed to go toward reforming methane alone.…”

“…Moreover, the high pressure (>30 bar), temperature (∼1000 K), and carbon footprint (∼400 gCO 2,eq /kg MeOH ) of this process render it unsuitable for utilizing methane where it is emitted. Direct methane to methanol (DMtM) conversion in a single step shows promise in methane reformation by bypassing syngas production. − However, to date, DMtM conversion processes have encountered a fundamental limit (i.e., selectivity–conversion trade-off (Figure C)) that causes methanol selectivity to decrease as methane conversion increases. This is due to the high reactivity of methanol in an oxidizing environment which leads to its overoxidation into CO and CO 2 (Figure B).…”

“…Methanol, being more reactive than methane, gets overoxidized to undesired byproducts (including CO and CO 2 ) that result in a selectivity–conversion limit. (C) Both traditional thermal catalysis − and nonthermal plasmas ,,− have a selectivity–conversion limit in the DMtM process. As conversion increases, selectivity decreases, which constrains the maximum methanol yield.…”