Close the Carbon cycle

Carbon dioxide (CO₂) is in the lowest energy state of carbon because it is completely oxidized. To close the carbon cycle, it is essential to capture and reuse CO₂ through carbon capture and utilization. One promising method is the use of microwave plasma technology. This approach relies on electrical energy, offers rapid turn-on times, and is highly adaptable to fluctuating energy inputs. This makes it ideal for integration with intermittent renewable energy sources. Microwave plasma can split CO₂ into carbon monoxide (CO) and oxygen (O₂). When hydrogen (H₂) is added, the resulting gas mixture forms synthesis gas, which serves as a valuable starting material for renewable carbon-based chemistry.

Energy-efficient microwave plasma process

The Institute of Interfacial Process Engineering and Plasma Technology (IGVP) of the University of Stuttgart has developed an atmospheric microwave plasma torch [1] that converts CO₂ into CO using renewable electricity. The IGVP performed energy efficiency studies of the CO₂ plasma conversion [2]. Operating at a frequency of 2.45 GHz, the system is scaled up to a magnetron with a nominal power of 6 kW and can handle CO₂ flow rates of up to 74 standard liters per minute (slm) [3]. The influence of the flow rate at three different microwave powers is shown in graphic 1. The conversion graph (left) demonstrates the conversion rate decreases as the CO₂ flow rate increases, but improves with higher microwave power. In contrast, energy efficiency increases with higher flow rates. At elevated flow rates, the conversion rises linearly with microwave power, which keeps the energy efficiency constant. This operating point is particularly suitable for flexible power inputs from renewable sources and allows for maximum energy efficiency.