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47856Re: Vacuum Distillation Column

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  • bjpow42o
    Apr 7, 2011
      OK, sounds good. I do have another question...

      I am trying to get 95% abv off the top of the column. However, I would also like to remove most of the water from the solution in the boiler at the same time. Does anyone have a good idea on how to do this? I have a couple, but I am not sure how well they will work.

      The first is instead of connecting the column to the top of the boiler tank I would have the column free standing next to the boiler and have the vapor feed into the side of the tower near the bottom. Then the alcohol vapor would rise to the outlet of the column on the top and to the condenser while the water vapor would fall into a receiving tank at the bottom of the column (which could be cooled to prevent reboiling if necessary). I know I may not capture all of the alcohol this way, but a good portion of it hopefully while still getting 95% off the top of the column.

      Another idea, which I am trying to avoid because it would most likely be more energy intensive, is to basically have a multi-stage distillation. The first would act as a pot still and take of all of the alcohol and most of the water and feed it into another boiler tank. The next stage would be a traditional fractional distillation with the column directly on the boiler tank. I think this would work, but I am looking for a way to do this without heating twice.

      Any ideas? Thanks again for all the helpful wisdom!

      --- In Distillers@yahoogroups.com, "landrover_ffr" <sid.rains@...> wrote:
      > Hi,
      > Comments inserted bellow.
      > > The vacuum pump pulls down to 40 torr, that's what I meant "near" vacuum... why does that scare you?
      > Just checking. In my world you either pull a vacuum , or not. The term "near vacuum" got me worried that you had very little idea as to what you were attempting to do. Sorry.
      > >I read somewhere that at pressures of 70 torr or less the water/alcohol azeotrope does not exist.
      > That sounds familiar. Once the vacuum is removed though it will absorb moisture from the air again I believe. 40 torr is only about 1.5 psi if a remember correct, so not too bad to deal with.
      > >If I set the temperature no higher than the boiling point of alcohol at 40 torr could I not get pure alcohol off?
      > Nope, still need reflux to achieve the separation. As noted by another poster, the whole "temperature setting" concept is a fools errand.
      > > I am looking to scale up the design to about 50 liter capacity. I was planning on using SS scrubbers in the column if I can, but I am unsure of the size of the column and reflux ratio (if needed?).
      > Sound like an ok plan. I can't tell you what R/R to run (I could implement vacuum distillation in my software/model and see how it turns out). The key with the vacuum will be requiring less power input.
      > >I also read somewhere that it is better to have a wider column when distilling under a vacuum for some reason.
      > I've not herd this before. This is usually base on the moler flow rate expected in the column (among other things ;)
      > >Any ideas on the height of the column (didn't understand "by as high as particle")?
      > Sorry, my bad typing (after few too many glasses ;) I meant to say "as high/tall as practical".
      > >I'm trying to avoid getting another engineering degree if possibile :)
      > Yes, one is more than enough! I garner the help of two of my mates when things get too serious (one is a chemical engineer, the other and refrigeration engineer (among other things, two much education all together!)
      > Hope this help a little. I try too be of more use asap.
      > Regards,
      > Sid.
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