Use of phosphotartaric acid and the salts thereof for the treatment of water in water-conducting systems

Abstract

The present invention relates to the use of phospho-tartaric acid and/or the salts thereof for the treatment of water in water-conducting systems.

Claims

1. A method of treating water, comprising: adding at least one of phosphotartaric acid and salts thereof in water in a water-conducting system.

2. The method as claimed in claim 1, wherein the phosphotartaric acid is added to the water-conducting system in an amount of 0.1 to 10000 mg based on one liter of the water in the water-conducting system.

3. The method as claimed in claim 1, wherein the water in the water-conducting system has a conductivity in a range of 1 to 200000 S/cm.

4. The method as claimed in claim 1, wherein the at least one of the phosphotartaric acid and the salts thereof is added in the water-conducting system having a calcium hardness in a range of 0 to 30 mol based on one cubic meter of liquid of the water-conducting system.

5. The method as claimed in claim 1, wherein the at least one of the phosphotartaric acid and the salts thereof is in a form of one or more alkali metal salts and/or one or more ammonium salts.

6. The method as claimed in claim 1, wherein the at least one of the phosphotartaric acid and the salts thereof is a corrosion inhibitor.

7. The method as claimed in claim 1, wherein the at least one of the phosphotartaric acid and the salts thereof is a scale inhibitor.

8. The method as claimed in claim 1, wherein the at least one of the phosphotartaric acid and the salts thereof is constituent a) and added together with at least one of constituent b) and constituent c), wherein the constituent b) is at least one selected from the group consisting of aliphatic di-, tri- and oligocarboxylic acids comprising up to 6 carboxylic acid groups, aliphatic monocarboxylic acids having at least one hydroxyl group, amino acids, and salts thereof, and the constituent c) is at least one selected from the group consisting of inorganic polyphosphoric acid, meta-polyphosphoric acid and salts thereof, and water-soluble organic phosphonic acids and salts thereof.

9. The method as claimed in claim 8, wherein the constituent a) is added with the constituent b), and a weight ratio of the constituent a) to the constituent b), calculated in each case as pure substance, is in a range of 1:20 to 20:1.

10. The method as claimed in claim 8, wherein the constituent b) is at least one selected from the group consisting of tartaric acid, malic acid, lactic acid, glycolic acid, gluconic acid, citric acid, isocitric acid, mandelic acid, mevalonic acid, tartronic acid, hydroxyalkanoic acid, gallic acid, salicylic acid, hydroxybenzoic acid, aspartic acid, alkanedioic acids, unsaturated alkanedioic acids, and salts thereof.

11. The method as claimed in claim 10, wherein the alkanedioic acids have a formula COOH(CH.sub.2).sub.nCOOH, wherein n is in a range from 1 to 14.

12. The method as claimed in claim 8, wherein the constituent a) is added with the constituent c), and the constituent c) is at least one selected from the group consisting of polyphosphoric acid, metapolyphosphoric acid and salts thereof, and organic phosphonic acids.

13. The method as claimed in claim 12, wherein the polyphosphoric acid has a formula H.sub.n+2P.sub.nO.sub.3n+1, wherein n is in a range from 1 to 100.

14. The method as claimed in claim 12, wherein the meta-polyphosphoric acid has a formula H.sub.nP.sub.nO.sub.3n, wherein n is in a range from 3 to 100.

15. The method as claimed in claim 8, wherein the at least one of the phosphotartaric acid and the salts thereof is in a form of an aqueous solution or dispersion.

16. The method as claimed in claim 8, wherein the constituent b) is at least one selected from the group consisting of fumaric acid, maleic acid, butanetetracarboxylic acid, cyclohexanehexanecarboxylic acid, and salts thereof.

17. The method as claimed in claim 1, wherein the phosphotartaric acid is added with at least one biodispersant selected from the group consisting of polyalkylene glycols, terpenes, non-ionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

18. The method as claimed in claim 1, wherein the phosphotartaric acid is added with at least one biocide selected from the group consisting of chlorine, hypochlorites, hypobromites, bromochloride, chlorine dioxide, ozone, hydrogen peroxide, perborates, permanganates, organic peracids, di- and trichloroisocyanurates, glutardialdehyde, quaternary ammonium or phosphonium compounds, polyquaternary ammonium compounds, isothiazole compounds, copper or silver compounds, bronopol, benzoates, thiocarbamates, azines, 2,2-dibromo-2-cyanoacetamides, halohydantoins, and haloamines.

19. The method as claimed in claim 1, wherein the phosphotartaric acid is added with at least one selected from the group consisting of (A) at least one biodispersant selected from the group consisting of polyalkylene glycols, terpenes, non-ionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants, (B) at least one biocide selected from the group consisting of chlorine, hypochlorites, hypobromites, bromochloride, chlorine dioxide, ozone, hydrogen peroxide, perborates, permanganates, organic peracids, di- and trichloroisocyanurates, glutardialdehyde, quaternary ammonium or phosphonium compounds, polyquaternary ammonium compounds, isothiazole compounds, copper or silver compounds, bronopol, benzoates, thiocarbamates, azines, 2,2-dibromo-2-cyanoacetamides, halohydantoins, and haloamines, and (C) at least one selected from the group consisting of a corrosion inhibitor, a scale inhibitor, and a dispersant.

20. A composition comprising phosphotartaric acid and/or salts thereof and one or more hydroxycarboxylic acid(s) and/or salts thereof.

Description

DESCRIPTION OF FIGURES AND EXAMPLES

(1) The invention is illustrated in detail below by FIGS. 1 and 2 and Examples 1 to 5.

(2) FIG. 1 shows, by way of example, the course of the biological degradation of phosphotartaric acid (PTA) over a time period of 28 days according to test method OECD 302b,

(3) FIG. 2 shows, by way of example, a schematic experimental setup for determining the effect of a substance as a calcium carbonate scale inhibitor.

(4) FIG. 1 shows the course of the biological degradation of phosphotartaric acid (PTA) over a time period of 28 days according to the test method OECD 302b. The incubation time in days is shown on the x-axis and the degree of degradation in % on the y-axis. The OECD guideline 302b describes the modified Zahl-Wellens test. In this case, the sample is exposed to a microbiologically active inoculum over a time period of 28 days in the presence of mineral nutrients, air and heat. The degree of degradation is determined by measurement of the dissolved organic carbon content DOC and comparison with a sample-free control solution treated in the same manner. The activity of the inoculum is checked by means of a reference measurement using a standard (diethylene glycol). Erroneous measurement results due to so-called spontaneous elimination, which is caused by the adsorption (and the associated withdrawal of the sample from the system), is ruled out in this case by observing an equilibration period (ca. 210 min) before starting the DOC measurements. The biological degradability was investigated at two different concentrations, in each case as a duplicate. In FIG. 1, the mean of the 4 parallel installed degradation tests (2200 mg/L, 2350 mg/L) were plotted against the degradation time. The degree of degradation was calculated by means of the DOC value determined from Formula 1. The degree of degradation of the diethylene glycol reference exceeded 90% after 4 days which indicates sufficient activity of the inoculum. The degree of degradation was determined by measurement of the fraction of dissolved organic carbon (DOC in mg/L) and calculated according to Formula 1 below.

(5) $\begin{array}{cc}\mathrm{Degree}\mathrm{of}\mathrm{degradation}\mathrm{in}\mathrm{percent}=[1-\frac{{\mathrm{DOC}}_{\mathrm{Sample}}^t-{\mathrm{DOC}}_{\mathrm{Reference}}^t}{{\mathrm{DOC}}_{\mathrm{Sample}}^0-{\mathrm{DOC}}_{\mathrm{Reference}}^0}]100\%& \mathrm{Formula}1\end{array}$ DOC.sup.t.sub.sample=dissolved organic carbon in the sample over the test period t, DOC.sup.t.sub.reference=dissolved organic carbon in the reference substance over the test period t, DOC.sup.0.sub.sample=dissolved organic carbon in the sample at the start of the test, DOC.sup.0.sub.reference=dissolved organic carbon in the reference substance at the start of the test,

(6) If a degree of degradation of the test substance of ca. 70% is reached after 10 days, this is rated as readily biologically degradable. The phosphotartaric acid tetrapotassium salt investigated in this example reached a degree of degradation of 70% only after a test period of 20-24 days. Therefore, the phosphotartaric acid tetrapotassium salt can be classified as inherently biologically degradable and thus represents an attractive compromise between user-friendly robustness and environmental computability.

(7) In FIG. 2, the experimental setup for the determination of the effect of a substance as a calcium carbonate scale inhibitor is presented. 2 liters of the test water (composition see Table 7) are charged in a glass beaker 1 and the PTA concentration to be tested is added and the solution is pumped by means of a peristaltic pump 2 through a glass reflux condenser (heat exchanger 4) at a flow rate of 0.5 L/h over a time period of two hours and is collected in a measuring cylinder 5. The glass reflux condenser is heated with water, which is maintained at a temperature of 80 C. by means of a thermostat 3.

(8) For the following examples, the preparation of phosphotartaric acid is described in the prior art, for example in 142. Feodor Lynen and Hans Bayer: Phospho-d(+)-tartaric acid, from the University Chemistry Laboratory Munich, Biochemistry Department and the laboratory of Gebr. Bayer, Augsburg, received Apr. 2, 1952, No. 9-10/1952, Chemische Berichte Volume 1985, pp. 905-912; C. Neuberg and W. Schuchardt: ber die Synthese der Phospho-d-weinsure and ihre phosphatatische Spaltung (On the synthesis of phospho-d-tartaric acid and the phosphatatic cleavage thereof), from the Kaiser Wilhelm Institute for Biochemistry in Berlin-Dahlem, 28.111.36, pp. 39-47.

(9) In the following examples, phosphotartaric acid was prepared according to the method specification of Lynen and Bayer. The reaction in pyridine was selected as method variant (F. Lynen, H. Bayer; Chemische Berichte 1952, 85, 905-912). The dibrucin salt of phosphotartaric acid obtained was converted into the free acid according to the workup p. 910 of the abovementioned method specification via the ammonium salt and then deviating from this specification via treatment with a strongly acidic cation exchange resin (Amberjet 1200 hydrogen form). The pure phosphotartaric acid thus obtained was converted to the tetrapotassium salt with aqueous potassium hydroxide solution and, based on the tetrapotassium salt, a 60% aqueous solution was prepared.

Example 1

(10) Corrosion Inhibition of Steel

(11) 1 liter of the test water (composition see Table 1) was charged in a glass beaker, the phosphotartaric acid (PTA) concentration (60% solution of the tetrapotassium salt) to be tested was added and the test water was heated to 30 C. in a water bath. Three steel coupons (C 1010) are fixed to a holder and rotated vertically by means of a stirring motor in the test water at 100 revolutions/minute for a period of 24 hours. In this manner, the coupons are completely immersed in the test water.

(12) TABLE-US-00001 TABLE 1 Composition of the test water Parameter Unit Value Calcium Mol/m.sup.3 1.2 Magnesium Mol/m.sup.3 0.3 Hydrogen carbonate Mol/m.sup.3 1.9 Sulfate Mol/m.sup.3 0.4 Chloride Mol/m.sup.3 1.7 Sodium Mol/m.sup.3 2.2 Nitrates Mol/m.sup.3 0.8 pH 8.2

(13) The coupons are freed from adhering iron oxide/hydroxide in the test water by means of a brush and removed from the test water. The test water is homogenized by vigorous stirring, 50 ml are removed while stirring and transferred to a volumetric flask. The undissolved iron salts are dissolved by addition of concentrated hydrochloric acid and, after filling the volumetric flask with deionized water, the iron concentration of the solution is measured by atomic absorption spectroscopy in accordance with DIN 38 406-E7-1 with the following deviations from standard: 2.1 The application range is from 0.1 to 5.0 mg/L. 2.2 It is processed using an air-acetylene flame. The extinction is measured at a wavelength of 324.8 nm. 2.6 The nitric acid/cesium solution consists of: 500 ml of nitric acid, 500 ml of Suprapur deionized water and 100 g of cesium chloride p.a., copper stock solution, (Cu)=1000 mg/L, copper reference solution; (Cu)=5 mg/L the reference solution includes 1 ml of the nitric acid/cesium solution in 100 ml. the blank solution/zero value solution demineralized water without nitric acid. 2.7 The samples to be investigated are stored in plastic containers. The samples to be investigated are acidified directly after sampling with the nitric acid/cesium solution. 0.1 ml of acid solution is added to 10 ml of sample.

(14) The relative corrosion inhibition for steel (RCI.sub.Fe [%]) is derived from the measured iron concentration C.sub.Fe,c and the measured iron concentration without addition of inhibitor (blank value) C.sub.Fe,0 according to formula 2 below:
RCI.sub.Fe=(1C.sub.Fe,c/C.sub.Fe,0)100%.Formula 2:

(15) In Table 2, the measured iron concentrations and the relative corrosion inhibition for steel are shown as a function of the concentration of PTA. At a concentration of 20 mg/L, the corrosion of steel is reduced to about 89%.

(16) TABLE-US-00002 TABLE 2 measured iron concentrations and the relative corrosion inhibition of steel as a function of the concentration of PTA. Iron Concentration concentration PTA C.sub.Fe, c RCI.sub.Fe [mg/L] [mg/L] [%] 0 (blank) 36 0 10 32 11 20 28 22 30 3.0 92 40 3.1 91

Example 2

(17) Corrosion Inhibition of Steel

(18) Mixtures of phosphotartaric acid (PTA) (60% solution of the tetrapotassium salt) and another corrosion inhibitor were tested according to the test specification of Example 1. The sum of the individual inhibitor concentrations was always 20 mg/L, wherein the proportions of the inhibitors were varied.

(19) The relative synergy effect RS(M) of a mixture is derived from the measured relative corrosion inhibition RCI(M).sub.Fe,meas and the calculated relative corrosion inhibition RCI(M).sub.Fe,calc in accordance with formula 3 below:
RS(M)=RCI(M).sub.Fe,meas/RCI(M).sub.Fe,calc1.Formula 3:

(20) If RS is >0 a synergistic effect is present, if RS<0 an antagonistic effect.

(21) The calculated relative corrosion inhibition RCI(M).sub.Fe,calc is derived from the weighted mean of the measured relative corrosion inhibition RCI(A).sub.Fe,meas and RCI(B).sub.Fe,meas of the two individual components A and B alone, in accordance with formula 4 below:
RCI(M).sub.Fe,calc=c(A)/20.Math.RCI(A).sub.Fe,meas+c(B)/20RCI(B).sub.Fe,measFormula 4:

(22) Here, c(A) and c(B) represent the concentrations of the components A and B in the mixture. In Table 3, the results for corrosion inhibition are shown for mixtures of phosphotartaric acid (PTA) (60% solution of the tetrapotassium salt) and phosphonobutanetricarboxylic acid (50% acid in water) (PBTC). A synergistic effect is apparent for the mixture of phosphotartaric acid and phosphonobutanetricarboxylic acid in a ratio of 6:1 to 1:6.

(23) TABLE-US-00003 TABLE 3 Results for corrosion inhibition for mixtures of phosphotartaric acid (PTA) and phosphonobutanetricarboxylic acid (PBTC). Iron Concen- Concen- concen- tration tration tration PTA PBTC Ratio C.sub.Fe,c RCI.sub.Fe,meas RCI.sub.Fe,calc RS [mg/L] [mg/L] PTA/PBTC [mg/L] [%] [%] ((M) 20 0 28 22 22 0.0 17 3 5.7:1 23 36 21 0.8 13 7 1.9:1 15 58 18 2.2 10 10 1:1 19 47 17 1.8 7 13 1:1.9 25 31 15 1.0 3 17 1:5.7 25 31 13 1.4 0 20 32 11 11 0.0

(24) In Table 4, the results for corrosion inhibition are shown for mixtures of phosphotartaric acid (PTA) (60% solution of the tetrapotassium salt) and tartaric acid (TA). A synergistic effect is apparent for the mixture of phosphotartaric acid and tartaric acid in a ratio of 6:1 to 1:6.

(25) TABLE-US-00004 TABLE 4 Results for corrosion inhibition for mixtures of phosphotartaric acid (PTA) and tartaric acid (TA). Iron Concen- Concen- Concen- tration tration tration PTA TA Ratio C.sub.Fe,c RCI.sub.Fe,meas RCI.sub.Fe,calc RS [mg/L] [mg/L] PTA/TA [mg/L] [%] [%] (M) 20 0 28 22 22 0.0 17 3 5.7:1 12 68 32 1.1 13 7 1.9:1 3.2 91 46 1.0 10 10 1:1 3.3 91 56 0.6 7 13 1:1.9 3.0 92 66 0.4 3 17 1:5.7 3.3 91 79 0.2 0 20 4.0 89 89 0.0

(26) In Table 5, the results for corrosion inhibition are shown for mixtures of phosphotartaric acid (PTA) (60% solution of the tetrapotassium salt) and citric acid (60% in water) (CA). A synergistic effect is apparent for the mixture of phosphotartaric acid and citric acid in a ratio of 6:1 to 1:6.

(27) TABLE-US-00005 TABLE 5 Results for corrosion inhibition for mixtures of phosphotartaric acid (PTA) and citric acid (CA). Iron Concen- Concen- Concen- tration tration tration PTA CA Ratio C.sub.Fe,c RCI.sub.Fe,meas RCI.sub.Fe,calc [mg/L] [mg/L] PTA/CA [mg/L] [%] [%] RS(M) 20 0 28 22 22 0.0 17 3 5.7:1 20 43 26 0.7 13 7 1.9:1 7.8 78 31 1.5 10 10 1:1 13 64 35 0.8 7 13 1:1.9 15 58 39 0.5 3 17 1:5.7 13 65 44 0.5 0 20 19 48 48 0.0

Example 2a

(28) A mixture (MI) of 45% phosphotartaric acid (PTA) (60% solution of the tetrapotassium salt), 12% tartaric acid and 8% phosphoric acid in water was adjusted to a pH of 12.2 with aqueous potassium hydroxide solution and tested in accordance with the test specification of example 1.

(29) In Table 5a the results for corrosion inhibition are shown for the mixture. A relative corrosion inhibition of over 90% is already achieved at a concentration of 30 mg/L.

(30) TABLE-US-00006 TABLE 5a Results for corrosion inhibition for a mixture of phosphotartaric acid (PTA), tartaric acid and phosphoric acid. Iron Concentration concentration MI C.sub.Fe, c RCI.sub.Fe [mg/L] [mg/L] [%] 0 (Blank) 36 0 10 20 44 20 17 54 30 3.0 92 40 2.6 93

Example 3

(31) Corrosion Inhibition of Brass

(32) The tests were carried out according to the method described in example 1 using brass coupons (CDA 443) and, after completion of the test, the concentrations of copper and zinc in the test water were determined by atomic absorption spectroscopy.

(33) The relative corrosion inhibition for brass (RCI.sub.Cu [%]) according to formula 5 and (RCI.sub.Zn [%]) according to formula 6 is derived from the measured copper and zinc concentrations C.sub.Cu,c and C.sub.Zn,c respectively and the measured copper and zinc concentrations without addition of inhibitor (blank value) C.sub.Cu,0 and C.sub.Zn,0 respectively:
RCI.sub.Cu=(1C.sub.Cu,c/C.sub.Cu,0)100%Formula 5:
RCI.sub.Zn=(1C.sub.Zn,c/C.sub.Zn,0)100%Formula 6:

(34) In Table 6, the measured copper and zinc concentrations and the relative corrosion inhibition for copper and zinc are shown as a function of the concentration of PTA. At a concentration of 20 mg/L, the corrosion of copper and zinc is reduced to about 75% and 87% respectively.

(35) TABLE-US-00007 TABLE 6 Measured copper and zinc concentrations and the relative corrosion inhibition for copper and zinc as a function of the concentration of PTA. Copper Zinc Concentration concentration concentration PTA C.sub.Cu. c RCI.sub.Cu C.sub.Zn, c RCI.sub.Zn [mg/L] [mg/L] [%] [mg/L] [%] 0 (Blank) 0.77 0 0.78 0 20 0.19 75 0.10 87 60 0.16 79 0.05 94

Example 4

(36) Inhibition of Calcium Carbonate Deposits

(37) Example 4 was carried out to determine the effect of a substance as calcium carbonate scale inhibitor according to an experimental setup according to FIG. 2.

(38) TABLE-US-00008 TABLE 7 Composition of the test water Parameter Unit Value Calcium Mol/m.sup.3 5.4 Magnesium Mol/m.sup.3 1.8 Hydrogen carbonate Mol/m.sup.3 20 Sulfate Mol/m.sup.3 1.8 Chloride Mol/m.sup.3 10.8 Sodium Mol/m.sup.3 20 pH 8.5

(39) After a test period of 2 hours, the water remaining in the glass reflux condenser is carefully removed using the peristaltic pump. The calcium carbonate isolated on the glass wall is dissolved with hydrochloric acid. The hydrochloric acid collected in a beaker is made up to a defined volume (100 ml) with demineralized water and, after neutralization, the calcium concentration is determined by complexometric titration (0.01783 mol/L sodium EDTA solution, manufacturer Bernd Kraft GmbH, Item No.: 01083.3000). The titration endpoint is indicated by the color change of the calconcarboxylic acid indicator from red-violet to blue.

(40) The relative calcium carbonate inhibition (RCI [%]) is derived according to formula 7 from the consumption of the titration solution V.sub.c and the consumption of the titration solution without addition of inhibitor (blank) V.sub.0:
RCI=(1V.sub.c/V.sub.0)100%Formula 7:

(41) In Table 8, the consumptions of the titration solution and the relative calcium carbonate inhibition are shown as a function of the concentration of PTA (60% solution of the tetrapotassium salt). At a concentration of 4 mg/L, the calcium carbonate deposition is virtually completely prevented, and from 6 mg/L completely prevented.

(42) TABLE-US-00009 TABLE 8 Consumptions of the titration solution and the relative calcium carbonate inhibition as a function of the concentration of PTA. Concentration Consumption PTA V.sub.c RCI [mg/L] [ml] [%] 0 (Blank) 11.8 0 2 6.2 48 4 0.7 94 6 0 100 8 0 100 10 0 100

Example 5

(43) Determination of the Chlorine Stability of PTA

(44) The chlorine stability of PTA was determined analogously to commercial phosphonic acids by the partial conversion of the organically bound phosphate (org-PO.sub.4) to orthophosphate. The total phosphate (tot-PO.sub.4) and orthophosphate (o-PO.sub.4) content in the test solutions was determined in this case. The organically bound phosphate is derived from org-PO.sub.4=tot-PO.sub.4o-PO.sub.4.

(45) The tot-PO.sub.4 and o-PO.sub.4 were determined using the Laborautomat Ganimede P from Dr. Lange. The Ganimede analysis unit P enables the measurement of PO.sub.4 as total phosphate or orthophosphate by means of a photometric method according to DIN EN 1189 from 12/96.

(46) The total phosphate is determined after high-temperature digestion of organic phosphate to give orthophosphate. In this case, ca. 2 mL of sample are heated with a digestion reagent for 90 seconds at 150 C. and 6 bar. Two safety levels release a potential resulting overpressure at 7 and 9 bar. The sample is subsequently cooled to 90 C. by cooling in air. The digested solution is automatically pumped from the digestion cuvette into the analysis cuvette and the required reagents (color and reducing reagent) are added. The sample is further cooled to ca. 45 C. By heating the sample, the reaction time for the formation of the phosphorus molybdenum blue is shortened; the total phosphate content is then determined photometrically at 880 nm.

(47) To determine the orthophosphate content, the sample is pumped directly into the analysis cuvette without digestion, mixed with the reagents and measured photometrically at 880 nm.

(48) 2 L of Dsseldorf drinking water are placed in a glass beaker. A hypochlorite content of 1 mg/L (given as Cl.sub.2) is set using the NaOCl solution (0.013%). The pH is subsequently adjusted to 8.5 and 1 mg Br/L as sodium bromide is added to the raw material to be tested. The free chlorine content and the pH are checked every 15 minutes and adjusted as required.

(49) The duration of the test is 4 hours in total. Immediately after the test start and then half hourly a 50 ml sample is removed to determine the t-PO.sub.4 and o-PO.sub.4 content. The hypochlorite in the samples taken is decomposed with 1-2 mL of urea solution (4%). The tests were carried out at room temperature.

(50) The chlorine stability (Cl.sub.2St(t)) is derived from the percentage org-PO.sub.4 content at the experimental timepoint (org-PO.sub.4(t)) relative to the org-PO.sub.4 content at the start of the experiment (org-PO.sub.4(0)), according to: Cl.sub.2St(t)=(1(org-PO.sub.4(0)org-PO.sub.4(t))/org-PO.sub.4(0))*100%. The chlorine stability was determined on a 60% solution of the tetrapotassium salt of PTA. For comparison, the data for commercial phosphonic acids have been determined. This shows that PTA has a significantly higher chlorine stability than 3 of the 4 phosphonic acids investigated.

(51) TABLE-US-00010 TABLE 9 Chloride stabilities of PTA compared to commercial phosphonic acids as a function of time - all data in % unless otherwise stated. Test duration PTA, PBTC, ATMP, HEDP, HPA, [h] 20 mg/L 20 mg/L 10 mg/L 10 mg/L 10 mg/L org-PO4 (0) 2.6 mg/L 3.5 mg/L 4.6 mg/L 5.5 mg/L 5.5 mg/L 0.05 91 95 87 85 70 0.5 90 93 74 67 39 1 81 94 68 71 27 1.5 80 93 62 50 19 2 80 90 60 38 14 2.5 80 93 52 29 9 3 81 93 53 21 6 3.5 not 97 52 14 3 deter- mined 4 78 92 52 6 1
PBTC=phosphonobutanetricarboxylic acid 50%
ATMP=aminotrimethylenephosphonic acid 50%
HEDP=hydroxyethanediphosphonic acid 60%
HPA=hydroxyphosphonoacetic acid 50%