increasing exchange capacity of KATION and ANION resin

[devaxrayz]

my process enginering division have a program of increasing cation resin exchange capacity with NaOH solution. Base on experiment in our lab by put the cation resin in NaOH 2% solution bath about 2 hr with stirring, its exchange capacity can be improved.

I found it very strange since NaOH will do cation exchange with the resin and make the resin loaded. But my senior commpanion said it was OK since we can regenerate it again, and the purpose of caustic bathing is to remove the organic foulant which is covering active side of the resin thus decreasing its exchange capacity.

My question:
is my senior companion idea reasonable?

although we have "solution" for improving the cation exchange we haven't got any for the anion. Does anybody have any experience or know something about it?

thx
B-)

 

[EMKWR]

The idea is reasonable, organic foulants can be removed this way. I noticed however in practice another technique in which the ion exchange resin is treated with brine. It takes a longer contact time and of course adequate rinsing.

Good luck

Edwin

Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
Internet:

http://www.kema-water.nl

http://www.kema.com

 

[devaxrayz]

edwinkema:
Thx, so its right. And it means anion resin will lose its exchange capacity more slower than cation resin because it was regenerated by NaOH which also will remove the organic foulant. True???

So why our anion resin is also have capacity decreasing the same as the cation resin?

I'm still curious about method to increasing the anion resin exchange activity.

thx

 

[cub3bead]

To remove organic fouling from divinyl benzene (DVB)based anion resin requires regeneration with both NaOH and NaCl at the same time. The Cl causes the resin to swell maximally and the OH helps elute the organics.

If you have high organics in your source water you may have to do this periodically to restore lost exchange capacity. The other alternative is to use an acrylic resin which does not hold the organics as tightly as DVB resins and eluetes the organics during normal regenration. The acrylics typically have a greater FMA capacity than DVB resins but they cannot tolerate high temperature (95 deg F max). Silica is capacity is limited also. If low SiO2 make sure you consider that aspect also.

Do you have an organic trap in the system?

If your primary purpose is to operate an ion exchange system with the objective of producing the maximum amount of water at the least cost then some of these efforts may not be on that path. The reason for this is that you have put the resins through a triple regenration inorder to remove the Na from the cation and Cl from the anion. The special regeneration techniques and additional regnerates may only consume more time (i.e. less production) and more regenerants (i.e. more costs).