CO2 dissociation from low to high pressure in plasma torch and surfaguide

The power to gas technology aims to store excess energy into gas by conversion of CO2 into chemical fuels to reduce the CO2 produced from the transportation sector. One step of the green-fuels production process consists in the dissociation of CO2 into CO. In this work the dissociation of CO2 into CO is investigated in a 2.45 GHz microwave plasma torch and a 2.45 GHz surfaguide. The two plasma sources are studied in the pressure range from 5-1000 mbar (surfaguide 5-60 mbar, plasma torch 60-1000 mbar). The gas temperature is found to increase from 1400 K to 3000 K with pressure in the range between 5-60 mbar and no significand differences are found between the two setups. The CO2 conversion is found to be comparable in the two setups when the same power, pressure and input flow are used. In the plasma torch, above circa 120 mbar, a sudden transition from a radially diffuse to a contracted plasma regime is reported. The latter is accompanied by a sharp increase of gas temperature from 3000 K to 6000 K in the plasma core. The CO2 dissociation is strongly influenced by the discharge parameters, exhibiting peak values in the 100-200 mbar range, and usually increase with power. The measured CO2 conversion and energy efficiency are compared to the conversion expected for a hot CO2 gas at thermal equilibrium.