Gasoline, water, alcohols mixtures...

[Externet]

Hi.

Ethanol mixes with gasoline,

Water mixes with ethanol;

What happens if ethanol with some water dissolved in it is mixed with gasoline ?

 

Is there separation ? What are the components that separate ? Is there a ratio when it does not separate ?

 

What if it is methanol ?

[Externet]

Just tried. With isopropyl alcohol at 50% into gasoline.

 

Water does separate. So gasoline has pure alcohol dissolved in it now. Is it fine to suspect the same for other alcohols ?

 

The ethanol that is being added to commercial gasoline has to be very pure, or the bottom of fuel tanks in automobiles would have water; right ?

[John Cuthber]

Depending on the composition of the gasoline, methanol might not mix with it.

One of the big problems with adding ethanol to gasoline is that it's difficult to get the last of the water out of the alcohol and if you get a layer of water in the bottom of the tank it messes up the engine.

[Enthalpy]

Wouldn't water+ethanol+gasoline make a colloid? I imagine water droplets surrounded by a monolayer of alcohol in a matrix of gasoline. Provided water isn't too abundent, of course.

 

In Externet's experiment, how to know if the alcohol is still mixed with the gasoline only? I'd expect some to mix with water as well, though isopropylic is less hydrophilic than ethanol or methanol. And what happens on stirring? Does it get translucent like milk?

[CaptainPanic]

I don't think that ethanol can be considered a surfactant actually. I'm not an expert in interfaces, but I think that ethanol is basically too short to be a good surfactant. Its non-polar 'tail' is too short.

 

What you essentially get is a mixture that behaves as a "ternary mixture": it has three components (and we shall treat gasoline as a single component). Depending on the ratio in which these three are present, you can get one phase (complete mixing), or multiple phases (probably two phases: a non-polar and a polar phase).

 

If you get two phases, then all your three components will be present in both phases, but in different ratios. You will get a non-polar gasoline phase, which still contains minor amounts of water, and an aqueous phase which contains traces of gasoline. And the ethanol will be distributed over those phases, but I actually don't know in what ratio.

 

So, whether the water will separate out into a separate phase will depend on: (1) the amount of water, (2) the amount of ethanol, and (3) the polarity of the gasoline phase. You could probably add some components to gasoline to increase or decrease the amount of ethanol/water that you can blend in.

 

Some useful keywords are "Liquid liquid equilibriua", or "extractions".

[khlor]

Perhaps fractional distillation can work.