50% NaOH, storage in non-sealed tank, Crystals formed - NaCO3?

[Subystud]

Hello -

50% NaOH is utilized. It is stored in 5500 gal HDPE double-walled tanks.

Crystals have been found in wye strainers, at threaded fittings/unions (glue joints fine).

My reading has indicated that the crystals are probably NaCO3 that formed from reaction with atmospheric CO2.

Anyone with experience in this? Do the tanks require heat trace / insulation? Or do I need to get a N2 blanket on top of the chemical tank?

Are the unions / fittings points at which CO2 are entering the plumbing?

Any reference or relevant chemsitry / physics is appreciated.

Currently, we are considering shifting to 25% NaOH; which we may do anyway. But would we not have the issue of crystals with 25%?

Thanks -

 

[siretb]

You should keep 50% NaOH above 8°C. Could you have reached a lower temperature? If yes some solids can form (NaOH, xH2O
we do not trace such tanks, but we use them only indoors. Otherwise we switch to 30% wh NaOH

 

[Subystud]

So, you would not expect the crystals that are formed to be Na2CO3? You'd expect NaOH-xH2O?

 

[siretb]

No this is not what I mean.
If the temperature went low, then NaOH cristallization will occur. You can hane Na2CO3 cristals.
It should be easy to check that. The Na2CO3 cristals will dissolve much more slowly into water and they do not release CO2, when put in contact with an acid.
I think the key issue is: what is the outside temperature and what is the bulk temperature.

Again, unless you have very good reasons to stick to 50% wt, using a 30% wt solution is a lot easier.

 

[Subystud]

Tanks are in doors in north Florida. I think that temperatures are getting below 46oF due to a large roll up door, and probably not running the thermostat.

What temperature would you expect 25% to crystallize?

 

[TD2K]

http://msdssearch.dow.com/Published...soda/pdfs/noreg/102-00011.pdf&fromPage=GetDoc

About -20C, see page 7