Regeneration of anion exchange resins

Abstract

The invention relates to a method for converting strong-base anion exchange resins from the monovalent anion form to the hydroxide form. A . .solution.!. .Iadd.source .Iaddend.of polyvalent anions is first passed through the resin to displace the monovalent anions. A solution of alkali metal hydroxide is then passed through the resin to convert it to the hydroxide form, and to produce an effluent solution of hydroxide ions and polyvalent anions. This effluent solution is then neutralized with an acid containing .Iadd.a source of .Iaddend.polyvalent anions, and the neutralized solution is passed through a second batch of resin in the monovalent anion form. In the preferred embodiment, a portion of the effluent is retained without neutralization and is delivered to the second batch of resin after the neutralized effluent to perform a portion of the hydroxide regeneration.

We claim: 
     
       1. A method for converting strong-base anion exchange resin having quaternary ammonium active groups from the monovalent anion form to the hydroxide form comprising: passing a . .solution.!. .Iadd.source .Iaddend.of polyvalent anions through a first batch of said resin, whereby to displace said monovalent anions . .with said polyvalent anions.!.; subsequently passing a solution of alkali metal hydroxide through said resin to convert said resin to the hydroxide form, and to produce an effluent solution of hydroxide anions and . .divalent.!. .Iadd.polyvalent .Iaddend.anions; neutralizing said effluent with an acid containing .Iadd.a source of .Iaddend.polyvalent anions whereby to form a neutralized . .solution.!. .Iadd.source .Iaddend.of polyvalent anions; and passing said neutralized . .solution.!. .Iadd.source of polyvalent anions .Iaddend.through a second batch of said resin in the monovalent anion form. 
     
     
       2. The method as defined in claim 1 wherein said monovalent anion form is the chloride form. 
     
     
       3. The method as defined in claim 1 wherein said polyvalent anions are divalent anions. 
     
     
       4. The method as defined in claim 3 wherein said divalent anions are sulfate anions. 
     
     
       5. The method as defined in claim 1 wherein said alkali metal hydroxide is sodium hydroxide. 
     
     
       6. The method as defined in claim 5 wherein said sodium hydroxide has a concentration in the range of 3.5 to 5.0 normal. 
     
     
       7. A method for converting strong-base anion exchange resin having quaternary ammonium active groups from the monovalent anion form to the hydroxide form comprising: passing a . .solution.!. .Iadd.source .Iaddend.of polyvalent anions through a first batch of said resin, said solution having a concentration not exceeding about 0.5 normal, to displace said monovalent anions . .with polyvalent anions.!.; subsequently passing a solution of alkali metal hydroxide through said resin to convert said resin to the hydroxide form and to produce an effluent comprising an alkali metal hydroxide solution; neutralizing at least a portion of said effluent with an acid containing .Iadd.a source of .Iaddend.polyvalent anions, whereby to form a neutralized effluent . .solution.!. .Iadd.source .Iaddend.of polyvalent anions; and passing said neutralized effluent . .solution.!. .Iadd.source of polyvalent anions .Iaddend.through a second batch of said resin in the monovalent anion form whereby to displace said monovalent anions. 
     
     
       8. The method as defined in claim 7 wherein a first portion of said effluent is neutralized, and further comprising the steps of storing a second portion of said effluent alkali metal hydroxide solution; and passing said effluent alkali metal hydroxide solution through said second batch of resin after said neutralized effluent. 
     
     
       9. The method as defined in claim 8 further comprising the step of passing a fresh alkali metal hydroxide solution through said resin after said effluent alkali metal hydroxide. 
     
     
       10. A method for converting strong-base anion exchange resin having quaternary ammonium groups from the chloride form to the hydroxide form comprising: passing a solution of sodium sulfate having a concentration not exceeding 0.5 normal through a first batch of said resin to displace said chloride ions with sulfate ions; subsequently passing a solution of sodium hydroxide through said resin in an amount sufficient to convert said resin to the hydroxide form, and to produce an effluent comprising a solution of sodium hydroxide; neutralizing said effluent with sulfuric acid, whereby to form a neutralized effluent solution of sodium sulfate; and passing said neutralized effluent solution through a second batch of said resin to convert said second batch to the sulfate form. 
     
     
       11. The method as defined in claim 10 further comprising the steps of storing a second portion of said effluent sodium hydroxide solution; passing said second portion of said effluent sodium hydroxide solution through said second batch of resin after passing said neutralized effluent through said resin; and subsequently passing a fresh sodium hydroxide solution through said second batch of said resin.