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They said carbon neutral, so I'm assuming the idea would be to use carbon dioxide and hydrogen to make kerosene to begin with. Then you can burn it and get the

They said carbon neutral, so I'm assuming the idea would be to use carbon dioxide and hydrogen to make kerosene to begin with. Then you can burn it and get the carbon dioxide back to start over. It's not carbon from the process entirely, but instead simply not adding additional carbon dioxide to the atmosphere.

morpheos137 5y ago
ok. I see. Due to conservation of energy it takes energy to synthesize fuel hydrocarbons. So you might start with carbon dioxide, run it through some energy consuming process exposed to hydrogen and get hydrocarbons and water as the byproduct from the excess oxygen. I don't know enough chemistry to know what the exact synthesis method would be but I do know it would require substantial energy input. Thus the kerosene serves as a kind of battery. It is not a primary energy source any more. If this is feasible why not make carbon-neutral gasoline too?
- frosted-flakes 5y ago
  Too much energy loss. For airplanes it might still be worthwhile because the weight-savings are so subatantial.
- wiml 5y ago
  Yes, exactly. There are/have been various small scale projects along those lines. Hydrogen and CO2 to methane, to longer-chain hydrocarbons that can be put into existing engines. As you say, the synthetic fuel is just an energy (and carbon) carrier, you have to put all of that energy into the system somewhere — ideally from solar or wind or nukes or something.
- Sanguinaire 5y ago
  New Zealand synthesized fuel like this in the 80's during an oil crisis, as did Nazi Germany in the 1940's. It's well-understood chemistry, just too expensive right now. Probably will remain that way until it's too late unless we can put a ~$200/t tax on carbon emissions globally.
  - morpheos137 5y ago
    My understanding is Nazi Germany made synthetic fuels from carbon monoxide, eg from coking coal, which is a more reactive substance than carbon dioxide.
- kragen 5y ago
  Right! The idea is that kerosene is a more convenient form of energy storage than many alternatives, despite the lower efficiency and higher capital costs for recharging it. Compared to, say, Li-ion, kerosene has numerous order-of-magnitude advantages; for example: - safety: lithium-ion batteries explode if you look at them funny, and are full of poisons, while kerosene can put out a lit match and can be safely imbibed; - materials availability: carbon is about ten times as abundant in earth's crust as lithium, and there are readily available ways to concentrate carbon from the air such as planting forests, while concentrating lithium from seawater is somewhat trickier; - specific energy: Li-ion batteries can store 0.5 MJ/kg, and kerosene is 43 MJ/kg, which is a huge advantage for things like trucking and aviation; - energy density: Li-ion batteries store 1 MJ/liter, kerosene is 35 MJ/liter, which is also important for things like aviation; and - capital cost of storage facilities: you can store 200 liters of kerosene in a US$10 barrel, while 200 liters of lithium-ion batteries would be about 12,000 18650s, which costs on the order of US$50,000. Gasoline does indeed share most of these advantages and can also be used in cheaper engines that can rev faster. Other fuels that might be reasonable to synthesize in the same way include hydrogen itself, methane, LP gas (propane/butane), and ammonia (!!).
  - morpheos137 5y ago
    The best way to compare batteries is energy density per unit mass, energy input and output per unit cost, and cost of production/charging. Long chain hydrocarbons have a much higher density than Li and are easy to pump and store and work in existing vehicles, but a higher cost of production and they are essentially one time use, non rechargeable since the discharge mechanism is combustion. The ideal solution would be efficient solar bioreactors where bioengineered algea converted solar energy into fats as a bioproduct of a photosynthetic process sequester CO2 that could be esterfied into alkanes or that directly produced alkanes. Long chain alkanes, my understanding is, are not toxic to life. It is the short chain stuff and aromatic ring based stuff like benzene that is hazardous. https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/1751-7915.12423 https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/175...
    - kragen 5y ago

morpheos137 5y ago

ok. I see. Due to conservation of energy it takes energy to synthesize fuel hydrocarbons. So you might start with carbon dioxide, run it through some energy consuming process exposed to hydrogen and get hydrocarbons and water as the byproduct from the excess oxygen. I don't know enough chemistry to know what the exact synthesis method would be but I do know it would require substantial energy input. Thus the kerosene serves as a kind of battery. It is not a primary energy source any more. If this is feasible why not make carbon-neutral gasoline too?

frosted-flakes 5y ago
Too much energy loss. For airplanes it might still be worthwhile because the weight-savings are so subatantial.
wiml 5y ago
Yes, exactly. There are/have been various small scale projects along those lines. Hydrogen and CO2 to methane, to longer-chain hydrocarbons that can be put into existing engines. As you say, the synthetic fuel is just an energy (and carbon) carrier, you have to put all of that energy into the system somewhere — ideally from solar or wind or nukes or something.
Sanguinaire 5y ago
New Zealand synthesized fuel like this in the 80's during an oil crisis, as did Nazi Germany in the 1940's. It's well-understood chemistry, just too expensive right now. Probably will remain that way until it's too late unless we can put a ~$200/t tax on carbon emissions globally.
- morpheos137 5y ago
  My understanding is Nazi Germany made synthetic fuels from carbon monoxide, eg from coking coal, which is a more reactive substance than carbon dioxide.
kragen 5y ago
Right! The idea is that kerosene is a more convenient form of energy storage than many alternatives, despite the lower efficiency and higher capital costs for recharging it. Compared to, say, Li-ion, kerosene has numerous order-of-magnitude advantages; for example: - safety: lithium-ion batteries explode if you look at them funny, and are full of poisons, while kerosene can put out a lit match and can be safely imbibed; - materials availability: carbon is about ten times as abundant in earth's crust as lithium, and there are readily available ways to concentrate carbon from the air such as planting forests, while concentrating lithium from seawater is somewhat trickier; - specific energy: Li-ion batteries can store 0.5 MJ/kg, and kerosene is 43 MJ/kg, which is a huge advantage for things like trucking and aviation; - energy density: Li-ion batteries store 1 MJ/liter, kerosene is 35 MJ/liter, which is also important for things like aviation; and - capital cost of storage facilities: you can store 200 liters of kerosene in a US$10 barrel, while 200 liters of lithium-ion batteries would be about 12,000 18650s, which costs on the order of US$50,000. Gasoline does indeed share most of these advantages and can also be used in cheaper engines that can rev faster. Other fuels that might be reasonable to synthesize in the same way include hydrogen itself, methane, LP gas (propane/butane), and ammonia (!!).
- morpheos137 5y ago
  The best way to compare batteries is energy density per unit mass, energy input and output per unit cost, and cost of production/charging. Long chain hydrocarbons have a much higher density than Li and are easy to pump and store and work in existing vehicles, but a higher cost of production and they are essentially one time use, non rechargeable since the discharge mechanism is combustion. The ideal solution would be efficient solar bioreactors where bioengineered algea converted solar energy into fats as a bioproduct of a photosynthetic process sequester CO2 that could be esterfied into alkanes or that directly produced alkanes. Long chain alkanes, my understanding is, are not toxic to life. It is the short chain stuff and aromatic ring based stuff like benzene that is hazardous. https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/1751-7915.12423 https://sfamjournals.onlinelibrary.wiley.com/doi/10.1111/175...
  - kragen 5y ago