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Q & A: Separating vegetable oil and gasoline

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Most recent answer: 10/22/2007
Q:
How can you seperate vegetable oil from gasoline?
- krisi (age 32)
gladstone, mo, usa
A:

  Hi Krisi,

  Vegetable oil should dissolve very nicely in gasoline.  In the past, Iíve used gasoline to dissolve grease on a bicycle chain.  This is entirely not recommended, as gasoline is flammable and explosive, and prolonged exposures to its vapors can be harmful.  But itís a great solvent.  Other solvents, like turpentine, are also flammable, and some, like benzene, are carcinogenic.

  Gasoline is also very volatile -- it evaporates quickly at room temperature in air.  You can take advantage of this and put your gasoline-oil solution in a tray or something and let it evaporate, taking extra caution to ventilate it well so that gasoline vapors do not build up to an explosive mixture, and to keep all sparks and flames away.

  One problem with this is that gasoline has many component hydrocarbons of differing volatilities.   It even contains paraffins (waxes).  Even after most of it is gone, some bits may still be left.  Iíd not try to put the remaining vegetable oil on my salad.

  If your plan was to recover the gasoline and not the oil, you may want to re-condense the gasoline vapors somewhere else with a cooled condenser coil.

  Extra bonus fun facts:  Diesel fuel is a mixture of oil and gasoline -- you can do your own separation ("refining") in this way.

  Soybean oil is commonly extracted from soybeans by grinding them up and dissolving the oil with hexane, a hydrocarbon, which is a component of gasoline.  The hexane is evaporated, leaving the oil behind.  The hexane  can be re-condensed for recycling in the process.  Itís better to use pure hexane than gasoline here because gasoline has all kinds of other stuff which may contaminate the oil.

 Tom

(published on 10/22/2007)

Follow-Up #1: de-watering oil

Q:
I am using vegetable oil instead of diesel for fuel in my vehicle. I need to dewater the oil. I was trying to find out at what vacuum I need to get the oil if I am to boil out the water at lets say 120 degrees farenheit. Thank you A chart of some kind would be very helpful....again thanks
- John Boeckstiegel (age 53)
Jacksonville,Fl,USA
A:
Iím not sure how thoroughly you need to remove the water. A little bit will actually dissolve as individual molecules in the oil. Iím not sure thatís a problem, although some sites refer to a problem with biodiesel being hydrophilic, so perhaps it is.
 
If what youíre talking about is removing any little water drops, we can figure that out. They have about the same boiilng point in oil as in pure water. So to find the necessary vacuum pressure at some temperature, all you need is to look up the vapor pressure of water at that temperature in a standard table. One is available on this link, found by a quick google


If youíve got to remove much of the dissolved water, you may have trouble, because its vapor pressure will drop below that of pure water as soon as the concentration falls below the saturation level.

Mike W.

(published on 10/22/2007)

Follow-up on this answer.