Methanation

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Methanation is the conversion of COx to methane CH4 through hydrogenation. The methanation reactions of COx were first discovered by Sabatier and Senderens in 1902.[1]

COx methanation has many practical application it is a means of carbon oxide removal from process gases and is also being discussed as an alternative to PROX in fuel processors for mobile fuel cell applications.[2]

Methanation as a means of producing synthetic natural gas has been considered since the 1970s.[1] More recently it has been considered as a way to store energy produced from solar or wind power. This would also allow it to serve as a potential carbon capture mechanism.

Chemical reactions[edit]

The following reactions describe the methanation of carbon monoxide and carbon dioxide respectively:

-206 kJ/mol
-164 kJ/mol

The methanation reactions are classified as exothermic and their energy of formations are listed.[1]

There is disagreement on whether the CO2 methanation occurs by first associatively adsorbing an adatom hydrogen and forming oxygen intermediates before hydrogenation or dissociating and forming a carbonyl before being hydrogenated.[3] CO methanation is believed to be methanated through a dissociative mechanism where the carbon oxygen bond is broken before hydrogenation with an associative mechanism only being observed at high H2 concentrations.

Methanation reaction over different carried metal catalysts including Ni,[4] Ru [5] and Rh[6] has been widely investigated for the production of CH4 from syngas and other power to gas initiatives.[3] Nickel is the most widely used catalyst due to its high selectivity and low cost.[1]

Industrial applications[edit]

Creation of synthetic natural gas[edit]

Methanation is an important step in the creation of synthetic or substitute natural gas (SNG).[7] Coal or wood undergo gasification which creates a producer gas that must undergo methanation in order to produce a usable gas that just needs to undergo a final purification step.

The first commercial synthetic gas plant opened in 1984 and is the Great Plains Synfuel plant in Beulah, North Dakota.[1] It is still operational and produces 1500 MW worth of SNG using coal as the carbon source. In the years since its opening, other commercial facilities have been opened using other carbons sources such as wood chips.[1]

Ammonia synthesis[edit]

In ammonia production CO and CO2 are considered poisons to most commonly used catalysts.[8] Methanation catalysts are added after several ammonia synthesis steps to prevent carbon oxide buildup as methane does not have similar adverse effects on ammonia synthesis rates. 

References[edit]

  1. ^ a b c d e f Rönsch, Stefan; Schneider, Jens; Matthischke, Steffi; Schlüter, Michael; Götz, Manuel; Lefebvre, Jonathan; Prabhakaran, Praseeth; Bajohr, Siegfried (2016-02-15). "Review on methanation – From fundamentals to current projects". Fuel. 166: 276–296. doi:10.1016/j.fuel.2015.10.111. 
  2. ^ Yong Men, «Selective methanation of carbon oxides in a microchannel reactor—Primary screening and impact of gas additives», Catalysis Today, 2007, p. 81-87 ([doi:10.1016/j.cattod.2007.02.017 lire en ligne])
  3. ^ a b Miao, Bin; Ma, Su Su Khine; Wang, Xin; Su, Haibin; Chan, Siew Hwa (2016-06-13). "Catalysis mechanisms of CO2 and CO methanation". Catalysis Science & Technology. 6 (12). ISSN 2044-4761. doi:10.1039/C6CY00478D. 
  4. ^ K.O. Xavier, «Doping effects of cerium oxide on Ni/Al2O3 catalysts for methanation», Catalysis Today, 1999, p. 17-21
  5. ^ Toshimasa Utaka, «CO removal from reformed fuels over Cu and precious metal catalysts», Applied Catalysis A: General, 2003, p. 117-124 ([10.1016/S0926-860X(03)00048-6 lire en ligne])
  6. ^ Paraskevi Panagiotopoulou, « Selective methanation of CO over supported noble metal catalysts: Effects of the nature of the metallic phase on catalytic performance», Applied Catalysis A: General, 2008, p. 45-54 ([10.1016/j.apcata.2008.03.039 lire en ligne])
  7. ^ Kopyscinski, Jan; Schildhauer, Tilman J.; Biollaz, Serge M. A. (2010-08-01). "Production of synthetic natural gas (SNG) from coal and dry biomass – A technology review from 1950 to 2009". Fuel. 89 (8): 1763–1783. doi:10.1016/j.fuel.2010.01.027. 
  8. ^ Khorsand, Kayvan (2007). "Modeling and simulation of methanation catalytic reactor in ammonia unit" (PDF). Petroleum & Coal. 49: 46–53.