Cane Sugar Refining - Purolite

Cane Sugar Refining with Ion Exchange Resins
Cleaning of Organically Fouled Anion Resins
40
Caustic salt treatments to elute organic and other foulants from strongly basic
anion exchangers.
These treatments consist of a partial caustic regeneration and displacement, followed
by warm (150°F) brine (15% NaCl) treatment. This is repeated as many as six times,
or until the maximum color eluted during the brine step drops to one fifth of the highest
color eluted (which occurs during the first treatment). The procedure is as follows:
1. The anion bed is backwashed as per usual.
2. Regenerate with warm 2% to 5% NaOH as usual, but the amount of caustic is
limited to about one third of the normal dosage (1.0 to 2.0 lbs/ft 3 ), flowrate at
about 0.2 gpm/ft 3 .
3. Slow rinse or displace for 10 minutes at the same 0.2 gpm/ft 3 .
4. Inject warm 10% to 15% NaCl solution (at 150 °F) at 6.5 to 8.0 lbs/ft 3 , also at
0.2 gpm/ft 3 flowrate.
5. Slow rinse or displace for 10 minutes at 0.2 gpm/ft 3 . Observe for the most
concentrated salt (by hydrometer) in the effluent, at which time the color eluted
will be the highest.
6. Without backwashing, repeat the above steps 2 through 5 several times, until
the color eluted during the salting period drops to one fifth of that observed
during the first treatment.
Note: Although a mixture of 10% NaCl and 1% NaOH solution is effective for
removing color, the above cyclic method is preferred. The alternate application of NaOH
and NaCl causes alternate expansion and contraction of the resin, which loosens the
coagulated or foreign matter from the beads by a mechanical or sponge action, as well
as by the chemical elution.
This procedure is best done on a regular or periodic schedule before the anion resin
is appreciably fouled. If organic matter in the influent is high, this procedure may have
to be done every 15 to 30 days. When heavy metals (such as Cu or Fe) are also present
in the anion resin, concentrated 30% HCl may have to be applied (1.5 gallons of 30%
HCl) as well. Hopefully the underdrain is not made from stainless steel, because HCl
attacks it; in this case, the resin will have to be moved to a treatment vessel with a
PVC/polypropylene screened underdrain.