Sciencemadness Discussion Board - Fractional distillation questions

Fractional distillation questions

jemis - 2-3-2016 at 04:55

Hello,

i would like to setup a Fractional distillation appartus, but before i start i would be very grateful if you can help me on some questions

1) what would be the most appropriate ground glass joint size for distilling small quantity of organic solvents (approx ~100mL) ? 19/26, 24/29?
2) i often read that vigreux column are not efficient for Fractional distillation because of their limited theorical plates, what would you advise me to use instead ? a humpel column with glass raschig rings ?
3) what would be the ideal length for the fractionating column knowing that i would like to distill small quantity of solvents (approx 100mL)

that's all i wanted to know

thank you alot

[Edited on 2-3-2016 by jemis]

blogfast25 - 2-3-2016 at 09:59

Quote: Originally posted by jemis

Hello,

i would like to setup a Fractional distillation appartus, but before i start i would be very grateful if you can help me on some questions

1) what would be the most appropriate ground glass joint size for distilling small quantity of organic solvents (approx ~100mL) ? 19/26, 24/29?
2) i often read that vigreux column are not efficient for Fractional distillation because of their limited theorical plates, what would you advise me to use instead ? a liebig condenser with glass raschig rings ?
3) what would be the ideal length for the fractionating column knowing that i would like to distill small quantity of solvents (approx 100mL)

that's all i wanted to know

thank you alot

These are broad questions.

1) For these small quantities I'd go 19/26. Others will undoubtedly disagree with me.

2) All other things (length and internal diameter) being equal the highest separation is obtained as follows:

packed column > Vigreux column > empty column

Packing can be Raschig rings, spheres, saddles etc.

3) There's no 'ideal' length. Separation power will not only depend on column packing and column length (for a given system to separate) but also strongly on reflux ratio.

[Edited on 2-3-2016 by blogfast25]

Herr Haber - 2-3-2016 at 10:56

Quote: Originally posted by blogfast25

These are broad questions.
1) For these small quantities I'd go 19/26. Others will undoubtedly disagree with me.

Not necessarily

I have a whole distillation set of Duran Rodaviss in 19/26 and as you say it's perfect for small quantities.
I use is mostly when I distill HNO3 because... well, there's teflon everywhere and being Duran I've never had a "stuck" part

Now, if I wanted to recover solvents from my experiments or work with volumes of more than 500ml or 1L I would go for something bigger.
But then, you can always get adapters to fit a big RBF on your 19/26 setup or whatnot. I hope you are well organized and have a bottle of aspirin in that case!

[Edited on 2-3-2016 by Herr Haber]

Damn, what am forgetting in formatting my answer?!!

[Edited on 2-3-2016 by Bert]

One stinkin' bracket added... More readable now.

[Edited on 2-3-2016 by Bert]

jemis - 2-3-2016 at 11:09

thanks blogfast and Herr Hebel

so a 19/26 or 24/29 is the perfect size for distilling 100ml ?
and a hempel column with raschig rings is way better than a vigreux column right ?

Sulaiman - 2-3-2016 at 12:06

jemis,
if RECOVERY of solvents is all you need then a simple distillation setup is sufficient.

If you want to SEPARATE solvents then it would be easier for members if you can be specific
because in my VERY limited experience,
separating solvents of different b.p. is not as easy as it sounds.

I can dis-recommend 10/19 size ... capillary tubing!
(I still like it for it's 'cuteness' though)
If I was starting from scratch then 24/29 here in UK and 24/40 in USA or whatever is cheap from China.
Buy 2x 'Distillation Kit' for a great fractionating refluxing system.

Don't forget heating, stirring, clamps, stands, cooling system,
and tubing vented to somewhere safe for vapours.
And all of the safety considerations with boiling solvents.
Turns out that the glassware is just part of the cost/consideration.

Despite the above, I hope to soon re-try stainless steel wool as packing of a fractionating column for my 10/19 kit, no reflux.
My two previous attempts resulted in a flooded column, after which, things just got worse

for a limited number of runs, a diy setup may be sufficient ?
ethanol/moonshine distillers have some amazingly efficient diy stills,
the principles can be used at different temperature ranges.

Sulaiman - 2-3-2016 at 12:09

I thought that Herr Haber had gone crazy with an editing tool,
then it happened to my post.

jemis - 2-3-2016 at 12:27

Quote: Originally posted by Sulaiman

jemis,
if RECOVERY of solvents is all you need then a simple distillation setup is sufficient.

If you want to SEPARATE solvents then it would be easier for members if you can be specific
because in my VERY limited experience,
separating solvents of different b.p. is not as easy as it sounds.

I can dis-recommend 10/19 size ... capillary tubing!
(I still like it for it's 'cuteness' though)
If I was starting from scratch then 24/29 here in UK and 24/40 in USA or whatever is cheap from China.
Buy 2x 'Distillation Kit' for a great fractionating refluxing system.

for a limited number of runs, a diy setup may be sufficient ?
ethanol/moonshine distillers have some amazingly efficient diy stills,
the principles can be used at different temperature ranges.

thanks sulaiman for the response

i would to achieve a nearly complete separation
for example i would to purify small quantity of xylene with unkown impurities as much as possible, i would like also to isolate major components of essential oils

yeah i know about the other pieces i need, i just want to know what would be the ideal setup for getting very pure compounds
as for the safetly, i'm experimenting outside and i work only with small quantity so no worries

aga - 2-3-2016 at 12:34

24/29 is my preference for glassware joints.

A 250mm or 300mm vigreux works quite well, and is simple to use.

'Very Pure' requires more than just a distillation rig - it all depends on exactly how pure you want to go.

Edit:

Herr Haber deleted a single closing square bracket from the auto-inserted quote text. I U2U'd about it but Bert beat HH to the editing.

[Edited on 2-3-2016 by aga]

Herr Haber - 2-3-2016 at 12:47

Quote: Originally posted by Sulaiman

I thought that Herr Haber had gone crazy with an editing tool,
then it happened to my post.

I have gone crazy with all the terrible gasses they made me do 1 century ago

Thanks for Aga for his help !

I'm curious Sulaiman, why stainless steel wool? I do understand that the surface must be bigger than any other medium but is it also to distill something in particular?
That's a very interesting idea in any case. But what about heat transfer? Steel must conduct heat quite well on top of having a bigger surface.

Magpie - 2-3-2016 at 12:57

Without knowing the scale of your distillations, ie, the quantity to be distilled, your question is a bit like asking "what size boat should I buy for fishing?"

And I want to only catch the most wily fish.

In the US, the common sizes are: 14/20, 19/22, and 24/40. These would correspond to small, medium, and large, respectively.

Most of my distillations are in the range of 25-250 ml. For this range I prefer 19/22. But I also have a 24/40 kit for the few times I want to distill larger amounts.

As aga says, for ultrapure separations you will need, a long or specialized column, really good packing, and a column head that will allow the tuning of the reflux ratio. Even then you may still have 1000-10,000 ppm of impurities in the distillate.

This question is really application specific.

[Edited on 3-3-2016 by Magpie]

JJay - 2-3-2016 at 13:34

I mostly use 24/29 and buy replacement pieces that are 24/40. You can distill quantities as small as 5 mL in a 24/40 setup, but I wouldn't generally recommend distilling anything under 25 mL in one. I have been thinking about picking up a 14/20 set for small distillations. 14/20 pieces are generally compatible with 14/10 ones, so you can use compatible equipment for distilling quantities of less than a microliter to 500 mL.

Most professional chemists I know prefer 19/22 for home use.

DJF90 - 2-3-2016 at 13:36

@Magpie - The OP specified the scale of distillation:

Quote: Originally posted by jemis

1) what would be the most appropriate ground glass joint size for distilling small quantity of organic solvents (approx ~100mL) ? 19/26, 24/29?

I'll agree with others here that 19/26 is probably ideal for the target quantities (100 mL in a 250 mL flask). B24 may be slightly oversized, but will allow you to process larger quantities if that becomes a future requirement.

Quote: Originally posted by jemis

2) i often read that vigreux column are not efficient for Fractional distillation because of their limited theorical plates, what would you advise me to use instead ? a humpel column with glass raschig rings ?

I would only use a vigreux column for rough fractionation of a larger quantity. Collecting fractions with a bp range of ca 20 *C sounds about right. These could then be re-processed by careful fractionation in a more efficient column.

Quote: Originally posted by jemis

3) what would be the ideal length for the fractionating column knowing that i would like to distill small quantity of solvents (approx 100mL)

The type of column packing determines the height-equivalent theoretical plate (HETP). The length of the column divided by the HETP will provide the theoretical plates of the column. To acheive separation, you'll need enough theoretcial plates and a sufficient reflux ratio. Simple packed columns have a significantly smaller ("better") HETP than vigreux, dufton or snyder columns, and they're much cheaper too. The trade-off is that they also tend to have a larger hold-up. I suggest looking at the section on fractional distillation in Vogel, available in the forum library.

aga - 2-3-2016 at 13:55

Quote: Originally posted by Magpie

As aga says, for ultrapure separations you will need, a long or specialized column, really good packing, and a column head that will allow the tuning of the reflux ratio.

!!!

I just said that it's not so simple !

The detail is all credit to you Magpie, not i.

jemis - 2-3-2016 at 14:56

thanks to you all!!!

you really helped me alot unlike other places where i got either locked thread, rude responses or no responses !
time to start experimenting now :cool:

[Edited on 2-3-2016 by jemis]

chemrox - 2-3-2016 at 16:09

added to what aga said you might want to heat the column too. Bring it close to the bp of your liquid. I'd be looking at building a 14/20 system for the small quantities you're talking about. Also you might want a non-reactive pusher liquid the boils a bit higher than your target liquid to get the last out.

Magpie - 2-3-2016 at 16:43

Quote: Originally posted by DJF90

@Magpie - The OP specified the scale of distillation:

Ah, yes. Sorry.
---------------------
I edited my post to change from 14/10 to 14/20. 14/20 is probably more common and gives you another 10mm of sealing length.

jemis - 2-3-2016 at 17:09

Quote: Originally posted by chemrox

added to what aga said you might want to heat the column too. Bring it close to the bp of your liquid. I'd be looking at building a 14/20 system for the small quantities you're talking about. Also you might want a non-reactive pusher liquid the boils a bit higher than your target liquid to get the last out.

yes this what i want to do, but someone told it was a stupid lol

anyway thank you guys you rock!!

testimento - 3-3-2016 at 04:09

For efficient and high fractionation to occur one will need a column with packing and a reflux cooler with flow control before the condenser. This allows a reflux ratio of 10:1 or more. Passive fractionation works to some extent but unless the boiling point difference is large (in scale of 30C) and distillation speed is slow, the resulting distillate will be impure.

blogfast25 - 3-3-2016 at 06:55

Quote: Originally posted by jemis

yes this what i want to do, but someone told it was a stupid lol

anyway thank you guys you rock!!

It would be stupid if you don't have a reflux controller on top. A column heated to near the BP, w/o a reflux controller, would act like a well insulated steam pipe. In short, it wouldn't actually do anything!

jemis - 4-3-2016 at 08:16

Quote: Originally posted by blogfast25

Quote: Originally posted by jemis

yes this what i want to do, but someone told it was a stupid lol

anyway thank you guys you rock!!

i didn't find anything about reflux controller , can you explain me what it is and what it look like?
how can i heat the column near a certain bp point ?do i need a special column ?

[Edited on 4-3-2016 by jemis]

[Edited on 4-3-2016 by jemis]

[Edited on 4-3-2016 by jemis]

[Edited on 4-3-2016 by jemis]

blogfast25 - 4-3-2016 at 09:04

Here's what some of these (expensive!) beauties look like:

http://www.sigmaaldrich.com/labware/glassware-catalog/distil...

http://www.sigmaaldrich.com/catalog/product/aldrich/z273120?...

http://www.sigmaaldrich.com/catalog/product/aldrich/z602876?...

It's what controls the reflux ratio R:

Left: 'passive' distillation. Reflux is caused by natural condensation. Typical column type is Vigreux.

Right: fractionation with reflux head allows to achieve high values of R and control them well (at point 'C', condenser flow is split into D and L). Column is usually thermally insulated but (rarely heated, IMHO).

[Edited on 4-3-2016 by blogfast25]

aga - 4-3-2016 at 10:29

Wow ! Some of those disty heads look awesome.

Gotta get me a fraction cutter (if only i knew what it, or the 4 valves each did).

blogfast25 - 4-3-2016 at 10:41

Quote: Originally posted by aga

Wow ! Some of those disty heads look awesome.

Gotta get me a fraction cutter (if only i knew what it, or the 4 valves each did).

You can also build one yourself: our moonshining friends have some nifty all-copper designs.