A Diode Laser and Modeling Study of Mixed (CH₄−H₂−O₂) AC Plasmas

Abstract

Infrared diode laser spectroscopy has been used as a diagnostic probe to measure the concentrations of the methyl radical and stable products in an ac methane/hydrogen/oxygen (CH4−H2−O2) plasma. Among the products detected were all of the stable C-2 hydrocarbons and oxygen-containing species including methanol, formaldehyde, formic acid, carbon monoxide, and carbon dioxide. A simple one-dimensional chemical modeling program has been written to calculate and compare the model concentrations of all the detected species with their observed concentrations. Good agreement between these values has been obtained which enables some insights to be gained into the gas-phase mechanism in mixed methane plasmas.

Partial oxidation of methane to synthesis gas by a microwave plasma torch

“…To add oxygen will yield OH radical and favor the CO ϩ OH 3 CO 2 ϩ H reaction, to lead to the reduction of S CO . 13 Figure 6 shows that the molar fraction of CO 2 apparently increased from 0.045 to 1.71% at 13.3 kPa, and increased only from 0.016 to 0.754% at 93.3 kPa, by increasing the O 2 /CH 4 ratio from 0.3 to 1.5 at 600 W.…”

“…13,14 In addition, at a lower O 2 /CH 4 ratio, a much greater S H2 was found at 600 W than that at 160 W, whereas at a higher O 2 /CH 4 ratio, the S H2 was slight higher at 600 W than that at 160 W. By elevating the O 2 /CH 4 ratio from 0.5 to 1.5 at 600 W, experimental results showed that S H2 decreased significantly from 89.7 to 28.4% at 13.3 kPa, as well as decreasing from 97.6 to 29.4% at 93.3 kPa (Figure 2a). The large amounts of H 2 O, yielded at a higher O 2 /CH 4 ratio, led to a reduction of H 2 selectivity.…”

“…The selectivity of CO is also strongly dependent on the oxygen supply because CO is primarily formed by the following sequential reactions 13 (Figure 2b). The results indicated this discharge approach might be adapted to operate at near atmospheric pressure not only to favor the syngas formation but also to save the consumption of pumping power.…”

“…An abundance of free radicals is produced by the electron impaction-dissociation of CH 4 13,24 Although the stoichiometric ratio of O 2 /CH 4 equaled 0.5 (0.5O 2 ϩ CH 4 3 CO ϩ 2H 2 ) for producing syngas, the product compositions showed that at O 2 /CH 4 ratio Ͻ 1, syngas was the major product, and at O 2 /CH 4 ϭ 1, H 2 O and CO were the major compounds and H 2 and CO 2 were the minor products. At O 2 /CH 4 ratio Ͼ 1.5, CO 2 and H 2 O were the main products because of their high thermodynamic stability in an oxygen-rich environment.…”

Reaction Mechanism of Ethylene Oxide at Various Oxygen/Ethylene Oxide Ratios in an RF Cold Plasma Environment

“…By applying the calculation process described in the previous section, we get the total dissociation rate constant. Then, the rate ratio of three following CH 4 dissociation reactions suggested by Fan et al (1999) …”