Sciencemadness Discussion Board

Condenser overpowering and joint size?

Fyndium - 25-3-2021 at 13:36

I've gotten twice in a situation when 24* condenser flooded, and I noted that the condenser length doesn't have to be much more than 200, tops 300mm, after when the height doesn't matter anymore because reflux will choke the throat and cause further issues. When I got 4-necked flask, I just added a second condenser, but I began thinking that for larger glassware it would be very clever to pre-emptively obtain a vessel with at least one 45/40 or larger joint. Further issue is, that it seems that no condensers are made for larger joints than 29*, so it effectively renders the condenser ineffective - unless one would obtain a claisen for two or more 29* condensers. Of course, the original idea of using multiple condensers would work if one can get flasks with enough necks, four, five or even more. The devices are generally fitted with stirrer, thermoprobe, condenser and an addition port, so no more room would be left. Adding claisen to 24* would still keep the choking issue.

Any ideas, apart from cooling the flask itself?

dawt - 25-3-2021 at 14:15

Quote: Originally posted by Fyndium  
it seems that no condensers are made for larger joints than 29*

Nah, there's plenty of condensers in 45/50 and larger, and you can find cheap ones on eBay for use with soxhlet extractors, rotavaps etc.

Fyndium - 25-3-2021 at 14:52

The soxhlets have very narrow reflux gate, much smaller than 24* joint.

Sulaiman - 25-3-2021 at 14:52

why do you need a rapid boiling for refluxing ?
would it not be sufficient to operate at a lower boiling rate
- the temperature will be the same.

Fery - 25-3-2021 at 22:46

condenser acc. to Dimroth length 600mm 2x 45/40 glass connector
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zed - 26-3-2021 at 00:28

Only condensers I can recall having flooding problems with, have been Grahams.

But, I know either flooding or overwhelming, can be problems.

Bigger flasks; maybe bigger problems. Also, really vigorous reaction conditions.

Not much call for 22Liter reaction flasks around here, but I'm pretty sure a 24/40 condenser couldn't handle the reflux output.

In this example, a vigorous Fe/HCl reduction requires two condensers, to keep the reflux in check. Of course, the reagents in question, aren't very obtainable anymore.

But, similar reaction conditions might be applied to the reduction of a Nitrobenzene or Nitrotoluene.

[Edited on 26-3-2021 by zed]

Fyndium - 26-3-2021 at 00:59

It was actually 2-liter flask I have got both of these issues. First one I solved by using water bath to buffer the temp a bit earlier when the reaction kicks off so it almost go without reflux at all, and the other one can probably be solved by changing reaction kinetics.

I want zero risk of vapor/liquid/reaction contents shooting out of a vessel. Some consider geysers an experience, I consider them a catastrophic failure.

Ah, the good old Chemland. Seems to be always saving the day.

greenlight - 26-3-2021 at 07:32

I have had a violent reflux before using a 2 litre flask with a 19/26 300 mm9 condenser on top and a large amount of vapour was escaping. I put another condenser on top of the initial one and connected the two with a tube and ran them both from the one pump. Fixes the issue of escaping gases but wont solve the problem of geysers .

[Edited on 26-3-2021 by greenlight]

Sulaiman - 26-3-2021 at 23:42

Would an anti-splash/bump head/adapter be worthwhile?

Fyndium - 27-3-2021 at 05:31

Actually, anti-geysir trap could be made from chromatography reservoir. For larger vessels it's a little of help, but adding 1L reservoir for 2L reaction flask doubles the headspace for foam/whatever stuff that's coming over.

The anti-splash adapter I bought earlier does not have drain holes for some reason, and when it fills quickly even from natural condensation to walls of it and stillhead, and when it reaches the exhaust holes, it will form water-lock and cause major issues for everything. Don't know what it's for, but definitely not useable at all for distillation.

CharlieA - 27-3-2021 at 15:56

It seems to me that this may be a matter of technique. If you are performing a simple reflux, it seems that you may be heating the flask to too high a temperature. At a constant temperature, the rate of reaction is constant. If the reaction is proceeding too fast, perhaps you can change the apparatus setup to provide for a controlled addition of one of the reagents to gain control over the rate of reflux....Just random thoughts from an old fart.;)

Fyndium - 27-3-2021 at 22:46

I'm purely looking here for a protection against any too vigorous reaction conditions. Whenever possible, I always use gradual addition, dilution, effective stirring, coarseness of material and other factors to limit reaction speed and also use waterbaths for reactions that would need additional cooling so I can respond to that in an in instance. For example, exothermic initiation of benzaldehyde was such a reaction. Running it full blast will cause reflux choking and vapor and even liquid escaping, but carefully heating it with waterbath to the edge of the initiation, and slowly adding cold water to waterbath will buffer it to a very controllable state.

A very specific case. Another case when it comes a matter is if flask size goes big enough. Then, 24* joint is simply too small to handle the common reaction rates at that scale.

zed - 28-3-2021 at 03:41

Ummm. In some cases, reactions work better if you let it rip, and use more condensers.

Not the way I would have engineered things, if I had been asked. But, I wasn't asked.

I'm stocked-up with extra condensers. Kinda short on flasks with multiple necks though. I've got 2 and 3 neck adapters in 24/40.... Which at a certain point, might be overwhelmed.

Sigh.... So many ways to encounter disaster.

Oh well, better to ponder the problem here, than to be surprised by it under reflux.

[Edited on 28-3-2021 by zed]

Fyndium - 29-3-2021 at 00:45

I got half a dozen of condensers, and I don't buy anymore other than min 3 neck flasks, except if I need to risk a sacrificial flask. It is very difficult to stir, measure temp, reflux/distill and add stuff at the same time through one hole.

SWIM - 30-3-2021 at 12:43

A really big Dewar condenser can do the trick sometimes.

The large volume around the ice reservoir helps stop any geyser action.

Also, if the condenser chokes spattering will tend to be caught in the condenser body.

Helps to put an Allihn condenser on top as a belt and suspenders measure sometimes.

zed - 30-3-2021 at 22:05

Ummm. Dewar condenser. Interesting idea.

Thank you.