Sabatier Process for Biogas Upgrade

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I. Introduction: The Sabatier Reaction

The Sabatier Reaction¹ was discovered in 1912 by French chemist Paul Sabatier and it is as follows:
CO2 + 4H2 -----> CH4 + 2H2O. The National Aeronautics and Space Administration (NASA)¹ and its subcontractor, United Technologies Corporation² are investigating the use of the Sabatier Reaction for recover from exhaled carbon dioxide, for use on the International Space Station and on future Mars³ expeditions. The other resulting chemical, methane, would most likely be dumped overboard. As half of the input becomes wasted as methane, additional hydrogen would needed to be supplied from Earth to make up the difference. However, this creates a nearly closed cycle between water, oxygen and carbon dioxide which requires a relatively modest amount of imported hydrogen to maintain. Another reaction being investigated by NASA for the same purpose is the Bosch Reaction⁴ discovered in 1931 by the German chemist Carl Bosch and is as follows:
CO2 + 2H2 -----> C + 2H2O.

The purpose of this discussion is to propose the Sabatier Process for upgrading of the methane produced by anaerobic digestion and methanation of the carbon dioxide produced as well as recycled carbon dioxide with hydrogen from electrolysis⁵ of recycled water and water from a dehumidifier⁶.

II. Summary

A Sabatier Process utilizes anaerobic digestion of biomass at a collection site to produce biogas which is used by a power plant for power production after it is upgraded by methanated carbon dioxide produced in the Sabatier Reactor.

III. Sabatier Process

The Sabatier Reaction is the basis for the Sabatier Process described in Fig. 1. An ideal application for the Sabatier Process is at a natural gas fueled power plant utilizing an anaerobic digester with organic waste feed. The biogas mixture of methane and carbon dioxide would be introduced into the Sabatier Reactor it is reacted over a Ruthenium catalyst with hydrogen from an electrolyzer fed by water from the Sabatier Reactor condensate and from atmospheric air dehumidification (air has a low CO2 content (0.037%) and a high moisture content (2-6%)). Additional carbon dioxide is provided from the power plant flue gas and possibly by combustion of the anaerobic digester digestate with oxygen from the electolyzer. Process conditions are shown in Fig.2. The catalyst shown is mounted on ceramic foam⁷.

Reaction 1 is the standard Sabatier Reaction described as investigated by the U.S. NASA spacecraft application in Wikipedia and is illustrated by US 4,847,231 and assigned to the Gas Research Institute as well as US 4452626 and US 5505824 assigned to United Technologies Corporation.
Carbon dioxide for this process may be obtained by oxidation of carbonaceous material such as coal or pyrolysis char. Also, CO2 may be obtained from the atmosphere by utilizing a collector such as illustrated by WO2006/036936 assigned to Global Research Technologies, LLC.
Additional CO2 is produced with biogas from anaerobic digestion and this process can be used to upgrade the biogas to pipeline-quality natural gas.
Hydrogen for this process may be obtained by electrolysis of water obtained from the atmosphere by dehumidification.
Due to the mildness of the process, the methanation of carbon dioxide can be performed in the presence of methane since additional costs would be required for separation of the methane and carbon dioxide.
An ideal application for the Sabatier Process is at natural gas fueled power plant utilizing an anaerobic digester with organic waste feed. The biogas mixture of methane and carbon dioxide would be introduced into the Sabatier Reactor where it is reacted over a Ruthenium catalyst with hydrogen from an electrolyzer fed by water from the Sabatier Reactor condensate and from atmospheric air dehumidification. Additional carbon dioxide is provided from the power plant flue gas and possibly by combustion of the solid anaerobic digestate.
Conversation Processes can be located at www.ricestrawmarket.org under consulting, energy and chemicals.

IV. Conclusions:

1. The Sabatier Reaction developed for space applications should be utilized to upgrade biogas from an anaerobic digestor and to methanate recycled carbon dioxide.

V. Recommendations:

1. Establish an anaerobic digester at a power plant equipped to use methane as a fuel, Design and fabricate a Sabatier Reactor for use as the nucleus of a Sabatier Process at this power plant.

R. J. Robinson
Conversion Processes
9700 Elmira Circle
Sacramento, CA 95827-1120
916-363-9705
ROBSACROB@cs.com

We thank R. J. Robinson for submitting this specific information to: abc-alternative-energy.de

VI. References: Biogas Upgrade Process

¹ http://en.wikipedia.org/wiki/Sabatier_reaction
² McElroy, James F., United Technologies Corporation, US Patent 5,505,824, April 9.1996
³ Baker, D.,Gwynne, O., and Zubrin, Mars Direct. AIAA 91-0326, 29th Aerospace Sciences Meeting, Reno, NV, January 1991
⁴ http://en.wikipedia.org/wiki/Bosch_reaction
⁵ Newman, Daniel D. And Rosen Harold D., Hughes Aircraft Company. US Patent 3,520137. July 7, 1970
⁶ http://www.air-a-water.com/Dehumifidier-Buying-Guide.htm
⁷ Richardson J.T., and Twigg,M.V., "Theory and Application of Veramic Foam Catalysts", Trans.IChem E 80 (2002) 183.