From gas: steam reforming
The most common industrial process to produce hydrogen is the steam reforming of natural gas. The main component of natural gas is methane (CH4). At high temperatures (between 700 and 1100°C), water vapour reacts with methane to produce carbon monoxide and hydrogen. This mixture of hydrogen and carbon monoxide is commonly referred to as ‘synthetic gas’. If the process is undertaken in the presence of excess water vapour, the carbon monoxide is further oxidized to yield carbon dioxide, which also leads to additional hydrogen production. The hydrogen is then purified under high pressures (20 Atmospheres). In this process, for each kg of hydrogen produced, 10kg of CO2 are emitted.