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Methanol

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  • Harry
    Ok, let s clear up this methanol thing. Consider the following: Methanol is a hydrocarbon, comprised of carbon, hydrogen and oxygen. Its chemical formula is
    Message 1 of 11 , Feb 19, 2010
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      Ok, let's clear up this methanol thing.  Consider the following:

      Methanol is a hydrocarbon, comprised of carbon, hydrogen and oxygen. Its chemical formula is CH3OH.

      Methanol is an alcohol and is a colorless, neutral, polar and flammable liquid. It is miscible with water, alcohols, esters and most other organic solvents. It is only slightly soluble in fats and oils.

      Methanol can form an azeotrope with some other materials.  Ideally, when a mixture of two liquids is distilled the lower boiling material vaporizes first and is collected separately from the second material.   However, sometimes the two materials form a constant boiling mixture and are collected together even though they have different boiling points.  This is exactly what the Greek word azeotrope means, "constant boiling".

      Listed below are some of the binary (two-component) azeotropes of methanol:

      Acetone (BP=56.15)
      methanol/acetone  azeotrope: BP=55.5, ratio of components in yield=12%/88% by wt.

      Ethyl acetate (BP=77.1)
      methanol/eth.acet. azeotrope: BP=62.25, ratio of components in yield= 44%/56% by wt.

       

       ..and some of the notable substances methanol does not form azeotropes with:

      Acetaldehyde (BP=20.2C)
      Ethanol (BP=78.5C)
      Isopropyl alcohol (BP=82.3C)
      Water (BP=100C)

      So what does all this mean to the hobby distiller?  Let's look at the facts.
       
      Colorless means it looks the same as pure water.
      Neutral means it has no odor and no taste.
      Polar means it is dipole-charged (think magnet), and can bond with other dipole-charged molecules (e.g. water) just like magnets can bond together.
      Flammable means it will burn.
      Miscible means it can be mixed uniformly with other liquids (or gases if it is a gas), in any concentration without separation of phases.

      Those who claim they can smell or taste it are deluded.  They are confusing methanol with other substances that may be present (e.g. ethyl acetete or 'nail polish remover').

      Some very careful distillers have noted the methanol/eth.acet. azeotrope: BP=62.25 in many previous posts.  Now you know what it is.  :)

       

      It can mix with water, and ethanol (beverage alcohol).

      It forms azeotropes with many of the esters and substances found in beverage distilling, notably Acetone and Ethyl acetate.

      It does NOT form azeotropes with either water of ethanol..

      At first glance you would think methanol could be completely removed by fractionation because of the non-azeotrope situation with both water and ethanol.
      HOWEVER, because of the fact it DOES form azeotropes with other materials (acetone, some esters & higher alcohols) it will be present in a distillation as an azeotrope with those substances.

      This is why careful removal of these materials and also prevention of formation of these substances in the first place, is so important to yielding a good quality ethanol (e.g GNS & Vodka).

      It should be obvious however, that beverages that REQUIRE some of these materials for flavour profile (the brown spirits) will never be ENTIRELY free of some small amount of methanol, due to the azeotropic formations with some esters & higher alcohols.

      Having said all that, it is a known fact that there's far more methanol in a 30ml shot of ORANGE JUICE, than there is in a 30ml shot of whisk(e)y.

      I hope this clears it up for you.  Happy distilling folks.

       

      Slainte!
      regards Harry

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