hi, whats the difference between a 200mm and a 500mm condenser ? how does it affect reflux?User - 30-9-2009 at 16:09
-A lot of money.
-More effective cooling.
Well it does depend on your purpose and batch sizes.
Also if you have a smaller cooler the flow rate must be lower to obtain higher yields.
[Edited on 1-10-2009 by User]friendlyterry - 30-9-2009 at 16:12
for small batches is 200mm ok?
[Edited on 1-10-2009 by friendlyterry]entropy51 - 30-9-2009 at 17:28
Although I have mostly 300mm condensers, I recently bought a couple of 200 mm and I like them very much. They seem adequate for everything except the
very low boiling point solvents. They take up less space for a downward distillation and don't crowd the hood as much as longer condensers. So far I
have had no trouble refluxing ethanol, chloroform, ethyl acetate, toluene, or acetic acid with a 200 mm condenser. The ring of condensate doesn't
rise more than a couple of cm into the reflux condenser. When refluxing there's no need to see how fast you can boil it because the reaction
temperature will not go above the BP of the solvent, no matter what.
Also if you have a smaller cooler the flow rate must be lower to obtain higher yields.
User, I don't
understand. Higher yields of what? Distillate?
[Edited on 1-10-2009 by entropy51]JohnWW - 30-9-2009 at 18:27
For a shorter water-cooled condenser (with the water flowing through either a coiled tube or a jacket), you would certainly need either a faster flow
of cooling water, or water at a lower temperature, to obtain higher yields of condensate, compared to a longer condenser, because of the smaller
heat-transfer surface. The extent of cooling and condensation of the vapor desired to be collected in a flask would also depend on the thermal
conductivity of the material (usually borosilicate glass) of the coiled tube containing the water or (in a jacket type) the partition between the
water and the vapor.UnintentionalChaos - 30-9-2009 at 19:08
If you want to reflux, I suggest you try to pick up a Freidrich condenser on a good deal. They'll cost a bit more than the average condenser, but I've
never had condensing solvent make it even halfway up the cooling section. It's essentially a high-efficiency cold finger in it's own housing.
If you want multipurpose, a longer leibig will give better condensing for low boiling solvents, but they are bulky when being used for standard
distillation.User - 1-10-2009 at 05:19
@entropy51
Sorry i was a bit unclear.
I meant that a shorter condenser is more likely to loose product thus decreasing the amount obtained.
I would recommend spending a bit more money when its your first condenser, this would provide more applications.
What i often do is: using a vacuum adapter and a flask on the receiver end under ice or cold water.
This will make up a little for condenser loss as the gas that failed to condensate in the cooler will on the walls of the receiver.
I do this only when I am working with small amounts, and volatile substances.
* damn entropy you were faster relying than me editing *
[Edited on 1-10-2009 by User]entropy51 - 1-10-2009 at 05:23
If you lose product, you're distilling too fast! Turn down the fire.
Especially if you're fractionating something, you must distill slowly to get any separation of the components.gsd - 1-10-2009 at 08:12
Especially if you're fractionating something, you must distill slowly to get any separation of the components.
Separation of components in fractionation principally depends upon 1) Height and effectiveness of packing and 2) Reflux Ratio.
The "Size of Fire" must be so adjusted to avoid the flooding of column.
gsdentropy51 - 1-10-2009 at 09:26
I'm not going there. This has been hashed out repeatedly in several other threads.
Anyone who ever did a careful fractionation knows that you have to distill slowly to get good separation. The best column in the world won't separate
anything if you rush it. Simple as that. No armchair theorizing needed here.gsd - 1-10-2009 at 14:57
Armchair theorizing? LOL!
I have been doing "careful" fractionation of close boiling cuts for past several years.
Your confusion is evident when you say slowly. Which probably means using very high reflux ratio thereby taking out very little amount of product as
compared to the amount of vapours going to the condenser.
In practice if you are actually adjusting your heating rate so as to reduce amount of vapour reaching condenser, then what you are unknowingly doing
is increasing the "internal reflux ratio"
And BTW keep your comments to the content of the post. Not on your perceived state of the poster
Which probably means using very high reflux ratio thereby taking out very little amount of product as compared to the amount of vapours going to the
condenser.
I have been doing "careful" fractionation of close boiling cuts for past several years.
If you had done
them slowly you could have done them in a month or so instead of repeating them over and over with no separation.
[Edited on 1-10-2009 by entropy51]gsd - 1-10-2009 at 16:06
@entrioy51
I am liberal enough to appreciate your pathetically laughable attempt to generate humour by twisting the meaning of a sentence. A very nice way to win
an argument when you are devoid of any substance
*
