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Author: Subject: Thoughts and observations relating to a cheap Vigreux column and condenser
Sulaiman
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[*] posted on 14-5-2020 at 07:24
Thoughts and observations relating to a cheap Vigreux column and condenser


Being far from my chemistry stuff yet wanting to ferment sugar to ethanol
and then distill the ethanol to >=90 %ABV
(to make hand sanitiser fluids, and do a little chemistry)
I bought a typical cheap 'distillation kit' from China. (at home I would use a Hempel (packed) column)
The kit arrived with broken flasks
but I have been using the Vigreux column and condenser from the kit for distillation.
Here are some thoughts on this particular Vigreux column and condenser:

1) the condenser is good;
1.1) I have been using ice-water for cooling giving a difference in temperature across the condenser wall of up to 100oC
so far 14 distillations with no sign of condenser failure
1.2) the effective cooling power is good so a reasonable throughput can be achieved,
up to four drops of distillate per second (I ran at about 3 drops per second)

2) the Vigreux column is not so good;
2.1) the reflux rate is about one drop per three seconds (ambient temperature <=30oC)
so my reflux ratio was negligible
2.2) when a drop of refluxed liquid drops from the upper indentations it causes an avalanche of drops to return to the pot
2.3) running the distillation at a rate to match the condenser
the Vigreux column added less than 1/2 of a theoretical plate
2.4) running EXTREMELY slowly (about 1cm of the condenser used) the Vigreux column added almost one theoretical plate

My conclusions;

for ethanol:water distillation the Vigreux column is far too small for the supplied condenser

it may be possible to achieve more than one theoretical plate using a Vigreux column
but the production rate would be intolerably low.

The only use for a Vigreux column would be for very slow, small scale distillations of easily separable high boiling point liquids,
where very low holdup is required.

So, for the average user I think that a Vigreux column is literally and practically a waste of time.

Comments ?

P.S. I now have a Hempel column on order
https://www.ebay.co.uk/itm/100-400mm-14-23-19-26-24-29-29-32...
(and a reflux condenser for condenser/cooling controlled vapour management operation)
https://shopee.com.my/SOLO-200mm-24-29-Borosilicate-Glass-3....

[Edited on 14-5-2020 by Sulaiman]




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SWIM
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[*] posted on 14-5-2020 at 09:25


I agree that Vigreux columns are of low power, but also there are Vigreuxs and there are Vigreuxs.

Some columns of the same length have very different number of spikes and sizing of the spikes differs widely too.

This isn't just cheap glass vs expensive glass: Many older Pyrex columns have pretty lame spike patterns.
I don't think you should be able to see down a Vigreux column at all.

It seems that the 14/20 and 19/22 columns I've seen have much less open space in the column and are probably more effective per unit length for that reason as well as their smaller diameter.

I've seen claims of 1 plate per 100 mm for columns in 14/10 microscale Vigreux, but I expect the very narrow tube is doing a lot of the work there.


In your particular case the low reflux rate may be a big part of the problem. I know you're short of equipment there, but if you wrap a few turns of rubber hose around the top end of the Vigreux or the distillation head it ought to up the reflux ratio a bit. Or perhaps you could just aim a fan at the column.

Okay, so it won't turn the column into a Hempel, but it may help.

EDIT: Totally missed the fact you just ordered a Hempel anyway.




[Edited on 14-5-2020 by SWIM]




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[*] posted on 14-5-2020 at 11:02


my 300mm Vigreux also had the issue of just being poor at separating compounds, even with max care cor heat input, insulation and reflux. right now i got better results (still not perfect) by packing the column with cheap glass beads, it looks diy as fuck, but better than the vigreux by itself




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[*] posted on 14-5-2020 at 12:03


http://www.sciencemadness.org/talk/viewthread.php?tid=155286

I won't be performing fractional distillations without this setup anymore. Active reflux ratio with packing will increase the capacity of the column by order of magnitude, and the column is easy to insulate. If it has a mantle, it can be evacuated with a pump for maximal effectiveness.

I managed to pull 90% EtOH not at drip but constant flow rate by merely running it alone and azeotrope by adjusting the reflux ratio to constant drip. Apparatus with decent heater can easily take over 1-4 liters of azeo ethanol per hour.
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Sulaiman
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[*] posted on 14-5-2020 at 12:49


@SWIM ... I had considered a fan but this particular Vigreux has very few 'spikes'
(7 sets of 3 spikes ... mostly an empty tube)
so I've decided to abandon the Vigreux until I find a use for it.

@Ubya ... what do you use to stop the balls/beads from dropping out of the bottom ?
(steel wool at a guess ?)

@Refinery ... If I was going to regularly make a lot of 'shine' then a purpose built still would make sense,
but I don't drink, and my stills are just for small scale general chemistry,
ethanol distillation is just 'because I can' and it is cheap,
and there is lots of data to compare my results with.

Putting it another way: has anyone here found a Vigreux column to be useful ?
if so, for what ?




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[*] posted on 14-5-2020 at 13:40


I find them useful as air condensors although straight tubes would probably also suffice.
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S.C. Wack
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[*] posted on 14-5-2020 at 15:43


Vacuum.

Quote: Originally posted by SWIM  
I've seen claims of 1 plate per 100 mm


#metoo

Quote: Originally posted by SWIM  
for columns in 14/10 microscale Vigreux, but I expect the very narrow tube is doing a lot of the work there.


The question of the effect of scale is interesting, but otherwise I'm thinking no.

Quote: Originally posted by SWIM  
Or perhaps you could just aim a fan at the column.


Great for air condensers. Perhaps a vertical temperature gradient would be superior to horizontal in this application.




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[*] posted on 14-5-2020 at 17:42


@Sulaiman yup i use a piece of steel mesh screen simply jammed at the end of the joint




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[*] posted on 15-5-2020 at 10:01


I think it's a mistake to cool a vigreux (or packed) column for fractional distillation. You actually want to insulate the column. Any cooling should be done above the column so that you create a temperature differential along the column. The whole point is that you have at any point in the column cooler liquid descending and warmer vapour ascending, which then need to find a new thermal and VL equilibrium. This is upset if you are losing (or in the case of below ambient distillations of low bp compounds , gaining) thermal energy out of the walls of the column, resulting in a less efficient process. Even large scale industial refinery fractionation columns are insulated and they don't suffer the same volume : surface area issues as we do at lab scale.
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[*] posted on 15-5-2020 at 11:48


@RedDwarf: You are absolutely correct except for one thing: Simplicity. Cooling the column will reduce efficiency, but it's simpler to build and run. I wonder how much you loose, simple logic suggests 50% but when has that ever worked in real life?

As for vigreux's I think they're a simple solution for non-demanding tasks. They add a little separation with little holdup and no pressure drop or risk of chocking. That might not be "sexy", but sometimes it's the simplest way to get the job done. Besides I think they look nice.




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[*] posted on 15-5-2020 at 18:35


Quote: Originally posted by Ubya  
my 300mm Vigreux also had the issue of just being poor at separating compounds, even with max care cor heat input, insulation and reflux. right now i got better results (still not perfect) by packing the column with cheap glass beads, it looks diy as fuck, but better than the vigreux by itself


Isn't that what you are supposed to do?
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[*] posted on 24-5-2020 at 06:07


What is a Vigreux condenser?
I have 2 Vigreux columns that supposedly should be good for fractional destillations ie. separating compounds with boiling points pretty close to each other.

Many years ago now, when distilling ethanol i have this all aluminium unit with built in heating that can take 25L of alcoholic media produced by sugar and yeast.
It has a aluminium column about 6-8cm in diameter and its filled with lots of small, short pieces of ceramic tubes.
The cooling water also passes right through the column on 2 places.
From the top of the column is connected an aluminium condenser.
This unit is made for ethanol distillation and i get about 92% ethanol out of it.
This raw alcohol is diluted to about 40% and put in a 5L upside down pail (with bottom cut off) with a plastic pipe fitted that is filled with activated carbon. In the end of the plastic pipe is a valve regulating drip rate.
If i get good stone charcoal the ethanol produced with this setup is much better than store bought vodka.
And i mean much better.
However its much work making the fermenting brew and then distilling and cleaning up the ethanol with charcoal.
So i haven't used the unit in 15 years now as i have stopped drinking alcohol.
But i have plans on firing it up again just to make some 95% ethanol for chemistry use.
This will require a double destillation, one as described above with coal cleaning and then diluting the ethanol again and distilling a second time.
Last % i plan on using molecular sieves to get last water out.
But with the high cost for absolute ethanol its definitely worth it.
I dont know if one can get 95% ethanol with a glassware destillation setup.
Maybe with a glass column filled with glass balls or short pieces of glass tubing.
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Sulaiman
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[*] posted on 24-5-2020 at 08:58


I have no direct experience but I believe that aluminium is corroded by hot ethanol,
the aluminium hydroxide formed (due to water present) will end up in your product,
so you will be consuming aluminium, which is not a good idea.




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[*] posted on 24-5-2020 at 10:54


Oh, im sorry.
I just remembered wrong, it´s made of stainless steel, all of it.
When you brought it up i remember.
So long since i used it now.
Sorry for that.
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