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The sweet spot for synthetic fuel, in most cases, is anhydrous ammonia. It stores in liquid form at room temperature under mild compression. Ammonia can be burn

by ncmncm 5y ago

The sweet spot for synthetic fuel, in most cases, is anhydrous ammonia. It stores in liquid form at room temperature under mild compression. Ammonia can be burned in place of natural gas in generators, and in place of bunker oil in ships given retrofitted tankage and plumbing. It is probably practical for retrofitted freight trucks, rail locomotives, and farm machinery. Its volumetric energy density is lower than kerosene's, but usually tolerably so. It is unlikely to find use in cars. Anyplace where LH2 aircraft operate, kerosene-powered airframes will be simply unable to compete. It is not clear that existing airframes can be retrofitted, and build-out of LH2 craft may take a long time. By 2040, if civilization has not collapsed yet, probably the majority will be LH2, and old kerosene airframes will be on marginal routes. Synthetic hydrocarbon fuel will have strong demand for at least a decade or two, maybe longer depending on many factors including various costs, taxes, and regulations.

coderenegade 5y ago
Maybe. Ammonia is certainly the best carbon-free fuel, the only real issue with it is its toxicity. Methanol is a lot easier to handle since it's a liquid at SSL conditions, and generally less dangerous, but it has it's own downsides (it's hygroscopic, for example). But I agree with you in the sense that, to me at least, the two most sane options for an e-fuel are methanol and ammonia. I think the path of trying to make synthetic petrol and diesel is probably the wrong choice.
- jabl 5y ago
  > Ammonia is certainly the best carbon-free fuel, the only real issue with it is its toxicity If we don't care about toxicity, might as well go with hydrazine, which is liquid at room temperature and has higher energy density than ammonia. ;) (No idea about the cost of hydrazine synthesis, though) > most sane options for an e-fuel are methanol and ammonia The article seems to say their process produces ethanol. If it really works as well as they claim it does, it could be a gamechanger.
  - ncmncm 5y ago
    We do, in fact, care about toxicity, so do not e.g. expect to see ammonia powering cars. NASA and ESA are phasing out use of hydrazine because of its unfortunate handling characteristics. But solid hydrazone might still find uses. Among the chief attractions of ammonia is that it is very simply synthesized with free feedstock. You bond hydrogen stripped from water to nitrogen from air. Although toxic, it is a lot lighter than air, so if it leaks it goes up, and does not hang about poisoning people in a broadening area. The main problem with hydrocarbons as synthetic fuel is that you need the carbon, which in air is at below 0.05% concentration. It is certainly possible, but seems unlikely to approach ammonia in cost.
    - jabl 5y ago
      > NASA and ESA are phasing out use of hydrazine because of its unfortunate handling characteristics. I read about various 'green propellant' efforts over the years, but it seems in practice hydrazine is still used for orbital manouvering systems. Of course for those the volumes are small compared to the launch rockets themselves. For launch vehicles it seems only old Russian and Chinese designs still use hydrazine. > Although toxic, it is a lot lighter than air, so if it leaks it goes up, and does not hang about poisoning people in a broadening area. Eventually yes it will dissipate upwards, but typically ammonia accidents result in a vapour cloud traveling close to the ground. E.g. https://www.youtube.com/watch?v=qIi4_Poo2HY https://www.youtube.com/watch?v=qIi4_Poo2HY > The main problem with hydrocarbons as synthetic fuel is that you need the carbon, which in air is at below 0.05% concentration. It is certainly possible, but seems unlikely to approach ammonia in cost. There's certainly a largish cost to concentrating CO2 from the atmosphere. Carbon Engineering, one of the companies in the DAC space, claims 8.8 GJ/ton. Just some back of the napkin comparison to the enthalpy of formation for CO2 and H2O (+ adding an assumed 70% efficiency for CO2 dissociation and water electrolysis), and assuming we're building hydrocarbons with a 2:1 H:C ratio, that would mean a roughly 40% energy penalty compared to starting with a concentrated CO2 feedstock. One the plus side you get a fuel with cheaper and safer handling, better energy density, and compatibility with existing equipment. Hard to say which approach will win. Might well be as you said, that for large industrial users that can take appropriate precautions like maritime shipping or peaker power plants ammonia will be a better solution, but for other smaller scale usage synthetic hydrocarbons will win.

by ncmncm 5y ago

coderenegade 5y ago

Maybe. Ammonia is certainly the best carbon-free fuel, the only real issue with it is its toxicity. Methanol is a lot easier to handle since it's a liquid at SSL conditions, and generally less dangerous, but it has it's own downsides (it's hygroscopic, for example). But I agree with you in the sense that, to me at least, the two most sane options for an e-fuel are methanol and ammonia. I think the path of trying to make synthetic petrol and diesel is probably the wrong choice.

jabl 5y ago
> Ammonia is certainly the best carbon-free fuel, the only real issue with it is its toxicity If we don't care about toxicity, might as well go with hydrazine, which is liquid at room temperature and has higher energy density than ammonia. ;) (No idea about the cost of hydrazine synthesis, though) > most sane options for an e-fuel are methanol and ammonia The article seems to say their process produces ethanol. If it really works as well as they claim it does, it could be a gamechanger.
- ncmncm 5y ago
  We do, in fact, care about toxicity, so do not e.g. expect to see ammonia powering cars. NASA and ESA are phasing out use of hydrazine because of its unfortunate handling characteristics. But solid hydrazone might still find uses. Among the chief attractions of ammonia is that it is very simply synthesized with free feedstock. You bond hydrogen stripped from water to nitrogen from air. Although toxic, it is a lot lighter than air, so if it leaks it goes up, and does not hang about poisoning people in a broadening area. The main problem with hydrocarbons as synthetic fuel is that you need the carbon, which in air is at below 0.05% concentration. It is certainly possible, but seems unlikely to approach ammonia in cost.
  - jabl 5y ago
    > NASA and ESA are phasing out use of hydrazine because of its unfortunate handling characteristics. I read about various 'green propellant' efforts over the years, but it seems in practice hydrazine is still used for orbital manouvering systems. Of course for those the volumes are small compared to the launch rockets themselves. For launch vehicles it seems only old Russian and Chinese designs still use hydrazine. > Although toxic, it is a lot lighter than air, so if it leaks it goes up, and does not hang about poisoning people in a broadening area. Eventually yes it will dissipate upwards, but typically ammonia accidents result in a vapour cloud traveling close to the ground. E.g. https://www.youtube.com/watch?v=qIi4_Poo2HY https://www.youtube.com/watch?v=qIi4_Poo2HY > The main problem with hydrocarbons as synthetic fuel is that you need the carbon, which in air is at below 0.05% concentration. It is certainly possible, but seems unlikely to approach ammonia in cost. There's certainly a largish cost to concentrating CO2 from the atmosphere. Carbon Engineering, one of the companies in the DAC space, claims 8.8 GJ/ton. Just some back of the napkin comparison to the enthalpy of formation for CO2 and H2O (+ adding an assumed 70% efficiency for CO2 dissociation and water electrolysis), and assuming we're building hydrocarbons with a 2:1 H:C ratio, that would mean a roughly 40% energy penalty compared to starting with a concentrated CO2 feedstock. One the plus side you get a fuel with cheaper and safer handling, better energy density, and compatibility with existing equipment. Hard to say which approach will win. Might well be as you said, that for large industrial users that can take appropriate precautions like maritime shipping or peaker power plants ammonia will be a better solution, but for other smaller scale usage synthetic hydrocarbons will win.