FDA Conditioning of Ion Exchange Resin Before Food Use

Ion exchange resins tend to be insoluble and infusible polymers. Even immediately after processing, however, there are still more soluble impurities which should be removed prior to most applications. The removal can take place by many methods which include a simple water rinse using several bed volumes of water, a chemical regeneration followed by a water rinse, and the most rigorous cleanup which would include an acid/alkali cycling period.

As part of the preparation, Purolite cation resins are steam cleaned to remove all residuals to meet the United States F.D.A. Standards CFR-21 Para.173.25 of the Food Additives Regulations. This procedure is not recommended for anion resins in the free base or hydroxide form. Anions steamed or boiled in the above forms can cause extreme loss of capacity over a very short period.

Anion resins with amine functional groups have a slight odor, especially after storage in highly heated or closed containers. This odor can be washed out and usually only persists through a few cycles.

The standard ionic forms for Purolite resin are sodium form for the strong acid cations, hydrogen form for the weak acid cations, chloride form for the strong base anions and the free base form for the weak base anions. Other ionic forms are supplied by Purolite upon request.

Resins are prepared for conditioning like the ion exchange regeneration procedure:

1. Resins should be transferred to the column and soaked in water for approximately one hour, allowing the resin to come to equilibrium.

2. Backwash the resin to reclassify the bed so that the finer particles are on the top and the coarse particles are on the bottom.

3. Cease backwashing and allow the bed to settle. Then drain the water to 1 inch above the bed.

4. General Conditioning Steps

To a bed of resin in the normal backwashed, settled, and drained condition,

1. Add three bed volumes of 4% NaOH at a rate sufficient to allow 45 minutes contact time;

2. Rinse with five bed volumes of potable water at the same flow rate;

3. Add three bed volumes of 10% H₂SO₄ or 5% HCl at a flow rate sufficient to allow 45 minutes contact time;

4. Rinse with five bed volumes of potable water;

5. Convert the resin to the ionic form desired for use, using the normal regeneration techniques.

The above conditioning treatment is for all acidic and basic ion exchange resins with the following modifications.

Cation exchange resins to be used in the H⁺ cycle are conditioned as outlined. If they are to be used in the Na⁺ cycle, the above order of application of acid and base are reversed. If the equipment involved will not tolerate acid, the following substitutions can be made in the conditioning steps as tabulated: In step three, substitute 25 bed volumes of 0.5% CaCl₂ for the 10% H₂SO₄ or 5% HCl, or exhaust with tap water. In Step one, substitute 10% NaCl for the 4% NaOH.

Anion exchangers to be used in the chloride or hydroxide cycle can be conditioned as outlined above. Again, it is recommended that chloride conversion using 10% NaCl be used in place of the 10% sulfuric acid in Step 3.