Methods to Produce Hydrogen
Hydrogen is the third most abundant element on Earth but is rare in pure form. Hydrogen is normally a gas and leaks in space because Earth's gravity is insufficient to hold on to the extremely light hydrogen atoms. Hydrogen can be liberated from many different compounds by using laboratory and industrial methods.
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Metal-acid Reactions
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Many different combinations of metals and acids may be reacted to yield hydrogen gas and a metal salt. The general metal-acid reaction can be shown as M + HA -> MA + H. In this equation, M is a metal and HA is an acid. A is some element or compound known as a conjugate base. A common example of a metal-acid reaction is with zinc (Zn) and hydrochloric acid (HCl). The following equation shows this reaction: Zn + 2HCl -> ZnCl2 + H2.
Electrolysis
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Electrolysis is the process of splitting water (H2O) into hydrogen and oxygen with electricity. This can be demonstrated by mixing an electrolyte in the water to allow it to conduct electricity. The 2 leads from a battery are placed in the water so that they don't touch each other. The electrolyte completes the circuit and the energy from the electricity splits the bond between the hydrogen and oxygen atoms.
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Extraction from Methane
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Natural gas is mostly methane (CH4) and provides the most commercially important source of hydrogen. Methane and water combine to form hydrogen and carbon monoxide (CO) gas as the following equation shows: CH4 + H2O -> 3H2 + CO. This reaction requires high heat (700 to 1,100 degrees Celsius) and pressure (20 atmospheres).
Secondary Reaction
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Adding excess water to the above reaction will prevent the methane from breaking down into carbon instead of carbon monoxide. This allows additional hydrogen to be recovered from a reaction between water and carbon monoxide as follows: CO + H2O -> CO2 + H2. This secondary reaction requires a catalyst such as iron oxide in order to proceed readily. The equal mixture of carbon monoxide and hydrogen in this reaction is known as water gas.
Additional Reactions
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The partial oxidation of methane is another common method of obtaining hydrogen from methane. Methane can be burned in the presence of pure oxygen to yield hydrogen and carbon monoxide as the following equation shows: 2CH4 + O2 -> 2CO + 4H2. Another reaction known as the coal reaction involves passing steam over red-hot coke to produce water gas as follows: C + H2O -> CO + H2.
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