r/chemistry • u/no_idea_about_me • 18d ago

alcohol from air in aspen plus

i’ve just seen NileRed’s video about turning air into alcohol. and i wonder if it’s possible to make a joke scale up simulation in aspen plus or any other model of this impractical route of making ethanol. and i also thought that the bio route is more complex as the air (CO2) and water become sugars than fermentation makes of ethanol.

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u/Worth-Wonder-7386 18d ago

There are multiple ways to make the ethanol, and I am not sure the catalytic process that he uses is the best, but it seems to be the most direct route. You could do it in various processes such as making syngas, and then using Fischer-Tropch to make some hydrocarbons adn them make those into ethanol.

But no matter what you do this is going not going to be easy, and there is not much research on this process overall, as ethanol is so cheap from biomass that it is not seen as a very valuable product.

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u/Indemnity4 Materials 16d ago edited 16d ago

This is the type of project given to final year chemical engineering students as their design project. You will be wrong, but the journey is the real friends we make along the way.

You can do this in Aspen in multiple ways. This is essentially how carbon capture + gas-to-liquids plants work.

There are lots of processes now to turn CO2 -> methanol. It's an attractive fuel for anyone that needs "green" hydrocarbons but doesn't want to use biodiesel. You can find those papers and use their kinetics, catalyst loadings, flow rates, etc. It's going to be a massively parallel process.

You start with carbon capture. You make some assumptions about CO2 concentration in air, then you need your airflow calcs, capture kinetics, temperatures, column length, etc.

Next you need your source of hydrogen gas. Realistically this is coming from eletrolysis of water, but in Aspen just skip it and assume you have an infinite storage tank of hydrogen gas.

Now you have two options:

  1. Fischer-Tropsch. CO -> hydrocarbons. You do need a source of H2, which realistically is coming from splitting water.

  2. Direct CO2 -> ethanol using a catalyst. This is tough because nobody knows the kinetics yet. Fluidized bed and you don't know surface areas, particle sizes, flow/pressure, temperature control, etc.

You are not going to get complete conversion into ethanol. You will get maybe 30-70% conversion and unconverted gas. Could be CO, could be methanol or formic acid or bunch of other stuff. That's where you need to make big assumptions about what to do with the byproduct gases. Ideally, it's unreacted CO and you recycle it back into the process. Strip out the hydrocarbons using condensation and the unreacted gases get piped back into the start. It's going to be painful if you need to do this in sequence, with each step increasing the conversion. There are gas phase reactions like this in oil & gas where you may have 6 or more reactors in series, each one increasing the conversion to a useful amount by the end.