Partial oxidation (POX) is a type of
chemical reaction
A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...
. It occurs when a
substoichiometric fuel-air mixture is partially
combusted in a reformer, creating a hydrogen-rich
syngas
Syngas, or synthesis gas, is a mixture of hydrogen and carbon monoxide in various ratios. The gas often contains some carbon dioxide and methane. It is principally used for producing ammonia or methanol. Syngas is combustible and can be used as ...
which can then be put to further use, for example in a
fuel cell
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel (often hydrogen fuel, hydrogen) and an oxidizing agent (often oxygen) into electricity through a pair of redox reactions. Fuel cells are different from most bat ...
. A distinction is made between ''thermal partial oxidation'' (TPOX) and ''catalytic partial oxidation'' (CPOX).
Principle
Partial oxidation is a technically mature process in which
natural gas
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
or a heavy hydrocarbon fuel (
heating oil
Heating oil is any petroleum product or other oil used for heating; it is a fuel oil. Most commonly, it refers to low viscosity grades of fuel oil used for furnaces or boilers for home heating and in other buildings. Home heating oil is often ...
) is mixed with a limited amount of oxygen in an
exothermic
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
process.
* General reaction:
+ \frac\mathit -> \mathit + \frac\mathitH2
* Idealized reaction for heating oil:
+ 6O2 -> + 12H2
* Idealized reaction for coal:
+ 12O2 -> + 6H2
The formulas given for coal and heating oil show only a typical representative of these complex fuels. Water may be added to lower the combustion temperature and reduce soot formation. Yields are below stoichiometric due to some fuel being fully combusted to carbon dioxide and water.
TPOX
TPOX (''thermal partial oxidation'') reaction temperatures are dependent on the
air-fuel ratio or oxygen-fuel ratio. Typical reaction temperatures are 1200
°C and above.
CPOX
In
CPOX (''catalytic partial oxidation'') the use of a
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
reduces the required temperature to around 800°C – 900°C.
The choice of
reforming technique depends on the
sulfur
Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
content of the fuel being used. CPOX can be employed if the sulfur content is below 50
ppm. A higher sulfur content can poison the catalyst, so the TPOX procedure is used for such fuels. However, recent research shows that CPOX is possible with sulfur contents up to 400ppm.
[Electricity from wood through the combination of gasification and solid oxide fuel cells](_blank)
Ph.D. Thesis by Florian Nagel, Swiss Federal Institute of Technology Zurich, 2008
History
1926 – Vandeveer and Parr at the
University of Illinois
The University of Illinois Urbana-Champaign (UIUC, U of I, Illinois, or University of Illinois) is a public university, public land-grant university, land-grant research university in the Champaign–Urbana metropolitan area, Illinois, United ...
used oxygen to replace air.
''Industrial Gas Handbook'', Frank G. Kerry, p. 230
See also
*Hydrogen production
Hydrogen gas is produced by several industrial methods. Nearly all of the world's current supply of hydrogen is created from fossil fuels. Article in press. Most hydrogen is ''gray hydrogen'' made through steam methane reforming. In this process, ...
*Industrial gas
Industrial gases are the gaseous materials that are Manufacturing, manufactured for use in Industrial sector, industry. The principal gases provided are nitrogen, oxygen, carbon dioxide, argon, hydrogen, helium and acetylene, although many other ...
* PROX
* Small stationary reformer
*Glossary of fuel cell terms
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to ...
* Timeline of hydrogen technologies
References
{{reflist
Chemical reactions
Hydrogen production
Industrial gases
Redox