Inhibitor Na2Cr2O7 alternative for ammonia/water carbon steel

[virk]

Hello!

We use the salt Na2Cr2O7 as corrsion inhibitor for ammonia/water solution to protect the carbon steel equipment. This corrosion inhibitor is well known since a hundred years, but more or less toxic.

Is there any proven alternative available?
Will ammonia/water NOT affect stainless steel? (304 or 316)

Who can help me with some information or an appropriate link?

Kind regards

virk

 

[unclesyd]

I don't have any details as yet and probably want be able to find any, but will try. This information is strictly from recall so don’t run with the details given, as some are on the money and some are little off. This is just to give you some leads. The fact that it was done with something other than Na2Cr2O7 tells you that it’s worth the effort to keep looking.

We recovered Anhydrous NH3 from 20% Aqueous NH3 in CS columns and used a very small amount of NaOH, probably less than 1% , was added to prevent corrosion to the columns. If I recall correctly it prevented the formation of Ammonium Carbamate. The small amounts of CO2 came from our processes where we recovered the NH3 vapors by water scrubbing gas streams.

We routinely monitored the column tails for NH3, NaOH, Na2co3.

The columns (6) were approximately 3' in dia and 40' tall and used an “ice house condenser”.
All the equipment in this service was CS and all components stress relieved.
If I recall the columns operated at a little over 200°C @ 450 psig.
The columns were 25 years old when taken out of service and all were in excellent condition.
The columns were packed with ceramic Raschig rings.
We had no SS in this system except for a few instrument bodies, all of which were 316 SS.


There should be some literature on this process as it was the primary way to recover ammonia vapors from different processes at the time.

 

[virk]

unclesyd, thank you for your advice. I was looking after NaOH and really found some links, which might be useful. I will see.

Kind regards

virk