Editing Steam reforming (section)

== Reactions ==
Steam reforming reaction kinetics, in particular using [[nickel]]-[[alumina]] catalysts, have been studied in detail since the 1950s.<ref>{{Cite journal|last1=Akers|first1=W. W.|last2=Camp|first2=D. P.|date=1955|title=Kinetics of the methane-steam reaction|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/aic.690010415|journal=AIChE Journal|language=en|volume=1|issue=4|pages=471–475|doi=10.1002/aic.690010415|bibcode=1955AIChE...1..471A |issn=1547-5905|url-access=subscription}}</ref><ref name=":0">{{Cite journal|last1=Xu|first1=Jianguo|last2=Froment|first2=Gilbert F.|date=1989|title=Methane steam reforming, methanation and water-gas shift: I. Intrinsic kinetics|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/aic.690350109|journal=AIChE Journal|language=en|volume=35|issue=1|pages=88–96|doi=10.1002/aic.690350109|bibcode=1989AIChE..35...88X |issn=1547-5905|url-access=subscription}}</ref><ref name=":1">{{Cite journal|last1=Hou|first1=Kaihu|last2=Hughes|first2=Ronald|date=2001-03-15|title=The kinetics of methane steam reforming over a Ni/α-Al2O catalyst|url=https://www.sciencedirect.com/science/article/pii/S1385894700003673|journal=Chemical Engineering Journal|series=FRONTIERS IN CHEMICAL REACTION ENGINEERING|language=en|volume=82|issue=1|pages=311–328|doi=10.1016/S1385-8947(00)00367-3|issn=1385-8947|url-access=subscription}}</ref>

=== Pre-reforming ===
[[File:Steam Reforming (SMR) Process Flow.jpg|alt=Depiction of the general process flow of a typical steam reforming plant. From left to right: Desulphurisation, pre-reforming, steam reforming, shift conversion, and pressure-swing-adsorption. |thumb|616x616px|Depiction of the general process flow of a typical steam reforming plant. (PSA = [[Pressure swing adsorption]], NG = Natural gas)]]
The purpose of pre-reforming is to break down higher hydrocarbons such as [[propane]], [[butane]] or [[naphtha]] into [[methane]] (CH<sub>4</sub>), which allows for more efficient reforming downstream.

=== Steam reforming ===
The name-giving reaction is the steam reforming (SR) reaction and is expressed by the equation:

<math>[1]\qquad \mathrm{CH}_4 + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CO} + 3\,\mathrm{H}_2
\qquad \Delta H_{SR} = 206\ \mathrm{kJ/mol}</math>

Via the [[water-gas shift reaction]] (WGSR), additional hydrogen is released by reaction of water with the carbon monoxide generated according to equation [1]:

<math>[2]\qquad \mathrm{CO} + \mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CO}_2 + \mathrm{H}_2
\qquad \Delta H_{WGSR} = -41\ \mathrm{kJ/mol}</math>

Some additional reactions occurring within steam reforming processes have been studied.<ref name=":0" /><ref name=":1" /> Commonly the direct steam reforming (DSR) reaction is also included:

<math>[3]\qquad \mathrm{CH}_4 + 2\,\mathrm{H}_2\mathrm{O} \rightleftharpoons \mathrm{CO}_2 + 4\,\mathrm{H}_2
\qquad \Delta H_{DSR} = 165\ \mathrm{kJ/mol}</math>

As these reactions by themselves are highly endothermic (apart from WGSR, which is mildly exothermic), a large amount of heat needs to be added to the reactor to keep a constant temperature. Optimal SMR reactor operating conditions lie within a temperature range of 800&nbsp;°C to 900&nbsp;°C at medium pressures of 20-30 bar.<ref name=":2">{{Cite book|last=Speight|first=James G.|url=https://www.worldcat.org/oclc/1179046717|title=The refinery of the future|date=2020|publisher=Gulf Professional Publishing|isbn=978-0-12-816995-7|edition=2nd|location=Cambridge, MA|oclc=1179046717}}</ref> High excess of steam is required, expressed by the (molar) steam-to-carbon (S/C) ratio. Typical S/C ratio values lie within the range 2.5:1 - 3:1.<ref name=":2" />