Method for treating a liquid sample in order to remove interference by iron

Abstract

The invention relates to a method for treating a liquid sample, which comprises disturbing iron and at least one organic compound of interest. The, the method comprises addition of a reagent comprising an ammonium salt, alkali metal salt or earth alkali metal salt of hexacyanoferrate to the sample. Iron in the sample is allowed to interact with the reagent and to form a reaction product, the reaction product of iron is separated from the sample, and the amount of the at least one compound of interest is determined from the sample. The invention relates also to use of salt of hexacyanoferrate.

Claims

1. A method for treating a liquid sample, the sample comprising iron in the form of iron (II) and/or iron (III) and at least one organic compound of interest, the method comprising (i) adding ascorbic acid to the sample in order to reduce any iron (III) in the sample to iron (II); (ii) after or simultaneous to the addition of ascorbic acid further adding a reagent comprising an ammonium salt, alkali metal salt or earth alkali metal salt of hexacyanoferrate to the sample; (iii) allowing the iron in the sample to interact with the reagent and to form an insoluble iron containing reaction product; (iv) separating the resultant insoluble reaction product comprising iron from the sample; and (v) determining the amount of the at least one organic compound of interest in the sample; wherein the method does not include the addition of any other reactants which promote the formation of another insoluble iron containing reaction product and/or the method does not include the removal of another insoluble iron containing reaction product from the sample.

2. The method according to claim 1, wherein the organic compound of interest is a synthetic organic compound, a natural polymer or a biopolymer.

3. The method according to claim 1, wherein the organic compound of interest is an organic compound selected from the group consisting of scale inhibitors, corrosion inhibitors, friction reducers, and polymers used in oil field applications or oil recovery processes.

4. The method according to claim 1, wherein the method comprises a step of adjusting pH of the sample to a pH value≤7, before addition of the reagent.

5. The method according to claim 1 wherein the reagent comprises hexacyanoferrate(II).

6. The method according to claim 1, wherein the reagent comprises ammonium or potassium hexacyanoferrate.

7. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 1:2 to 20:1.

8. The method according to claim 1, wherein the total concentration of iron is >0.5 ppm.

9. The method according to claim 1, wherein the method comprises separating the reaction product by filtering, centrifuging or sedimentation.

10. The method according to claim 1, wherein the method comprises adding a flocculation agent to the sample after addition of the reagent and separating the reaction product by flocculation.

11. The method according to claim 1, wherein the method comprises determining the amount of iron in the sample and adjusting the amount of reagent on basis of said determination.

12. The method according to claim 8, wherein the total concentration of iron is >75 ppm.

13. The method according to claim 12, wherein the total concentration of iron is >100 ppm.

14. The method according to claim 4, wherein the pH ranges from 3 to 5.

15. The method according to claim 4, wherein the pH ranges from 1 to 3.

16. The method according to claim 8, wherein the total concentration of iron ranges from 10 ppm to ≥50 ppm.

17. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 4:5 to 15:1.

18. The method according to claim 5 wherein the molar ratio of hexacyanoferrate to iron in the sample ranges from 1:1 to 10:1.

19. The method according to claim 1, wherein the insoluble reaction product is removed by filtration.

Description

EXPERIMENTAL

(1) Some embodiments of the invention are described in the following non-limiting examples.

(2) Iron removal using hexacyanoferrate(II) was tested in synthetic brine having a composition given in Table 1.

(3) TABLE-US-00001 TABLE 1 Brine composition Component Concentration [g/l] NaCl 35.03 MgCl2 × 6H2O 1.46 CaCl2 × 2H2O 2.24 KCl 0.21 BaCl2 × 2H2O 0.13 SrCl2 × 6H2O 0.10

(4) Chemicals used in Example 1 and their preparation were as follows Deionized water (milliQ) which pH was adjusted to pH 2 by addition of 197 μl of 37% HCl to 200 ml of water Brine as defined in in Table 1. pH of the brine was adjusted to pH 2 by addition of 470 μl 37% HCl to 500 ml of brine Ascorbic Acid 0.5004 g of ascorbic acid was dissolved into 4.5 ml of deionized water FeSO.sub.4 1.2443 g of FeSO.sub.4x7H.sub.2O was dissolved into 25 ml of deionized water as defined above Hexacyanoferrate 1.8911 g of potassium hexacyanoferrate(II)×3H.sub.2O was dissolved into 25 ml of deionized water as defined above. The resulting pH of the solution was pH 5 Scale inhibitor KemGuard 2253 (Kemira Oyj, Finland)

Example 1

(5) Scale inhibitor was added in a dose of 102 ppm, which corresponds to a dose of 30 ppm, calculated as active component, to 50 ml of brine. Iron content of the brine samples was adjusted with FeSO.sub.4. Hexacyanoferrate and ascorbic acid (reduction agent) were added to the samples according to the present invention. After that the amount of scale inhibitor was measured with a method employing time-resolved luminescence, as described in WO 2015/075308.

(6) The results are given in Tables 2 and 3.

(7) From the results shown in Tables 2 and 3 it can be seen that after the treatment with hexacyanoferrate and ascorbic acid the scale inhibitor could be determined from the liquid sample without interference of iron. The results were repeatable.

(8) A constant hexacyanoferrate addition could be used for low iron content samples. However, a large excess of hexacyanoferrate might cause a slight interference. Addition of ascorbic acid does not interfere with the measurements.

(9) TABLE-US-00002 TABLE 2 Results of Example 1. Ascorbic Hexacyano Determined Scale Test FeSO.sub.4 Acid ferrate(II) Filtered, Inhibitor, active # [μl] [μl] [μl] 0.45 μm [ppm] 1 — 97 250 yes 28 2 — 97 625 yes 28 3 — 97 2500 yes 17 4 250 — 250 yes 26 5 250 97 250 no 17 6 250 97 250 yes 33 7 250 97 250 yes 31 8 250 97 2500 yes 12

(10) TABLE-US-00003 TABLE 3 Results of Example 1. Ascorbic Hexacyano Determined Scale Test FeSO.sub.4 Acid ferrate(II) Filtered, Inhibitor, product # [μl] [μl] [μl] 0.45 μm [ppm] 0 — 100 — yes 97.8 1 — 100 250 yes 99.9 2 — 100 500 yes 90.0 3 — 100 750 yes 85.9 4 — 100 1000 yes 81.7 5 — 100 250 yes 102 6 250 100 300 yes 105 8 250 100 300 yes 102 9 250 1000 300 yes 101 10 250 5000 300 yes 98.4

Example 2

(11) Chemicals used in Example 1 and their preparation were as follows Deionized water (milliQ) which pH was adjusted to pH 2 by addition of 470 μl of 37% HCl to 425 ml of water Brine as defined in in Table 1. pH of the brine was adjusted to pH 2 by addition of 37% HCl Ascorbic Acid 0.2004 g of ascorbic acid was dissolved into 1.8 ml of deionized water FeSO.sub.4 0.6252 g of FeSO.sub.4x7H.sub.2O was dissolved into 12.5 ml of deionized water as defined above Hexacyanoferrate 0.7502 g of potassium hexacyanoferrate(II)×3H.sub.2O was dissolved into 10 ml of deionized water as defined above. Scale inhibitor KemGuard 2253 (Kemira Oyj, Finland)

(12) Scale inhibitor was added to 25 ml of brine in variable amounts, the dose of active component varying from 1 ppm to 95 ppm. Iron content of the brine samples was adjusted with FeSO.sub.4. Hexacyanoferrate and ascorbic acid (reduction agent) were added to the samples according to the present invention. After that the amount of scale inhibitor was measured with a method employing time-resolved luminescence, as described in WO 2015/075308.

(13) The results are given in Table 4.

(14) TABLE-US-00004 TABLE 4 Results of Example 2. Deter- Scale mined Inhib- Ascor- Scale itor, bic Hexacyano- Inhibitor, Test active FeSO.sub.4 Fe acid ferrate(II) Filtered active # [ppm] [ul] [ppm] [ul] [ul] 0.45 um [ppm] 1 1 250 50 100 300 yes 1 2 5 250 50 100 300 yes 4 3 15 250 50 100 300 yes 15 4 30 250 50 100 300 yes 28 5 95 250 50 100 300 yes 91 6 2 250 50 100 300 yes 2 7 3 250 50 100 300 yes 3 8 1 500 100 100 600 yes 1 9 1 — 0 100 300 yes 1

(15) From the results shown in Table 4 it can be seen that after the treatment with hexacyanoferrate and ascorbic acid the scale inhibitor could be determined from the liquid sample without interference of iron even at low concentration. The results were repeatable.

(16) Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.