The authoritative public forum
  for Metal Finishing since 1989
-----

Why is degassor after Strong Acid Cation and before Strong Base anion?

March 25, 2011

Dear sir
Why degassor is always after Strong Acid Cation and before Strong Base anion?

I also want to know, can we check Degassor performance?
What is the method of check Degassor performance?

Regards
Mahendra singh Chouhan

Mahendra Singh Chouhan
Chemist - Nimbahera Rajasthan India

---

The answer to your question can be found in the CO2/HCO3-/CO3= equilibrium as a function of pH. If you google this, you should be able to get a very informative graph of this equilibrium.

At a neutral pH, most of the carbon dioxide is present as bicarbonate ion, HCO3-. Passing through a cation exchange resin in the hydrogen form reduces the pH, usually to between 2 and 3. This drop in pH converts virtually all of the HCO3- ion to dissolved, non-ionic CO2 which is then free to outgas and leave the water.

So, degassing after the cation exchange resin can remove most of the bicarbonate ion that was present in the feed water. This can significantly reduce the ionic loading on the anion resin and reduce the amount of sodium hydroxide [affil links] needed to make de-ionized water.

There are may ways to tell if your degassifier is working. One is to measure the total inorganic carbon in the water before the cation exchanger and after degassing. Another is by the pH. The pH as previously mentioned will fall to between 2 and 3 when it leaves the cation exchanger. After a properly operating degassifier, the pH will rise significantly, probably to a value between 4.5 and 6. The precise pH values will vary with the initial water pH and bicarbonate concentration, and how well your degassifier works, but, assuming that your feed water does not change, the values should be very close to the same, day after day.

Lyle Kirman
consultant - Cleveland Heights, Ohio
March 28, 2011