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KIT spin-off producing synthetic natural gas from green hydrogen and CO2 from sewage sludge

Chemical reactor company INERATEC, a spinoff of Karlsruhe Institute of Technology (KIT), and the Spanish company GAS NATURAL FENOSA have built a plant in Spain that produces synthetic natural gas from CO2 and renewable hydrogen. The process is based on the production of hydrogen by electrolysis (renewable power-to-gas) and its reaction with CO2 from biogenic sources—e.g. sewage sludge.

At the sewage treatment plant of the city of Sabadell near Barcelona, large amounts of the basic materials required are available, INERATEC’s Managing Director Tim Böltken said.

The process uses energy from renewable sources and stores it in the chemical energy carrier methane. In the past four years, Spain already produced 40% of its power from renewable energy sources, mostly wind energy.

—Tim Böltken

With a power-to-gas process, excessive or decentrally produced power from renewable sources, such as solar or wind power, is converted into methane. The renewable gas can be stored in the existing gas infrastructure and transported to areas all over Spain. Gas storage capacity in Spain amounts to about 30 terawatt hours, which means that the power produced by wind power plants there can be stored for half a year.

However, so far, such decentralized production has not been economically efficient, as the chemical process usually requires extremely expensive, large chemical facilities. The INERATEC founders succeeded in developing a compact modular facility, such that the capacity can be increased as required.


The INERATEC chemical reactors are so compact that the entire plant fits into a shipping container. (Photo: INERATEC)

For the time being, the pilot plant at Sabadell is to produce 100 m3 gas per day. It is additionally equipped with a catalyst developed by the Catalonian Institute for Energy Research (IREC) for the conversion of CO2 from biogenic sources.

The plant is part of the Spanish project Synthetic Fuels – Combustibles Sintètics (CoSin) that is funded by the European Regional Development Fund.

INERATEC offers a range of processes for the production of synthetic natural gas, synthetic fuels, chemicals and methanol. The INERATEC chemical reactors can be integrated into containerized plants; the plants are modular and can therefore be applied to various energy related sectors.

Depending on the application, different reactor systems can be integrated and combined in the plant. The reactors allow a dynamic and load-flexible operation.



This is not that difficult to do in areas where NG is expensive and/or scarce.


Sewage sludge is about 27% carbon so that should be a solid starting point for biofuels itself, not just the off-gassed CO2 from digestion.  Of course this means dealing with the high ash content, but what are challenges for?  Find a way to convert it into clean gas, some of which will be methane already.

No matter what method is selected, it's certain to be more efficient than electrolyzing water at low temperature and reacting the hydrogen with CO2 at 78% max efficiency conversion to methane.


Lots of carbon sources, ethanol plants produce carbon neutral CO2.


The most expensive artificial gas in the world, with no future.


Rather an absolute statement when oil is $1000 per barrel.

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