Steam reforming

Steam reforming with partial oxidation, CO conversion and carbon dioxide absorption ( primary reformer , oxygen feed , secondary reformer , CO conversion , washing tower ).



The steam reforming (in the technical parlance as steam reforming , English steam reforming ) is currently the most important industrial-scale process for the production of hydrogen from carbonaceous fuels and water. Natural gas is currently the most important raw material; in principle, many aliphatic hydrocarbons such as light petrol , methanol , biogas or biomass are suitable as starting materials. Steam reforming is an endothermic reaction in which the required heat must be added to the reaction. The process can also be carried out autothermally by simultaneous partial oxidation of the hydrocarbons . The efficiency (natural gas to hydrogen) is around 60 to 70%.

history

The development of steam reforming goes back to Carl Bosch , who was looking for inexpensive hydrogen sources for the Haber-Bosch process in the 1920s . The first patent was granted to Georg Schiller by IG Farben , who succeeded in steam reforming methane using a nickel oxide catalyst. IG Farben granted Standard Oil of New Jersey a license. As early as 1931, the company started producing hydrogen through steam reforming at its plant in Baton Rouge , Louisiana . The steam reforming of natural gas produced around 48 percent of the hydrogen used globally in 2014, of which the Haber-Bosch process used around 60 percent.

Reactions

Steam reforming is an allothermic process that works according to the following equation:

${\displaystyle \mathrm {CH_{4(g)}+H_{2}O_{(g)}\;\rightleftharpoons \;CO_{(g)}+3\ H_{2(g)},\ \Delta H=+206{,}2kJ/mol} }$

( Methane + water vapor → carbon monoxide + hydrogen; endothermic )

The required heat of reaction can be applied through partial oxidation:

${\displaystyle 2\ \mathrm {CH_{4(g)}} +\mathrm {O_{2(g)}} \;\rightleftharpoons \;2\ \mathrm {CO_{(g)}} +4\ \mathrm {H_{2(g)}} \qquad {\Delta H=-71\ \mathrm {kJ/mol} }}$

( Methane + oxygen → carbon monoxide + hydrogen; exothermic )

To increase the hydrogen yield, the resulting carbon monoxide can be converted into carbon dioxide and further hydrogen in a further reaction, the water-gas shift reaction .

${\displaystyle \mathrm {CO_{(g)}+H_{2}O_{(g)}\;\rightleftharpoons \;CO_{2(g)}+H_{2(g)},\ \ \ \Delta H=-41{,}2\ kJ/mol} }$

(Water gas shift reaction; slightly exothermic)

To do this, hot water vapor is mixed with the gas to be reformed (for example natural gas) or with evaporated liquid (for example light gasoline) and converted into the gas phase over a heterogeneous catalyst with constant energy supply .

Solids

Since complex solids such as wood, sewage sludge or municipal waste cannot be evaporated, they have to be reformed under different conditions. The reforming is carried out using supercritical water on a heterogeneous catalyst at 250-300 bar, 400-550 ° C and a large excess of water. The formation of air pollutants, such as in waste incineration, is practically irrelevant under these extreme conditions.

Methanol reformer

→ Main article : Methanol reformers

Web links

• Process scheme (SVG)
• Forschungszentrum Jülich GmbH - information about reforming

swell

1. ^ Anton Karle: Electromobility. Basics and practice . Munich 2017, p. 40f.
2. ↑ Patent US2083795 : Production of hydrogen. Published on June 15, 1937 , inventors: Georg Schiller, Gustav Wietzel. ‌
3. ↑ Vaclav Smil: Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production. MIT Press, 2001, ISBN 978-0-262-69313-4 , p. 242.
4. ↑ Fangming Jin (Ed.): Application of Hydrothermal Reactions to Biomass Conversion. Springer, 2014, ISBN 978-3-642-54457-6 , p. 221.
5. ^ NW Johanson, MH Spritzer, GT Hong, WS Rickman: Supercritical water partial oxidation . In: Proceedings of the 2001 DOE Hydrogen Program Review . 2001 ( PDF ).