Octane Options

[Madswede]

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

Wow....great question.

Any Petrochem Engineers out there?

Well, I'm a chemical engineer, but I haven't worked in the petroleum field since college. Still, I don't think it would be wise to put water into an ethanol-gasoline blend. Ethanol and water are soluble in each other, so the ethanol-fuel mixture would simply dissolve the water until it couldn't anymore, at which point phase separation would occur. But the mixture of ethanol-fuel will hold the water (in this case, the fuel mixture would be the solvent, water would be the solute). One might have some success by using a vast quantity of water and pouring some ethanol-fuel into it, gently mixing it to get the ethanol and water to mix, then letting the mixture re-separate, but I don't think that would work very well - it would be a competing dissolution process and I don't know the equilibrium constants for ethanol in water vs. ethanol in gasoline. Better separation technologies would be needed such as fractional distillation, solvent-extraction with a better solvent than water (I think), possibly using a resin bed of some kind as a catalyst for separation.

EDIT: see here... http://www3.epa.gov/otaq/regs/fuels/rfg/waterphs.pdf

[bretth]

Is it usually only the 91 octane that comes as ethanol free? From what I am seeing on the pure-gas.org site so far they are all listing 91 octane in the 'details' section.

Brett

[914_teener]

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

Wow....great question.

Any Petrochem Engineers out there?

Well, I'm a chemical engineer, but I haven't worked in the petroleum field since college. Still, I don't think it would be wise to put water into an ethanol-gasoline blend. Ethanol and water are soluble in each other, so the ethanol-fuel mixture would simply dissolve the water until it couldn't anymore, at which point phase separation would occur. But the mixture of ethanol-fuel will hold the water (in this case, the fuel mixture would be the solvent, water would be the solute). One might have some success by using a vast quantity of water and pouring some ethanol-fuel into it, gently mixing it to get the ethanol and water to mix, then letting the mixture re-separate, but I don't think that would work very well - it would be a competing dissolution process and I don't know the equilibrium constants for ethanol in water vs. ethanol in gasoline. Better separation technologies would be needed such as fractional distillation, solvent-extraction with a better solvent than water (I think), possibly using a resin bed of some kind as a catalyst for separation.

EDIT: see here... http://www3.epa.gov/otaq/regs/fuels/rfg/waterphs.pdf

There ya go Mark.....like making Crack or Meth....I love this place.

Now I know why I am a Civil Eng.......hated chemistry.

[GregAmy]

I'm no chemist (and I don't play one on TV) but...one of the tests I do as an SCCA scrutineer is to determine the amount of ethanol in the fuel (we allow 10% max).

The method I use is to take a sample of fuel from the car and pour it into a 100mL graduated cylinder to the 90mL mark. I then pour in 10mL of water. Shake it up briskly and then let it sit. The water will "capture" (whatever the correct word is) the ethanol from the gasoline and a clear line will emerge between the gasoline and the water/ethanol mix. The difference between the measurement of the mix and my original 10mL of water is how much alcohol was in the fuel; simple math (difference divided by 90) tells me what the percentage was.

If this is something you wanted to do yourself, you can, but it presents a couple problems to you:

One, the water/ethanol mix goes to the bottom, but how are you going to decant the gasoline off the top efficiently and at the production levels you're looking for? And what are you going to do with the resulting dregs (please don't pour it down the drain!)

Two, as noted above, ethanol increases octane (which is why SCCA limits max level). If you decant out all the ethanol, you have no way of knowing what the resulting octane of your gasoline is. And it's not a linear add/subtract ratio (i.e., you can't add 50/50 94 octane and 110 octane together and call it 102; it comes out to more like 98).

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

GA

[DRPHIL914]

Is it usually only the 91 octane that comes as ethanol free? From what I am seeing on the pure-gas.org site so far they are all listing 91 octane in the 'details' section.

Brett

our ethanol-free "marine gas" sold here is 87 octane so that is what i put in the 914. today its $2.15, same price as premium 93 octane at the same station. Our regular gas just today hit $1.59 btw

[Mark Henry]

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

That's why I never tried it, in my area 91 premo is pure gas.

Thank's for the info Madswede, I just brought this up because there's a couple guy's doing this on youtube.
I know nothing on the chemistry end other than how to do the simple test for ethanol.

[Madswede]

I'm no chemist (and I don't play one on TV) but...one of the tests I do as an SCCA scrutineer is to determine the amount of ethanol in the fuel (we allow 10% max).

The method I use is to take a sample of fuel from the car and pour it into a 100mL graduated cylinder to the 90mL mark. I then pour in 10mL of water. Shake it up briskly and then let it sit. The water will "capture" (whatever the correct word is) the ethanol from the gasoline and a clear line will emerge between the gasoline and the water/ethanol mix. The difference between the measurement of the mix and my original 10mL of water is how much alcohol was in the fuel; simple math (difference divided by 90) tells me what the percentage was.

If this is something you wanted to do yourself, you can, but it presents a couple problems to you:

One, the water/ethanol mix goes to the bottom, but how are you going to decant the gasoline off the top efficiently and at the production levels you're looking for? And what are you going to do with the resulting dregs (please don't pour it down the drain!)

Two, as noted above, ethanol increases octane (which is why SCCA limits max level). If you decant out all the ethanol, you have no way of knowing what the resulting octane of your gasoline is. And it's not a linear add/subtract ratio (i.e., you can't add 50/50 94 octane and 110 octane together and call it 102; it comes out to more like 98).

You're far better off finding a local supplier of non-ethanol fuel. Easier, cheaper, less mess and hassles.

GA

Yeah OK, I sit corrected! (IMG:style_emoticons/default/smile.gif) I was mistaken in my conclusion, obviously since it works, and yet I had all the evidence on why! What I mean is, the more I think about it, as long as water and ethanol are infinitely soluble in each other and have limited (or in water's case, no) solubility in gasoline, then it stands to reason that EtOH-water would dissolve in each other then separate from the gasoline ... clearly the solubility of EtOH in water must be higher than in gasoline! In fact, that is exactly what solvent-solvent extraction is, which is one of the things I suggested. Hey ho, I'm rusty in that area. Thanks for the correction!

What you went on to say makes a lot of sense to me ... as you concluded it seems very hard to separate the water by decanting (maybe a large container with a valve at the bottom would work if some gasoline was sacrificed, but there sure are easier ways, like just buying EtOH-free gas. I like your point about the octane rating too. Makes sense to me.