Can someone explain the chemistry around adding Isopropyl Alcohol to water contaminated gasoline - why does this help?

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So there are many products on the market sold as fuel additives; some (like 'Heet' brand) are nothing more than 99.9% isopropyl alcohol in a nice package.

When trying to understand how they work and what they actually do you hear vague things like "Removes water in fuel. The alcohol will bond with water and solubilize water into gasoline so it can be burned and pass out exhaust"

From what I understand alcohol and water don't 'react' -> there is no chemical formula change. They simply mix really well. But how does this make this new mixture 'mix' with gasoline better?

I know that if you take 50% isopro (other 50% is water) and light it on fire, it will burn. But I understand that it's only the 50% of alcohol molecules burning, not the water. So at the end you'll still end up with the water remaining (excluding some evaporation from the heat).

I also read this on a chemistry forum: "Alcohol will not solubilize water into gasoline, and water cannot be burned. A mixture 50% ethanol or isopropanol + 50% gasoline dissolves less than 1% water."

What's going on? Can someone explain the actual chemistry please!?
 
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Ethanol (or methanol for that matter) does not literally remove the water from gasoline, but since water is miscible with the alcohol it will solubilize more water than gasoline will. All it does is keep it in solution. All the water that is present will stay but will be less susceptible to separation and freezing. This was the original advantage to Heet and other gas line antifreeze products. If you're buying E10 already then there is little reason to add more alcohol.
 
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Water wants to mix with alcohol. It doesn't want to mix with petroleum products including gasoline, but it can stay in suspension in gasoline for a long time before separating. That's the source of water contamination.

Alcohol in turn can also mix with gasoline, and straight alcohol is combustible in your engine.

This is very simplified and someone is going to fuss that I didn't dot every last "i", but it should give you the general idea.
 
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I know alcohol molecules are smaller than water molecules. They, "fit in between" each other. I remember a test we did in science class where we poured a carefully measured 100 ML of water into the exact same amount of alcohol.

The total volume was less than 200 ML because the alcohol molecules would slip in between each other. I think the same happens with the gasoline. The alcohol allows the gas and water to be "picked up" in a type of blend.

Ethanol Shield does this quite well. This video shows how it "eats up" the water. The same principal works with "Heet". From what I understand, that product does contain some alcohol, or methanol.

 
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This is my high school attempt at explaining what I was taught 100 years ago.

Basic n-heptane is C6H14. This is the backbone of gasoline. Six carbons and 14 Hydrogen atoms strung together.
Water is H2O. This is the backbone of water. Two Hydrogen atoms clinging to one Oxygen atom.
Isopropyl Alcohol is C3H8O. This is the backbone of isopropyl alcohol. It has 3 Carbon atoms that have seven Hydrogen atoms bonded to them with one little oxygen atom clinging on to a carbon atom. Attached to that Oxygen atom is another Hydrogen atom.

Fuel is pure hydrocarbon - no oxygen
Water is a hydroxyl group because it bonds hydrogen and oxygen together.
Alcohol is a hydroxyl group because it bonds hydrogen and oxygen together.

Water clings to the alcohol because of the "O-H" chemical bond the two share. Alcohol clings to fuel because of the "C-H" bond the two share. Water settles out of the fuel because there is no chemical bond between water and gasoline.

Most hydroxyl compounds will remove water from gasoline because of the "O-H" bond . Alcohol is cheap and relatively safe to deal with and it increases the octane of the finished fuel product, so it is used.

The next questions is: Why does isopropyl alcohol cause the water to fall out of suspension while ethyl alcohol causes the water to stay in suspension and be passed through the system along with the fuel?
 
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Basic n-heptane is C6H14. This is the backbone of gasoline. Six carbons and 14 Hydrogen atoms strung together.
Water is H2O. This is the backbone of water. Two Hydrogen atoms clinging to one Oxygen atom.
Isopropyl Alcohol is C3H8O. This is the backbone of isopropyl alcohol. It has 3 Carbon atoms that have seven Hydrogen atoms bonded to them with one little oxygen atom clinging on to a carbon atom. Attached to that Oxygen atom is another Hydrogen atom.

The next questions is: Why does isopropyl alcohol cause the water to fall out of suspension while ethyl alcohol causes the water to stay in suspension and be passed through the system along with the fuel?
Ethanol and isopropyl alcohol will act similarly to each other in this respect. Both are miscible with gasoline and water.

And gasoline is a wide variety of molecules but the primary hydrocarbon has longer or shorter chain length than heptane plus aromatics.
 
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What's going on? Can someone explain the actual chemistry please!?
We arent talking about gallons of water here.

but a few oz can settle out then freeze.

The alcohol keeps it in suspension. and its eventually burned.
if you already use 10% ethanol fuel adding HEET etc does nothing.
 
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looked at a few chickanic vids EXCELLENT!! very clear + precise in detail!!
 
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Gasoline with Ethanol will actually absorb even more moisture into your tank especially when left sitting for awhile the water separates out and ends up at the bottom of your tank which is especially bad for motorcycles, ATVs, lawn mowers, etc... things that tend to sit around a lot when not being used such as over winter.

Me personally I would rather just use straight gas and just treat it accordingly with Heet or Seafoam if I was trying to combat water in the fuel.

When you add the alcohol to the fuel it absorbs the water and allows it to be burned in the combustion chamber, most likely you will get reduced performance but it's still better than trying to burn water.
 
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Gasoline with Ethanol will actually absorb even more moisture into your tank especially when left sitting for awhile the water separates out and ends up at the bottom of your tank which is especially bad for motorcycles, ATVs, lawn mowers, etc... things that tend to sit around a lot when not being used such as over winter.

Me personally I would rather just use straight gas and just treat it accordingly with Heet or Seafoam if I was trying to combat water in the fuel.

When you add the alcohol to the fuel it absorbs the water and allows it to be burned in the combustion chamber, most likely you will get reduced performance but it's still better than trying to burn water.
The water is still there.

And you're only getting water in the tank if there is something wrong with the fuel system. I've opened up a 25-year old BMW tank and it was pristine inside, as have been other tanks including on my old Accord and my ECHO. None had any water or corrosion or anything amiss I could see. I live in an EPA nonattainment area so all we have is E10.
 
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The water is still there.

And you're only getting water in the tank if there is something wrong with the fuel system. I've opened up a 25-year old BMW tank and it was pristine inside, as have been other tanks including on my old Accord and my ECHO. None had any water or corrosion or anything amiss I could see. I live in an EPA nonattainment area so all we have is E10.
This is not correct - the gas tank has to move air in and out - from temperature changes and through the evap canister as well as when you start with a full tank and end with an empty tank, there is more air in your tank. The air contains moisture and it condenses. Not to mention the gas station has the same problem and water condenses in their tank and is absorbed by the ethanol.

It should not rust your tank since its either going to be plastic or galvanized, but it can settle out and freeze your fuel line if the conditions are right. As mentioned, if you have E10 it likely just gets absorbed and burns up - it will not settle out unless left for months.
 
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Talks about motorcycles but can be applied to automobiles just as well, here is a quote from that site.

"Be careful if you don't ride a lot. Using ethanol motorcycle fuel in bikes that will be stored for lengthy periods of time can be troublesome. The fact that ethanol motorcycle fuel can absorb some water is beneficial but there is a maximum to what it will absorb. Large amounts of condensation will induce the ethanol and water to separate inducing the water to gravitate to the bottom of the tank where the fuel pickup is located."

The way I've understood it is that as long as there is moisture in the air the ethanol absorbs it into the fuel which in turn adds to the moisture content making it even more diluted with water.
 
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Don't know the exact chemistry, but as others noted the alcohol is miscible with both gasoline and water. I don't know about adding 70% isopropanol since the rest is water. But the issue isn't necessarily that the water is perfectly miscible, but that it can hopefully reduce it to tiny little droplets that aren't sucking in just liquid water into a fuel injector. I've heard that can cause pretty nasty damage. I remember Red Line's water remover doesn't use alcohol, but they claim it disperses water into smaller droplets and that it lubricates the water phase so that it's less likely to damage fuel injectors.



However, given that the vast majority of gasoline these days contains ethanol (or maybe MTBE) there's generally no need to add anything to make water miscible. It would be pretty bad if it exceeded the ability of E10 to mix water and gasoline. At least until there's phase separation. These demonstrations of maybe 10% water contamination are unrealistic.
 
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Talks about motorcycles but can be applied to automobiles just as well, here is a quote from that site.

"Be careful if you don't ride a lot. Using ethanol motorcycle fuel in bikes that will be stored for lengthy periods of time can be troublesome. The fact that ethanol motorcycle fuel can absorb some water is beneficial but there is a maximum to what it will absorb. Large amounts of condensation will induce the ethanol and water to separate inducing the water to gravitate to the bottom of the tank where the fuel pickup is located."

The way I've understood it is that as long as there is moisture in the air the ethanol absorbs it into the fuel which in turn adds to the moisture content making it even more diluted with water.

The issue with that is that it depends on the integrity of the fuel system. Modern cars have fuel systems that are purged of atmospheric air. Not sure about motorcycles though.

Now I've seen phase separation in a lawn mower tank, but those systems aren't well sealed.
 
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One molecule larger than the other (regardless of which), would net the same result.

Can't explain that, but:

Water is H2O.. That's two hydrogen atoms and one oxygen atom in each molecule of water.

Ethanol is C2H5OH. That's two carbon atoms, six hydrogen atoms, and one oxygen atom in each molecule of ethanol.

It should be easy to see that a molecule (water) consisting of only 3 atoms would be smaller than a molecule (ethanol) containing 9 atoms.
 
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