METHOD FOR DETERMINING SCALE INHIBITOR CONCENTRATION IN SALT WATER WITH A CALCIUM/MAGNESIUM IONSELECTIVE ELECTRODE

Abstract

The present invention relates to a method for determining a concentration of a scale inhibitor in a salt water comprising an analysis with a calcium/magnesium ionselective electrode of a dialyzed first sample of the salt water, and a dialyzed second sample of the salt water which was supplemented with a known concentration of the scale inhibitor. The invention further relates to a method for inhibiting incrustation in a plant which contains a salt water comprising the steps of adding a scale inhibitor to the salt water at a desired concentration, determining the actual concentration of the scale inhibitor in the salt water as above, and adding further scale inhibitor to the salt water to adjust the desired concentration. The invention further relates to a device for determining a concentration of a scale inhibitor in a salt water by the method above comprising a calcium/magnesium ionselective electrode, a dialyzing unit, and a dosage unit for supplementing the scale inhibitor to the second sample of the salt water.

Claims

1 . A method for determining a concentration of a scale inhibitor in a salt water comprising an analysis with a calcium/magnesium ionselective electrode of a) a dialyzed first sample of the salt water, and b) a dialyzed second sample of the salt water which was supplemented with a known concentration of the scale inhibitor.

2. The method according to claim 1 further comprising the analysis with a calcium/magnesium ionselective electrode of c) a dialyzed third sample of an untreated salt water which is free of the scale inhibitor.

3. The method according to claim 1 wherein the salt water comprises at least one salt selected from the group of an alkaline metal salt, an alkaline earth metal salt and mixtures thereof.

4. The method according to claim 1 wherein the salt water comprises from 0.001 to 10% by weight the salt, based on the total weight of the salt water.

5. The method according to claim 1 wherein the salt water is chosen from process water, ground water, river water, brackish water, or sea water.

6. The method according to claim 1 wherein the dialyzed samples of the salt water are obtainable by dialysis with a semi-permeable membrane which has a pore size of up to 10000 Da.

7. The method according to claim 1 wherein the conductivity of the dialyzed samples of the salt water is up to 200 μS/cm.sup.2.

8. The method according to claim 1 wherein the dialyzed second sample of the salt water is supplemented with known concentration of 0.1 to 50 ppm of the scale inhibitor.

9. The method according to claim 1 wherein the scale inhibitor has a number average molecular weight M.sub.n in the range from 200 to 250000 g/mol.

10. The method according to claim 1 wherein the scale inhibitor is a polycarboxylic acid or a phosphonate.

11. The method according to claim 1 wherein the scale inhibitor is a polyacrylic acid selected from photopolymers prepared from a monoethylenically unsaturated monocarboxylic acid, copolymers prepared from a monoethylenically unsaturated monocarboxylic acid and at least one comonomer, and mixtures of these photopolymers and copolymers.

12. The method according to claim 11 wherein the scale inhibitor comprises a copolymer prepared from a monoethylenically unsaturated monocarboxylic acid and at least one comonomer, and wherein the at least one comonomer is selected from the group consisting of methacrylic acid, crotonic acid, maleic acid or maleic anhydride, itaconic acid, fumaric acid, citracronic acid and citracronic anhydride, vinylphosphonic acid, vinylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (AMPS), (meth)acrylic acid derivatives, (meth)acrylamide, vinylformamide, alkali metal (3-methacryloyloxy)propane-sulfonate, dimethylaminoethyl acrylate, 2-acryloyloxyethyltrimethylammonium chloride, dimethylamino methacrylate, polyethylene glycol methyl ether(meth)acrylate, or a combination thereof.

13. A method for inhibiting incrustation in a plant which contains a salt water comprising the steps of x) adding a scale inhibitor to the salt water at a desired concentration, y) determining the actual concentration of the scale inhibitor in the salt water as defined claim 1, and z) adding further scale inhibitor to the salt water to adjust the desired concentration.

14. The method according to claim 13 wherein the plant is chosen from a desalination plant for sea water, a cooling tower in an industrial plant, a cooling circuit in an industrial plant, or a boiler water treatment in an industrial plant.

15. A device for determining a concentration of a scale inhibitor in a salt water by the method as defined in claim 1, wherein the device comprises a calcium/magnesium ion selective electrode (6), a dialyzing unit (8), and a dosage unit (12) for supplementing the scale inhibitor to the second sample of the salt water.

16. The method according to claim 1 wherein the conductivity of the dialyzed samples of the salt water is up to 100 μS/cm.sup.2.

17. The method according to claim 1 wherein the conductivity of the dialyzed samples of the salt water is up to 50 μS/cm.sup.2.

18. The method according to claim 1 wherein the dialyzed second sample of the salt water is supplemented with known concentration of 0.5 to 10 ppm of the scale inhibitor.

19. The method according to claim 1 wherein the dialyzed second sample of the salt water is supplemented with known concentration of 1 to 3 ppm of the scale inhibitor.

20. The method according to claim 11 wherein the scale inhibitor comprises a copolymer prepared from a monoethylenically unsaturated monocarboxylic acid and at least one comonomer, and wherein the at least one comonomer is selected from the group of maleic acid, maleic anhydride or 2-acrylamido-2-methyl-propanesulfonic acid.

Description

[0087] FIG. 1 show a typical example of a method and device according to the invention:

[0088] The salt water flows through a plant in a pipeline 1. The flow direction of the salt water is indicated with arrows.

[0089] The scale inhibitor is added to the salt water at the inlet 2 into the pipeline 1, usually with a pump P from a storage tank 3 containing the scale inhibitor.

[0090] At outlet 4 a sample can be taken to prepare the dialyzed third sample of the untreated salt water. The outlet 4 is usually before the inlet 2, where the scale inhibitor is added.

[0091] At outlet 5 a sample can be taken to prepare the dialyzed first and second sample of the salt water. The outlet 5 is usually after the inlet 2, where the scale inhibitor is added.

[0092] The calcium/magnesium ionselective electrode 6 is connected by a valve 7 to a circuit 16 where the samples from outlet 4 and outlet 5 are added at the valves 17 and 18, respectively.

[0093] The dialyzing unit 8 has an outlet 9 and an inlet 10 for the deionized water.

[0094] The conductivity sensor 11 is connected via the circuit 16 to the dialyzing unit 8.

[0095] The dialyzed second sample of the salt water can be supplemented with a known concentration of the scale inhibitor by a dosage unit 12 which comprises a pump P and a reservoir 13 of the scale inhibitor. The dosage unit 12 is connected to a mixer 14 to ensure a good mixing. The mixer may contain an outlet 15 to empty the whole circuit 16.