Sciencemadness Discussion Board

Filtering Hydroxide solution

wakatutu - 10-6-2018 at 16:46

Hi everybody!

I realize this is probably a topic already covered here, but using the search engine on such a basic thing rewards me with every topic on the site!

I'm having a difficult time filtering an aqueous solution of mixed lipophilic organic acids in excess hydroxide. Vacuum filtration induces foaming and an emulsifying of layers which is diffuse throughout the solution. This is probably OK but it is a hassle to deal with the foaming.

Gravity filtration takes longer than I want to spend doing it, though it is very effective.

Is there a better solution to this problem?

happyfooddance - 10-6-2018 at 17:38

So you have soap that's basic, am I correct?

If that is the case then I have also experienced your frustration with this. It is extremely difficult (and time consuming) to break the emulsions that form. Pulling a vacuum and removing dissolved gasses can help with emulsions, but it doesn't work in this case because you just get froth sucked into your pump.

Gentle heating and stirring are also pretty useless here.

For what it's worth, the emulsions are a little better when the solution is made acidic: that is, after the initial (almost) unavoidable evolution of fine CO2 bubbles...

I too, would like a good solution for my application.

vmelkon - 10-6-2018 at 19:54

This has been a problem for me as well. Perhaps a bubble popper would help. I would have to build one.
I have seen some chemists has something to reduce the foaming in some cases.

SWIM - 11-6-2018 at 09:19

There are a lot of soaps that just won't foam in salt water.

Don't know exactly what you're doing here, but would salting the solution before filtering be feasible?

Forcing the liquid through the filter under pressure instead of sucking it through might solve a lot of your problems if you can rig that up somehow.