Plasma-Based CH₄ Conversion into Higher Hydrocarbons and H₂: Modeling to Reveal the Reaction Mechanisms of Different Plasma Sources

Abstract

Plasma is gaining interest for CH 4 conversion into higher hydrocarbons and H 2 . However, the performance in terms of conversion and selectivity toward different hydrocarbons is different for different plasma types, and the underlying mechanisms are not yet fully understood. Therefore, we study here these mechanisms in different plasma sources, by means of a chemical kinetics model. The model is first validated by comparing the calculated conversions and hydrocarbon/H 2 selectivities with experimental results in these different plasma types and over a wide range of specific energy input (SEI) values. Our model predicts that vibrational− translational nonequilibrium is negligible in all CH 4 plasmas investigated, and instead, thermal conversion is important. Higher gas temperatures also lead to a more selective production of unsaturated hydrocarbons (mainly C 2 H 2 ) due to neutral dissociation of CH 4 and subsequent dehydrogenation processes, while three-body recombination reactions into saturated hydrocarbons (mainly C 2 H 6 , but also higher hydrocarbons) are dominant in low temperature plasmas.

On the transition of reaction pathway during microwave plasma gas‐phase synthesis of graphene nanosheets: From amorphous to highly crystalline structure

“…By increasing MW power, availability of C 2 n + 1 H x compounds is suppressed more than C 2 n H x . As published by Heijkers et al, [ 24 ] lower temperatures (and lower pressures) favour recombination processes, resulting in the formation of C 3 compounds. Higher temperatures (and higher pressures) induce dehydrogenation reactions, resulting in more unsaturated HCs, explaining the high C 2 H 2 , CO and H 2 selectivities and generation of solid carbon.…”

“…However, air‐containing atmospheres decrease plasma gas temperature, favouring decomposition routes with H 2 , H 2 O, CO and CO 2 as gaseous products. [ 23 ] Increase of MW power and neutral gas temperatures (above 3000 K) induced dehydrogenation reactions [ 24 ] of the produced hydrocarbons, resulting in the formation of more unsaturated hydrocarbons. C, C 2 , C 2 H and C 2 H 2 are then the only carbonaceous products, which are crucial for the formation of GNS.…”

Plasma polymerization of hexamethyldisiloxane: Revisited

“…[ 111,121 ] Furthermore, the concept of SEI has also been applied to different emerging gas conversion applications such as CO 2 splitting, methane conversion, and N 2 fixation. [ 122–124 ]…”

Modelling excited species and their role on kinetic pathways in the non-oxidative coupling of methane by dielectric barrier discharge

“…Plasma discharges can be operated under different conditions of temperature and pressure, at varying degree of deviation from thermal equilibrium. Some non-equilibrium plasmas, like gliding arcs, sparks, nanosecond pulsed discharges (Delikonstantis et al, 2020, Dors et al, 2014, Heijkers et al, 2020, Scapinello et al, 2019 or microwave discharges (Dors et al, 2014, Heijkers et al, 2020, operate at high gas temperature (>800K), while others, like corona (Yang, 2003a) or dielectric barrier discharges (DBD) (Nozaki and Okazaki, 2013, Saleem et al, 2019, Toth et al, 2018, Wang et al, 2013, Xu and Tu, 2013, operate at much lower gas temperature (generally below 500K).…”