Carbon dioxide valorisation with partial oxidation of methane in a water cooled DBD plasma

Abstract

The valorisation of carbon dioxide in chemical plasmas implies as a principal reaction step its energy efficient dissociation into carbon monoxide. For hydrogen production, the reaction carbon monoxide with water (WGS) may lead to the generation of green hydrogen and reusable carbon dioxide. Beyond hydrogen, most valorisation processes require the removal of O₂ to avoid its recombination with CO on any downstream hot catalytic surface. Moreover, if the oxygen scavenging is performed directly inside the plasma volume, it can also shift the dissociation equilibrium that is responsible for the well-known trade-off between energy efficiency and conversion, thus improving efficiency when larger specific energy densities are applied. In this paper we first report on the plasma dissociation of pure CO₂ in a water cooled, high power(<2 kW), Dielectric Barrier Discharge with high gas flow regime (<3600sccm), and then we explore the synergistic oxygen removal by the partial oxidation of methane for syngas production. The presence of CH₄, even in small amounts, removes oxygen from the outstream and from the discharge region, as confirmed by mass and optical emission spectroscopies, and enhances the process in two ways: it allows to feed the system with gas having a low CH₄ to CO₂ ratio (0.1–0.3) instead of pure CO₂, where landfill and waste gases are undesired climate altering emissions with a similar composition that currently require flaring; it will allow to use directly the reactor outstream into a WGS reactor, or any other CO valorisation process without the necessity to remove downstream O₂.