Sabatier trial

The Sabatier process or the Sabatier reaction , named after the French chemist Paul Sabatier and discovered by him in 1902 with Jean Baptiste Senderens , describes a chemical reaction in which carbon dioxide and hydrogen are converted into methane and water .

reaction

The reaction is described by the following reaction equations:

${\displaystyle \mathrm {CO+3\;H_{2}\rightarrow CH_{4}+H_{2}O} \qquad \Delta H^{0}=-206{,}2\,\mathrm {kJ/mol} }$.

${\displaystyle \mathrm {CO_{2}+4\;H_{2}\rightarrow CH_{4}+2\;H_{2}O} \qquad \Delta H^{0}=-165{,}0\,\mathrm {kJ/mol} }$.

The reaction is highly exothermic: the temperature increase per volume% CO ₂ is 60 K (first case).

At elevated temperature and elevated pressure, the reaction proceeds using a Nickel - catalyst from effectively using is ruthenium on an alumina substrate. A Sabatier process in connection with water electrolysis is also often technically relevant, since methane and oxygen can be generated in this way (see Power-to-Gas ).

The reaction equation then reads

${\displaystyle \mathrm {CO_{2}+4\;H_{2}\rightarrow CH_{4}+2\;H_{2}O\rightarrow CH_{4}+O_{2}+2\;H_{2}} }$.

Early history

The formation of methane from carbon dioxide, carbon monoxide and water mixtures by means of electrical discharge was discovered by Brodie in 1872. The catalytic conversion was found in 1902 by Sabatier and Senderens, who also developed many other catalytic hydrogenations (Sabatier received the Nobel Prize for this). HS Ellworthy and HW Williamson received the first patents in 1904/05 (in England and Germany) and the first attempts at technical implementation were made in England from 1909 to 1911 with city ​​gas cleaning (Cedford process, which at that time did not reach industrial maturity) .

Life support systems for spacecraft and space stations

Oxygen is currently being extracted from the electrolysis of water on the International Space Station . The excess hydrogen is released into space. When the astronauts consume the oxygen, carbon dioxide is released, which is chemically bound and removed from the process. This solution assumes that relatively large amounts of water are regularly transported to the ISS, which are then used for oxygen production, but also for consumption, hygiene and more. When planning future, longer missions and reducing water requirements, alternatives to the previous concept are being examined.

For example, NASA is currently researching the application of the Sabatier reaction to recover the water in the exhaled "water vapor". Furthermore, the CO ₂ is said to react with 2 H ₂ (H ₂ from electrolysis, which is fed by solar power) to form water, with methane (CH ₄ ) being formed unintentionally . This additional product would likely be released into space. Since half of the required hydrogen would be lost in the form of methane, hydrogen would have to be replenished at regular intervals. Nevertheless, the cycle would be closed much better and correspondingly less hydrogen would be required compared to the previous process, which used the much heavier water.

The reaction equations of the process are as follows:

${\displaystyle \mathrm {2\;H_{2}O\rightarrow O_{2}+2\;H_{2}\rightarrow (Atmung)\rightarrow CO_{2}+2\;H_{2}+2\;H_{2}(hinzugef{\ddot {u}}gt)\rightarrow 2\;H_{2}O+CH_{4}(entnommen)} }$

The Bosch reaction , which via the direct route

${\displaystyle \mathrm {CO_{2}+2\;H_{2}\rightarrow C+2\;H_{2}O} ,\qquad \Delta H^{0}=-178{,}3\,\mathrm {kJ/mol} }$

Water generated is also being investigated for the application described. However, the deposition of solid carbon on the catalyst currently still causes problems, since it reduces the effective area of ​​the catalyst.

Making rocket fuel on Mars

The Sabatier process with subsequent electrolysis of the water (see above) theoretically offers the possibility of obtaining fuel in the form of methane and oxygen from resources available on Mars ( English in-situ resource utilization ). Hydrogen obtained from the ice caps at the poles and carbon dioxide, which is the main component of the Martian atmosphere, would be consumed . The stoichiometric mixture of the fuel components is 3.5: 1 (proportions by mass) of oxygen to methane, with the simple Sabatier process only achieving a value of 2: 1. In order to increase the oxygen yield, it is advisable to also allow the water-gas shift reaction to proceed in reverse order, resulting in the following reaction equation

${\displaystyle \mathrm {3\;CO_{2}+6\;H_{2}\rightarrow CH_{4}+2\;CO+4\;H_{2}O} }$.

The reaction is slightly exothermic, and electrolysis of the water could achieve a mixing ratio of 4: 1 (slight excess of oxygen). Alternatively, the methane generated in the Sabatier reaction could be partially pyrolyzed (see previous section). The resulting hydrogen could be used again in the Sabatier reactor in order to achieve the desired product quantity ratio.

Conversion of electricity

→ Main article : RE gas

A new approach is the conversion of electricity to synthetic natural gas. With excess electricity, hydrogen is first generated by electrolysis with an efficiency of 57 to 73 percent. With the Sabatier process, hydrogen and carbon dioxide are then converted into methane, whereby the methane (CH ₄ ) can be stored on site or fed into natural gas pipelines and temporarily stored in large natural gas storage facilities. When burning in the z. Z. (2011) the most modern gas turbine SGT5-8000H , the efficiency is 60.3% and thus the loss in this process section is 39.7%.

A demonstration system with an electrical connected load of 25 kilowatts, developed by the Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Stuttgart and the Fraunhofer Institute for Wind Energy and Energy System Technology (IWES) in Kassel and built with the participation of SolarFuel GmbH, has been in operation since In operation at the ZSW in 2009. The CO ₂ source was the ambient air. The system, which is transportable in a container, was also operated for a long time on the CO ₂ exhaust stream of the biogas processing of a biogas gas system from EWE AG in Werlte and on the raw biogas stream of a biogas plant in the Morbach energy landscape for a long time . Evidence of the generation of a DVGW- compliant natural gas substitute was provided in all cases.

As part of the subsequent Power-to-Gas project, which ran from April 1, 2011 to March 31, 2014 and was funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, the ZSW in October 2012 in Stuttgart, with the participation of IWES and SolarFuel, installed a 250 kW -Research facility put into operation. In it, in particular, the system technology for fast dynamic control is to be tested, which is necessary for the sensible use of such a system to compensate for the fluctuations in power generation of photovoltaics and wind energy. With this system, the preliminary stage for industrial use is reached at the same time. With system sizes between one and 20 megawatts, economic operation is expected. The aim of the project is to lay the foundations for the commissioning of the first 6-kilowatt pilot plant used by Audi to generate gas for motor vehicles at the Werlte biogas plant of the project partner EWE, the construction of which has already begun by SolarFuel. The gas will be fed to the gas filling stations via the public natural gas network, and Audi is also investing in four wind turbines in the Riffgat offshore wind farm for the electricity from renewable energy .

See also

• Methanation
• Fischer-Tropsch synthesis

Web links

• NASA page on the subject
• NASA page on oxygen production ( Memento from October 19, 2011 in the Internet Archive )
• Development of an improved Sabatier reactor
• Improvement of the Sabatier reaction for in situ applications on Mars missions ( Memento from July 17, 2012 in the Internet Archive ) (PDF file; 1.1 MB)
• Morbach energy landscape

Individual evidence

1. ↑ for example Georg Somló on the reduction of carbon oxides to methane , dissertation ETH Zurich, 1945, pdf
2. ↑ Sabatier La catalyse en chimie organique , 1913, p. 66. Sabatier also received a German Imperial Patent for this in 1913.
3. ^ Sabatier, Senderens Compte Rendu Acad. Sci., Vol. 134, 1902, p. 689.
4. ↑ K. Büker: Use of CO ₂ in fossil energy conversion cycles. (PDF; 1.4 MB) In: ThyssenKrupp 13th Brandenburger Energietag. Retrieved July 5, 2012 . 
5. ↑ Matthias Brake: Natural gas pipelines as storage for wind energy. In: Telepolis. Retrieved April 18, 2011 . 
6. ↑ Audi AG (Ed.) :: Audi e-gas project - The environmental balance sheet. February 2014, accessed March 26, 2018 . 
7. ↑ ZSW (Hrsg.), Fraunhofer IWES (Hrsg.), SolarFuel GmbH (Hrsg.): Joint project "Power-to-Gas" ( Memento of the original from September 29, 2013 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 115 kB). 
8. ↑ ZSW (Hrsg.), Fraunhofer IWES (Hrsg.), SolarFuel GmbH (Hrsg.): The world's largest power-to-gas plant for methane production goes into operation: preliminary stage for industrial application reached ( memo from November 14th 2012 in the Internet Archive ). Press release, October 30, 2012.
9. ↑ Werlte: Audi starts building a methanation plant. In: Neue Osnabrücker Zeitung (July 27, 2012).
10. ↑ Jürgen Pander: Audi Balanced Mobility: A car manufacturer as an eco-activist. In: Spiegel-Online (May 13, 2011).