Hydrogen production and conversion to chemicals: a zero-carbon puzzle?

Abstract

Abstract Hydrogen is currently used as an intermediate product in the chemical (mostly ammonia and methanol) and refining industries. It is produced mostly from natural gas in large scale plants using steam methane reforming, a very mature technology. Hydrogen produced from natural gas has a high carbon footprint, considering that about 6–9 tons of CO2 are co-produced (and emitted to the atmosphere) per ton of produced hydrogen, depending on natural gas composition. For this reason, hydrogen produced from fossil fuels is nowadays named as “grey” hydrogen. The current production of hydrogen is responsible of about 2.5 % of CO2 emissions worldwide. For hydrogen remaining in business, and then becoming a factor in the energy transition period and later, decarbonizing its production is a must. Partially decarbonized hydrogen produced from fossil fuels, through CO2 capture, is named “blue” hydrogen. A completely different path is followed for the production of fully decarbonized, or “green” hydrogen. This path is already commercially available, though on a smaller scale than required for wide industrial application. It is the electrolysis of water, i.e. the use of electric power from renewable sources to break the water molecule into its constituent hydrogen and oxygen. Pros & cons of these two options will be critically examined.