Caustic(Sodium Hydroxide) corrosion problem

[snr.sr2006]

I am using castic as heating / Cooling media for the reactors in my lab. MOC of my reactor and pipeline is CS. Can anyone tell how to prevent / minimise this?

 

[chemisttree]

You might try adding a bit of sodium carbonate with the hydroxide. The carbonate will produce a passivating iron carbonate coating on the interior of the CS (carbon steel?) tubes.

Why such an exotic teat transfer fluid?

 

[snr.sr2006]

Thank you sir,
Let me tell you in somewhat detail, we are using caustic in the reactors for the PVC process. Since the reaction is exothermic and controlled at around 105°C to 115°C, we can not use water, so we use this as heating / cooling media. Now I am observing the lines are getting punctured mostly near bends or in between. so in the first observation I doubt on Hot Caustic solution which is corrosive as all know. We are using 12 to 15 % concentration caustic.

As suggested by you we have to use Sodium carbonate with caustic . Can we use Calcium carbonate? and If yes then How much we have to add in my system where I am using 12% caustic solution? Thanks in advance.

 

[chemisttree]

Calcium carbonate won't do any good. It's not soluble enough in the NaOH solution. It sounds like you are getting some galvanic corrosion near the bends due to stress or the welds. You might try to increase the carbonate levels and perhaps think of entirely replacing the NaOH with the carbonate.

Have you ever sectioned a bend to see if scaling is a problem as well?

 

[snr.sr2006]

I will open the line but it will take some time but once I do that definitely will give feedback to you. Now can Calcium carbonate / sodium carbonate will give temperatures upto 110°C. How can I test that in my lab? will there be any problem of dipostion in my reactor which will then reduce the heat transfer? Can it be very simple as by keeping in the beaker and heating it and checking how much temp. increases? In the same test I can try the corrosion test also. What do you suggest?