Effects of Regeneration Procedures on the Performance of Reverse-Cycle Ion Exchange in the Purification of Sugarcane Juices

Abstract

Investigations of the chemical requirements for regeneration of the first-anion and the cation-exchanger beds of the reverse-cycle system were undertaken in these studies, but no attempt was made to establish the requirements for the second-anion exchanger bed. A large dosage of NaOH to provide superior exchanger capacity was used for the highly basic anion resin in first position, and by recycling usable portions of the waste regenerant in a subsequent test, an average of 114 percent of the stoichiometric quantity of NaOH was consumed per test. No change in performance of the exchanger system was detected following adoption of such a regenerant recycling procedure. Efforts to obtain satisfactory regeneration of the weakly acid cation exchanger with H₂SO₄ were discouraging. The quantity of material which could be processed per test was less, the percentage removals of ash and protein were less, and the ash-percent-dry solids remaining in the product juices was 79-percent greater than when HCl was employed as regenerant. Juice purities following ion-exchange processing were found to have increased by approximately one-half as much with H₂SO₄  regeneration as with HC1. Examination of the product juices revealed that their potassiumion contents were much greater during H₂SO₄  regeneration tests than while HC1 was used. Apparently the large quantities of calcium and magnesium ions found in cane juices were not efficiently regenerated from the exchanger resin by H₂SO₄ , and that part which remained in the resin during subsequent juice deionization increased the leakage of potassium ions into the product juices. Although HC1 was much more expensive than H₂SO₄, the recycling of excess regenerant to reduce the quantity consumed to approximately 105 percent of the necessary stoichiometric requirement would make the use of this more costly acid economically attractive. Information was obtained in these tests which showed the importance of efficient backwashing of the highly basic first anion bed in order to eliminate significant quantities of Mg(OH)₂, and organic materials precipitated on the resin particles during passage of juices through the bed. The effective backwashing obtained in the semipilot-plant column was not always attained in the smaller laboratory column and some insoluble materials remained following backwashing and regeneration.