Thorsteinn I Sigfusson

The Taming of the Proton

Appendix II

Hydrogen Production Processes – Key Chemistry

All hydrogen production processes are based on a separation of hydrogen from hydrogen-containing feedstock. There are primary three methods to separate hydrogen; thermal, chemical and biological. Of which biological is still in the exploratory research and development phase.

 

Hydrogen from hydrocarbons:

 

Steam reforming

CnHm + 2nH2O ® nCO2 + (2n + m)/2 H2

 

 

 

 

Partial oxidation

CnHm + nO2 ® nCO2 + m/2 H2

 

 

 

 

Pyrolytic cracking

CnHm ® nC + m/2 H2

 

 

 

Hydrogen from coal:

 

Coal gasification

C + 2H2O ® 2H2 + CO2

 

 

 

 

Steam-iron process

 

 

(1)

C + H2O ® H2 + CO

 

(2)

H2 + Fe3O4 ® 3FeO + H2O

 

(3)

CO + Fe3O4 ® 3FeO + CO2

 

(4)

6FeO + 2H2O ® 2Fe3O4 + H2

 

(1 + 2 + 3 + 4)

C + 2H2O ® 2H2 + CO2

 

 

The advantage of the steam-iron process is that step 4 can be separated from the previous three steps thus giving a pure hydrogen.

 

Gasification of biomass:

 

Gasification

(C6H10O5)n + 7nH3O ® 6nCO2 + 12nH2

 

Hydrogen from electrolysis:

 

Electrolysis

 

 

Cathode

2H2O + 2e- ® H2 + 2OH-

 

Anode

H2O ® ½ O2 + 2H + e-

 

 

258 kJ + H2O ® H2 + ½ O2

 

 

 

Thermochemical cycles:

 

Thermochemical cycles

 

(1)

 6FeCl2 + 8H2O ® 2Fe3O4 + 12HCl + 2H2

650°C

(2)

2Fe3O4 + 3Cl2 + 12HCl ® 6FeCl3 6H2O + H2

<200°C

(3)

6FeCl3 ® 6FeCl2 + 3Cl2

350°C

(1+2+3)

2H2O ® 2H2 + O2

 

 

 

Hybrid processes:

 

Hybrid process

(1)

 SO2 + Br + 2H2O ® H2SO4  + 2HBr

50-100°C

(2)

2HBr ® H2 + Br2

Electrol.

(3)

H2SO4 ® H2O + SO2 + ½ O2

730-830°C

(1+2+3)

H2O ® H2 + ½ O2