Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
Author: Subject: Vaccum Distilling Xylene - Foaming and Boil Over - How to Prevent?
Hazard to Others

Posts: 163
Registered: 27-8-2018
Member Is Offline

[*] posted on 14-12-2022 at 12:12
Vaccum Distilling Xylene - Foaming and Boil Over - How to Prevent?

Been trying to vacuum distill xylene BP 138c at a 6mbar vacuum.
vacuum BP should be at 10c.

Im using a water bath with strong magnetic stirring and tried heating it up slowly but at some point it
rapidly starts foaming up and volcanoing immediately though the condenser into the receiving flask.

is there a trick to prevent this?

Im using a short path distillation setup.
would putting a claisen adapter on top of it help?

and the condenser water temperature ... if its at 0c it will be sufficient to liquidize the
10c xylene vapors?
View user's profile View All Posts By User
International Hazard

Posts: 524
Registered: 22-12-2021
Member Is Offline

[*] posted on 14-12-2022 at 16:08

Optional: Insert a thermowell into the solution.

Slowly apply a vacuum until the mixture begins to boil. You will notice the solution temp began to drop.
If you continue to pull more vacuum the solution will boil out of control until the temp drops.

Basic rules for any vacuum distillation

[Edited on 15-12-2022 by Rainwater]

"You can't do that" - challenge accepted
View user's profile View All Posts By User
International Hazard

Posts: 1192
Registered: 12-7-2020
Location: Not in USA
Member Is Offline

[*] posted on 17-12-2022 at 00:32

In case of foaming, I don't know.

In case of bumping, you will wanna use stronger stirring (overhead preferably), or if not available, a capillary bleeder.

Some stuff is very prone to bumping and I have found boiling chips of any sort (from porcelain to activated carbon) be of little help. Only thing that universally works is strong (overhead) stirring. Capillary bleeder works most of the time, but it is a bit tricky to draw and set up, and the capillary is easily blocked, so you will have to re-draw it. The needle needs to be only such that microscopic aerosol bubbles are formed when you blow through the tube underwater, under vacuum these bubbles will expand into big blasts of expanding gas.

And like said, you must never apply vacuum OR boiling chips to a heated reaction, both will cause it to violently blow over. You can never apply chips, but with vacuum, you can carefully jerk it up by gradually applying vacuum with a valve, and some will initially boil over very quickly, but as energy is drawn from the reaction, it will balance out, and eventually allow for sustained vacuum boiling.
View user's profile View All Posts By User
National Hazard

Posts: 488
Registered: 24-8-2019
Location: Within EU
Member Is Offline

[*] posted on 21-12-2022 at 05:25

Have you tried not to use any vacuum?
140°C isnt high temp, or are there any other resons for using the vacuum?
View user's profile View All Posts By User

  Go To Top