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Author: Subject: How to adjust reflux ratio ?
National Hazard

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Mood: really starting to feel the Specioprin HCl now

[*] posted on 28-10-2018 at 19:15

Have you considered spiral prismatic packing?
I just picked up a liter of 3 mm for like $25.

It's much less likely to flood, and it's supposed to be very efficient.
There's a lot on Ebay from the Russian Federation. (Stainless steel, various sizes )

If you need something more corrosion-proof, Nanshin now sells glass coils (12 x 4 mm labeled , "glass coil spring filter use for chromatography.) ) which look identical to the ones Synthware sells as distillation packing.

They are more fragile though in my experience, but cost a bit less. I can get 200 grams here for $23.

Synthware says such coils are intermediate between Raschig rings and single turn helices in efficiency.

That sounds pretty good to me. Have you ever priced single turn helices?

A Clevenger trap can act as a partial take off head. Really more like a solvent distillation head with a tiny reservoir, but it should work.

The problem with quotes on the internet is that it's hard to determine their authenticity. -Abraham Lincoln.
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International Hazard

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[*] posted on 28-10-2018 at 20:07

A clevenger or dean-stark w/ take-off is probably the best way to go.

There is an alternative though using one of these valves:

The valve can work with a regular distillation adapter and 15 degree adapter to make a clevenger.

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National Hazard

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[*] posted on 29-10-2018 at 00:09

Quote: Originally posted by Sulaiman  
Although the still that I am building is also a work in progress,
I chose all glass so that I could watch and learn and ponder :)
It turns out that ALL parts with upward flowing vapour need to be thermally insulated
so I see nothing without disturbing equilibrium a little by opening thermal insulation to have a peep :(

Well in essence they do not need to be thermally insulated, but you got to have enough power pumped into the boiler to overcome the the thermal losses through the outer surfaces of the system. The whole apparatus partly works like a reflux condenser due to the heat losses....if insulation is applied the effect is minimised, but still there.
So if you wish to observe the operation of the column in the exposed state you have to consider a more powerful heat input. Then again if your column is of too small a diameter you might run into trouble with excessive vapour speed disturbing the smooth operation. This problem is especially apparent with small systems that intrinsically have a bigger surface covering less volume, hence the losses have a greater effect upon operation.
The geometry and nature of column packing is also very important in terms of reaching a stable operation with acceptable output and no sharp flooding conditions. The packing shall effectively rob part of the internal column volume and hence there is less free space for vapors to travel through. This shall increase the vapour speed and alter the pressure gradient in the coulmn leading to a condition where downcoming reflux is pressed up in the column by the high speed vapour coming from below....flooding shall happen.
Spheres or cylinders are by far the most restricting packing types and will effectively take up the most amount of free volume in the column, leading to flooding conditions at even moderate heat input. In theory you would want a packing that has a lot of surface area, yet lacks volume....something like thin walled glass tube sections, metal chips/scrubbers/meshes or some of the specialised geometry packings with saddle or other intricate shapes.
For practical purposes tube sections and metallic scrubbers probably are the most accessible and economical options. The specialised packing materials usually cost quite a bit if any considerable column volume has to be filled.

Exact science is a figment of imagination.......
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