Green hydrogen refers to hydrogen gas that is produced using renewable energy sources, such as solar or wind power, through a process called electrolysis. Unlike gray hydrogen, which is produced from fossil fuels like natural gas through steam methane reforming (SMR), green hydrogen is considered a more environmentally friendly and sustainable option.
To produce green hydrogen from natural gas, a process called methane pyrolysis or methane cracking can be employed. Here's a general overview of the process:
- Methane Reforming: Natural gas (mainly methane, CH4) is initially reformed to produce hydrogen gas (H2) and carbon monoxide (CO) through a process called steam methane reforming (SMR). This is a well-established industrial process and is commonly used to produce hydrogen.
CH4 + H2O → CO + 3H2
Carbon Separation: In the next step, the carbon monoxide produced in the reforming process is separated from the hydrogen gas. This can be achieved through various methods, such as pressure swing adsorption or membrane separation.
Methane Pyrolysis: The separated carbon monoxide is then subjected to high-temperature pyrolysis, typically above 700°C. This process breaks down the carbon monoxide into carbon (C) and carbon dioxide (CO2).
CO → C + CO2
- Hydrogen Production: Finally, the carbon dioxide produced in the pyrolysis step is removed, and the remaining hydrogen gas is collected. This hydrogen gas is considered "green hydrogen" as it is produced without direct carbon emissions, unlike traditional SMR processes.
It's worth noting that while this process avoids direct CO2 emissions, the overall carbon footprint of green hydrogen production from natural gas still depends on the source of the electricity used for the electrolysis process. To achieve a truly sustainable and carbon-neutral green hydrogen, it is preferable to use renewable energy sources for the electrolysis step.