Production of ultra pure salt

• US 20040047781A1
• Filed: 09/09/2002
• Published: 03/11/2004
• Est. Priority Date: 09/09/2002
• Status: Active Grant

• Current Assignee: Akzo Nobel N.V. (Nouryon BV), United Brine Services Company, LLC
• Original Assignee: Akzo Nobel N.V. (Nouryon BV)
• Inventors: Becenel, Lawrence F. Jr.
• Granted Patent: US 7,037,481 B2
• Time in Patent Office: Days
• US Class Current: 423/46
• CPC Class Codes: C01D 3/14 Purification
• CPC Class Codes: C25B 15/08 Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Abstract

This invention relates to methods and installations for producing ultra pure sodium chloride salt crystals primarily for use in saturating depleted brine resulting from the electrolytic decomposition of saturated brine in chlor alkali membrane cells for the production of chlorine, caustic soda and hydrogen. More particularly, this invention relates to the production of ultra pure sodium chloride salt crystals by processing primary treated brine by first acidifying the primary treated brine, then stripping the carbonic acid produced by acidification as carbon dioxide, and then returning the brine to a pH of about 6 or higher which is sufficient for processing it in evaporation equipment where the ultra pure salt crystals are produced.

Claims

1. :

The method for producing ultra pure salt, containing below 500 parts per billion (ppb) of calcium and other multivalent metal ions, which comprises;

acidifying primary treated brine from pH 9.5 to 12 to ph 2 to 4, thereby converting the calcium, barium, strontium, and other reactive multivalent metal compounds to soluble chlorides, such acidification also converting excess sodium carbonate and hydroxides to salt, water, and dissolved carbon dioxide,

removing the carbon dioxide by stripping,

neutralizing the stripped material to a pH of at least 6 but not exceeding 8, thereby preventing metals corrosion, at pH less than 6, and carbon dioxide uptake from the surroundings, at pH above 8,

concentrating the neutralized stripped brine, and washing the crystals so produced, to produce ultra pure salt crystals.

2. :

The method of claim 1 wherein the ultra pure salt is fed to a membrane chlor alkali electrolytic cell plant to re-saturate depleted recycle brine, said plant including a secondary brine treating system, thereby substantially decreasing the ion exchange regeneration frequency requirements of said secondary brine treating system, whereby acidification, neutralization, and resin costs are reduced.

3. :

The method of claim 2 wherein the ultra pure salt is fed to a membrane chlor alkali electrolytic cell plant to re-saturate acidified, chlorinated, depleted recycle brine thereby permitting the elimination of the membrane plant secondary brine treating system.

4. :

The method of claim 2 wherein the ultra pure salt is fed to a membrane chlor alkali electrolytic cell plant to re-saturate acidified, chlorinated, depleted recycle brine, and wherein the acidification acid is first employed to acid wash product salt, when the washing systems within the plant do not operate at sufficiently high wash ratios, thereby permitting the elimination of the membrane plant secondary brine treating system.

5. :

The method of claim 1 wherein the ultra pure salt produced contains 5 to 200 ppb calcium and other multivalent metal ions.

6. :

The method of claim 1 wherein the concentrating is by evaporation.

7. :

The method of claim 1 wherein the stripping is by an inert gas.

8. :

The method of claim 1 wherein the stripping is by air stripping.

9. :

The method of claim 1 wherein the stripping is by vacuum stripping with nitrogen.

10. :

The method of claim 1 wherein the stripping is by steam stripping.

11. :

The method of claim 1 wherein aqueous concentrated hydrochloric acid is employed in acidifying the primary treated brine.

12. :

The method of claim 11 wherein the hydrochloric acid is introduced into the primary treated brine through a pipeline reactor.

13. :

The method of claim 1 wherein liquid concentrated sodium hydroxide is employed to neutralize the stripped material.

14. :

The method of claim 1 wherein the stripped material is introduced into a water scrubber to reduce emissions of brine droplets.

15. :

The method of claim 1 wherein concentrator condensate is employed in washing the crystals.

16. :

The method of claim 1 wherein the primary treated brine has a pH of about 10 and is acidified to a pH of about 3.

17. :

An installation for processing primary treated brine to produce ultra pure salt containing below 500 parts per billion (ppb) of calcium and other multivalent metal ions, which comprises;

an acidification reactor for converting metal carbonates in the primary treated brine to carbon dioxide,

a stripper for removal of carbon dioxide generated during acidification,

a neutralization system returning the brine pH to a value above about 6 thereby avoiding metals corrosion,

and a concentrator for evaporating the neutralized stripped brine to produce the ultra pure salt.

18. :

The installation of claim 17 having means for removing entrained acidic brine droplets from the stripper vent gas.

19. :

The installation of claim 18 wherein a water scrubber is employed to remove the entrained brine droplets from the stripper vent gas.

20. :

The installation of claim 17 wherein the acidification reactor is a pipeline acidification reactor.

21. :

The installation of claim 17 wherein the concentrator is a mechanical vapor recompression evaporator.

22. :

The installation of claim 17 having means for removing carbon dioxide.

23. :

The installation of claim 22 wherein a stripper is employed to remove the carbon dioxide.

24. :

The installation of claim 17 wherein the equipment employed in the plant installation is free of fouling by precipitated multivalent metal compounds.

25. :

The installation of claim 17 wherein the ultra pure salt is fed to a membrane chlor alkali electrolytic cell plant to re-saturate depleted recycle brine.

26. :

The installation of claim 25 wherein the ultra pure salt is fed to a nearby membrane chlor alkali electrolytic cell plant thereby simplifying transport of the salt thereby avoiding contamination of the ultra pure salt.

27. :

The installation of claim 25 wherein the membrane chlor alkali electrolytic cell plant has a secondary brine treatment installation including a re-saturated brine filtration system and an ion exchange purification system.

28. :

The installation of claim 25 wherein the ultra pure salt fed to the membrane chlor alkali electrolytic cell plant permits the elimination of said plant'"'"'s secondary brine treating system.

29. :

The installation of claim 25 wherein the ultra pure salt fed to the membrane chlor alkali electrolytic cell plant permits the elimination of said plant'"'"'s neutralization and acid adjustment systems.