METHOD FOR THE DETERMINATION OF A CONCENTRATION OF A POLYACRYLIC ACID IN AN AQUEOUS MEDIUM

Abstract

The present invention relates to a method for the determination of a concentration (C) of a polyacrylic acid (PAA) in an aqueous medium (AM) wherein the determination is performed photometrically in the presence of a dye (I). The present invention furthermore, relates to a method for the determination of a concentration (C) of a polyacrylic acid (PAA) in an aqueous medium (AM) wherein at least two different transmittance values are measured using at least two different wavelengths and wherein the at least two different transmittance values are analyzed to determine the concentration (C) of the polyacrylic acid (PAA). The present invention also relates to the use of a dye (I) for the determination of the concentration (C) of a polyacrylic acid (PAA).

Claims

1-14. (canceled)

15. A method for the determination of a concentration (C) of a polyacrylic acid (PAA) in an aqueous medium (AM), which comprises the polyacrylic acid (PAA), wherein the determination is performed photometrically in the presence of a dye of the general formula (I) ##STR00006## wherein R.sup.1 is selected from the group consisting of H, C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.10-aryl and NR.sup.5R.sup.6, wherein R.sup.5 and R.sup.6 are independently of one another selected from the group consisting of H, C.sub.1-C.sub.10-alkyl and C.sub.6-C.sub.10-aryl, R.sup.2 is selected from the group consisting of H, C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.10-aryl and NR.sup.7R.sup.8, wherein R.sup.7 and R.sup.8 are independently of one another selected from the group consisting of H, C.sub.1-C.sub.10-alkyl and C.sub.6-C.sub.10-aryl; R.sup.3 is selected from the group consisting of H, C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.10-aryl and NR9R.sup.10, wherein R.sup.9 and R.sup.10 are independently of one another selected from the group consisting of H, C.sub.1-C.sub.10-alkyl and C.sub.6-C.sub.10-aryl; R.sup.4 is selected from the group consisting of H, C.sub.1-C.sub.10-alkyl, C.sub.6-C.sub.10-aryl and NR.sup.11R.sup.12, wherein R.sup.11 and R.sup.12 are independently of one another selected from the group consisting of H, C.sub.1-C.sub.10-alkyl and C.sub.6-C.sub.10-aryl; X.sup.+ is selected from the group consisting of NH.sup.+, O.sup.+ and S.sup.+; Y is N or CH; Z.sup. is selected from the group consisting of OH.sup., F.sup., Cl.sup., Br.sup., I.sup., SO.sub.4.sup.2, PO.sub.4.sup.3, HCO.sub.3.sup. and CO.sub.3.sup.2. comprising the steps: a) providing the aqueous medium (AM), which comprises the polyacrylic acid (PAA), comprising the steps: a1) providing an electrolyte-containing aqueous medium (EAM), which comprises the polyacrylic acid (PAA) and at least one electrolyte, a2) passing the electrolyte-containing aqueous medium (EAM) through a dialysis unit to give a dialyzed aqueous medium, which comprises the polyacrylic acid (PAA) and a3) adding deionized water to the dialyzed aqueous medium obtained in step a2) to obtain the aqueous medium (AM), b) addition of the dye (I) to the aqueous medium (AM) to obtain a dye-containing aqueous medium (DAM), which comprises the polyacrylic acid (PAA) and the dye (I), c) providing the dye-containing aqueous medium (DAM) obtained in step b) to a photometer, d) using at least two different wavelengths to measure at least two different transmittance values of the dye-containing aqueous medium (DAM) using the photometer and e) analysing the at least two different transmittance values obtained in step d) to determine the concentration (C) of the polyacrylic acid (PAA).

16. The method according to claim 15, wherein step b) and step c) are carried out simultaneously.

17. The method according to claim 15, wherein in step a3) the conductivity of the aqueous medium (AM) is <1000 S/cm.sup.2.

18. The method according to claim 15, wherein the electrolyte-containing aqueous medium (EAM) comprises at least one electrolyte selected from the group consisting of an alkaline metal salt, an alkaline earth metal salt and mixtures thereof.

19. The method according to claim 15, wherein the electrolyte-containing aqueous medium (EAM) comprises from 0.001 to 10% by weight of the at least one electrolyte, based on the total amount of the electrolyte-containing aqueous medium (EAM).

20. The method according to claim 15, wherein the aqueous medium (AM) comprises a residue of the at least one electrolyte.

21. The method according to claim 20, wherein the aqueous medium (AM) comprises from 0 to 70 ppmw of the at least one electrolyte, based on the total weight of the aqueous medium (AM) and wherein the ppmw of the at least one electrolyte comprised in the aqueous medium (AM) are smaller than the % by weight of the at least one electrolyte comprised in the electrolyte-containing aqueous medium (EAM).

22. The method according to claim 15, wherein a first wavelength and a second wavelength is used in step d) and wherein the first wavelength is in the range from 180 to 700 nm and the second wavelength is in the range from 200 to 800 nm and wherein the first wavelength and the second wavelength are different from each other.

23. The method according to claim 15, wherein a first wavelength and a second wavelength is used in step d) and wherein the first wavelength is in the range from 553 to 585 nm and the second wavelength is in the range from 620 to 652 nm.

24. The method according to claim 15, wherein the dye (I) is toluidine blue O.

25. The method according to claim 15, wherein the aqueous medium (AM) comprises from 0.01 to 100 ppmw of the polyacrylic acid (PAA), based on the total weight of the aqueous medium (AM).

26. The method according to claim 15, wherein the polyacrylic acid (PAA) has a number average molecular weight M.sub.n in the range from 1000 to 250 000 g/mol.

27. A method for the determination of a concentration (C) of a polyacrylic acid (PAA), said method comprising: photometrically determining said concentration of (C) of (PAA) by using a dye (I).

Description

EXAMPLES

Example 1: Precision of the Inventive Process

[0278] To determine the precision of the inventive process over a longer period of time, the concentration (C) of a polyacrylic acid (PAA) is measured for 50 hours. Sea water comprising as the at least one electrolyte 3.5% by weight of sea salt (Italian sea salt, Orto Mio) is used as electrolyte-containing aqueous medium (EAM). The sea water additionally comprises 4 ppmw of polyacrylic acid (PAA) (Sokalan PM 15 I).

[0279] The sea water is passed through a dialysis unit (step a2)) to obtain the dialyzed aqueous medium and then transferred to a vessel, wherein deionized water is added (step a3)) to obtain the aqueous medium (AM). The aqueous medium (AM) is recycled from the vessel (step a3)) to the dialysis unit as electrolyte-containing aqueous medium (EAM) (step a2)) until the conductivity of the aqueous medium (AM) measured in the vessel is 30 S/cm.sup.2.

[0280] Then 1.21 ppmw of toluidine blue O (dye (I)) are added to the aqueous medium (AM) and the thus obtained dye-containing aqueous medium (DAM) is provided to a photometer. The photometer is a diode array spectrometer comprising two diodes. The first diode has a wavelength of 569 nm and the second diode has a wavelength of 536 nm. At these two different wavelengths two transmittance values of the aqueous medium (AM) are measured (step d)). A first transmittance value and a second transmittance value are obtained.

[0281] The concentration (C) of the polyacrylic acid (PAA) is determined by the determination of the ratio of the first transmittance value to the second transmittance value using a calibration curve.

[0282] The results obtained can be found in FIG. 1. The x-axis gives the time (t) of the measurement in hours (h), the y-axis gives the concentration (c) of the polyacrylic acid (PAA) in ppmw. It can clearly be seen that the concentration (c) of 4 ppmw of a polyacrylic acid (PAA) can be determined very accurate with a standard deviation of 2 ppmw.

[0283] This clearly shows that the inventive method is sufficient accurate to determine the concentration (C) of a polyacrylic acid (PAA) in an aqueous medium (AM).

[0284] The first six values in FIG. 1 are close to 0. This is because at the beginning of the measurement a sea salt solution is used without polyacrylic acid (PAA) to stabilize the measuring device.

Example 2: Concentration (c) of a Polyacrylic Acid (PAA) in a Desalination Plant

[0285] An electrolyte-containing aqueous medium (EAM) from a process stream of a desalination plant is used. Natural sea water comprising 3.5% by weight of sea salt, which was concentrated to a concentration of 4.7% by weight (47000 ppmw) of sea salt, was used as electrolyte-containing aqueous medium (EAM). At the beginning, the electrolyte-containing aqueous medium (EAM) moreover comprises 10 ppmw of the polyacrylic acid (PAA) (Sokalan PM 15 I).

[0286] The drop of the concentration (c) of the polyacrylic acid (PAA) in the electrolyte-containing aqueous medium (EAM) is monitored over 12 hours every 144 minutes using the method as described in example 1.

[0287] FIG. 2 shows the results. The x-axis gives the time (t) in minutes (min) for which the measurements were carried out, the y-axis gives the concentration (c) of the polyacrylic acid (PAA) in ppmw.

[0288] FIG. 2 shows that the concentration (c) of the polyacrylic acid (PAA) drops within 12 hours from 10 ppmw to approximately 3 ppmw.

Example 3: Concentration (c) of a Polyacrylic Acid (PAA) in a Water Circuit

[0289] An electrolyte-containing aqueous medium (EAM) from a process stream of a cooling water circuit is used. The cooling water circuit comprises two different strands (K1 and K2) of cooling water, to which the cooling water is added from the same cooling water pipe. 50 ppmw of the polyacrylic acid (PAA) (Antiprex AD 2020 S) are added to the cooling water pipe. Therefore, the two different strands should comprise the same concentration (c) of the polyacrylic acid (PAA).

[0290] Samples of the electrolyte-containing aqueous medium (EAM) of each of the two different strands of cooling water are taken every 30 minutes for 24 hours and are dialyzed as described above for example 1. Then 666 ppmw of toluidine blue O (dye (I)) are added to each of the samples. The measurement of the two transmittance values of each of the two samples and the analysing of the transmittance values is performed as described above for example 1.

[0291] FIG. 3 shows the results. The x-axis gives the time (t) in hours (h) for which the measurements were carried out, the y-axis gives the concentration (c) of the polyacrylic acid (PAA) in ppmw. The diamonds give the results for strand K1, the squares give the results for strand K2.

[0292] FIG. 3 shows that the concentration of the polyacrylic acid (PAA) differs for the two different strands of cooling water. The difference in the concentration is a result from the uneven distribution of the cooling water from the cooling water pipe.