09-05-04 04:19
No 529617
In the detailed methods post, you talk about distilling mdp2p in a 22L. How much vac can a 22L take? I’ve seen 5L implode, and it wasn’t fun. I thought that 5L is as big as you can go with high vac, and even then you are getting dodgy with the heavy wall thermal stress.
Just for some chm porn, what sort of 22L dist rig was it? 29/42 or 45/50 jointed 200mm glass packed column, then on to a 600mm leibig?
(Hive Bee)
09-18-04 12:49
No 532023
Check with your chem supplier, there is 22L rotovap catalog. It is a standing one.
Hope this helps as this post does not tell you the answers of "How much vac can a 22L take". Anyway, SWIM does not understand the question at all. Define vaccum, relate that to 22L volume, is that what you are asking?
Thermal stress under heating of rotovap is still ok. There might be slight scratches that led to your experience of implosion of 5L flask. And that thermal stress causes great thermal difference of the in wall and outer of the flask, and oops, there you go.
oops i did it again
(Hive Adickt)
09-19-04 02:52
No 532122
A round bottom flask will stand all the wacuum you can pull eaven in the 100L size. Butt if iy has a star(crak) it wount hold.
(Stranger)
09-19-04 22:05
No 532283
The flask in qwestion is a 22l 4neck. The one that blew on me was a two neck. I always assumed that I had missed some damage on it. Yeah, spheres are great, its all the extra necks I'm worried about. I'm sure it will be fine with aspirator vac. That can get the goods into a 5L RB. That is untill I get that 22L rotovap... Holy shit, that would be the day I take over the world. My rotary pill press would be showing up right after that.
I still wanted to hear the setup of the 22L rig that yeilds "water white" mdp2p :)
(arrogant bee of the day)
09-20-04 04:11
No 532312
What is the big deal, what is it that you want to know?
The full set up?
Well chances are it was a real size like 34/35 not the shit that you mention (and it was 20L not 22L). But assuming you are in some back-ass-wards country using some ridiculous sizes and measurements, then the vacuum distillation set would be completed with an appropriately sized stillhead and condenser and vac adapter and receiving flask like I have. Exactly the same as a 1L setup but bigger. Now the micro stuff, that's cool!!
ANy RBF of any size will handle the most vacuum that you can deliver.
I'm not fat, I'm just too short for my weight.
http://www.whatreallyhappened.com
(Stranger)
09-20-04 17:21
No 532399
Just like I asked in the starting post, the column was my real interest. At that 22l size the joint size, internal diameter, length, design and packing all have huge effects on reflux rate, warm up time and effective separation. But then again, we all know this. I just was hoping to gain some insight into what has effectively worked for others. No need to go through r&d and inventing the wheel, when a simple, "300mm vigreux, vac jacked in 45/50 worked for me" would do. This glass is expensive and difficult to obtain. I would rather not have to struggle unnecessarily. I have personal experience, like most here, with vigreux and hemple columns of various lengths and different packing in the hemples. I see that most of the plant scale columns are perforated plate. Are these the hot ticket? I wouldn’t know. How about oldershaw columns? Once again, I was hoping that I could just hear about what has worked for others. This is a dangerous and expensive game we play and I was just looking for some help. Sorry if the questions are ignorant.
(Stranger)
09-22-04 17:37
No 532756
How much vacuum can be applied to big-sized flasks depends on the wall strength and the curve of the flask.
Smaller flasks have a strong curve, compared to big flasks, but the wall thickness is usually not proportionally higher as well, but rather just slightly higher than with smaller ones.
With round bottom flasks, the pressure difference between inner and outer atmosphere is the same at all points (almost). The pressure capacity solely depends on how much of the working force the walls can absorb, and this depends on their thickness as well as their shape (curvature in this case).
(A will break far more likely than B, although the same force works on them)
Therefore smaller flasks can be evacuated completely without any risk, whereas with bigger flasks, this has to be done with great precaution.
(arches of a bridge can carry more weight the higher their curvation is. With "flat" arches, bridges are usually not that stable - and gates and windows of old churches are another example...)
indole_amine