Vacuum Distillation Exhaust

[Salomon Solis]

This is pretty basic but I have a couple of questions regarding what happens to the most volatile part of the vegetable mercury I'm distilling during a vacuum distillation... I was wondering -- wouldn't the most volatile part be sucked out of the system by the vacuum during the distillation? (I want to use a water aspirator)

Or is it that you're supposed to first set the vacuum and then close off the system with a valve for the entire duration of the distillation? (in which case wouldn't pressure build up in the system... and possibly explode?)



Also if somebody has advice on joint grease --- if I have, say, grease on the joint of my receiving flask... after my distillation is done, as I'm pouring the distillate out of the flask, wouldn't it spill over the joint grease? Doesn't that contaminate my product?

Thank you,
S

 

[Jimmy Rig]

This is pretty basic but I have a couple of questions regarding what happens to the most volatile part of the vegetable mercury I'm distilling during a vacuum distillation... I was wondering -- wouldn't the most volatile part be sucked out of the system by the vacuum during the distillation? (I want to use a water aspirator)

Not if what you are distilling is able to be condensed back into a liquid before the reciever. The goal with vacuum distillation is to reduce the temperature required to change states. This can be helpful to preserve the substance and reduce oxidation and thermal degradation.

Or is it that you're supposed to first set the vacuum and then close off the system with a valve for the entire duration of the distillation? (in which case wouldn't pressure build up in the system... and possibly explode?)

View attachment 4084

You want some sort of constant suction to achieve and maintain your vacuum. I recommend the water aspirator as you mentioned because it also gives the option to scrub harmful gases that may escape the apparatus if you can't condense everything.

Also if somebody has advice on joint grease --- if I have, say, grease on the joint of my receiving flask... after my distillation is done, as I'm pouring the distillate out of the flask, wouldn't it spill over the joint grease? Doesn't that contaminate my product?

Thank you,
S

Use PTFE joint sleeves or don't lute the joints.. the ptfe ones work well.

 

[Lux Natura]

For really volatile / low boiling point compounds, sometimes the receiving flask itself is chilled, often to below zero, for example by placing it inside another container with a mixture of dry ice / acetone. There's some pretty neat stuff out there where they distill at vacuum into a cryogenically cooled receiving flask, especially when they are wanting to liquefy certain gases. You can also daisy chain your receiving flasks, so several are connected in series, and the first one is room temperature, the second one is chilled - this way you can actually monitor if there are any gasses escaping from the first one, because they would condense in the second one.

I believe some of the more advanced methods of dry distilling the acetates will use this method, with at least a second receiving flask that is cooled to close to 0 or below.

 

[Salomon Solis]

Not if what you are distilling is able to be condensed back into a liquid before the reciever. The goal with vacuum distillation is to reduce the temperature required to change states. This can be helpful to preserve the substance and reduce oxidation and thermal degradation.

You want some sort of constant suction to achieve and maintain your vacuum. I recommend the water aspirator as you mentioned because it also gives the option to scrub harmful gases that may escape the apparatus if you can't condense everything.

Use PTFE joint sleeves or don't lute the joints.. the ptfe ones work well.

Thank you!

Ok, so you would just use PTFE joint sleeves which you slip over the male joint and that seals it nicely for a vacuum distillation and prevents gripping?

If I don't lute the joints, and just connect male to female ground glass joints, don't I risk gripping them for sure, whether it be vacuum or non-vacuum distillation?

Thanks for your help.

 

[Salomon Solis]

You can also daisy chain your receiving flasks, so several are connected in series, and the first one is room temperature, the second one is chilled - this way you can actually monitor if there are any gasses escaping from the first one, because they would condense in the second one.

Ok! I think I've heard this, this is what they call a "cold trap", by, for example setting the second receiving flask in an iced water bath? Thanks for the advice.

 

[Jimmy Rig]

Thank you!

Ok, so you would just use PTFE joint sleeves which you slip over the male joint and that seals it nicely for a vacuum distillation and prevents gripping?

If I don't lute the joints, and just connect male to female ground glass joints, don't I risk gripping them for sure, whether it be vacuum or non-vacuum distillation?

Thanks for your help.

Yes I would use PTFE joint sleeves with vacuum distillation to prevent leaks and locking up of joints. I don't use them for regular distillation.

 

[Salomon Solis]

Yes I would use PTFE joint sleeves with vacuum distillation to prevent leaks and locking up of joints. I don't use them for regular distillation.

Thanks Jimmy. Sorry for the extra message, but I'd really want to be sure I don't grip and ruin my glassware straight away. I've always heard that you need to have either grease or the PTFE joint sleeves so that the glassware doesn't get stuck... even when for normal atmospheric distillation.

You're saying you don't use anything for regular distillation? That's safe? You never had a problem?

 

[Jimmy Rig]

Thanks Jimmy. Sorry for the extra message, but I'd really want to be sure I don't grip and ruin my glassware straight away. I've always heard that you need to have either grease or the PTFE joint sleeves so that the glassware doesn't get stuck... even when for normal atmospheric distillation.

You're saying you don't use anything for regular distillation? That's safe? You never had a problem?

Sort of depends on what you are distilling! Never had an issue without them when distilling ethanol as an example. Same goes for water experiments. I would use them with anything that you are worried if it were to leak. I just learnt about joint sleeves about a year ago prior to this I was not using them. Same with vacuum. So having those two tools in the tool box can potentially increase the safe options available if that makes sense. (with some other important equipment such as fume hoods, safety equipment. ) Its not a one size fits all sort of thing. Alot of stuff you can do without the fancy gear (spagyrics).

 

[Salomon Solis]

Sort of depends on what you are distilling! Never had an issue without them when distilling ethanol as an example. Same goes for water experiments. I would use them with anything that you are worried if it were to leak. I just learnt about joint sleeves about a year ago prior to this I was not using them. Same with vacuum. So having those two tools in the tool box can potentially increase the safe options available if that makes sense. (with some other important equipment such as fume hoods, safety equipment. ) Its not a one size fits all sort of thing. Alot of stuff you can do without the fancy gear (spagyrics).

Thanks.

 

[Jimmy Rig]

For really volatile / low boiling point compounds, sometimes the receiving flask itself is chilled, often to below zero, for example by placing it inside another container with a mixture of dry ice / acetone. There's some pretty neat stuff out there where they distill at vacuum into a cryogenically cooled receiving flask, especially when they are wanting to liquefy certain gases. You can also daisy chain your receiving flasks, so several are connected in series, and the first one is room temperature, the second one is chilled - this way you can actually monitor if there are any gasses escaping from the first one, because they would condense in the second one.

I believe some of the more advanced methods of dry distilling the acetates will use this method, with at least a second receiving flask that is cooled to close to 0 or below.

Do you use the dry ice acetone on some occasions Lux? Just wondering because I have used ice water almost religiously because of its simplicity but can see a need for better cooling capacities. I have purchased some implements to put together a calcium chloride solution cooling system but of course this is somewhat corrosive to plumbing so you have to be selective about components. But the idea was basically to have a 5 gallon bucket of solution sitting in the deep freezer as the reservoir or cold sink leading to apparatus. Its a cool idea though because the deep freezer cant reach its -52 deg C freezing point.
Other members have mentioned using antifreeze. I am not sure but I figure that would also work well.
At the time being i rely on a ice cold condenser and sometimes the receiving flask sitting on ice but it is not ideal under some circumstances (though still passable.) IMO

 

[Lux Natura]

Do you use the dry ice acetone on some occasions Lux? Just wondering because I have used ice water almost religiously because of its simplicity but can see a need for better cooling capacities.

I do not use sub zero for any of the lab works I do. Mainly just room temperature water or cold water.

I can think of a few cases where sub zero is useful to condense something in a higher purity than it can otherwise be condensed when using just normal water or cold water. I don't really deal with the kind (or concentration) of solvents which require sub zero though, but work with them in their ranges where just normal (above zero) temperatures can be used.

If I remember correctly, I think Ando had mentioned he had some stuff that required -24c or thereabouts to keep in liquid form. I have a 'hobby laboratory' - but any alchemical works I do really don't require any of that stuff - the laboratory is basically for distilling alcohol, and various experimentation for my own exploration and amusement, but none of it is for 'alchemy'.

Were you thinking of using a cold trap, or cooling a condenser (and receiving flask)? How cold do you need to go?

 

[Jimmy Rig]

Thanks for answering!

I do not use sub zero for any of the lab works I do. Mainly just room temperature water or cold water.

I can think of a few cases where sub zero is useful to condense something in a higher purity than it can otherwise be condensed when using just normal water or cold water.

Were you thinking of using a cold trap, or cooling a condenser (and receiving flask)? How cold do you need to go?

Cooling a condenser; and a receiving flask but I don't really think that the subzero temperatures are required in my case; if they are its a little too complicated for what they had available back in the day. Technically I think cool cellar temperatures would work with air cooling alone but I figure we have access to modern tools; and it gives more experimental options.

I would say that my lab is not equipped like a professional lab but as much as I can I don't treat it like a hobby and thus have some safety gear and as good of ventilation as I can have practically with the area I have..
Its gotten better over the years; but I am practical and like to make improvements without recklessly spending or prioritizing lab work over family life etc. Its kind of a balancing act of keeping the candle lit.

Things like this cooling question sort of keep things interesting for me; I haven't really "needed" better than ice water but can see some advantages to having -20's liquid always on hand for distillations if its not too cumbersome to set up and run.