Cleaning of Organically Fouled Anion Resins in Cane Sugar Refining

This process involves a partial caustic regeneration and displacement, followed by a 65.6 °C (150 °F), 15% NaCl treatment. The process is repeated until the maximum color eluted during the brine step drops to 1/5 of the highest color eluted during the first treatment. It can take as many as six times. Details of the procedure described above are as follows:

1. The anion bed is backwashed

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 lb/ft³), and the flowrate should be about 0.2 gpm/ft³

3. Slow rinse or displace for 10 minutes at the same 0.2 gpm/ft³

4. Inject warm 10% to 15% NaCl solution (at 150 °F) at 6.5 to 8.0 lb/ft³, also at 0.2 gpm/ft³ flowrate

5. Slow rinse or displace for 10 minutes at 0.2 gpm/ft³; 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 1/5 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.

It is important to realize the procedure is best completed on a regular or periodic schedule before the anion resin is appreciably fouled. If organic matter in the affluent is high, the above steps should be taken every 15 to 30 days.

Also, if the underdrain is made of stainless steel, the HCl will attack it, and the resin will have to be moved to an alternate treatment vessel with a PVC/polypropylene screened underdrain.