Thermal decomposition of water is occurring only in the temperature above 5177 o C (practically imposible) which is practically impossible to achieve nowadays. However, execution of decomposition in two cycles allows decreasing this temperature to 3067 o C:
CO + H2O > H2 + CO2 (477 degC)CO2 > CO + 1 O2 (3067 degC) Profitability of this method is strictly connected with possessing the cheap source of carbon monoxide (for instance gasification or incomplete combustion of coal) because the full cycle is too expensive in realisation, caused by the cost of achieving the temperature needed to decompose CO2.
Ad. But there are a lot of termochemical cycles which enables "low" temperature operations as:
Ispra Mark 2 (1972)
T 100C: Na2O.MnO2 + H2O = 2 NaOH + MnO2 T 487C: 4 MnO2 = 2 Mn2O3 + O2 T 800C: Mn2O3 + 4 NaOH = 2 Na2O.MnO2 + H2 + H2O
Ispra Mark 7B
T 1000C: 2Fe2 O3 + 6Cl2 (g) = 4FeCl3 + 3O2 (g)T 420C: 2FeCl3 = Cl2 (g) + 2FeCl2 T 650C: 3FeCl2 + 4H2 O = Fe3 O4 + 6HCl + H2 (g) T 350C: 4Fe3 O4 + O2 (g) = 6Fe2O3 T 400C: 4HCl + O2 (g) = 2Cl2 (g) + 2H2O
University of Tokyo Cycle #3 (UT- 3) (nuclear heat water-splitting)
1) Water splitting with HBr formation (1000 K):CaBr2 + H2O = CaO + 2 HBr 2) Oxygen formation (823 K) CaO + Br2 = CaBr2 + 1/2 O2 3) Bromine regeneration (493 K) Fe3O4 + 8 HBr = 3 FeBr 2 + 4 H2O + Br2 4) Hydrogen formation from FeBr 2 (923 K)3 FeBr2 + 4 H2O = Fe3O4 +6 HBr + H2
Modified Calcium-Bromine Cycle (nuclear heat water-splitting)
[1] Water splitting with HBr formation (1000 K):CaBr2 + H2O = CaO + 2 HBr [2] Oxygen formation (823 K) CaO + Br2 = CaBr2 + 1/2 O2 [3] Bromine regeneration (non- thermal plasma) 2 HBr + plasma = H2 + Br2
GA Sulfur-Iodine (nuclear heat water-splitting)
T 850C: 2 H2SO4 = 2 SO2 + 2H2O + O2T 300C: 2 HI = I2 + H2 T 100C: I2 + SO2 + 2 H2O = 2HI + H2SO4 Please see details @:
INITIAL SCREENING OF THERMOCHEMICAL WATER-SPLITTING CYCLES FOR HIGH EFFICIENCY GENERATION OF HYDROGEN FUELS USING NUCLEAR POWER: http://web.gat.com/pubs-ext/miscpubs/A23373.pdf
CO + H2O > H2 + CO2 (477 degC)CO2 > CO + 1 O2 (3067 degC) Profitability of this method is strictly connected with possessing the cheap source of carbon monoxide (for instance gasification or incomplete combustion of coal) because the full cycle is too expensive in realisation, caused by the cost of achieving the temperature needed to decompose CO2.
Ad. But there are a lot of termochemical cycles which enables "low" temperature operations as:
Ispra Mark 2 (1972)
T 100C: Na2O.MnO2 + H2O = 2 NaOH + MnO2 T 487C: 4 MnO2 = 2 Mn2O3 + O2 T 800C: Mn2O3 + 4 NaOH = 2 Na2O.MnO2 + H2 + H2O
Ispra Mark 7B
T 1000C: 2Fe2 O3 + 6Cl2 (g) = 4FeCl3 + 3O2 (g)T 420C: 2FeCl3 = Cl2 (g) + 2FeCl2 T 650C: 3FeCl2 + 4H2 O = Fe3 O4 + 6HCl + H2 (g) T 350C: 4Fe3 O4 + O2 (g) = 6Fe2O3 T 400C: 4HCl + O2 (g) = 2Cl2 (g) + 2H2O
University of Tokyo Cycle #3 (UT- 3) (nuclear heat water-splitting)
1) Water splitting with HBr formation (1000 K):CaBr2 + H2O = CaO + 2 HBr 2) Oxygen formation (823 K) CaO + Br2 = CaBr2 + 1/2 O2 3) Bromine regeneration (493 K) Fe3O4 + 8 HBr = 3 FeBr 2 + 4 H2O + Br2 4) Hydrogen formation from FeBr 2 (923 K)3 FeBr2 + 4 H2O = Fe3O4 +6 HBr + H2
Modified Calcium-Bromine Cycle (nuclear heat water-splitting)
[1] Water splitting with HBr formation (1000 K):CaBr2 + H2O = CaO + 2 HBr [2] Oxygen formation (823 K) CaO + Br2 = CaBr2 + 1/2 O2 [3] Bromine regeneration (non- thermal plasma) 2 HBr + plasma = H2 + Br2
GA Sulfur-Iodine (nuclear heat water-splitting)
T 850C: 2 H2SO4 = 2 SO2 + 2H2O + O2T 300C: 2 HI = I2 + H2 T 100C: I2 + SO2 + 2 H2O = 2HI + H2SO4 Please see details @:
INITIAL SCREENING OF THERMOCHEMICAL WATER-SPLITTING CYCLES FOR HIGH EFFICIENCY GENERATION OF HYDROGEN FUELS USING NUCLEAR POWER: http://web.gat.com/pubs-ext/miscpubs/A23373.pdf
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