Check pH in TEG

[binbin73]

Hi ALL,

our gas processing has TEG generation system that required to check pH in lean TEG weekly.
the procedure to test pH of lean TEG as below:
PROCEDURE
4.3.1 Calibrate the meter, using the buffer solutions, in accordance with the manufacturer's
instruction manual.
4.3.2 Measure 11 ml of glycol sample and 239 ml distilled water into a 250ml beaker. Mix
thoroughly.
4.3.3 Place pH electrode and thermometer into the solution.
4.3.4 Adjust temperature compensation control on pH meter to correspond to solution
temperature.
4.3.5 Read pH directly from meter scale and record.
4.3.6 Rinse electrodes with distilled water

I do not figure out why to add distilled water for the test. the man made procedure already has retired.
I would appreciate your advice on the master.
thanks all in advance!

 

[pierreick]

Hi,
Let you check with your lab manager and/or request a 3rd party to perform the analysis.
My 2 cents
Pierre

 

[MortenA]

I second pierreick,

WRT the water i guess its about measuring pH. I dont think that acids will dissociate (when the acid donate the proton like HCL <=> H+ + Cl- )in TEG so you need to add water to be able to measure the pH. But its been too long since i did chemictry in a lab so i dont recall this part.



--- Best regards, Morten Andersen

 

[IRstuff]

What is the pass/fail criteria? What is your production pH requirement?

I can see doing something like this to check for contaminants or consistency in the TEG process.

see

https://assets.fishersci.com/TFS-Assets/LSG/Application-Notes/AN-PHNONAQS-E 1014-RevA-WEB.pdf

for a possible explanation for diluting the sample.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[MortenA]

So the text IRstuff refers to give 5 reasons, the first three being someting to do with the measuring principle and the last one the reason i gave. In the case with TEG i think its 4) and/or 5) but im not sure.

--- Best regards, Morten Andersen

 

[binbin73]

Thanks all for your comments/advice.
I also wonder about volume TEG (11ml)and distilled water (239ml). where do numbers come from? or related to ASTM?
thanks again

 

[MortenA]

probably not since its in ml =250 ml. ASTM would have chosen something in fl oz i would guess. 250 ml is most likely just because is a normal type of beaker. The ratio water/sample is to achieve the correct dillution to be able to measure pH.

--- Best regards, Morten Andersen

 

[georgeverghese]

Who is manufacturer of this meter, and what type electrode is this? Have you asked the meter manufacturer?
Literature from BS&B for a Ag/AgCl electrode requires a 1:1 v/v dilution of the lean glycol sample with de ionised water, while you have stated a 1:22 v/v. dilution.

 

[pierreick]

Hi,
Consider reading this thread:

https://www.eng-tips.com/viewthread.cfm?qid=160469

Pierre

 

[binbin73]

Thanks ALL for your advice.
actual the problem is normally pH of lean TEG in our system is about 7.3 and it has maintained for longtime (about 20 years) but recently we found it drops to 6.0
then I look back to procedure to test pH in TEG as showed diluted with distilled water in strange ratio (TEG/distilled water: 11/239)
Now we are attempting to refresh TEG in the treatment system.
other my concern is the solubility of H2S in TEG to cause low pH?
thank you!

 

[georgeverghese]

pH of 6 for a 50% solution of glycol in water is considered acceptable for new TEG.
See this doc on pages I16 to I19 for relevant details re interference of H2S on Karl Fischer titration for manual test for water content of TEG.

https://pacs.ou.edu/media/filer_pub...th_glycol_solutions_by_pearce_and_sivalls.pdf

 

[pierreick]

Hi,
Weird answer from last poster. AI?
Meaningless.
Pierre