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Author: Subject: which is the better reflux condenser? allihn vs friedrich
EmmisonJ
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[*] posted on 30-7-2010 at 05:18
which is the better reflux condenser? allihn vs friedrich


from the little bit of info i've read it seems like the friedrich is the way to go. i have a 200mm allihn that serves me well for a myriad of refluxing tasks but i am in need of a 400mm reflux condenser so i'm thinking of getting a friedrich. it will be used for refluxing a variety of things from mild refluxing of random solvents to heavy vigorous refluxing of gas-laden solvents.

i've googled all last night and this morning and have a slight grasp on why the friedrich is better but am curious if any of the experts here have any personal experience they wish to contribute to sway my decision one way or the other?

i'm also curious, why do so many people slam graham condensers as being nearly useless? from the diagram, they would appear to be the most efficient at condensing vapors because of the long path the vapors have to travel while being surrounded by the coolant. certainly i'm missing some logic in this.

as always, thanks

[Edited on 30-7-2010 by EmmisonJ]
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Vogelzang
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[*] posted on 30-7-2010 at 13:35


Which ever one works best for your application.
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BromicAcid
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[*] posted on 30-7-2010 at 16:35


Similar to a Fredrich is a jacketed coil condenser. It depends though on what you want to reflux and why, i.e., if you're going to be off-gassing during the reflux you do want the wide bore of a West or Allihn condenser (I also see these called bubble condensers). But if you're just trying to knock solvent back into a pot then a jacketed coil condenser works pretty darn good.



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azo
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[*] posted on 30-7-2010 at 17:50


thats exactly right bromic acid.


? graham condensers can't be used for reflux what a load of bullshit


azo
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EmmisonJ
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[*] posted on 30-7-2010 at 18:27


thanks BromicAcid, off-gassing is the opposite of what i want to happen. i will be refluxing a wide variety of different bp compounds but the one that raises the most concern with me is trying to condense a compound that has a bp of -6C. it's obviously a gas a room temperature but will be solvated in MeOH, however when the exothermic reaction begins to pick up steam and the MeOH refluxes then there's worry of losing the gas that is solvated in it. so i'd like to be able to condense both the gas at -6C and the MeOH. so i'm wondering if the friedrich would shine over an allihn in a situation like that.

of course this also brings up the topic of what coolant to use to feed through the condenser to be able to condense something that has a bp of -6C. i saw a post on here that had a great listing of different freezing mixtures with the ratios included. NaCl + ice got down to around -20C if i remember correctly however wouldn't a dewar be needed in that particular example? jon made a good point about using antifreeze + dry ice instead of feeding that through the condenser, that should reach a cool -30C or so. in fact i remember seeing pics of someone running antifreeze through their condenser for a distillation here but it was awhile back that i read that thread and can't seem to find that post anymore. the only thing that concerns me with the use of antifreeze is if it would tear up a plastic fountain pump or any other similar plastic water recirculating pump.

i'm not looking for anything like IPA + dry ice as that is overkill. just wondering which condenser would be better suited for the example above... and perhaps also if the antifreeze idea would be worth looking into or not

[Edited on 31-7-2010 by EmmisonJ]
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matei
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[*] posted on 31-7-2010 at 10:03


Quote: Originally posted by azo  
? graham condensers can't be used for reflux what a load of bullshit


That's not a "load of bullshit", that was the personal opinion of a graduate student who has been doing organic synthesis in an academic setting for the past five years, and who happens to TA organic chemistry labs ever since.
You should try and express your ideas in a more apropriate manner, this is a science forum after all.
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BromicAcid
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[*] posted on 31-7-2010 at 14:18


Amusingly enough if you search Graham condenser on google the first hit is the wiki article on distillation. The reason it pops up is because there is a picture in the article of someone refluxing toluene using a Graham condenser.



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matei
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[*] posted on 31-7-2010 at 14:40


Quote: Originally posted by EmmisonJ  
i'm also curious, why do so many people slam graham condensers as being nearly useless? from the diagram, they would appear to be the most efficient at condensing vapors because of the long path the vapors have to travel while being surrounded by the coolant. certainly i'm missing some logic in this.

[Edited on 30-7-2010 by EmmisonJ]


EmmisonJ was obviously referring to to the "second configuration" as Wiki calls it (as opposed to the "first configuration" depicted in the picture you're reffering to) of Graham condenser, in which the vapours to be condensed have to pass through a narrow spiral tube surrounded by a water jacket.
I'd appreciate very much BromicAcid if you can show me a picture on the internet of a setup (made by a professional chemist) which has the "second configuration" of Graham used for refluxing.
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[*] posted on 31-7-2010 at 14:57


BromicAcid and azo, here is an excerpt from "Organikum - Organisch-chemisches Grundpraktikum", 21 Aufl., Wiley-VCH, Weinheim, 2001, pp. 4 -5.


condenser.bmp - 900kB
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entropy51
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[*] posted on 31-7-2010 at 16:22


Gentlemen, it does make a difference whether the coolant is circulated inside the coil or inside the jacket. These coiled condensers come in two flavors: the one with the coolant in the jacket is not good for reflux, the one with coolant in the coil is good for reflux.

[Edited on 1-8-2010 by entropy51]
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[*] posted on 31-7-2010 at 16:29


For those who don't speak German, the text says something like
'Narrow Graham condensers (lit. 'snake condensers') may never be used as reflux condensers, as the condensate in the narrow coil cannot run down well, [and] may often be ejected from the top of the condenser and thereby cause accidents. In vertically descending orientation the Graham condenser is ...'

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[*] posted on 31-7-2010 at 17:08


Some more info on condensers:

http://www.sciencemadness.org/talk/viewthread.php?tid=2473#p...

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BromicAcid
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[*] posted on 31-7-2010 at 17:21


Quote: Originally posted by EmmisonJ  
I'd appreciate very much BromicAcid if you can show me a picture on the internet of a setup (made by a professional chemist) which has the "second configuration" of Graham used for refluxing.


I freely admit that I've never heard of this 'second configuration' being called a Graham condenser, I've only heard it referred to at my plant as an inverted coil condenser and I have never seen someone using this. However, I have to wonder what your qualifications would be for a professional chemist? There are plenty of idiot chemists that simply get advanced in rank because they have stuck around their companies for so long, believe me, I know, so perhaps you should have specified a competent chemist? But then what would be the measure for that :D




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[*] posted on 31-7-2010 at 21:19


Graham is for reflux, it cant be used for fractional destilation. Here is photo of my graham it had both ends the same only size are diferent so it cant be used for destilation :P I read in soviet book "Laboratory work methods" that graham is for reflux. And i am chemistry student (second year in university) and working in Institute of Solid State Physics (www.cfi.lv)
http://img529.imageshack.us/img529/8594/dzesinatajs.jpg

[Edited on 1-8-2010 by Mildronate]

[Edited on 15-4-2011 by madscientist]
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EmmisonJ
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[*] posted on 31-7-2010 at 22:29


nice pic Mildronate, that condenser looks good for reflux but i've heard of condensers that look like that as simply being called a "reflux style condenser", very generic sounding i know but that's what i've heard them being called.

here is a picture of 2 different graham condensers. the one on the left looks like yours where the coolant goes through the coils and i've heard called "reflux style condenser", theoretically i would think it would be like a friedrich as far as efficiency goes for refluxing. the one on the right however is where the vapor itself goes through the coils and the coolant goes through the jacket like an allihn. the one on the right is the one i hear people talking trash about. i guess i could see how the one on the right could clog easily if a heavy reflux was going because condensate would be slow to travel down through the thin coils with all those turns and perhaps it would choke easily. also the one on the right would probably not work at all for distillations? i'm guessing because it'd have to defy gravity to travel upward through the top part of the coils, even if it were angled i think it'd have a hard time. i'm sure the one on the right would do a great job at condensing because it'd have so much surface area and the vapors would spent more time in contact with the coolant because of the vapors having to travel through the coils, but that would also be it's downfall too cuz i think anything beyond a mild mild reflux would choke it, no?



thanks for the link magpie i'm going to read that thread now but so far it's looking like the friedrich is right for me based on BromicAcid's comment that a wider condenser like an allihn is better for off-gassing, which is the opposite of what i want since i want to condense the solvent vapor but condense the gas to subzero temps too. i'm going to go read that thread but now am wondering how that "reflux style" graham condenser mentioned above compares to a friedrich

[Edited on 1-8-2010 by EmmisonJ]
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[*] posted on 1-8-2010 at 17:24


I have both these style of condenser(400ml). The one on the right is useless for reflux,but excellent for condensing highly volatile solvents.As a second stage condenser for ether sythesis for instance.They need to be set vertically or there is remnant in the coil.



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[*] posted on 3-8-2010 at 12:59


I think some of you are mixing up the names here and getting confused.

A COIL condenser is one in which the coolant goes through the spiral and the vapours travel around the sides.

A GRAHAM condenser is one where the vapour travels through the spiral and the water forms a jacket around it. These are also called INLAND REVENUE condensers.

The Wiki is incorrectly calling both the same thing. If you shop around a lot of the big name glass suppliers, you'll see them making this distinction. The article has been written by a spazztard with too much time to spend in paint. I'm quite amazed it hasn't been torn apart by some more knowledgeable chemist as of yet. I have begun instigating that process by flagging the article, adding a note about the inaccuracies and then discussing it in the talk page. It needs a cathartic purging of it's errors.

If you're refluxing, a GRAHAM condenser (vapours through the spiral) is a bad idea, as there's a high chance of it clogging or flooding. Which will either blow the liquefied solvent out the top or pop the glass as the pressure builds inside should it clog. You want an Allihn or a COIL (water through spiral). Allihns in particular are designed for refluxing and a lot of them come with very wide male sockets on the base to fit the equally wide top of a Soxhlet extractor; which needs to be wide to load the thimble. At the top, you'll notice a lot of them don't have a ground socket, it's a bare tube. That's because it isn't designed for connection to other glassware, it's intended to go on a Soxhlet for reflux.

I've seen people referring to COIL condensers as Friedrich's before. A genuine Friedrich differs from a coil as the cold element is usually a cold finger with a spiral groove up the side (not a long tube), and it's a tight fit in the outer glass. They're usually used on rotovaps.

If refluxing is your main deal, get an Allihn. Personally, I'd say get a good COIL condenser and you'll get excellent performance during reflux or distillation. I can have my plate at 380C boiling sub 100C solvents and they won't get past the first turn or two of the coil.

The jacketed condensers are aimed more towards the major pain in the ass to condense solvents, like ether. My coil will easily do DCM, which boils at ?47C?. COIL condensers are sometimes actually called REFLUX condensers.

This...



is a COIL condenser, NOT a Grahams / Inland Revenue.

The following are the names the manufacturers themselves apply to the glassware, not what I've chosen to call them or worked out from other references.

QuickFit is an ACTUAL BRAND of glass blown in England, not a generic name for all ground glassware. You can see the brand logo in the following pictures, it's a big Q with Pyrex QuickFit UK written inside it.

WHAT CHEMGLASS CALL A COIL CONDENSER;


WHAT SIGMA CALL A COIL CONDENSER. THEY ALSO HAVE IN BRACKETS (GRAHAMS), BUT THIS IS A QUICKFIT BRANDED CONDENSER, AND QUICKFIT THEMSELVES DO NOT GIVE IT THIS NAME, AND HAVE A DIFFERENT NAME FOR THE TWO, AS YOU'LL SEE IN A SECOND;


WHAT SIGMA CALL A GRAHAMS CONDENSER;


A QUICKFIT COIL CONDENSER (I actually have this precise coil, it works beautifully for aggressive reflux & precise distillation. Note the kink in the end of the spiral, you'll see that on other coils sometimes as a loop. It's a drip tip, there specifically to drip refluxing solvent back into the centre of a stir vortex or thimble and it keep it away from the tapers, where it'll wash grease back with it; you can see this happening the in the Wiki image at the top);


A QUICKFIT INLAND REVENUE CONDENSER;


[Edited on 3-8-2010 by peach]




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