CO₂ is the most abundant greenhouse gas, and its global emissions have been steadily increasing. Some industries, however, are difficult to electrify because CO₂ emissions are intrinsic to the process. In such cases, CO₂ can be selectively captured from flue gases or air.
K₂CO₃ has interesting properties that match some of these requirements. CO₂ and H₂O co-adsorb onto K₂CO₃ forming KHCO₃. K₂CO₃ is an abundant material that makes it cheap. Limitations of using K₂CO₃ as a CO₂ sorbent are high regeneration energies and slow adsorption and desorption kinetics. In a conventional CCU process, KHCO₃ is heated to 120-200°C to regenerate the sorbent. However, an alternative approach for the desorption step using plasma can be implemented. Because a plasma can simultaneously desorb and chemically activate CO₂, both processes can be carried out in the same unit operation via integrated carbon capture and utilization.
In this study, researchers investigated plasma-assisted decomposition of KHCO₃ in a dielectric barrier discharge reactor. In the XRD patterns of the spent sample, peaks that are assigned to K₂CO₃ can be observed. In the FTIR spectra of the gaseous products, only peaks for CO₂, CO, and H₂O are observed. Additionally, H₂ and O₂ were detected by the GC. The carbon balance was 99.8% ± 0.1%.
When a coolant flow at 10°C is applied, no significant decomposition of KHCO₃ occurs. Without a coolant flow, 95% of KHCO₃ has been decomposed within one hour. This suggests that the thermal effect induced by plasma heating is the dominating mechanism for KHCO₃ decomposition. COₓ production occurs only if a reactor surface temperature above 110°C has been reached, where thermal decomposition of KHCO₃ can occur.
At higher plasma power, the time required for complete KHCO₃ conversion decreases. Doubling the power from 21 to 42 W reduced the desorption time from 72 to 33 min, while energy consumption remained nearly constant at approximately 125 GJ·t⁻¹ COₓ. CO₂ conversion decreased from 9.0% ± 0.2% at 21 W to 2.0% ± 0.1% at 42 W. The maximum conversion and energy efficiency obtained were 9.0% ± 0.2% at 3.1% ± 0.1% respectively, with a syngas ratio of 0.35 ± 0.01.
The energy consumption for decomposition is more than one order of magnitude higher compared to the thermal approach reported in the literature. The study notes that the syngas ratio achieved is 0.46, which is much lower than the ideal ratio required for applications like methanol synthesis.
DOI
10.1007/s11705-025-2614-6