Method and apparatus for determining film-forming amines in liquids
阅读说明：本技术 测定液体中成膜胺的方法和设备 (Method and apparatus for determining film-forming amines in liquids ) 是由 乌特·拉明格 乌尔里希·尼克尔 约尔格·方德里奇 于 2018-04-03 设计创作，主要内容包括：用于测定液体中成膜胺的光度法,其包括以下步骤：a)提供pKa≥4.5的弱酸和pKa≤1的强酸的缓冲溶液；b)使用给定体积的水稀释缓冲溶液的等分试样,并测定所述稀释的缓冲溶液的pH值；c)向所述稀释的缓冲溶液中加入给定量的试剂,并测量含有试剂的所述稀释的缓冲溶液的初始吸光度；d)通过将给定体积的含有成膜胺的液体添加到缓冲溶液的等分试样中来制备样品溶液,并测量样品溶液的pH值；e)通过添加计算量的强酸来调节样品溶液的pH值,使其与稀释的缓冲溶液的pH值匹配；以及f)将给定量的所述试剂加入到pH调节后的样品溶液中以形成有色配合物,并在光度计中测量pH调节后的含有试剂和有色配合物的样品溶液的吸光度。(A photometric method for determining a film-forming amine in a liquid comprising the steps of: a) providing a buffer solution of weak acid with pKa more than or equal to 4.5 and strong acid with pKa less than or equal to 1; b) diluting an aliquot of a buffer solution with a given volume of water and determining the pH of the diluted buffer solution; c) adding a given amount of reagent to the diluted buffer solution and measuring the initial absorbance of the diluted buffer solution containing reagent; d) preparing a sample solution by adding a given volume of a liquid containing a film-forming amine to an aliquot of a buffer solution, and measuring the pH of the sample solution; e) adjusting the pH of the sample solution to match the pH of the diluted buffer solution by adding a calculated amount of strong acid; and f) adding a given amount of the reagent to the pH-adjusted sample solution to form a colored complex, and measuring the absorbance of the pH-adjusted sample solution containing the reagent and the colored complex in a photometer.)
1. A method for assaying a film-forming amine in a liquid by adding a reagent to the liquid to form a colored complex of the amine and the reagent, wherein the colored complex is measured photometrically, the method comprising the steps of:
a) providing a buffer solution of weak acid with pKa more than or equal to 4.5 and strong acid with pKa less than or equal to 1;
b) diluting an aliquot of the buffer solution with a given volume of water and determining the pH of the diluted buffer solution;
c) adding a given amount of said reagent to said diluted buffer solution and measuring the initial absorbance of said diluted buffer solution containing said reagent;
d) preparing a sample solution by adding a given volume of the liquid containing the film-forming amine to an aliquot of the buffer solution, and measuring the pH of the sample solution;
e) adjusting the pH of the sample solution to match the pH of the diluted buffer solution by adding a calculated amount of the strong acid; and
f) adding a given amount of the reagent to the pH-adjusted sample solution to form the colored complex, and measuring the absorbance of the pH-adjusted sample solution containing the reagent and the colored complex.
2. The method of claim 1, wherein the film-forming amine is represented by the formula R- (NH-R)1)n-NH2Wherein R is an alkyl group having 12 to 24 carbon atoms, R1Is a methylene or alkylene group having 2 to 4 carbon atoms, and n is an integer of 0 to 7.
3. The method of claim 1 or 2, wherein the liquid is feed water or process water.
4. The method according to any one of the preceding claims, wherein the agent is a xanthene dye, preferably fluorescein, eosin, rose bengal or phloxine B, most preferably phloxine B.
5. The process according to any of the preceding claims, wherein the weak acid is acetic acid and wherein the strong acid is hydrochloric acid.
6. The method according to any one of the preceding claims, wherein the pH of the diluted buffer solution is from 2.5 to 2.9.
7. The method according to any one of the preceding claims, wherein the amount of strong acid to be added to the sample solution is calculated using a first calibration curve or an algorithm based on the following formula:
log[Ac-]＝log([HAc]total/KHAc)+pHsample，
wherein the content of the first and second substances,
[Ac-]is the anion concentration of the weak acid dissociated in the solution;
[HAc]totalis the total concentration of said weak acid in said solution;
KHAcis the association constant of said weak acid; and is
pHsampleIs the measured pH of the solution.
8. The method according to any one of the preceding claims, wherein the concentration of the film-forming amine in the liquid is calculated from the measured absorbance of the pH adjusted sample solution containing the reagent and the coloured complex using a second calibration curve or an algorithm based on the following formula:
[Amine]＝(Asample–Ao)/f；
wherein the content of the first and second substances,
[ Amine ] is the concentration of the filming Amine in the sample solution;
Asampleis the measured absorbance of the sample solution containing the reagent and the colored complex;
Aois the initial absorbance measured of the diluted buffer solution containing the reagent; and is
f is a factor corresponding to the slope of the second calibration curve.
9. The method according to any of the preceding claims, wherein the method is performed manually or semi-automatically.
10. An apparatus for assaying filming amines using the method of any of claims 1 to 9, wherein the apparatus comprises:
a mixing chamber and a photometer connected to the mixing chamber;
a pH sensor disposed within the mixing chamber; and
a control unit connected to the mixing chamber and the photometer;
wherein the mixing chamber is connected to a feed of a strong acid and water, and the mixing chamber further comprises an inlet line for a buffer solution, an inlet line for a treatment liquid, and an inlet line for a reagent solution; and is
Wherein the control unit comprises means for controlling the amounts of the buffer solution, the treatment liquid and the reagent solution supplied to the mixing chamber and means for calculating and introducing the amounts of the strong acid and water into the mixing chamber based on the input signal received from the pH sensor, and wherein the control unit further comprises means for calculating the amount of film-forming amine in the treatment liquid based on the input signal received from the photometer.
Technical Field
The invention relates to a method and a device for determining film-forming amines in liquids, in particular in the water-steam cycle of nuclear power plants.
Background
Feedwater additives based on film-forming amines are used for internal treatment or coating of pipes, tubes or reactors in industrial plants to protect these items from corrosion. The film-forming amine is typically a polyamine or a monoamine, such as a fatty amine. Amines are used in particular as additives in the water-steam cycle of nuclear power plants to prevent corrosion of the internal surfaces used in the water-steam cycle.
WO 2013/127844 discloses a method for cleaning and conditioning a circulation system of a power station, in particular a water-steam circulation of a nuclear power station. According to the method, the film-forming amine is metered into a working medium circulating in the circulation system, wherein the film-forming agent forms a hydrophobic film on the inner surfaces of the circulation system. At least one measurement point is provided in the circulation system, and the concentration of the film-forming agent is monitored during operation of the decontamination and conditioning process. The metered addition of the film former is stopped as soon as the concentration of film former in the working medium has reached a value of 1ppm to 2ppm at least one measuring point.
The treatment of the concentration of the film-forming amine in the liquid working medium is critical, meaning that the concentration must be carefully measured to ensure successful treatment or coating and to avoid unnecessary excess addition of amine which may have adverse effects such as filter plugging.
EP 0562210 a1 proposes a method for simple and sensitive determination of polyamines in liquids, and a photometer for carrying out the method. Color formation of the polyamines in the samples was measured by near monochromatic light from a conventional LED and filtered by a colored glass filter. The color-forming reaction is based on the reaction of the polyamine to be tested with rose bengal (rosebengal), wherein the reaction is carried out in a pH buffered solution using acetic acid.
Yu.m.evtushenko, v.m.ivanov and b.e.zaitsev disclose similar methods in "Photometric Determination of Octadecylamine with Methyl Orange" using Methyl Orange, Journal of Analytical Chemistry, 2002, volume 57,
Katrin Stiller, Tobias Wittig and Michael Urschey describe The treatment concept of water-steam cycles based on filming Amines in "Analysis of Film-Forming Amines-Methods, Possibilities, limitations and Recommendations (The Analysis of Film-Forming Amines-Methods, Possibilities, Limits and Recommendations)", Powerplant Chemistry 2011, 13 (10). Again, the investigation of the assay for film-forming amines was based on the method using rose bengal as shown in EP 0562201 a 1. The pH of the sample was maintained between 2.3 and 3.3. The results show that the method is very sensitive to pH and that after addition of the reagent the pH of the sample must be absolutely between 2.3 and 3.3 to ensure that reliable amine concentration measurements are obtained.
WO 2014/166542 a1 proposes determining the presence and concentration of a film-forming amine by reacting the amine with a reagent to form a colored complex and by further adding a solution containing hydrochloric acid to lower the pH of a sample solution containing the reagent and the film-forming amine to a value below the pKa of the reagent. Preferably, the pH is lowered to 2.3, preferably 2.0, by addition of hydrochloric acid. To perform the method, a liquid sample containing a film-forming amine is introduced into a mixing chamber. An aqueous solution of the xanthene dye is added to the liquid in the mixing chamber, while a hydrochloric acid solution is also added to lower the pH of the sample solution in the mixing chamber to a value less than the pKa of the xanthene dye. Then, the sample solution containing the xanthene dye and hydrochloric acid was passed through a photometer in which measurement was performed in a monochromatic wavelength range of 400 to 560nm in terms of the xanthene dye.
Known concepts for determining the concentration of polyamines in a liquid include titration against methyl orange or photometric measurement using eosin or rose bengal. However, these methods require time consuming sample preparation or lack accuracy.
The on-line measurement method disclosed in the patent literature can be used as a prototype.
Disclosure of Invention
It is an object of the present invention to provide an accurate, rapid and repeatable photometric determination of film-forming amines using harmless reagents to monitor the course of amine concentration changes during amine application in nuclear power plants with different water chemistry protocols.
The present invention achieves this object by a method for determining a film-forming amine in a liquid, wherein a reagent is added to the liquid to form a coloured complex of the amine and the reagent, wherein the coloured complex is measured photometrically, and wherein the method comprises the steps of:
a) providing a buffer solution of weak acid with pKa more than or equal to 4.5 and strong acid with pKa less than or equal to 1;
b) diluting an aliquot of a buffer solution with a given volume of water and determining the pH of the diluted buffer solution;
c) adding a given amount of said reagent to said diluted buffer solution and measuring the initial absorbance of said diluted buffer solution containing said reagent;
d) preparing a sample solution by adding a given volume of a liquid containing a film-forming amine to an aliquot of a buffer solution, and measuring the pH of the sample solution;
e) adjusting the pH of the sample solution to match the pH of the diluted buffer solution by adding a calculated amount of strong acid; and
f) a given amount of the reagent is added to the pH-adjusted sample solution to form a colored complex, and the absorbance of the pH-adjusted sample solution containing the reagent and the colored complex is measured.
The inventors have surprisingly found that the accuracy and reproducibility of the method can be significantly improved when the pH of a sample solution containing a film-forming amine is adjusted and matched to the pH of a reference solution used to measure the initial absorbance or transmission intensity of the reagent in a weak acid solution prior to the addition of the reagent. Adjusting the pH of the sample solution to match the pH of the reference solution prevents distortion of the measured absorbance due to the dependence of the molar extinction coefficient of the reagent on the pH of the solutions in the sample test cell and the reference test cell.
Photometric measurement of the colored complex in a weak acid solution also prevents unwanted side chain reactions of the complex. The pH adjustment may be performed automatically using a metering device or manually using a suitable chart or table. The method can also be performed in an in-line measurement device to ensure continuous monitoring of the film-forming amine in the process liquid.
Accordingly, the present invention also provides an apparatus for assaying filming amines using the above method, wherein the apparatus comprises:
a mixing chamber and a photometer connected to the mixing chamber;
a pH sensor disposed within the mixing chamber; and
a control unit connected to the mixing chamber and the photometer;
wherein the mixing chamber is connected to a feed of a strong acid and water and further comprises an inlet line for a buffer solution, an inlet line for a treatment liquid and an inlet line for a reagent solution; and is
Wherein the control unit comprises means for controlling the amount of buffer solution, treatment liquid and reagent solution supplied to the mixing chamber and means for calculating and introducing the amount of strong acid and water into said mixing chamber based on the input signal received from the pH sensor, and wherein the control unit further comprises means for calculating the amount of film-forming amine in the treatment liquid based on the input signal received from the photometer.
Drawings
Fig. 1 shows an example of a calibration curve for calculating the amount of strong acid for pH adjustment to be added to a sample solution containing a film-forming amine.
Fig. 2 shows a schematic view of an on-line measuring device for carrying out the method of the invention.
Detailed Description
The interior surfaces of pipes, tubes and boilers in industrial plants are treated or coated with additives such as film-forming amines to prevent corrosion of the surfaces. The film-forming amine is preferably a polyamine or monoamine, such as a fatty amine, of the formula R- (NH-R)1)n-NH2Wherein R is an alkyl group having 12 to 24 carbon atoms, R1Is a methylene or alkylene group having 2 to 4 carbon atoms, and n is an integer of 0 to 7.
Preferably, the film-forming amine is used as an additive to a treatment liquid, wherein the liquid is feed water or industrial water. In particular, filming amines are effective corrosion inhibitors that form very thin films on the interior surfaces of the components and pipes of the water-steam cycle of a nuclear power plant. It is therefore preferred to inject the film-forming amine as an additive into the process liquid flowing through the water-steam cycle of the nuclear power plant, in particular the feed water for the water-steam cycle.
The concentration of the film-forming amine in the liquid is determined by adding a reagent to the liquid sample to form a colored complex of the amine and the reagent, and the colored complex is measured photometrically. The agent for forming a coloured complex with the amine is preferably a xanthene dye, more preferably a xanthene dye selected from the group consisting of fluorescein, eosin, rose bengal and phloxine b (phloxine b).
Most preferably, the agent is phloxine B. Phloxine B is also known as phloxine (cyanosine) or IUPAC chemical name: disodium 2',4',5',7' -tetrabromo 4,5,6, 7-tetrachloro-3-oxospiro [ 2-benzofuran-1, 9 '-xanthene ] -3',6 '-diolate (disodium 2',4',5',7 '-tetrabromo-4, 5,6, 7-tetrachloro-3-oxopiro [ 2-benzofuranon-1, 9' -xanthene ] -3',6' -diolate) and has an absorption maximum at 546-550 nm.
For concentration measurements, aqueous buffered solutions of weak acids and strong acids are provided, wherein the weak acids have a pKa ≧ 4.5 and the strong acids have a pKa ≦ 1. Preferably, the weak acid is acetic acid and the strong acid is hydrochloric acid.
An aliquot of the buffer solution was diluted with a given volume of water and the pH of the diluted buffer solution was determined. Preferably, the pH of the diluted buffer solution is controlled to be in the range of 2.5 to 2.9, preferably in the range of 2.7 to 2.8.
Thereafter, a given amount of reagent was added to the diluted buffer solution, and the initial absorbance of the diluted buffer solution containing the reagent was measured. The initial absorbance of the diluted buffer solution can be measured using a commercially available photometer, or a diluted stock solution containing the reagent can be prepared and measured using the above-described apparatus for measuring a film-forming amine in a liquid.
Next, a sample solution was prepared by adding a given volume of the liquid containing the film-forming amine to an aliquot of the buffer solution, and the pH of the sample solution was measured. Preferably, the volume of the liquid containing the film-forming amine corresponds to the volume of water added to form the diluted buffer solution, and the aliquots of the buffer solution used to provide the diluted buffer solution and the sample solution have the same volume.
Since the processing liquid containing the film-forming amine is a basic solution with a pH >7, the pH of the diluted buffer solution and the sample solution will differ due to the neutralization of the film-forming amine and optionally other amines present in the liquid by the weak or strong acid of the buffer solution. Thus, according to the present invention, the pH of the sample solution is adjusted by adding a calculated amount of strong acid to match the pH of the diluted buffer solution.
Preferably, the amount of strong acid to be added to the sample solution is calculated using a first calibration curve or an algorithm based on the following formula:
log[Ac-]＝log([HAc]total/KHAc)+pHsample
wherein the content of the first and second substances,
[Ac-]is the anion concentration of the weak acid dissociated in the solution;
[HAc]totalis the total concentration of weak acids in the solution;
KHAcis the association constant of the weak acid; and is
pHsampleIs the measured pH of the solution.
Those skilled in the art should understand thatUnderstanding that the above formula is at KHac[H+]>>1 is effective.
Figure 1 shows a calibration curve in which the logarithm of the anion concentration of the dissociated weak acid is specified as a function of the pH value. Point a represents the case of a dilute buffer solution. The vertical dotted line indicates the pH (pH) of the diluted buffer solutionref). Horizontal dotted line indicates at pHrefThe anion concentration of the weak acid and the total concentration (logarithm) of the weak acid selected.
The vertical arrows pointing to points B and C simulate the measured pH in an exemplary sample solution containing a film-forming amine, optionally with ammonia, ethanolamine, morpholine, or other amines. The pH measurements were performed separately using the same volume of diluted buffer solution and sample solution. pH value (pH) of sample solution due to partial neutralization of weak acid1Or pH2) Above pHref. This corresponds to a higher weak acid [ Ac ] in the sample solution compared to the diluted buffer solution-]The anion concentration values, which are indicated in fig. 1 by the horizontal arrows at points B and C.
Based on the measured pH of the sample solution (e.g., pH in FIG. 1)1Or pH2) The increase in weak acid anion concentration, and thus total amine content, of each sample solution can be determined via a calibration curve.
After log reduction, the reference pH value is obtained which must be added to the sample solution in order to make the pH of the sample solution and the diluted buffer solutionrefThe amount of strong acid matched. The advantage of this method step is that only a short pH adjustment is required since there is no need to titrate the solution to the target pH value.
The amount of film-forming amine in the sample solution is then determined photometrically. According to the present invention, a given amount of reagent is added to the pH-adjusted sample solution to form a colored complex of the film-forming amine and the reagent, and the absorbance of the pH-adjusted sample solution containing the reagent and the colored complex is measured using a commercially available photometer.
Preferably, the concentration of the film-forming amine in the treatment liquid is calculated from the measured absorbance of the pH-adjusted sample solution containing the reagent and the colored complex using a second calibration curve or an algorithm based on the following formula.
[Amine]＝(Asample–Ao)/f
Wherein the content of the first and second substances,
[ Amine ] is the concentration of filming Amine in solution;
Asampleis the measured absorbance of the solution;
Aois the initial absorbance of the diluted buffer solution containing the reagent measured; and is
f is a factor corresponding to the slope of the calibration curve and which includes characteristics of the reagent and the measurement cell
Optical path length and molar extinction coefficient.
A second calibration curve may be obtained by measuring the absorbance of a plurality of sample solutions containing the reagent and the chromonic complex at a given pH and containing a known amount of the film-forming amine.
Preferably, the photometric measurement is performed semi-automatically or automatically. Furthermore, it is also possible to correct, by means of software integrated in the photometer, the measured absorbance of the sample solution containing the reagent and the coloured complex according to the pH value of the solution, in order to account for any differences in the pH value of the sample solution used to obtain the second calibration curve.
Fig. 2 shows a schematic view of a measuring device 10 which can be used for carrying out the method of the invention. The apparatus 10 includes a mixing chamber 12 and a luminometer 14 connected to the mixing chamber via a conduit 16. The mixing chamber 12 comprises an inlet line 18 for a buffer solution, an inlet line 20 for a treatment liquid and an inlet line 22 for a reagent solution. The amount of buffer solution, treatment liquid and reagent solution flowing into the mixing chamber 12 is controlled by metering valves 24, 26 and 28 arranged in the inlet lines 18, 20 and 22. Furthermore, the mixing chamber 12 is connected to a feed of strong acid and water (feedstock) via supply lines 30, 32 equipped with metering valves 34 and 36. A pH sensor 38 is provided within the mixing chamber. The metering valves 24, 26, 28, 34, 36, the pH sensor 38 and the photometer 14 are connected to a control unit 40.
The inlet line 20 for the treatment liquid may be connected to one or more measurement points (not shown) at a bypass in the steam-water cycle of the nuclear power plant. Connecting the inlet line 20 directly to the measurement point allows continuous monitoring of the free film-forming amine in the process liquid present in the water-steam cycle.
In order to obtain the reference values required for the pH adjustment of the sample solution and the absorbance of the colored complex, the pH value of the diluted buffer solution is determined and preferably input into the control unit 40. A given amount of reagent is added to the diluted buffer solution and water is added to provide a target volume of diluted buffer solution containing the reagent. The diluted buffer solution containing the reagent is then transferred to a measurement cell of a luminometer to measure the initial absorbance of the reagent in the diluted buffer solution.
The measurement of the reference pH and the initial absorbance of the diluted buffer solution may be performed using the apparatus of fig. 2. Preferably, however, the measurement is performed using an external measurement device. The reference values obtained from these measurements are preferably used as input parameters for the control unit 40.
To determine the concentration of the film-forming amine in the process liquid, the control unit 40 operates the metering valves 24, 26 in the inlet lines 18, 20 to introduce predetermined amounts of process liquid and buffer solution into the mixing chamber 12 to form a sample solution. The amount of the treatment liquid used to form the sample solution is the same as the amount of water used to prepare the diluted buffer solution. The pH of the sample solution is measured in the mixing chamber 12 by a pH sensor 38. Then, the control unit 40 compares the measured pH value of the sample solution with the reference pH value of the diluted buffer solution, and calculates the amount of strong acid that must be added to the sample solution so that the pH value of the sample solution matches the reference pH value of the diluted buffer solution. Thereafter, the control unit 40 provides a signal to the metering valves 34, 36 and introduces calculated amounts of strong acid and water into the sample solution.
After the pH adjustment of the sample solution, the control unit 40 operates the metering valve 28 in the inlet line 22 for the reagent solution and mixes the reagent with the sample solution in the mixing chamber 12 to form a colored complex of the film-forming amine and the reagent. The amount of reagent added to the sample solution corresponds to the amount of reagent in the diluted buffer solution, so the reagent concentration in both solutions is the same.
The sample solution containing the reagent and the colored complex is then transferred to the luminometer 14 via the conduit 16, preferably by operation of a metering valve 42 in the conduit 16, and the absorbance of the solution is measured.
Then, the control unit 40 calculates the amount of the film-forming amine in the treatment liquid from the measured absorbance by comparing the measured absorbance of the sample solution containing the reagent and the colored complex with a calibration curve obtained by measuring the absorbance of a plurality of reference solutions containing the reagent and the colored complex at a given pH value and a known amount of the film-forming amine.
The control unit 40 may further include software for correcting the measured absorbance according to the pH value of the pH-adjusted sample solution. To perform this correction, initial absorbances are measured at a plurality of reference pH values in the range of 2.5 to 2.9, and a factor is applied to the measured absorbances to account for the difference between the pH value of the reference solution used to obtain the second calibration curve and the actual pH value of the pH-adjusted sample solution.
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