Making chemicals by artificial photosynthesis 2

Making chemicals by artificial photosynthesis


By Gerald Ondrey |


Last month, Evonik Industries AG (Essen, Germany; and Siemens AG (Munich, both Germany; launched a second phase of their joint research project, Rheticus II, which aims to develop a test plant that will use CO2 and water, as well as electricity from renewable sources and bacteria, to produce specialty chemicals. In the Rheticus I project, Siemens and Evonik worked for two years to develop the technically feasible basis for artificial photosynthesis using a bioreactor and electrolyzers (see “Solar Chemistry Heats Up,” Chem. Eng., March 2018, pp. 12–16; Now, the two companies are combining these two, previously separate, plants in a test facility at Evonik’s site in Marl, Germany. Rheticus II will run until 2021 and will receive funding of around €3.5 million from Germany’s Federal Ministry of Education and Research (BMBF; Bonn;

The test facility is scheduled to start operating in early 2020. It comprises electrolyzers and a bioreactor. In a first step, CO2 and water are electrolyzed into synthesis gas (syngas; CO and H2). Microorganisms then metabolize the syngas into chemicals.

The synthesis module came on stream at Evonik in spring 2019. At its heart is an 8-m-high stainless-steel, 2,000-L bioreactor, which operates continuously. Siemens has developed a fully automated CO2 electrolyzer, which was integrated into a container in summer 2019. The world’s first CO2 electrolyzer comprises ten cells, and the total surface area of the electrodes is 3,000 cm2.

In the test facility, bacteria will produce butanol and hexanol for research purposes. These substances are used as starting products, for example, for specialty plastics and food supplements. However, other specialty chemicals are conceivable, depending on the bacterial strain and conditions, says Evonik.

Another advantage of Rheticus is that the technology platform also contributes to the reduction of carbon dioxide levels in the atmosphere, as it uses CO2 as a raw material. Three tons of CO2 would be needed to produce one ton of butanol, for example.


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