Method for inhibiting scale formation and/or dispersing iron in reverse osmosis systems

• US 5,256,303 A
• Filed: 07/20/1992
• Issued: 10/26/1993
• Est. Priority Date: 07/20/1992
• Status: Expired due to Term

• Current Assignee: Ecolab USA Incorporated (Ecolab, Inc.)
• Original Assignee: Nalco Chemical Company (Ecolab, Inc.)
• Inventors: Pierce, Claudia C., Zeiher, E. H. Kelle, Fivizzani, Kenneth P., Soderquist, Cynthia A.
• Primary Examiner(s): Sever, Frank
• Application Number:
  US07/916,905
• Time in Patent Office: 463 Days
• Field of Search: 210/701, 210/696, 210/697-700, 210/702, 210/723-725, 210/729, 210/734, 210/735
• US Class Current: 210/700
• CPC Class Codes: B01D 2311/04 Specific process operations in the feed stream; Feed pretreatment
• CPC Class Codes: B01D 2311/103 Heating
• CPC Class Codes: B01D 2311/12 Addition of chemical agents
• CPC Class Codes: B01D 2311/18 pH control
• CPC Class Codes: B01D 2321/162 Use of acids
• CPC Class Codes: B01D 2321/168 Use of other chemical agents
• CPC Class Codes: B01D 61/025 Reverse osmosis; Hyperfiltration
• CPC Class Codes: B01D 61/04 Feed pretreatment
• CPC Class Codes: B01D 65/08 Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: C02F 5/12 containing nitrogen C02F5/14 takes precedence
• CPC Class Codes: C02F 5/14 containing phosphorus
• CPC Class Codes: Y02A 20/131 Reverse-osmosis

Abstract

A method for inhibiting calcium sulfate scale formation and deposition and/or dispersing iron from a feedstream passing through a reverse osmosis system which comprises the steps of: controlling the pH of the feedstream within the range between about 6.0 to about 7.0; controlling the temperature of the feedstream within the range between about 50° to about 80° F.; and adding a scale inhibitor and/or iron disperant to the feedstream in an amount between about 0.002 ppm per ppm hardness (as CaCO₃) of the feedstream to about 0.005 ppm per ppm hardness (as CaCO₃) of the feedstream, the scale inhibitor comprising a water-soluble organic phosphonate and an N-substituted acrylamide polymer containing an amide structure as follows: ##STR1## where R₂ is hydrogen or methyl, R₁ is a hydrogen or an alkyl, and R is alkylene or phenylene and X is sulfonate, (poly) hydroxyl, (poly) carboxyl or carbonyl, and combinations thereof, with the weight ratio of polymer to phosphonate being within the range of about 0.2:1 to about 2:1; provided that when X is sulfonated then R--X-- is selected from the group consisting of sulfomethyl and 2-sulfoethyl.

Claims

1. A method for inhibiting calcium sulfate scale formation and deposition from a feedstream passing through a reverse osmosis system which comprises the steps of:

a. controlling the pH of said feedstream within the range between about 6.0 to about 7.0;

b. controlling the temperature of said feedstream within the range between about 50°

to about 80°

F.; and

c. adding a scale inhibitor to said feedstream in an amount between about 0.002 ppm per ppm hardness (as CaCo₃) of said feedstream to about 0.005 ppm per ppm hardness (as CaCO₃) of said feedstream, said scale inhibitor comprising a water-soluble organic phosphonate which comprises a 2-phosphonobutane-1,2,4-tricarboxylic acid and a 1-hydroxyethane-1,1-diphosphonic acid, and an N-substituted acrylamide polymer containing an amide structure as follows;

##STR4## where R₂ is hydrogen or methyl, R₁ is a hydrogen or an alkyl, and R is alkylene or phenylene and X is sulfonate, (poly) hydroxyl, (poly) carboxyl or carbonyl, and combinations thereof, with the weight ratio of polymer to phosphonate being within the range of about 0.2;

1 to about 2;

1.

2. The method according to claim 1 wherein said N-substituted acrylamide polymer is an acrylic acid/acrylamide/acrylamidomethylsulphonic acid polymer having a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid within the range between about 13-95 to about 0-73 to about 5-41, respectively;

and wherein the polymer has a weight average molecular weight within the range of about 7,000 to about 82,000.

3. The method according to claim 2 wherein said polymer has a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid within the range of about 40-90 to about 0-50 to about 10-40, respectively;

and wherein said polymer has a weight average molecular weight within the range of about 10,000 to about 40,000.

4. The method according to claim 3 wherein said polymer has a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid of 50:

30;

20.

5. The method according to claim 1 wherein the phosphonate dosage includes a ratio of 2-phosphonobutane-1,2,4-tricarboxylic acid to 1-hydroxyethane-1,1-diphosphonic acid within the range of about 0.5:

1 to about 4;

1.

6. The method according to claim 1 wherein the pH of the feedstream is controlled by the use of sulfuric acid in an amount such that only CaSO₄ is precipitated, not CaCO₃.

7. The method according to claim 1 wherein said scale inhibitor is added to said feedstream in a ratio between about 0.3:

1 to about 20;

1 ppm polymer actives per ppm hardness (as CaCO₃).

8. The method according to claim 1 wherein the pH of the feedstream is not greater than 6.5.

9. A method for dispersing iron disposed in a feedstream passing through a reverse osmosis system which comprises the steps of:

a. controlling the pH of said feedstream within the range between about 6.0 to about 8.5;

b. controlling the temperature of said feedstream within the range between about 30°

to about 80°

F.; and

c. adding an iron dispersant to said feedstream, said iron dispersant comprising a water-soluble organic phosphonate which comprises a 2-phosphonobutane-1,2,4-tricarboxylic acid and a 1-hydroxyethane-1,1-diphosphonic acid, and an N-substituted acrylamide polymer containing an amide structure as follows;

##STR5## where R₂ is hydrogen or methyl, R₁ is a hydrogen or an alkyl, and R is alkylene or phenylene and X is sulfonate, (poly) hydroxyl, (poly) carboxyl or carbonyl, and combinations thereof, with the weight ratio of polymer to phosphonate being within the range of about 0.2;

1 to about 2;

1.

10. The method according to claim 9 wherein said N-substituted acrylamide polymer is an acrylic acid/acrylamide/acrylamidomethylsulphonic acid polymer having a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid within the range between about 13-95 to about 0-73 to about 5-41, respectively;

and wherein the polymer has a weight average molecular weight within the range of about 7,000 to about 82,000.

11. The method according to claim 10 wherein said polymer has a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid within the range of about 40-90 to about 0-50 to about 10-40, respectively;

and wherein said polymer has a weight average molecular weight within the range of about 10,000 to about 40,000.

12. The method according to claim 11 wherein said polymer has a mole ratio of acrylic acid to acrylamide to acrylamidomethylsulphonic acid of 50:

30;

20.

13. The method according to claim 9 wherein the phosphonate dosage includes a ratio of 2-phosphonobutane-1,2,4-tricarboxylic acid to 1-hydroxyethane-1,1-diphosphonic acid within the range of about 0.5:

1 to about 4;

1.

14. The method according to claim 9 wherein said iron dispersant is added to the feedstream in a ratio of dispersant to iron of about 0.6:

1 or greater.

15. A method for inhibiting calcium sulfate scale formation and for dispersing iron from a feedstream passing through a reverse osmosis system which comprises the steps of:

a. controlling the pH of said feedstream within the range between about 6.0 to about 7.0;

b. controlling the temperature of said feedstream within the range between about 50°

to about 80°

F.; and

c. adding a product polymer capable of both inhibiting scale formation/deposition and dispersing iron to said feedstream in an amount between about 0.002 ppm per ppm hardness (as CaCO₃) of said feedstream to about 0.005 ppm per ppm hardness (as CaCO₃) of said feedstream, said product polymer comprising a water-soluble organic phosphonate which comprises a 2-phosphonobutane-1,2,4-tricarboxylic acid and a 1-hydroxyethane-1,1-diphosphonic acid, and an N-substituted acrylamide polymer containing an amide structure as follows;

##STR6## where R₂ is hydrogen or methyl, R₁ is a hydrogen or an alkyl, and R is alkylene or phenylene and X is sulfonate, (poly) hydroxyl, (poly) carboxyl or carbonyl, and combinations thereof, with the weight ratio of polymer to phosphonate being within the range of about 0.2;

1 to about 2;

1.

16. The method according to claim 17 wherein said product polymer is added to the feedstream in a ratio of product polymer to iron of about 0.6:

1 or greater.