biomechem
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Steam distillation- vapour temperature, vacuum
Hello again,
Does vapour temperature have to exceed a boiling point of a steam-distilled compound, or maybe H2O molecules will "carry" the other
molecules anyway?
Also does the steam distillation is a special type of an azeotropic distillation and so the vapour temp. has to exceed a specific value different for
particular case?
Finally does steam-vacuum distillation exist? I've never find any info about it, so I assume that not, but why? IMHO water has specific heat capacity
so in industrial processes it could help save energy.
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wg48
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I suggest you read https://en.wikipedia.org/wiki/Steam_distillation
Why do you think the specific heat of water would help save energy?
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biomechem
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@wg48
Okay I've got my answer, when steam distilling temperature will always be lower than a temperature of boiling point of water.
I meant that reducing pressure would make the water+ substance "x" boil in even lower temperature, so it wouldn't be necessary to use that much heat
(energy). Great value of specific heat = much heating.
Ofc some energy would be used to power the pumps, but overall it would save the used energy.
Thank you for answer, I should have focus more on the wiki.
I forgot to ask one more question.
When steam distilling compounds with "sensitive" groups like ketones or aldehydes does it make sense to add sodium bicarbonate in order to prevent
aldol condensation?
As e.g. acids catalyze this reaction, and distilled water is likely to absorb CO2 the addition of the salt would neutralize it, and
moreover it would act as boiling chips. Am I right?
[Edited on 9-9-2017 by biomechem]
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wg48
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@biomechem
Reduced pressure does lower the boiling temperature but it requires approximately the same energy to vaporize a boiling liquid ie the heat of
vaporization.
I thought Adol condensations were catalysed by both acids and alkali.
Sodium bicarbonate when dissolved water does reduce bumping as it releases CO2 on heating but only until its all converted to carbonate.
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SWIM
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I had some dealings back in the 1990s with an essential oil company out in Santa Cruz that said they vacuum steam distilled most of their products.
I don't know if that's the industry standard or not. They seemed pretty proud of it.
I don't think energy saving was their concern, but rather limiting decomposition of their products.
If you want to save energy by using a vacuum on distillation the way to go is multiple effect distillation. The vapors from the first still are
condensed via a heat exchanger by the contents of another boiler which is held under vacuum, so the condensing point of the vapors is able to boil the
stuff in the second boiler under vacuum. This can be extended to several boilers at different pressures before the law of diminishing returns kicks
in.
I think some guy in the sugar industry came up with that to save fuel costs on boiling down sugar solutions in their refining process.
[Edited on 9-9-2017 by SWIM]
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biomechem
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@wg48
Aldol condensation is obviously catalyzed by both, but in the case I described distilled water can only absorb acid (dissolve CO2 gas) from
air.
@SWIM
Very interesting I'll keep that in mind.
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