Molecular Sieves aqueous uses; To sieve, or not to sieve?

[aspearin1]

We have a system where we are developing a new product. Unfortunately this new product leaves long-chained polymers at the 8-20 ppm levels in our process solution that other processes also use. We've been able to remove this very well using natural zeolite. The problem with this is that it leaches unwanted metals into the solution, which could be worse than the polymers. We have a finishing step using cation exchange beads to remove these metals to a rather low level, but it still leaves high levels of potassium, aluminum, sodium and dissolved silica. My preference is to move to a substance that's more calcium rich, which has been easier to get rid of. The 5A molecular sieve seems to fit this description, only I haven't come across much material that suggests its use in aqueous solutions. We've shown the 3A molecular sieve (potassium rich) to work, though. So I ask of anyone who has familiarity with any of this to speak out! Can you propose any alternatives to these zeolite type media? (Activated carbon didn't work. Polymer is too large) Are there notable aqueous applications to the molecular sieves, especially at low pH? Also, I'm thinking of using a quat enhanced filter to remove dissolved silica. Any thoughts on this? All responses, and out-of-the-box ideas are welcome!!!

 

[rbcoulter]

I don't know much about molecular sieves but you mentioned that you used a cation exchange bed to remove the metals. It appears as though you are using a cation bed that is recharged with a salt solution which only removes hardness metals and leaves sodium, silica, etc. Why not do hydrogen cation exchange and anion exchange (recharge with sulfuric acid and caustic soda)? This should remove all the metals.

 

[aspearin1]

rbcoulter,
Very good observation. And yes, it's been tested. The problem is, though, that we are running at under acidic conditions (pH~3), at which the cationic exchange beads (Amberlyst 15) have little affinity for the polymer (containing a quaternary amine) we're trying to remove. We have proven that it does work at a higher pH, but unfortunately, not at the acidity we are stuck with. The zeolite works like a champ, but alas, we're left with the sodium and silica.

 

[DeltaCascade]

Methinks that rbcoulter is saying, after the zeolite removal of the unwanted polymer, use hydrogen-cation (acid regenerated, H+), not sodium-cation (sodium chloride generated, Na+).
Hopefully your silica is dissolved, and not colloidal, as the latter is harder to remove. Still, a mixed bed cation-anion exchanger should do well to remove silica and the cationic metals. If your product cannot tolerate alkaline pH, a cation follwed by an anion bed may cause problems with low pH in regions of the anion resin bed? ... if so, perhaps a mixed cation-anion single bed would work.
Good luck.

 

[aspearin1]

The resin beads in question (Amberlyst 15) are strong (sulfonic acid) cation exchange beads. The main replacement cation is H+. They have shown not to work due to the acidic/reactive environment. The use of anionic exchange beads is cost prohibitive (believe it or not). There is a dilute amount of formate in the system. Though dilute, it is still a 3000 gallon system. The anion exchange beads prefers formate to silica 4:1. This would mean removal of all the formate prior to being able to remove the silica. The amount of exchange beads is too great. Any other suggestions?

 

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