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Comment by ZeroGravitas | Hacker News Reader

If this worked, then you'd still need it to be better than using the money expended to offset other other fossil carbon usage, one means of which could be converting gasoline using processes to use electricity directly.

As a result, I don't think this can ever make logical sense under any circumstances, very similar to carbon capture attached to fossil fuel generators. It just doesn't pencil out, even in theory.

Basically, gasoline isn't a particularly good fuel unless society is letting you dump the pollution for free, in which case it still isn't particularly good, but some other sucker is paying the price for it. And that other sucker is often you.

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It doesn’t make sense for cars (electricity is a practical alternative and if you wanted to use chemical fuels you would synthesize methane or 1-butanol, dimethyl ether or some other single-entity fuel for which the production process can be optimized)

Aviation is 30-40 years behind in fuels (they still use leaded gas.). The kind of Fischer-Tropsch chemistry that these guys are messing with has been basically abandoned for automotive use but is still being pursued for jet fuel because they are afraid to use any fuel which isn’t identical to existing fuels in composition…

Traditionally these processes start with a stream of hydrogen and carbon monoxide which can be made from coal or methane, the economics are gawdawful because the reactions that build up hydrocarbons and break them down have to be closely balanced —- polyethylene formation can be explosive, methane forms quickly if the temperature is too high. What it means is you have a big machine (high capital cost) that makes just a trickle of fuel. In the green era people like these guys are mixing up the chemistry so you can put CO2 in instead.

I have been thinking about how you would make plastic membranes from asteroid materials, we think some asteroids have something that is basically coal and the head end would turn that into ‘petrochemicals’ and might have a lot in common with fuel synthesizers… A lot of chemical processes will create waste CO2 which is precious in that context and has to be recycled.

> Aviation is 30-40 years behind in fuels (they still use leaded gas.).

In small aeroplanes yes, I don't think Jet-A has lead in though.

The only place aviation uses leaded gas is in the small, piston engine part of the market that represents primary training or hobbyist/personal transportation flying. In those cases, it's more like engine designs are 70 or 80 years behind current designs; and oftentimes the actual aircraft are not much younger.

There's no lead in jet fuel, and I'm just not exactly sure what you mean by aviation being "behind" in fuels in that respect. What's the leading edge supposed to be, in gas turbine technology, other than essentially kerosene?

Jet A is just fine in the context that you are making it from crude oil and you don’t mind the CO2 emissions.

If you want to make carbon neutral jet fuel based on biomass or direct captured CO2 on the other hand, kero is terribly hard to synthesize. Back in the bad old days politically isolated countries such as Nazi Germany and apartheid South Africa built expensive factories to make gasoline and diesel from coal using the same kind of chemistry that the authors of that paper are using.

Even then the economics were so bad it was an act of desperation and nobody would be attempting to synthesize hydrocarbons for ground transportation today because we have batteries, fuel cells, methane, alcohol and other fuels that can be bio based or synthesized more easily.

The Jet A problem is different from the leaded avgas problem but it comes from the same root that if your engine stalls out because of a fuel problem (say water separates out, freezes, clogs your fuel lines and all the engines fail) you have to hurry and find a place to land pretty quick, whereas if it happens to your car it is not so bad. There’s that any and also an unwillingness to make aviators upgrade their hardware (look at the 5G vs altimeters fight.)

> .. you would synthesize methane or 1-butanol, dimethyl ether or some other single-entity fuel ...

I agree that simple fuels makes more sense to synthesize. Methane is simple, but way more difficult to handle than gasoline. 1-butanol and other liquids would be great, but it is not so easy to produce in scale yet, I believe.

Methane is very low cost (where pipeline networks exist), will probably still be comparatively low cost in the synthetic fuel age, and is much easier to handle than hydrogen. Big airports could have LNG plants on site, smaller ones would have to truck it in.

Methane-based planes might have a lower TCO if the industry made the switch but the switch would be hard.

I don't think you can talk about the engines being the problem if the supposed alternative to kerosene-type fuels are methane and alcohol - the engines are probably the easy part of the problem there; it's the pressurization or cryogenic requirement for methane and the significantly lower (~half?) mass energy density for alcohol fuels.

Hydrocarbons are fantastic fuels when high energy density is required. In fact, airliners would be completely impossible without them. Even the most fantastic experimental batteries have nowhere near enough energy density for efficient powered flight. There are some plausible concepts for hydrogen powered planes, but those waste a lot more space on fuel tanks compared to hydrocarbon powered ones.

Synthetic hydrocarbons will probably remain the only option for carbon-neutral long-distance travel in the foreseeable future.

Simply offsetting the carbon, by replacing fossil fuel uses in other sectors, makes more financial/economic/practical sense than creating synthetic hydrocarbons to greenwash your own specific usage. People really are stuck in a fossil-fuel mindset when the real solution is to stop using them as fast as possible. A simple carbon fee does this without much fuss. People peddling synthetic hydrocarbons are, again like carbon capture and storage attached to fossil fuel generators, simply bullshitting. They might as well claim to be transitioning to perpetual motion powered flight that they have working today at lab scale. Because, basically that is what they are saying.

The concern about aviation is not so much today (being responsible for of 3.5% climate change)

https://research.noaa.gov/article/ArtMID/587/ArticleID/2667/...

but tomorrow, in that we expect a lot of growth in aviation. That might not be the case, why take a lover for a weekend to Paris when you can go to Montréal? A nuclear powered aircraft carrier could synthesize jet fuel from the ocean and atmosphere and even if it is $15 a gallon it is a bargain -- so the US Military sponsors this kind of research.

The best case for carbon capture now is this technology

https://en.wikipedia.org/wiki/Bioenergy_with_carbon_capture_...

applied to sugar cane alcohol factories in Brazil. You can catch CO2 from fermentation and not have to separate it from N2, compress to 1500 psi and inject into a saline aquifer. Those bioenergy plants are much better than bioenergy plants in the US by any economic or environmental metric. They'd have to get paid something per ton of CO2 captured to make it worth it. This industry is located close to populated areas such as São Paulo and does no harm to rainforests that Brazil must also protect.

Another case is the petrochemical industry in the southern US where CO2 streams are abundant and could be aggregated for scalable saline injection.

Any sort of space manufacturing will require a "circular economy" for carbon (it's precious) and whatever passes for a "petrochemical factory" will produce CO2 and that needs to have energy put into it into some form that can be put back into the "head end", methane would be great. The unique opportunity there is very high temperature chemistry with 24-7 sunlight concentrated with metallized plastic membranes made from the produce of the "petrochemical factory".

I'm optimistic about turquoise hydrogen, which is effectively the same thing as your bioenergy link, except you don't burn the biofuel then capture the CO2 you just remove solid carbon from it, and use the hydrogen as a chemical feedstock (or, if really, really necessary and there's literally no other option, as a fuel). And the key reason that would be better, is because burning biofuel is kind of crappy, just like burning fossil fuel is, and you're better off just directly using the cheap renewable electrical energy that you're going to waste seperating and storing the CO2 you create.

I'm also fairly sure electrical flight will be a thing long before we get to the last 3.5% of fossil fuel use anywhere on earth. Gasoline isn't magic, it's just something that we had a lot of lying around and didn't punish people for polluting and killing people with it, because the people with access to it became politically influential. That's it's only unique advantage, which thankfully seems to finally be fading.

How long ago were EVs totally impossible because of the amazing energy density of gasoline? Like 5 years maybe, and now that's laughable. EVs are clearly better. Did gasoline get suddently less energy dense in that period or was that always just BS supported by nothing more than status quo bias?

No, EVs were not "totally impossible" 5 years ago. The first GM EV1s with NiMH batteries were produced 23 years ago, and the first Tesla roadsters with Li-ion batteries 14 years ago. The battery capacity and weight of the roadster are not dramatically different from that of modern EVs.

In vehicles, energy density is not terribly important. The issue has always been the price of the cells. Only very recently they started becoming cost competitive compared to ICE powered vehicles.

The situation is very different in airplanes. At takeoff, something like 40% of the total mass of an airliner is just fuel. The best Li-ion cells have something like 50 times lower energy density than kerosine. It is simply not possible to fly any useful distance with such a low energy density.

Famous and highly cited energy theorist Vaclav Smil was still calling them an overhyped dead end 5 years ago, a decade ago he said "The myth that the future belongs to electric cars is one of the original misconceptions of the modern energy era".

And he literally wrote a book published in 2015 on the topic of energy density.

So I'm glad it's obvious now with 20/20 hindsight, but it seems a lot of people can be wrong about this stuff and have their opinions promoted.

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