separating water & glycerol

[Richard C]

I've read a few of your past posts, but didn't quite get the answers I need at present. I like to fidget with science projects, so this is not supposed to be rocket science, just hobbying around the back yard. Organic chemistry is also not my forte. In my present project, after desiccation of a volume of air with glycerol, I need to recover the water as well as re-use the glycerol. What would you suggest is the best & cheapest way to achieve this?

[Elite Engineer]

You could try and "salt out" the glycerol. Adding ammonium sulfate to the solution would remove the water interacting with the glycerol and essentially "dry it out". Not guaranteed to be 100% effective, but may get you as high a return as 70%-80% of water. However you're going to have a hard time isolating all the glycerol from the solution.

 

May I ask what you're going..more info helps me help you.

 

~EE

[BabcockHall]

What are the boiling points of water versus glycerol?

[John Cuthber]

You could try and "salt out" the glycerol. Adding ammonium sulfate to the solution would remove the water interacting with the glycerol and essentially "dry it out". Not guaranteed to be 100% effective, but may get you as high a return as 70%-80% of water. However you're going to have a hard time isolating all the glycerol from the solution.

 

May I ask what you're going..more info helps me help you.

 

~EE

I strongly suspect that adding ammonium sulphate would give you a solution of ammonium sulphate in wet glycerol.

Boiling out the water is a better bet.

Vacuum distillation is better yet- but needs more complex equipment.

[foxy john]

You could explore molecular sieves or silica gel. The correct pore size would remove water, leaving the glycerol. The water could be reclaimed by heating.

I've also seen a reference to crystallising the glycerol out by freezing.

[Richard C]

What are the boiling points of water versus glycerol?

Glycerol BP is 290°C. MP is17.9°C, but crystallizes at a much lower temp.

You could try and "salt out" the glycerol. Adding ammonium sulfate to the solution would remove the water interacting with the glycerol and essentially "dry it out". Not guaranteed to be 100% effective, but may get you as high a return as 70%-80% of water. However you're going to have a hard time isolating all the glycerol from the solution.

 

May I ask what you're going..more info helps me help you.

 

~EE

In a severe drought situation, we are running out of water. I'm looking at possible ways to get potable water out of the atmosphere for daily consumption when (if) the taps run dry.

You could explore molecular sieves or silica gel. The correct pore size would remove water, leaving the glycerol. The water could be reclaimed by heating.

I've also seen a reference to crystallising the glycerol out by freezing.

Freezing out sounds like a better option. Do you have any idea at what temperature Glycerol starts to crystallize?

Thanks for comments received. I have been away from home, traveling. Now I can start actually trying a few things. Had to order Ammonium Sulphate, - waiting. I'll start by trying to get atmospheric water into some Glycerol then see firstly how the freezing out may go.

[John Cuthber]

The problem with glycerol is that, when it is cold enough to freeze, it is too viscous to do anything much- so it only crystallises slowly.

 

Simple distillation is probably the easiest way to recover water.

Something like CaCl₂ or silica gel might be easier to reuse.

[Enthalpy]

Freezing the glycerol out doesn't work. Its mixes with water just stay liquid at quite cold temperature. Heat or low pressure (takes less energy) is the standard way.

 

Polyethylene glycol, especially tri- and tetra-, are more often used in this application than glycerol, possibly because water separation is a bit easier. Tetra isn't toxic (glycerol neither).

 

To maximize the contact between air and glycerol at moderate power expense, you may consider rotating disks resembling this

http://www.scienceforums.net/topic/70340-reactor-for-liquid-and-gas/

which are inspired from an air humidifier anyway.

 

Depending on where you live, you might try to extract humidity from air when it condenses to fog, hopefully every morning as in the Namib. Then a big net suffices to catch and collect the water. Demonstrated in an Andean country, possibly Perú.

 

Hi BabcockHall, nice to see you here!

Edited May 20, 2016 by Enthalpy