Rheticus Project Teams German Giants to Harvest CO2 in Artificial Photosynthesis

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©. Evonik Industries AG

Germans lead the world in implementing renewable energy infrastructure. But sometimes, there is too much of a good thing: the inability to store excess electricity reduces the efficiency of the renewable energy installations.

Meanwhile, carbon dioxide levels continue to rise, and hardly anyone doubts anymore that projects to pull carbon dioxide emissions out of the air will be a necessary transitional measure if the population of humans on Earth hope to continue energy-spurred growth while converting to renewable energy sources.

The Rheticus project offers solutions for both conundrums. Researchers from two German industrial giants, Siemens and Evonik, just announced that they will team up to demonstrate the feasibility of "technical photosynthesis." The idea is to use eco-electricity and harness the power of nature to convert CO2 into more complex chemical building blocks, like the alcohols butanol and hexanol.

Decentralization required

A key paradigm change for success: decentralization. The trend towards large chemical production facilities cannot be supported when sustainable raw materials are used. The generation of eco-electricity already turns the logic of large, centralized power plants on its head. Tapping the lower energy density provided from renewable sources means settling for more moderate production facilities.

Additionally, the process cannot be run efficiently on the density of CO2 found in the normal atmosphere. The process needs to use the emissions of other processes, such as brewing or cement and steel production. Tapping into these low density emissions streams instead of using petroleum feed-stocks also requires a decentralized approach: wherever an excess of CO2 arises, a sustainable artificial photosynthesis can capture the CO2 and store excess solar or wind energy in the process.

Energy storage

The ability to productively use as much renewable energy as can be generated can be considered a major benefit for the concept The process effectively "stores" excess electricity in the CO-rich gas mixture, known as syngas. The syngas then serves as the nutrients for anaerobic microbes that produce the value-added alcohols like butanol and hexanol as a by-product.

The valuable alcohols are easily separated from the reaction mixture in a process that promotes the re-use of the major components of the process, furthering the efficiency and reducing the potential waste generation of the process.

Technical photosynthesis of 1-butanol and 1-hexanol from CO2 and H2O

Thomas Haas, Ralf Krause, et. al. in Nature Catalysis/Promo imageThe alcohols generated by the process have a value of 2.2 times the cost of the electricity, assuming photovoltaic efficiency of 20%.

Next steps

The process has proven successful in lab conditions, with some of the technical obstacles that had to be overcome described in a recent paper in the journal Nature Catalysis, Technical photosynthesis involving CO2 electrolysis and fermentation.

The two-year project employs 20 researchers from the Siemens and Evonik teams working to scale up the laboratory process with the intent to bring a 20,000 t/y production facility online at Evonik's facility in Marl, Germany, by 2021. Butanol and Hexanol are already produced from petroleum at the Marl site.

The Rheticus project is one part of the Kopernikus Initiative for the Energy Transition in Germany. Rheticus is financed by 2.8 million Euro from the Federal Ministry of Education and Research [Bundesministerium für Bildung und Forschung (BMBF)], which amount is roughly matched by funds contributed by the two companies.