Caustic plus HCl---What happens? 2

[gladkenn]

Dear all,

I was trying to figured out from my mind as to what will be the effect of combining HCl and NaOH.
This was after one of our an auditor for our plant said that NaOH and HCl tanks should have separate drainage as when they combine "they could produce explosion".
Can any of you guys clear my mind? Im supposed that when acid and caustic is combined, a neutral pH arises (when same in qty).


gladkenn

 

[moltenmetal]

You forgot about the enormous release of heat...

 

[bimr]

Try these sites for chemistry 101, or buy some pizza's for the local high school chemistry class and they can explain it for you.

http://www.utexas.edu/cee/txmshp/

downloads/HazCom%20BasicChem.ppt

http://www.uth.tmc.edu/safety/chemsafety/hazcom/chemsegregation.doc

 

[bimr]

Correction for the link above:

http://www.utexas.edu/cee/txmshp/downloads/HazCom BasicChem.ppt

 

[NeedAHoliday]

gladkenn,

Heat of Neutralisation of HCl and NaOH is approx -57.1 kJ/gmol.

Lets say you have equal quatities of HCl and NaOH and have 10m3 of 48% NaOH at 40degreesC and stoichiometric equivalent of HCl then you have 14,922 kg NaOH solution which contains 7,162.6kg NaOH = 179,064gmol.

Therefore the energy from reaction is 10,224.6 MJ of heat, using 4.087 kJ/kg specific heat (as a roughy) with a start temp of 40degreeC then final temp roughly would be about 150degreeC.

As such you can see why you use seperate drain lines for the tanks as this energy will release suddenly if they mix quickly as opposed to a nice slow rise in temp.

Cheers.

 

[jmw]

Of course, you might also want to consider if you have adequate safeguards on tanker-unloading.
Is it possible, one cold Monday morning or rainy Friday night, that the tanker driver could couple up to the wrong tank inlet system?
I am doing some work for a company that is concerned about what might happen if the tanker delivers concentrated caustic into the nitric storage by mistake.
They are concerned enough to want to fit a variety of different sensors in the tanker unloading system so that they can "identify" the product and react if it isn't the product they expect i.e. make enough measurements to provide a high level of confidence that they have the right product going to the right tank.

JMW

http://www.ViscoAnalyser.com