[bozroniancw]

I am conducting testing to find a fluid for a liquid valve to be used in the petroleum industry; this fluid will consequently see exposure to gasoline and ethanol.  Testing has consisted of bubbling ethanol vapor though a jar of propylene glycol, which is our leading candidate.  Propylene glycol has all of the attributes we require for the proper operation of the valve, but as testing has progressed a white precipitation has formed in the propylene glycol-ethanol solution.  The test setup actually bubbles air through ethanol fluid to pick up ethanol vapor and then bubbles through the glycol, as a result the solution is an open system with plentiful exposure to air.

I am wondering if anyone can tell me what this white precipitate most likely is?  As the jars and fluid were clean, but not sterile, when starting the testing, the most likely candidates are biological growth or chemical reaction precipitate.  We are thinking chemical is more likely than biological, but have no basis for this.  In either case we are also wondering if the development of this material, which is only small floating particles right now, will continue and become a problem by blocking flow passages.  The test has been run for two weeks so far at a flow rate of about 15 SCFH, at 60F.

Any help will be appreciated.

[sondakem]

Are you sure it is a precipitate?
I mean does it settle out?  Can you filter it?

[bozroniancw]

It does settle to the bottom and can be filtered.  I am not a chemist and do not have the resources to do an analysis on what is filtered.  Before I go spending money at a lab, I thought I would ask to see if anyone might have an idea of what it could be, (i.e. if there is a know reaction between the two compounds).

[sondakem]

I don't know of any reactions between the two that might form a precipitate.

Is it possible that the pipes (tubes) are dirty?

Is it possible that the pipes and/or valves are actually reacting with the ethanol?

Have you checked the chemical resistance of the matereials (from a table or by soaking a sample of each component in each solvent seperately)?
 

[bozroniancw]

Thank you for your thoughts, I do not believe that the setup is reacting with the either material.  The setup consists of copper tubing, brass fittings and glass jars.  During previous testing of the compatibility of Dow D-200 silicone with ethanol on the same setup no similar product was formed.  Also, another test with the ethanol/propylene glycol was conducted in a stainless steel setup.  This test was run for 4 days after which, no significant amounts of precipitate had formed.  The ethanol/glycol solution that was left over after this test was put into a plastic jug and let sit for about 10 days at 60F.  This solution was then examined and showed precipitate formation.  All of these results lead me to think that it is the interaction of the two chemicals and not other environmental considerations. 

[sondakem]

Well, if you've found a way to make ethoxy-ethers of p-glycol the ppt should be waxy and gooey.

[bozroniancw]

Sondakem, can you elaborate on what ethoxy-ethers of p-glycol is?  I am not familiar with this compound.  Do you know what the reaction from p-glycol to ethoxy-ethers is? 

Thanks.

[sondakem]

p-glycol

              H
              O
HO-CH2-CH-CH3

ethoxyether

replace the H that is attached to either or both of the O's with CH3CH2-

You will get three different compounds.  I'm not sure this will actually happen.  Paper tolerates everything.