For improving CO2 conversions for a low-temperature CO2 methanation process, a mechanism of using reverse water gas shift (RWGS) reaction as an intermediate step to generate the more reactive CO species for the methanation process was developed. The challenge was to achieve useful conversions of RWGS reaction (CO2 to CO by hydrogenation) at low temperatures (200-300 °C), which is not possible with conventional catalytic reactors. Achieving useful conversions (up to ~50%) is not possible at the desired temperature window of 200-300 °C with a conventional catalytic reactor due to equilibrium limitations of the endothermic RWGS reactor.
A plasma-assisted RWGS technology was developed that achieved up to 80% CO2 conversions at low operating temperatures (<300 °C). The conventional fixedbed catalysis is an equilibrium-limited process with conversions limited to <50%, and requires temperatures in excess of 500 °C. With the nonthermal plasma-assisted catalytic approach, high CO2 conversions were achieved compared to the conventional process at much lower temperatures.
The proposed RWGS process uses conventional RWGS catalysts such as BaZrO3 packed in a thin-channel plasma reactor. The plasma reactor system uses a quartz or stainless steel-based tubular reactor with a high potential central electrode, a ground electrode, quartz dielectric barrier, and a plasma power supply for creating dielectric barrier discharge (DBD) plasma. The plasma-assisted RWGS reactor fed with 1:1 CO2:H2 feed operates at 200-300 °C under a plasma power of 10-50 W, and generates CO2 conversions to CO up to 80%.
The RWGS reactor is heated to the desired temperature, and high voltage (up to 5 kV RMS) is applied between the high voltage and ground electrodes to generate DB plasma within the RWGS catalyst bed. Product gas is sent through a knockout system to separate liquid water product. The gas product is sampled and analyzed for CO content.
The addition of a plasma component is a novel feature added for RWGS catalysis. It provides an improved mechanism for low-temperature and non-equilibrium RWGS process that can achieve high conversions. CO2 utilization technologies for producing chemicals or products important to industry can use the RWGS reaction as an intermediate step to produce the reactive CO species.