Hydrogen Production via Partial Oxidation Reforming of Methane with Gliding Arc Discharge Plasma

Abstract

Hydrogen production from partial oxidation reforming of methane in a gliding arc discharge (GAD) reactor is investigated. The effects of input power, the oxygen-carbon molar ratio (O/C), and residence time are studied, respectively. Products such as H 2 , CO, CO 2 , and C 2-C 4 hydrocarbons can be detected in the outlet gas. The experimental result shows that the input power of 36.4 W, the relitively low O/C of 0.705 and the 13.8 s residence time in this system will bring the highest H 2 energy yield. Compared to the decomposition of methane, partial oxidation of methane with air can maintain a stable discharge state and no carbon deposition on electrodes is observed during the reaction process. Optical emission spectroscopy (OES) is also employed to characterize this methane-air plasma. Based on the results of the experiment and OES, a possible mechanism of methane partial oxidation process was proposed, which points out that collisions of high-energy electrons and excited N 2 species (mainly N 2 (A)) with other species (such as O 2 , CH 4) in the plasma region are two main ways for the activation of this reforming system. Hydrogen is generated principally through the H-abstraction reaction and the H-coupling reaction.

Plasma‐Assisted Reforming of Methane

“…Using air instead of pure O 2 increases the conversion of CH 4 andO 2 but reduces the selectivity to syngas (H 2 and CO). Wang et al [192] used a GAD reactor to generate H 2 via a PAPOM reaction. They determined that the collisions of highenergy electrons and excited N 2 species (mainly N 2 (A)) with other CH 4 and O 2 species in the plasma region are the two main pathways for activating this reforming system.…”

“…These active oxygen species can further collide and react with other active particles in the plasma bulk, namely CH x , CO, H, and OH radicals, to produce the corresponding oxidation products, such as CO, CO 2 , CH 3 OH, and H 2 O (as in Reactions R3.26–R3.31). [ 128,135,192,290,291 ] $$$$\begin{equation}e + {{\rm{O}}}_2 \to e + 2{\rm{O}}\end{equation}$$$$ $$$$\begin{equation}e + {{\rm{O}}}_2 \to 2e + {\rm{O}} + {{\rm{O}}}^ + \end{equation}$$$$ $$$$\begin{equation}{\rm{CH}}_4 + {\rm{O}} \to {\rm{CH}}_x + {\rm{OH}} + \left( {3 - x} \right){\rm{H}}\end{equation}$$$$ $$$$\begin{equation}{\rm{CH}}_x + {\rm{OH}} + \left( {3 - x} \right){\rm{H}} \to {\rm{CH}}_3{\rm{OH}}\end{equation}$$$$ $$$$\begin{equation}{\rm{CH}}_x + {\rm{O}} \to {\rm{CO}} + x{\rm{H}}\end{equation}$$$$ $$$$\begin{equation}{\rm{H}} + {\rm{H}} \to {{\rm{H}}}_2\end{equation}$$$$ $$$$\begin{equation}{\rm{CO}} + {\rm{O}} \to {\rm{CO}}_2\end{equation}$$$$…”

“…[ 154 ] Arcs in RGA reactors can be generated by applying a discharge to a pair of electrodes in the laminar or turbulent gas flow, and a complete discharge cycle consists of three main stages: breakdown, balanced arc, and unbalanced arc. [ 192 , 193 ] In 3D space, when the applied voltage reaches the critical value of gas breakdown, the arc is always generated from the closest distance to the electrode. The arc length is extended due to the arc sliding caused by the rotating gas flow.…”

“…These active oxygen species can further collide and react with other active particles in the plasma bulk, namely CH x , CO, H, and OH radicals, to produce the corresponding oxidation products, such as CO, CO 2 , CH 3 OH, and H 2 O (as in Reactions R3.26–R3.31). [ 128 , 135 , 192 , 290 , 291 ] …”

“…[ 77 , 296 ] The inelastic collision of electrons with O 2 molecules can directly affect the single (O + ), double (O+ 2), and triple (O+ 3) ionization channels that can directly affect the plasma cracking process. [ 128 , 192 , 293 ] In addition, electrons can impact the O 2 molecule and metastable oxygen molecule O 2 (a 1 Δ g ) to generate O+ 2, while O + is generated by the electron impact ionization of O( 3 P), O( 1 D), and O 2 pair creation. [ 297 ]…”