Chemical engineer/author Robert Rapier, once a frequent contributor to Energy Collective, brings to hydrogen enthusiasts a harsh dose of reality: including fuel production, driving a car powered by "clean" hydrogen emits more greenhouse gases than one powered by gasoline:
"Praxair is one of the world’s largest producers of hydrogen, has broken down the carbon footprint associated with the individual process steps [of manufacturing hydrogen fuel]. I have converted their data to metric tons of carbon dioxide emitted by these process units per million ft3 of hydrogen produced.
- Combustion for reforming energy – 3.7 metric tons
- Combustion for steam – 2.5 metric tons
- Power for separation and compression – 0.1 metric tons
Adding this to the carbon dioxide produced from the natural gas reactions, the total becomes 19.3 metric tons of carbon dioxide produced per million ft3 of hydrogen. However, the Praxair paper noted that this is the theoretical minimum. Due to heat losses and inefficiencies, the actual number in practice in a large hydrogen plant is 21.9 metric tons.
This converts to 9.3 kilograms (kg) of CO2 produced per kg of hydrogen production. One kilogram of hydrogen is the energy equivalent of one gallon of gasoline, which produces 9.1 kg of CO2 when combusted."