Caustic Quality

[dipak2]

Dear All ,

Good Morning !!!

What are the impurities in the Sodium Hydroxide (NaOH)--(Caustic Soda )?Actually,On Commercial Basis---- Physical Appearance,Caustic NaOH % is checked ?

Pl. be enlighten on any other impurities ,Sludge that can affect the Washers Separators function of Nitrobenzene Production Unit ?

Hope for Positive Response.

Thanks in Advance to all of you.

 

[Zoobie]

I can't answer your question specifically since I no longer work in a plant that uses caustic and I can't remember everything. A few comments though:

How the caustic is manufactured impacts the types and quantities of impurities...membrane, diaphragm, or mercury cell processes (not as many around of these anymore). Membrane and mercury cell plants produce purer solutions.

Quality of dilutuion water can affect quality...waters vary all over the world.

Other anions that might be there: chlorides, carbonates, sulphates....????
Other cations that might be there: Ni, Fe, transition metals, alkali earths

You sometimes get some rust from storage tanks.

Do you already have sludge build-up? If so, what does it look like?

 

[dipak2]

Dear Zoobie ,

Yes I have sludge Build up frequently in Washers Separators.Like every two/three months.The sludge contains mainly FeSo4 rusts ,CaCo3 .Yes You right because We have Process Water with 92-100 ppm Total Hardness and I use dilute Batch of Caustic Soda (From 48 % to 13 % ) .I recive Caustic Soda which has around 48 % Concentration of Caustic Soda,around 0.08-0.1 % Na2Co3 ,around 60 ppm NaCl around ppm levels Fe.The Storage tank is of SS.So, no problem of Fe from Storage tank.

Yes,But Priminalary I agree with you that FeSo4,CaCo3 are creating the problem.

But How to prevent them ? because I need to Dilute my Caustic with Process Water.

What are the Solutions to prevent Rust FeSo4,CaCo3 Formations in the Washers ?

Thanks Zoobie,
Thanks in Advance

 

[Zoobie]

If you have sludges you might also want to check for magnesium hydroxide.

If you can't treat the water or use a better water source than you will have to deal with the formation of stuff. We used to dilute with de-ionized water (because we had to) so I have not had the specific problem. I suggest that you ensure that you have adequate retention time in storage so that there is time for precipitates to form and settle (I presume you would rather have them in the bottom of the tank as opposed to in the washers. You can occasionally dump the tank bottoms. If building from scratch you could make it cone bottomed and put in a dump valve.

I would also look at putting filters in wherever I could (caustic offloading, weak caustic to process).

 

[westcoastr]

some caustic producers remove sulphates during the purification process, but it is a settling process that can reduce yields if they try to get the levels too low. these are present at diferent concentrations depending the source for brine. try testing different suppliers or caustic made at diferent sites as they each use different brine sources. or ask fow low sulphate products..why should you have to make changes...make your supplier do some work!