FSC 432
Petroleum Processing

Hydrogen Production


Hydrogen Production

Although refineries produce a significant quantity of hydrogen needed for hydrotreating and hydroconversion processes, in most cases, additional hydrogen is needed particularly for refining the sour crudes. Therefore, a Hydrogen Plant is needed on site to provide the additional hydrogen demand. As seen in Figure 10.7, steam reforming of natural gas is most commonly used in the U.S. to produce hydrogen, whereas partial oxidation of heavy hydrocarbons is preferred in Europe [4].

For the partial oxidation process, a heavy hydrocarbon fraction, typically fuel oil, is reacted at high pressures (1300-1800 psig) with pure oxygen supplied in strictly controlled quantities for partial oxidation of hydrocarbons to carbon monoxide and hydrogen, as shown in Figure 10.7. Carbon monoxide produced in the reaction is converted to hydrogen by catalytic shift reaction with steam. In the purification step, CO2 produced in the shift reaction is removed by absorption in a basic solvent such as potassium carbonate.

Hydrogen Production outlined as described in above paragraph
Figure 10.7. Hydrogen demand and additional hydrogen production on site in the US and European refineries.
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Image reads:

Hydrogen Production

Demand: hydrotreating, hydrocracking

Supply: Catalytic reforming – not sufficient

Additional hydrogen needs to be produced

The principle method of hydrogen production in US refineries:

-Steam reforming of natural gas (CH4)

The principle method of hydrogen production in European refineries:

-Partain oxidation of heavy HC (e.g., fuel oil) is used to produce hydrogen

2CnHm + nO2 → 2nCO + mH2 (oxidation)

2nCO + 2nH2O → 2nCO2 (removed by absorption) + 2nH2

Credit: Dr. Semih Eser © Penn State is licensed under CC BY-NC-SA 4.0

Figure 10.8 illustrates the reactions in steam reforming of natural gas (CH4) to produce hydrogen in the U.S. refineries. In the reforming reaction, CH4 is converted to H2 and CO on a NiO/SiO2-Al2O3 catalyst at temperatures of 760-816°C. Reforming is followed by the water gas shift reaction at 343°C to shift CO to H2 and CO2 on a Cr2O3 and Fe2O3 catalyst in multiple catalyst beds with external cooling to control the temperature to achieve high conversion in the exothermic reaction. The product gas is purified by absorption of CO2 in an Amine Unit. In the final step of methanation, residual CO and CO2 is removed by hydrogenation on a Ni/Al2O3 catalyst at 370-427°C.

Outline of Steam Reforming of CH4 for hydrogen production, as described in above paragraph
Figure 10.8.  Steam reforming of CH4 for hydrogen production.
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Image reads:

Steam Reforming of CH4

1) Reforming

CH4 + H2O → CO + 3H2 (endothermic)

Catalyst: 25-40% NiO/low SiO2/ Al2O3

Carried out at 760-816ºC

2) Shift

CO + H​​​​​​​2​​​​​​​O → CO​​​​​​​2 + H​​​​​​​2 (exothermic)

Catalyst: Cr​​​​​​​2O​​​​​​​3 and Fe​​​​​​​2O​​​​​​​3

Carried out at 343ºC in multiple catalyst beds w/ external cooling

3) Gas Purification

CO​​​​​​​2 absorption in amine unit

4) Methanation - to remove residual CO and CO2

CO + 3H​​​​​​​2 → CH​​​​​​​2 + H​​​​​​​2O (Exothermic)

CO2 + 4H​​​​​​​2 → CH​​​​​​​2 + 2H​​​​​​​2O (Exothermic)

Carried out at 370-427ºC

Catalyst: Ni/Al​​​​​​​2O​​​​​​​3

Credit: Dr. Semih Eser © Penn State is licensed under CC BY-NC-SA 4.0

[4] Petroleum Refining, by J. H. Gary, G. E. Handwerk, M. J. Kaiser, 5th Edition, CRC Press NY, 2007, Chapter 13, Supporting Processes, pp. 273-278.