Rocket fuel

[Kevin_Hall]

While Elon is on its way to use CO2 to produce rocket fuel, I've got another question.
Is it actually possible to reduce plastic waste into rocket fuel?

[MigL]

Problem is, rocket fuel has to have a certain efficiency.
The thrust provided by the mass of propellant has to be able to acheive orbit.

[Ken Fabian]

2 hours ago, Kevin_Hall said:

Is it actually possible to reduce plastic waste into rocket fuel?

Given plastic waste can be turned into liquid hydrocarbons and those can be used as rocket fuel - yes. It doesn't look like an efficient means of either reducing plastic pollution or producing rocket fuel.

Ultimately we need to shift to recyclable/decomposable plastics and make rocket fuels using low emissions methods.

[Kevin_Hall]

21 hours ago, MigL said:

Problem is, rocket fuel has to have a certain efficiency.
The thrust provided by the mass of propellant has to be able to acheive orbit.

So, you think plastic waste will never become a source for producing rocket fuel, because it will have zero efficiency?
 

[exchemist]

23 hours ago, Kevin_Hall said:

While Elon is on its way to use CO2 to produce rocket fuel, I've got another question.
Is it actually possible to reduce plastic waste into rocket fuel?

Um, Kevin, Elon (Musk) is a person. Perhaps you mean Space X is on its way to using CO2  for rocket fuel.  However all I can find on this is some throwaway comment on social media from Musk. Do you have information about a concrete proposal from Space X to do this? How do they plan to do it?     

[Kevin_Hall]

4 minutes ago, exchemist said:

Um, Kevin, Elon (Musk) is a person. Perhaps you mean Space X is on its way to using CO2  for rocket fuel.  However all I can find on this is some throwaway comment on social media from Musk. Do you have information about a concrete proposal from Space X to do this? How do they plan to do it?     

I mean Elon claimed that SpaceX was going to absorb CO2 to create rocket fuel. I thought it was clear. 
Such solutions do already exist, such as NASA's one 
https://technology.nasa.gov/patent/TOP2-160

As a matter of fact, such technology has been used by Canadian company Carbon Engineering
https://www.nationalgeographic.com/science/article/carbon-engineering-liquid-fuel-carbon-capture-neutral-science

By the way, what is your personal opinion on creating rocket fuel using plastic waste, exchemist?

[exchemist]

26 minutes ago, Kevin_Hall said:

I mean Elon claimed that SpaceX was going to absorb CO2 to create rocket fuel. I thought it was clear. 
Such solutions do already exist, such as NASA's one 
https://technology.nasa.gov/patent/TOP2-160

As a matter of fact, such technology has been used by Canadian company Carbon Engineering
https://www.nationalgeographic.com/science/article/carbon-engineering-liquid-fuel-carbon-capture-neutral-science

By the way, what is your personal opinion on creating rocket fuel using plastic waste, exchemist?

Thanks, um, Kevin. These are nothing to do with Space X, I notice.

The NASA one seems to be a kind of artificial photosynthesis, but they don't explain what they aim to react with the CO2. If they want to make methane, they need hydrogen from somewhere. Is this water? Doesn't seem to be specified. All very unclear.

The National Geographic report is about capture of atmospheric CO2 (which I have read is being done at pilot plant scale in Iceland) and reacting that with hydrogen from electrolysis. So it requires a lot of electricity -  just as producing hydrogen itself does. For rocket fuel I can't see this has much advantage over simply producing hydrogen, which is a well established rocket fuel already.

As for Musk's claim, again I struggle to see the point if all it involves is reacting CO2 with a hydrogen source to produce a hydrocarbon fuel. When you burn it, you will get the CO2 back again. So what is the advantage over simply generating hydrogen and burning that?

Re plastic waste, there is a pyrolysis method for producing a mixture of light, medium and heavy hydrocarbons, rather analogous to the products of fractional distillation of crude oil. No doubt some of these fractions could potentially be used as rocket fuel, but since methane, propane, gasoline, diesel etc., are not used for rocket fuel today, I suspect the products of this process would not be first choice for rocket engineers.   

Edited January 5, 2022 by exchemist

[exchemist]

Actually I was wrong on one point: seems kerosene is used for rocket fuel. So no doubt they could collect a kerosene fraction from this pyrolysis process and use it.

But it's not very environmentally friendly, as the other fractions are carbon-rich fuels. I'm not sure we want to burn our waste plastic if we can help it.   

[Ken Fabian]

5 hours ago, exchemist said:

For rocket fuel I can't see this has much advantage over simply producing hydrogen, which is a well established rocket fuel already.

I think Hydrogen's greatest downside is it is difficult to store. That includes being bulky compared to other kinds of rocket fuel. It is challenging to use when all the infrastructure is on Earth and most of it gets used within minutes of launch; producing Hydrogen on Mars and using it for launching return journeys for example would be a lot more difficult. As would any long range missions, where the storage duration becomes an issue.

I don't know if carbonaceous asteroid material could be used to produce hydrocarbon liquid fuels - it seems likely it could.

Edited January 6, 2022 by Ken Fabian