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Production of Hydrogen

Commercial Production of Hydrogen

Hydrogen can be produced commercially through the following methods:

(1). From Water - Gas (this is a mixture of carbon(II) oxide and hydrogen). Water gas can be produced from:

(a). Hydrocarbons, e.g. Methane, CH₄ - when methane is passed into steam, over nickel catalyst at - 800^oC and 30 atm, water gas is produced.

CH_4(g) + H₂O_(g) → CO_(g) + 3H_2(g)

(b). From the passage of steam through a mass of hot coke at a very high temperature (about 1000^oC).

C_(s) + H₂O(g) → CO_(g) + H_2(g)

The water gas is mixed with more steam and passed over iron(III) oxide (as catalyst) at 450^oC. More hydrogen is produced and carbon(II) oxide gets oxidized to carbondioxide. I.e.

CO_(g) + 3H_2(g) + H₂O_(g) → CO_2(g) + 4H_2(g)

The carbondioxide is removed by dissolving the above products in water under 30 atm pressure - CO₂ dissolves.

H₂O_(g) + CO_2(g) → H₂CO_3(aq)

The gas is then passed through copper(I) methanoate in ammonia solution under pressure to absorb any trace of carbon(II) oxide which might be present as impurity if not removed - the hydrogen produced is pure.

(2). From the electrolysis of sodium chloride solution - hydrogen is obtained as a by product. It can also be produced through the electrolysis of water if it is cheap to obtain electrical energy.

(3). From the cracking of petroleum - When large hydrocarbon molecules are broken up, hydrogen is formed in large quantity as a by - product.

E.g. the cracking of butane.

C₄H_10(g) → C₄H_8(g) + H_2(g)

Laboratory Preparation of Hydrogen

(a). Hydrogen is commonly produced in the laboratory from the action of dilute mineral acids on certain metals. E.g. the action of dilute HCI on zinc.

Zn_(s) + 2HCI_(aq) → ZnCl_2(aq) + H_2(g)

The hydrogen gas obtained is collected above water (being insoluble in water)

Note: the degree to which any metal will react with a dilute mineral acid to produce hydrogen
depends on the position of the metal in the reactivity series, among other factors. This is summarized below:

K, Na, Ca, Mg, Al, Zn are attacked by dilute H₂SO₄ and HCl to produce H₂. Al will react with hot conc. HCl only.

H, Cu, Hg, Al are not attacked by dilute H₂SO₄ and HCl to produce H₂

Dilute HNO₃, being a very strong oxidizing agent, will not liberate hydrogen with metals, but water, except the metal is magnesium. Therefore, dilute HNO₃ is not used for hydrogen preparation. To prepare hydrogen in the laboratory, metals like Na and K are not used because their reactions with mineral acids are too violent (although hydrogen is produced).

(b). The reaction between certain metals and caustic alkalis will produce hydrogen: warmed sodium (or potassium) hydroxide solution will react with zinc, aluminium or silicon to liberate hydrogen. A solution of sodium (or potassium) tetrahydroxoaluminate(III), or trioxosilicate(IV) is left:

Zn(s) + 2NaOH_(aq) + 2H₂O_(l) → Na₂Zn(OH)_4(aq) + H_2(g)

2AI_(s) + 2NaOH(aq), + 6H₂O_(l) → 2NaAI(OH)_4(aq) + 3H_2(g)

Si_(s) + 2NaOH_(aq) + H₂O_(l) → Na₂SiO_3(aq) + 2H_2(g)

(c). The action of steam on heated iron:

3Fe(s) + 4H2O(g)

Fe3O4(s) + 4H2(g)

Related:

Hydrogen
Properties and Uses of Hydrogen