Pilot absorption and regeneration unit

The CoCCUS project aims to develop an innovative technology for CO₂ capture from flue gases of energy-intensive industries, which emit CO₂ as an inherent part of their processes. CO₂ capture is achieved via the use of an aqueous potassium carbonate (K₂CO₃) solution and novel carbonic anhydrase (CA) enzymes, aiming to use the captured CO₂ to produce high-value products.

As part of the project, a CO₂ capture pilot unit was developed using chemical absorption with a 20-30 wt.% K₂CO₃ solution. The unit consists of two packed bed columns—an absorber and a desorber—each one equipped with temperature sensors and liquid level electrodes to prevent flooding. In the absorption column, a CO₂/N₂ gas mixture (~20% CO₂) interacts counter-currently with the K₂CO₃ solution. The separated CO₂ is collected in the regeneration column through thermal processes, and the purified CO₂ is analyzed before being repurposed. The solvent is recycled for future use.

Image 1. Pilot plant for CO₂ capture, CERTH/CPERI Ptolemais

In the pilot unit, aqueous K₂CO₃ solutions were tested, both with and without the presence of carbonic anhydrase (CA) enzymes as catalysts.

In trials using pure K₂CO₃ (20 wt.%), the CO₂ absorption rate was measured at 15%, in agreement with the literature[1], primarily due to the slow reaction kinetics between K₂CO₃ and CO₂. The captured CO₂ exhibited a purity of 80%.

When K₂CO₃ was combined with CA enzymes (0.5 g/L), the absorption rate was significantly improved. Specifically, it was increased nearly threefold over the use of no enzyme, while the CO₂ purity was increased to 87%.

Simulation results

Using computational tools, the appropriate parameters were identified to achieve 90% CO₂ capture and 99% CO₂ purity at the outlet of the regeneration column in the pilot unit. Specifically, the chosen conditions were solvent and exhaust gas temperatures between 40-46 °C, an enzyme concentration of 1 g/L, and a solvent concentration of 20% w/w. The absorption column operated at atmospheric pressure, while the regeneration column was set to a pressure of 0.5 bar. The energy consumption of the reboiler, required to achieve 90% capture and 99% CO₂ purity in the pilot unit, ranged from 8 to 9.8 MJ/kg CO₂.

Following this, the absorption and regeneration column dimensions were calculated to adapt the process to three industrial sectors (cement, magnesia, and lime production). In these cases, by utilizing waste heat streams from the industries, reboiler energy consumption was estimated between 3 and 5.1 MJ/kg CO₂, while the cost of the capture technology ranged from €31 to €48 per ton of CO₂, depending on the specific industry producing the exhaust gas.

Enzyme as a catalyst for CO₂ capture

In the CoCCUS project, the enzyme carbonic anhydrase (CA) significantly enhances CO₂ capture efficiency by accelerating the conversion of CO₂ into bicarbonate ions (HCO₃^–) and protons (H⁺), thus increasing the absorption rate in the potassium carbonate (K₂CO₃) solution. The enzyme used, CA92, is particularly well-suited for industrial applications due to its exceptional thermal stability and resistance to alkaline environments, retaining over 90% of its activity after 6 hours at 80°C and more than 75% at 90 °C.

Tested under realistic conditions, CA92 was subjected to potassium carbonate solutions at 20% (w/v) with a pH of 11.5. It demonstrated strong structural integrity and catalytic activity even after 30 days of incubation, maintaining 90% of its original concentration and continuing to facilitate effective CO₂ capture. This makes CA92 one of the most thermally stable and durable carbonic anhydrase enzymes identified for industrial CO₂ capture applications. For this enzyme, a patent application was filled.

1.            Qi, G., et al., Integrated Bench-Scale Parametric Study on CO2 Capture Using a Carbonic Anhydrase Promoted K2CO3 Solvent with Low Temperature Vacuum Stripping. Industrial & Engineering Chemistry Research, 2016. 55(48): p. 12452-12459.

Publications in Peer-Reviewed Scientific Journals and Conferences

As part of the project implementation and in alignment with contractual obligations, results were published in peer-reviewed scientific journals and conferences.

1. Karali D., Peloriadi K., Margaritis N., Grammelis P., “CO₂ Absorption Using Potassium Carbonate as Solvent,” ASEC2022 3rd International Electronic Conference on Applied Sciences, online, 01-15 December 2022.
2. Kontodimos I., Papadelis C.E., Margaritis N., Grammelis P., “Valorization of Medicinal Plant Residues through Anaerobic Digestion,” 10th International Conference on Sustainable Solid Waste Management, Chania, Greece, 21-24 June 2023.
3. Karali D., Kalaitzi A., Grammelis P., Stenos V., “Production of Edible Proteins from Captured CO₂,” 47th International Technical Conference on Clean Energy, 23-27 July 2023, Florida, USA.
4. Kalaitzi A., Karali D., Koutsianos A., Margaritis N., Grammelis P., “Development of CO₂ Capture Technology from Industrial Flue Gases,” Regional Excellence Workshop ExcelWMac: “Presentation of Research Results of the Project ‘Development of New Innovative Low Carbon Footprint Energy Technologies to Enhance Excellence in Western Macedonia,” 7 June 2023, Kozani, Greece.
5. Konstantinos Rigkos, Georgios Filis, Pavlos Saridis, Dimitra Zarafeta*, Georgios Skretas*, “Discovery of a Novel Ultra-Thermostable Carbonic Anhydrase for Enzymatic CO₂ Sequestration Using High-Throughput Metagenomic Analysis,” Poster presented at the 16th International Symposium on Biocatalysis & Biotransformations (BIOTRANS 2023), France, June 2023. – Posted Paper
6. Konstantinos Rigkos, Georgios Filis, Pavlos Saridis, Dimitra Zarafeta*, Georgios Skretas*, “Discovery of a Novel Ultra-Thermostable Carbonic Anhydrase for Enzymatic CO₂ Sequestration Using High-Throughput Metagenomic Analysis,” 1st Biomedicine, Bioinformatics & Biotechnology Forum: Fostering Collaboration in Industry & Academia conference (Bio3), Greece, September 2023. – Posted Paper (Awarded with Honorable Mention)
7. Ioanna Gerogianni, Konstantinos Rigkos, Dimitra Zarafeta, Georgios Skretas, Evangelia D. Chrysina*, “Structural Studies of a Novel Ultra-Thermostable Carbonic Anhydrase,” 11th International Conference of the Hellenic Crystallographic Association (HeCrA), Greece, October 2023 – Posted Paper
8. Konstantinos Rigkos, Georgios Filis, Pavlos Saridis, Dimitra Zarafeta*, Georgios Skretas*, “CA-KR1: A Novel Ultra-Thermostable and Alkalistable Carbonic Anhydrase for Efficient CO₂ Sequestration Discovered Through High-Throughput Metagenomic Analysis,” ICB Workshop on Chemical Biology: Drug and Biomarker Discovery, Greece, November 2023 – Posted Paper
9. Konstantinos Rigkos, Georgios Filis, Pavlos Saridis, Dimitra Zarafeta*, Georgios Skretas*, “A Novel Ultrastable Carbonic Anhydrase for Efficient CO₂ Sequestration Discovered Through Large-Scale Metagenomic Analysis,” European Society of Applied Biocatalysis Digital Congress, online, November 2023. – Posted Paper/Presentation
10. Konstantinos Rigkos, Georgios Filis, Pavlos Saridis, Dimitra Zarafeta*, Georgios Skretas*, “A Novel Ultrastable Carbonic Anhydrase for Efficient CO₂ Sequestration Discovered Through Large-Scale Metagenomic Analysis,” 73rd National Conference of the Hellenic Society of Biochemistry and Molecular Biology (HSBMB), Greece, December 2023. – Posted Paper
11. Atsonios K., Papaioannou C., Plakia A., Grammelis P., “CO₂ Capture Technologies Using Renewable Electricity: Process Analysis and Comparison,” 37th International Conference on Efficiency, Cost, Optimization, Simulation, and Environmental Impact of Energy Systems, Rhodes, Greece, 30 June – 4 July 2024 – Abstract Submitted
12. Karali D., Peloriadi K., Margaritis N., Grammelis P., “CO₂ Absorption Using Potassium Carbonate as Solvent,” Eng. Proc. (2023), 31, 39.

Patent Application

1. Skretas G., Zarafeta D., Filis G., Rigkos K., “Heat- and Halo-Stable Carbonic Anhydrase for CO₂ Sequestration”