Explain briefly how hydrogen is manufactured on a large scale, from steam.

Step I

Reaction : Production of water gas

$\underset{\text{coke}}{\text{C}} + \underset{\text{steam}}{\text{H}$2\text{O}} \xrightarrow{1000 \degree \text{C}} \underset{\text{water gas}}{[\text{CO} + \text{H}2 ]} - \Delta

Reactants : White hot coke and steam
Temperature : Around 1000°C
Process : Passage of steam over white hot coke [carbon]
Chamber : Specially designed convertor

Step II

Reaction : Reduction of steam to hydrogen by carbon monoxide

$\underset{\text{water gas}}{[\text{CO} + \text{H}$2 ]} + \underset{\text{excess steam}}{\text{H}2\text{O}} \underset{\text{Fe}2\text{O}3} {\xrightarrow{450 \degree \text{C}}} \text{ CO}2 + 2\text{H}2 + \Delta

Reactants : Water gas and excess steam
Temperature : Around 450°C
Catalysts : Iron [III] oxide [Fe₂O₃], promoter chromic oxide [Cr₂O₃]
Process : Excess steam is mixed with water gas, passed over a catalyst at elevated temperatures.
[CO is converted to CO₂ with a further yield of hydrogen.]

Step III

Reaction : Separation of carbon dioxide [CO₂] and carbon monoxide from the above mixture

(a) CO₂ is removed by dissolving mixture in water under pressure [30 atmospheres], or caustic potash solution to dissolve CO₂.

2KOH + CO₂ ⟶ K₂CO₃ + H₂O

(b) CO is removed by dissolving mixture in ammoniacal cuprous chloride solution.

CuCl + CO + 2H₂O ⟶ CuCl.CO.2H₂O.

Thus, hydrogen gas is left over.