Glycol Leak Causing pH Depression 3

[Rpsfinest]

We had a small glycol leak into the condensate system at the plant. The condensate is controlled around 9.0 pH and is demineralized water. My question is on the chemical reaction between the glycol and the 9.0 pH demineralized water. It caused the conductivity to increase well out of our control range and dropped the pH down to 5. What causes this? what reaction is going on to turn the water acidic?

thanks guys...

 

[kenvlach]

Pure glycol & DI water don't really have stable pH's.
Gycols degrade to organic acids, aldehydes & ketones in the presence of heat or UV light plus oxygen. Metals such as aluminum and copper catalyze the degradation.

Any pure glycol used as a themal fluid should contain a stabilibilizer (Dow Chemical). Any glycol-water solution should contain a pH buffer and corrosion inhibitors to protect metals in the system.

See 'A Guide to Glycols' from the Dow Chemical Co.

http://www.dow.com/PublishedLiterature/dh_02aa/09002f13802aaf25.pdf

and
'Uninhibited Ethylene Glycol' from Thermo Electron Corp.

http://www.thermo.com/eThermo/CMA/PDFs/Various/File_26366.pdf

Glycol degradation usually results in a noticeable smell & darkening of color, along with the pH drop.

 

[Latexman]

If I recollect correctly, aqueous glycol (and alcohols) undergo an equilibrium reaction:

HOCH₂CH₂OH + H₂O <-----> HOCH₂CH₂O^- + H₃O⁺

There are published equilibrium parameters, called pKa's, that indicate the acidity of various glycols (and alcohols).

Good luck,
Latexman

 

[MedicineEng]

Can you please explain how do you have a pH9.0 demin water?
As far as I remember, demin water is acidic by nature, as it is purified water, but maybe I am wrong.

 

[bimr]

Demin water from the typical cation/anion or mixed bed demin unit usually has a pH of 9-10 units. That is because the ion leakage that exits the demineralizer unit is in the form of sodium hydroxide. The hydroxide ion causes the elevated pH.

For example, if you have .1 mg/l leakage from a demineralizer, the .1 mg/l would be as sodium hydroxide. Sodium is the first ion to leak from the cation unit. The sodium would then leach the hydroxide ion from the anion unit.

Note that since there is no buffering agent in demin water, it is relatively simple to have an agent cause a change in pH.

 

[kenvlach]

I was thinking that the condensate was condensed steam, so basically distilled water, plus some volatile additive in the boiler feedwater to raise pH & provide corrosion protection for the condensate system. Please clarify.

 

[Rpsfinest]

yes correct the condensate system is demineralized water treated with ammonia to raise ph...

 

[cub3bead]

Your glycol leak is going to cause havoc in your steam generator and steam system if you don't fix it. The glycol will degrade into a weird mix of organic acids and CO2. The organic acids and CO2 will carry over into the steam and when they start condensing you will have some very corrosive condensate. The higher the steam pressure the worse the problem.