Air-to-fuel: The chemistry

[JebKeb]

Now, if there are any comments about the economic viability of this, please go back and post them on the original thread. I want this to be a chemistry and engineering only discussion.

I've been developing a system to produce synthetic petroleum for quite a while. I first showed it to the KSP community on the original thread. Now, I'd like to iron out the chemistry until it's all sorted and I can write it up completely. (This is no university project, just a hobby.) I'll write out the concept and put italics on things which I am not certain of.

This is now the concept. Air is taken, and if it is dry, water is injected to provide a dew point above the freezing point of water. The air is heat exchanged with a coolant, then it travels along a large, inclined set of pipes with holes to extract humidity. The humidity is purified to near pure H₂O, then mixed with all the other streams of pure water from around the plant. It then is electrolysed into hydrogen and oxygen for use. 

The dehumidifies air is now compressed until the carbon dioxide is a liquid. It then goes down a similar system to the dehumidifier. The now pure air is vented. This carbon dioxide is taken, mixed with hydrogen and fed to a Sabatier process reactor, which produces water (which is drawn off) and methane. Some of the methane is odourised and pumped into the natural gas grid. Most of it is taken and mixed with pure oxygen, then catalytically partially oxidised in a reactor. The product of this reactor is syngas. The syngas is now altered to have desirable constituency, then it is fed into a Low Temperature Fischer-Tropsch reactor.

The LTFT syncrude is split in a reflux drum into gas, syncrude and water. The water has a large amount of alcohols in it, and these are seperated via fractionation into very pure chemicals. The syncrude is hydrotreated to turn alcohols into paraffins and water. The hydrotreated syncrude is then mixed with the gas, then put into a huge distillation column. Light naptha is isomerised, heavy naptha is catalytically reformed. The kerosene, diesel and lube fractions' fate has not yet been decided.

The gas rising out of the column is pressurised and fractionated. Unused syngas goes back to the LTFTR. CO₂ goes to the Sabatier reactor. Methane is CPOX'd. Ethane is cracked into ethylene, then blended in with the ethylene. Propane and propylene go on their merry ways. Butene and butane do something else. The butane is isomerised with the light naptha, then the isobutane and butene are alkylated into a high-octane petrol blending stock.

Atmo residue is taken to a vacuum distillation system. The light wax is put through a FCC, producing high octane crackate and cycle oil, which is mixed with the heavy wax and hydrocracked. The vacuum residue has an unknown path. Concept ends.

 

 

Now I shall submit my questions.

• Are there any other methods of producing syngas, not including gasification?
• Are there any non-sulphur using odourants for LPG and natural gas?
• What would be the most efficient method of capturing carbon dioxide and water?
• Would it be possible to use hydrogen to cleave C-O bonds in alcohols?
• What other things would be required to refine the kerosene, diesel and lube fractions?
• What is the composition of FCC product?

[Green Baron]

Question 3: from a palaeontological point of view the most efficient method of taking co2 out of one reservoir (atmosphere) and into another (biosphere) is - waiting, the biosphere does it. To put it simple: more co2 in atmosphere -> warmer climate -> more activity in biosphere -> more carbon is bound in plants and animals. It's (half of) a control loop. At least it was in the geological past. That cools the atmosphere that then holds less water in different isotopic fractions - that's where we get our climate records from.

With human pollution (kills portions of the biosphere capable of binding co2, burns old biosphere and sets the stored co2 free) the effect is probably weakened.

Can't help with chemical questions ... sorry ... but it sounds to my naive understanding as if you were putting a lot of energy (heating/cooling, pressure changes, electrolysis) in the system and getting little out.

 

[KSK]

Some questions and observations.

1. Why all the fiddling around humidifying and dehumidifying the air to start with? Not sure how you gain from that.

2. Check the CO2 phase diagram. You can compress air as much as you want but you won't get any CO2 out unless you also cool it down to around minus sixty Celsius. Even then the pitifully low partial pressure of CO2 in air is going to make the whole process horribly inefficient. 

3. For producing syngas, you might want to consider just going with the reverse water-gas shift reaction (CO2 + H2 ----> CO + H2O), take the water out (which you'll want to do anyway to drive the equilibrium of the WGSR the way you want it to go) and mix your carbon monoxide with hydrogen.

4. Efficiently extracting CO2 from air is a tough problem. Solve that one and you've just made the world a better place.

5. Reacting hydrogen with alcohols is apparently harder than it looks. I presume that it could be done with an appropriate catalyst at the right temperature. I'm not sure what you gain from it though as your end products are alkane and water, neither of which are as useful as the alcohol and both of which can be more cheaply made through other processes.

[wumpus]

Is this meant to be on Mars?  You simply skip most of that humidification/dehumidification process by merely choosing a non-desert climate on Earth and tapping a river filled by rain (a natural process that does all that for you).

Also the subject is rather misleading.  "Fuels" often imply an energy source, what you describe appears to be an energy sink (or more accurately, a low efficiency form of energy storage).  Obviously for lifting off Mars (or similar), it might not matter how inefficient your process is, as long as the end concentrates enough power to have TWR>>1

And as far as "keeping it to engineering", I'm glad I wasn't the one responsible for the debacle that caused my Chief Engineer's livid rant about "price is a spec"*.  If you can't get the price of this fancy system under the price of an oil well, it won't be a success.  There will be oil wells still around once there exists enough power from other sources to power this expensive process.  The only hope for this process is that the desire for fuel (for aerospace mainly?) and chemical feedstocks (and plastics if they use different wording) require more petro-products than the remaining oil wells can supply.

* You better believe heads rolled.  And more than a few laid off who had nothing to do with it, merely because of the lack of money it caused.

[YNM]

You can't fractionate alcohols out of water. Also, why would you humidify then undo it again...

[JebKeb]

14 hours ago, YNM said:

You can't fractionate alcohols out of water. Also, why would you humidify then undo it again...

Fractionate alcohols out of the water-alcohol solution, I should have wrote. Also, the dew point is too low sometimes, so the water would freeze. Putting some water in makes the dew point higher.

14 hours ago, wumpus said:

Is this meant to be on Mars?  You simply skip most of that humidification/dehumidification process by merely choosing a non-desert climate on Earth and tapping a river filled by rain (a natural process that does all that for you).

Also the subject is rather misleading.  "Fuels" often imply an energy source, what you describe appears to be an energy sink (or more accurately, a low efficiency form of energy storage).  Obviously for lifting off Mars (or similar), it might not matter how inefficient your process is, as long as the end concentrates enough power to have TWR>>1

And as far as "keeping it to engineering", I'm glad I wasn't the one responsible for the debacle that caused my Chief Engineer's livid rant about "price is a spec"*.  If you can't get the price of this fancy system under the price of an oil well, it won't be a success.  There will be oil wells still around once there exists enough power from other sources to power this expensive process.  The only hope for this process is that the desire for fuel (for aerospace mainly?) and chemical feedstocks (and plastics if they use different wording) require more petro-products than the remaining oil wells can supply.

* You better believe heads rolled.  And more than a few laid off who had nothing to do with it, merely because of the lack of money it caused.

In no way on mars!

I'm presently reviewing the entire energy situation on this idea.

 

[YNM]

7 hours ago, JebKeb said:

Fractionate alcohols out of the water-alcohol solution, I should have wrote. Also, the dew point is too low sometimes, so the water would freeze. Putting some water in makes the dew point higher.

Fractionate an azeotropic solution ? Really ?

[Shpaget]

You humidify the air to extract the humidity? Just use the water you were humidifying with.

Electrolysis is an expensive and inefficient way to produce oxygen and hydrogen. Electrolysis of ultra pure water is an impossible way to produce them as pure water can't be electrolyzed.

Getting CO2 from air is also inefficient. Thunderfoot did the math on the subject some time ago.

https://www.youtube.com/watch?v=dzq9yPE5Cbo

So, your first three steps are ridiculous. I can't comment on rest, but you are not going to get anywhere with these steps.

[JebKeb]

I dehumidify the air so it doesn't clog up the air processing.

15 hours ago, YNM said:

Fractionate an azeotropic solution ? Really ?

Only with the propanol fraction.

I've stumbled across something extremely peculiar. Take the following Fischer-Tropsch reaction:

2 CO + 5 H₂ -> C₂H₆ + 2 H₂O

CO takes 38kj/mol to produce, and high temp electrolysis produces H₂ for 216kj/mole. This means, per unit of feedstock, it takes 1156kj/unit to produce. What I've noticed is ethane produces 1560kj/mole in combustion, so this seems to leave a surplus of 404kj. 

404? That does seem suspicious...

Edited July 28, 2016 by JebKeb

[JebKeb]

With a bit more stuffing around the cost appears to have dropped from $200 billion to only $200 million. It still requires a 3.5 kilometre field, but it's a LOT smaller than the original, which was 13.5km! We can probably make it even smaller with wind and tide.

Edited July 28, 2016 by JebKeb

[shynung]

If the air is dry, it's much more efficient to look for places where the air is more humid, rather than injecting water into the intake air.

Also, what are the inputs and outputs? Only ambient atmosphere, or can it use other resources available nearby? What are the expected products?

[JebKeb]

21 hours ago, shynung said:

If the air is dry, it's much more efficient to look for places where the air is more humid, rather than injecting water into the intake air.

Also, what are the inputs and outputs? Only ambient atmosphere, or can it use other resources available nearby? What are the expected products?

Seeing how bad the energy scenario is playing out, I think I'll also be burning garbage to produce heat and carbon dioxide for the Air-To-Fuel system. (That's what I'm calling it.) It'll take in salt/seawater and water as well.

[shynung]

@JebKeb That would mean you're taking energy from the garbage, not the air. Essentially, you're taking a source of carbon (garbage), a source of water, and processing them into syngas, then into liquid hydrocarbons, which is then run through a standard hydrocarbon refinery processes to get fuels and chemicals usually produced by the petrochemical industry.

Waste-to-Fuel system, if you will. The same tech as coal liquefaction, just with different feedstock (garbage rather than coal).

Other than gasification, CO2 can be captured using scrubbers, which essentially absorbs CO2 that passed through it. This CO2 can later be extracted by running hot air through the scrubber.

Also, if you insist to get the the CO2 from the air (to save the environment, say), it's generally a good idea to tap them at the sources: the exhaust flue gas from coal power stations, industrial furnaces, and the like.

 

Edited July 29, 2016 by shynung

[Green Baron]

Found information on artficial photosynthesis:

https://news.uic.edu/breakthrough-solar-cell-captures-co2-and-sunlight-produces-burnable-fuel

I read a science-paper is in prep. ....

They say it could be used on mars if water was present.

Edited July 30, 2016 by Green Baron

[Tex_NL]

Humidifying the dry air only to dehumidify it immediately after makes no engineering sense. Better to just electrolyse the water you already have.

[StahnAileron]

On ‎7‎/‎27‎/‎2016 at 2:59 AM, JebKeb said:

[...] Also, the dew point is too low sometimes, so the water would freeze. Putting some water in makes the dew point higher. [...]

Like others here, I see no practical purpose to the humidification/dehumidification cycle. Your point it making the dew point higher just means you'll make it "easier" to extract the water from the air because you added more water. Dew point scales with the concentration of vapor in the air, so you'll still have the same dew point after you remove the moisture you added. This is an extraneous process that won't do anything other than waste energy. Just dehumidify the air. Or better yet, just get a ready source of liquid H₂O. Same with the CO₂ source, really. Unless your goal is to also have some form of CO₂ capture built into the process for whatever reason.

Oh, BTW, liquid CO₂ is impractical to produce. It takes over 5 atmospheres of pressure at around -60 degrees Celsius to produce CO₂ in liquid forms. Easy enough to actually do (5 atmospheres is around 75psi; you can put that much pressure in a bicycle tire), but it's also probably easier to just freeze the CO₂ directly out of the air at around the same temperature, move it, then reheat it to gas form.

As mentioned, electrolysis is a power-hungry process. You're not gonna get much back on your power investment. Although:

On ‎7‎/‎27‎/‎2016 at 0:52 PM, Shpaget said:

Electrolysis is an expensive and inefficient way to produce oxygen and hydrogen. Electrolysis of ultra pure water is an impossible way to produce them as pure water can't be electrolyzed.

...isn't quite true. Generate enough voltage and anything will eventually become a conductor. (If horribly inefficient. Or you wind up with a plasma...)The only thing I can think of that is a "perfect" (electrical) insulator is a perfect vacuum. And that's only because you don't have electrons (and therefore charges) there in the first place to kick around. (Huh... So the literal "nothing" is the perfect insulator, now that I think about it...)

Edited July 30, 2016 by StahnAileron

[JebKeb]

17 hours ago, Tex_NL said:

Humidifying the dry air only to dehumidify it immediately after makes no engineering sense. Better to just electrolyse the water you already have.

If I didn't do that, then the air processing system would clog up, as I said before.

On 29/07/2016 at 9:00 PM, shynung said:

@JebKeb That would mean you're taking energy from the garbage, not the air. Essentially, you're taking a source of carbon (garbage), a source of water, and processing them into syngas, then into liquid hydrocarbons, which is then run through a standard hydrocarbon refinery processes to get fuels and chemicals usually produced by the petrochemical industry.

Waste-to-Fuel system, if you will. The same tech as coal liquefaction, just with different feedstock (garbage rather than coal).

Other than gasification, CO2 can be captured using scrubbers, which essentially absorbs CO2 that passed through it. This CO2 can later be extracted by running hot air through the scrubber.

Also, if you insist to get the the CO2 from the air (to save the environment, say), it's generally a good idea to tap them at the sources: the exhaust flue gas from coal power stations, industrial furnaces, and the like.

 

The energy was never coming from the air. Amine scrubbing looks like another good bet.

15 hours ago, StahnAileron said:

Like others here, I see no practical purpose to the humidification/dehumidification cycle. Your point it making the dew point higher just means you'll make it "easier" to extract the water from the air because you added more water. Dew point scales with the concentration of vapor in the air, so you'll still have the same dew point after you remove the moisture you added. This is an extraneous process that won't do anything other than waste energy. Just dehumidify the air. Or better yet, just get a ready source of liquid H₂O. Same with the CO₂ source, really. Unless your goal is to also have some form of CO₂ capture built into the process for whatever reason.

Oh, BTW, liquid CO₂ is impractical to produce. It takes over 5 atmospheres of pressure at around -60 degrees Celsius to produce CO₂ in liquid forms. Easy enough to actually do (5 atmospheres is around 75psi; you can put that much pressure in a bicycle tire), but it's also probably easier to just freeze the CO₂ directly out of the air at around the same temperature, move it, then reheat it to gas form.

As mentioned, electrolysis is a power-hungry process. You're not gonna get much back on your power investment. Although:

...isn't quite true. Generate enough voltage and anything will eventually become a conductor. (If horribly inefficient. Or you wind up with a plasma...)The only thing I can think of that is a "perfect" (electrical) insulator is a perfect vacuum. And that's only because you don't have electrons (and therefore charges) there in the first place to kick around. (Huh... So the literal "nothing" is the perfect insulator, now that I think about it...)

Something I probably want to mention: I am NOT taking all of my water from the air.

Anyway. Is this maths faulty?

80,000bpd = 150l/s

150l x 45MJ/l = 6750MJ/s

1kj = 1kw second

1kw second = 1kw

so 6750MJ = 6750MW.

Let's assume solar panels are $0.50/w. 

Total cost of system: $3.4 billion. Cha-ching

[StahnAileron]

No offense, but it feels like you're trying to side-step each issue any of us point out that you have little to no idea about. I mean, you're entire first paragraph about the idea is italicized, meaning:

On ‎7‎/‎26‎/‎2016 at 2:37 AM, JebKeb said:

[...] things which I am not certain of.

We all basically say that entire process step is pointless. I'm not sure if you're doing it on purpose, but every time it's mentioned, it feels like you just dismiss it with a hand-waved "reason" and hope we either understand what you mean or just ignore it. You're asking for engineering help. You'll be questioned on every point that doesn't make sense to an engineer. Engineers generally try not to assume anything on a project.

Either you're not explaining this clearly enough or you really want to believe your idea would work despite the outside engineering opinion and review you requested.

Anyway, your numbers don't have much context behind them. I'm assuming you're trying to figure out costs, but the units you use indicate what looks more like POWER costs than material costs. I haven't checked the number and units, but I have a feeling you're using them incorrectly to estimate whatever it is you're trying to estimate. If you seriously want engineering help, you need to provide better details so we know what to work with. We can't read your mind.

[YNM]

I guess the biggest factor here would be efficiency. If it's not efficient enough, things would just fall apart in any other sense.

So, biggest question : what are the actual efficiency of each process ? Because a lot of things is actually not that efficient.

[JebKeb]

I don't know what I'm talking about, I post gibberish. Other people don't understand it, I don't understand their responses.

This has come together in a big mess. I don't even know what to write.

I'm practically certain I'm not describing this clearly enough. It seems that it makes sense to me, but when it goes into text even I don't really understand it.

I think I should spend some time away from this issue and let myself mull over these responses. I'll come back in a while with something far clearer, so I can actually have a conversation.

The chemistry has been sorted out. I now know everything I think I need to know on the processes. In the meantime, a diagram will be sorted out. Then hopefully I can communicate far more clearly in another thread.

 

[p1t1o]

I know Gizmodo is a news site for ten-year olds, but I sometimes browse looking at the pictures and to see what hilarious scrapes the Rio Olympics have gotten into recently, and I just saw this which might have some relevant links in it:

http://gizmodo.com/solar-capture-technique-turns-co2-into-burnable-fuel-1784522575

I take no responsibility for the quality of the article, but it seemed like legit science.

 

[Green Baron]

1 hour ago, p1t1o said:

I know Gizmodo is a news site for ten-year olds, but I sometimes browse looking at the pictures and to see what hilarious scrapes the Rio Olympics have gotten into recently, and I just saw this which might have some relevant links in it:

http://gizmodo.com/solar-capture-technique-turns-co2-into-burnable-fuel-1784522575

I take no responsibility for the quality of the article, but it seemed like legit science.

 

See my link further up. This seems to be serious and meets OPs requirements. Science paper is in prep. i read.

Edit: some work has been done before on "artificial photosynthesis"

 

Edited August 1, 2016 by Green Baron

[JebKeb]

Yeah, that photosynthetic cell looks good. I just wonder about it's efficiency, because natural photosynthetic cells look good. Somewhere in the abstract i read "24% CO faradaid efficiency", but I have no idea what that means. If it is the overall efficiency, then what is more efficient: 2030s solar panels with advanced catalytic reactors, or a 2030s photosynthetic cell?

[todofwar]

On Saturday, July 30, 2016 at 4:01 AM, Green Baron said:

Found information on artficial photosynthesis:

https://news.uic.edu/breakthrough-solar-cell-captures-co2-and-sunlight-produces-burnable-fuel

I read a science-paper is in prep. ....

They say it could be used on mars if water was present.

Apparently it uses a tungsten catalyst, so I'm betting that like Nocera's leaf it won't be practical on a massive scale. Still, interesting advance. 

[TheDestroyer111]

It's better to skip the second part of the procedure as well as most of the first part of it and just make hydrogen fuel IMO.

Edited September 11, 2016 by TheDestroyer111