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Steam reforming, hydrogen reforming or catalytic oxidation, is a method of producing hydrogen from hydrocarbons. On an industrial scale, it is the dominant method for producing hydrogen. Small-scale steam reforming units are currently subject to scientific research, as way to provide hydrogen to fuel cells.
Additional recommended knowledge
Steam reforming of natural gas, sometimes referred to as steam methane reforming (SMR) is the most common method of producing commercial bulk hydrogen as well as the hydrogen used in the industrial synthesis of ammonia. It is also the least expensive method. At high temperatures (700 – 1100 °C) and in the presence of a metal-based catalyst (nickel), steam reacts with methane to yield carbon monoxide and hydrogen.
Additional hydrogen can be recovered by a lower-temperature gas-shift reaction with the carbon monoxide produced. The reaction is summarised by:
The United States produces nine million tons of hydrogen per year, mostly with steam reforming of natural gas. The worldwide ammonia production, using hydrogen derived from steam reforming, was 109 million metric tonnes in 2004.
This SMR process is quite different from and not to be confused with catalytic reforming of naphtha, an oil refinery process that also produces significant amounts of hydrogen along with high octane gasoline.
A great deal of ethylene is produced by a non-catalytic process called "steam cracking" which cracks (i.e., reforms) large hydrocarbon molecules into smaller molecules). In the year 2003, there was 97,000,000 metric tons of ethylene (used to produce polyethylene and a host of other petrochemicals) manufactured worldwide by the steam cracking of various hydrocarbons (methane, ethane, LPG, naphtha, and fuel oils).
Fueling fuel cells
Steam reforming of liquid hydrocarbons is seen as a potential way to provide fuel for fuel cells. The basic idea is that for example a methanol tank and a steam reforming unit would replace the bulky pressurized hydrogen tanks that would otherwise be necessary. This might mitigate the distribution problems associated with hydrogen vehicles.
However, there are several challenges associated with this technology:
The reformer–fuel-cell system is still being researched but in the near term, systems would continue to run on existing fuels, such as natural gas or gasoline or diesel, but there is an active debate about whether using these fuels to make hydrogen is beneficial, when global warming is such an issue. The overall cost of making, transporting and storing the hydrogen fuel is also a key issue.
The chemical reactions that take place are:
The produced carbon monoxide can combine with more steam to produce further hydrogen via the water gas shift reaction.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Steam_reforming". A list of authors is available in Wikipedia.|