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something that tends to annoy me about hydrogen fuels - people emphasize that the combustion product is water. okay .. so that step is clean. but how was the h

something that tends to annoy me about hydrogen fuels - people emphasize that the combustion product is water. okay .. so that step is clean. but how was the hydrogen in the fuel cell produced in the first place? i guess it’s an energy consuming process that produces a decent level of pollution, whether it’s by electrolysis, heating of a chemical in the presence of a catalyst, etc.

namibj 7y ago
Fuel hydrogen is typically produced via steam reforming [0] and subsequent distillation/liquification. [0]: https://en.wikipedia.org/wiki/Steam_reforming https://en.wikipedia.org/wiki/Steam_reforming
- vbezhenar 7y ago
  CH4 + H2O ⇌ CO + 3 H2 CO + H2O ⇌ CO2 + H2 For every tonne of hydrogen produced this way, 9 tonnes of CO2 is also produced.
  - seventh-chord 7y ago
    Isnt the ratio closer to ~6 tons of CO2 per ton of H2? You get CO2 + 4 H2, which weigh 44 and 4*2 respectively. Also, isnt this a non-issue, because (at least in theory) the reaction is contained in your converter plant, where you can collect the CO2?
    - vbezhenar 7y ago
      That's quote from wikipedia. I think you're right with your calculations, so I don't really know where this number came from. What're you going to do with that collected CO2 other than releasing it to the atmosphere?
      - namibj 7y ago
        Separating from other gasses, followed by sequestering.
        vbezhenar 7y ago
        I guess that it would cost a lot. Technically you can do that with traditional coal plants.
        namibj 7y ago
        Those don't produce fuel. They produce electricity.
willis936 7y ago
Electrolysis does not produce pollution. If you are suggesting a mechanism by which it does, I would love to hear it. https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Water_splitting https://en.wikipedia.org/wiki/Water_splitting
- mac01021 7y ago
  The power generation mechanism you use to get the electric current for electrolysis may or may not be clean.
  - willis936 7y ago
    That’s entirely the point of hydrogen fuel. The process of producing or using hydrogen does not pollute. You have decoupled pollution from energy storage. Hydrocarbons pollute by their very nature. In order to have a carbon neutral hydrocarbon cycle you need an impractical number of CO2 capture facilities.
    - TeMPOraL 7y ago
      And to add to your comment, spelling it out in case it isn't obvious: you can also decouple pollution from energy production using photovoltaics, wind or hydro - and suddenly most of your power chain is clean (what remains dirty is manufacturing the power generator and power storage).
    - TheSpiceIsLife 7y ago
      > The process of producing or using hydrogen does not pollute. There’s no way this can be correct. You can’t use hydrogen to produce the electricity used in hydrogen electrolysis, because that’s not permitted in this universe.[1] Therefore the electricity has to come from some other source, which all generate life-cycle carbon emissions.[2] 1. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics https://en.wikipedia.org/wiki/Second_law_of_thermodynamics 2. https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...
pfdietz 7y ago
The water itself is also a problem, in the stratosphere. I think this places an ultimate limit on the number of rocket launches at about 1 million Starship launches per year.

namibj 7y ago

Fuel hydrogen is typically produced via steam reforming [0] and subsequent distillation/liquification. [0]: https://en.wikipedia.org/wiki/Steam_reforming https://en.wikipedia.org/wiki/Steam_reforming

vbezhenar 7y ago
CH4 + H2O ⇌ CO + 3 H2 CO + H2O ⇌ CO2 + H2 For every tonne of hydrogen produced this way, 9 tonnes of CO2 is also produced.
- seventh-chord 7y ago
  Isnt the ratio closer to ~6 tons of CO2 per ton of H2? You get CO2 + 4 H2, which weigh 44 and 4*2 respectively. Also, isnt this a non-issue, because (at least in theory) the reaction is contained in your converter plant, where you can collect the CO2?
  - vbezhenar 7y ago
    That's quote from wikipedia. I think you're right with your calculations, so I don't really know where this number came from. What're you going to do with that collected CO2 other than releasing it to the atmosphere?
    - namibj 7y ago
      Separating from other gasses, followed by sequestering.
      - vbezhenar 7y ago
        I guess that it would cost a lot. Technically you can do that with traditional coal plants.
        namibj 7y ago
        Those don't produce fuel. They produce electricity.

willis936 7y ago

Electrolysis does not produce pollution. If you are suggesting a mechanism by which it does, I would love to hear it. https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Electrolysis_of_water https://en.wikipedia.org/wiki/Water_splitting https://en.wikipedia.org/wiki/Water_splitting

mac01021 7y ago
The power generation mechanism you use to get the electric current for electrolysis may or may not be clean.
- willis936 7y ago
  That’s entirely the point of hydrogen fuel. The process of producing or using hydrogen does not pollute. You have decoupled pollution from energy storage. Hydrocarbons pollute by their very nature. In order to have a carbon neutral hydrocarbon cycle you need an impractical number of CO2 capture facilities.
  - TeMPOraL 7y ago
    And to add to your comment, spelling it out in case it isn't obvious: you can also decouple pollution from energy production using photovoltaics, wind or hydro - and suddenly most of your power chain is clean (what remains dirty is manufacturing the power generator and power storage).
  - TheSpiceIsLife 7y ago
    > The process of producing or using hydrogen does not pollute. There’s no way this can be correct. You can’t use hydrogen to produce the electricity used in hydrogen electrolysis, because that’s not permitted in this universe.[1] Therefore the electricity has to come from some other source, which all generate life-cycle carbon emissions.[2] 1. https://en.wikipedia.org/wiki/Second_law_of_thermodynamics https://en.wikipedia.org/wiki/Second_law_of_thermodynamics 2. https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emissions_of_energy_sources https://en.wikipedia.org/wiki/Life-cycle_greenhouse-gas_emis...

pfdietz 7y ago

The water itself is also a problem, in the stratosphere. I think this places an ultimate limit on the number of rocket launches at about 1 million Starship launches per year.