Site items in: Content by Author Cedric Philibert

How green are green and blue hydrogen?

In August, Robert Howarth and Mark Jacobson, respectively from Cornell and Stanford Universities, published “How green is blue hydrogen”, an examination of the lifecycle greenhouse gas emissions (GHG) of blue hydrogen, i.e., hydrogen from steam methane reforming with carbon dioxide capture and storage (CCS). How valid were the assumptions behind the study, were the calculations correct and can a realistic case be argued for blue hydrogen going forward?

Methane splitting and turquoise ammonia

Most hydrogen today is produced from fossil fuels – steam methane reforming of natural gas, partial oxidation of coal or oil residues – and entails large CO2 emissions. This fossil hydrogen can be called “grey hydrogen”. Or sometimes, brown. The same color scheme applies to the ammonia produced from it, so we have “grey ammonia.” Or brown ammonia, your call. The exact carbon footprint depends on the fuel used and the efficiency of the facility, so you could easily identify many shades of grey. There is, however, another option to deliver clean hydrogen – and now another colour: turquoise, or green-blue (or blue-green). This is the colour of hydrogen from methane pyrolysis, a process that directly splits methane into hydrogen and solid carbon. Instead of being a waste, like CO2, that must be disposed of safely, solid carbon is potentially a resource.