Concentrating NaOH

[Procman]

We are looking at installing a new process. However, this process requiress the use of large quantities of NaOH solution. Once we have treated our product with the caustic soda, the soda is washed out resulting in a NaOH solution of 5.5% As a result of using large quantities of NaOH, it will not be possible to dump the spent caustic and use fresh caustic in the process. We need to re-use the NaOH, but in order to be able to do so, we need to concentrate up from 5.5% to 50%.

Is there any technology other than evaporation that can be used (that will be more cost effective). If not, where can I obtain typical costs of such an evaporation plant?

 

[m777182]

Manufacturers of evaporation plant will gladly help you. There is some information on internet.Try googling with "NaOH concentration". Once I found a three stage evaporation plant flow sheet with emmbeded calulations program but I lost the source.
m777182

 

[JStephen]

Just wondering- if you chill the stuff, can you get the NaOH to crystallize out? Or is there any practical way to do that as a continuous process?

 

[nbucska]

I wonder if you could use the countercurrent method for
washing the product to increase the density from 5.5%.

The countercurrent principle can be used to reduce
the energy requirement of evaporation, too.

Plesae read FAQ240-1032
WEB: <

http://geocities.com/nbucska/>

 

[unclesyd]

I would take a look around this site as they are normally on top of the game when it comes to evaporation. I don't know how the economics will workout today but several years ago they weren't too good for concentrating NaOH on medium scale.

http://www.swensontechnology.com/evaporators.html

 

[Procman]

nbucska,

we are going to use couterncurrent washing, however, we need the caustic at a specific concentration, which means that we still have to concentrate up (therefore the figures given above). Thanks for the help anyway.

 

[marcusmcgee]

Procman,

Have you looked at membrane technology. The use of standard RO membranes may not be appropriate due to other ions in the solution. There are some new development in the field that could withstand the high concentrations you are looking for. This might not get you to 50% but it could be used ahead of evaporation to lower the amount of water to evap.

 

[nbucska]

Procman:
ENG-TIPS has a symbol for "thanks" -- it is a the red star...

Plesae read FAQ240-1032
My WEB: <

http://geocities.com/nbucska/>

 

[MJCronin]

Proc....

With concentration, you may be into some expensive materials due to caustic corrosion...

I was involved in an NaOH evaporator that used a shell and tube heat exchanger to drive a dilute solution to ~73%....
Steam was used as the hot fluid...

Many of the surfaces were pure nickle

Good information:

http://www.dow.com/causticsoda/safety/material.htm

http://www.hghouston.com/naoh_300.html

http://www.rohmhaas.com/process/naoh.html

-Let us know what you decide...

-MJC

 

[Procman]

marcusmcgee,

we are also looking at RO. We can prabably concentrate up to 20% via RO but still need to get to about 50% for our process to work.

Do you have any other suggestions?