Does alcohol really help to evaporate water?

[JackRuby]

Hi-

For years I have always known that Methyl Alcohol is used as a method of removing water from natural gas piping. For example - a pressurized natural gas pipe has a small amount of water trapped in it. The water, under certain flow, and temperature conditions will vaporize and cause problems at meters, regulators, burner tips etc. In some cases, Methyl Alcohol or Methyenol (please forgive the spelling on that) is injected (in liquid form) to help remove the water. Occasionally Isopropyl is used too. Does anyone know the explanation to as why this helps remove the water?

Thanks

 

[Gokul43201]

Usually, methanol or isopropanol (isopropyl alcohol, IPA) would used as an organic solvent, to help clean out any organic deposit (most impurities in natural gas are organic) from the pipes. I've used both for cleaning out vacuum pipes that had been pumped on, and hence had picked up some oil vapors from the pump.

The solvent isn't really used to evaporate the water, as such. Both methanol and IPA, being pretty volatile liquids, I doubt that their addition affects the boiling point of water in any significant manner. I suspect that the liquid merely flushes out the water, and being volatile, does not stay behind.

If the liquids are actually flushed through the pipes (ie : flow is important), rather than just filled into them, that will lend weight to my suspicion.

 

[Vern]

I always thought the alcohol absorbed the water and acted as a solvent so that water and alcohol were both absorbed by the subject petrol product.

 

[DaveC426913]

My brother the research scientist told me that alcohol is used to remove the last traces of water from cleaned lab equipment when even a small amount of water residue would affect the results. That would indicate very strongly that the technique works.

 

[DaveC426913]

Checked w/ my brother:

The exact mechanism is that they are highly soluble in one another (since both have hydroxyl groups ie. -OH), although ethanol has a lower boiling
(vaporization) temperature than water, hence evaporates more quickly at the same temperature, and has to take some water vapour along with it to do so.

Check this reference and a quote from same reference:
http://www.ucc.ie/ucc/depts/chem/dolchem/html/comp/ethanol.html
(Google - ethanol + boiling point)

"Although the boiling point of ethanol, 78.3 degC, is significantly lower than
the boiling point of water, 100 degC, these materials cannot be separated
completely by distillation." So when they say "cannot be separated completely by distillation", this means they both evaporate mostly together. You can't leave all the water behind and evaporate off all of the ethanol! It's impossible. If it were possible this would make alcohol distillation much simpler.

HOWEVER - you can reduce the water content in ethanol by distillation, so
ethanol does evaporate FASTER than water, but it takes many (5 or 6)
distillations to increase the ethanol content to greater than 50%. Given 10 or
20 distillations, you can get "absolute ethanol". This proves that water
evaporates along with the ethanol (and does not get left behind), BUT that
ethanol evaporates faster than the water.

 

[JackRuby]

Thak you very much. You have been very helpful!