sulfites in amines - why, where do they come from, consequences... 1

[planteng2010]

Hello,

Recently we got the analysis report back from our formulated MDEA in our refinery unit. The sulfites level was over 4000 mg/L, where all previous analysis showed levels below the labs detection limit.
Where would these sulfites be coming from?
What harm will they do to the system?
What can we do to deal with them?

Thanks for the help.

 

[rustbuster]

Sounds very odd, I would question the lab first (possibly a typo) then your solvent provider. Our maximum sulfate limit is 500 but normally 25 - 35 ppmw

 

[RogerH]

Planteng
You dont mention the service. If it is MDEA for a SRU tail gas treater I can see a reason for some SO2 slippage serve as a source for sulfite in the amine
The other possible source I can come to think about is if the MDEA storage isnt gas-blanketted i.e. contains oxygen that can serve as a oxidaton source.
Howwever I havent found any litterature sources to support this statement.
RH

 

[Jason5000]

RogerH is absolutely right about the tail gas unit issue. If you're short on hydrogen or have some catalyst damage, SO2 can breakthrough and form thiosulfate heat stable amine salts. This will likely be coupled with cloudy, low pH quench water, and possibly a lot of quench filter changes.

If oxygen is the contaminant from unblanketed tank breathing, then usually color of the solvent in the tank is the telltale of the problem. I've never seen that as a problem with MDEA even in tanks with no blanket system.

 

[planteng2010]

Sorry for not responding to you. I was on vacation! We had the lab re-run and it was an error, the actual level was slightly over 400 mg/L. It is not the TGTU, rather the main system. Talking to other people on the issue, we suspect that BFW was added to the system, and some of the chemicals used for treatment could do this as well.

Corrosion problems are the main concern here, correct?

 

[rustbuster]

That would be the main concern. Keeping the O2 out is also a good idea and only usting condensate as water make-up. BFW will cause solvent degradation.