HK1145539B - Method for determination of polymer concentration in water systems - Google Patents

Description

Method for determining the concentration of a polymer in an aqueous system

Background

Technical Field

The present invention relates generally to the detection of water soluble polymers in industrial water systems, such as cooling and boiler water systems. And more particularly to a method for determining the concentration or availability of anionic water-soluble polymers in industrial water systems based on the interaction of cationic dyes and water-soluble polymers.

Description of the related Art

It is well known to use water in various industrial processes, such as heat dissipation in process equipment and steam generation. However, in most industrial processes it is not possible to use untreated water, since the presence of impurities may affect the industrial process. For example, scale-forming inhibiting compounds are added to cooling towers and boiling water to prevent the formation or placement of scale in equipment used in these processes.

Most industrial waters contain metal cations such as calcium, barium, magnesium and sodium and anions such as bicarbonate, carbonate, sulfate, phosphate and fluoride. When the cation and anion combination is above a certain concentration, the reaction product precipitates on equipment surfaces in contact with the water in the process and forms scale or deposits. The presence of such scale or deposits results in non-optimal process conditions and results in costly and burdensome cleaning or removal of such scale or deposits, typically requiring process or system downtime. Therefore, in order to prevent the formation of such scale or deposits, it is preferable to treat the water with an appropriate chemical to suppress the formation thereof.

The formation of scale and deposits can be avoided by ensuring that the solubility of the cation-anion reaction products is not exceeded. Certain chemicals are known for this purpose, including water soluble polymers such as polymers derived from unsaturated carboxylic acid esters and unsaturated sulfonic acid esters and their salts. Some particularly useful water-soluble polymers include HPS-I, AEC, APES, and polyepoxysuccinic acid (all available from GE Beta, Trevose, Pa.), further described in U.S. Pat. Nos. 5,518,629, 5,378,390, 5,575,920, 6,099,755, 5,489,666, 5,248,483, 5,378,372, and 5,271, \\ 862. However, the presence of these polymers leads to additional related problems, which necessitate careful monitoring of the polymer concentration in the industrial water system. If too little polymer is used, scale may still be present, while with too much polymer, the treatment may not be cost effective. For each given system, it is desirable to achieve an optimal concentration level or range.

Methods for determining the concentration of water-soluble polymers in an aqueous system are known. For example, many methods use dyes to determine the content of a particular component. U.S. patent 4,894,346 describes a method for determining polycarboxylates in aqueous systems using calorimetry using specific cationic dyes. U.S. patent No. 6,214,627 to Ciota et al measures the concentration of anionically charged polymer in an aqueous solution containing a reactant, water, a nile blue dye and a chelating agent. In addition, the Hach polyacrylic acid method detects polyacrylic acid-based corrections with iron thiocyanate chelation. Other methods include monitoring industrial waters using luminol-labeled polymers in combination with fluorescent or chemiluminescent detection techniques, such as described in U.S. patent 5,958,778. Many cationic dyes are unstable in solution, as described in U.S. patent No. 6,524,350. In this patent, it is described that pinacyanol chloride is unstable in aqueous solution. However, these methods have many drawbacks, including instability in aqueous systems, narrow dynamic range, interference with natural polymers and sample ionic strength.

The current methods have a number of problems, particularly interference by various factors and components. Thus, there is a need for a simplified and more accurate test method that can be easily used to determine the concentration of water-soluble polymers in aqueous solutions, that exhibits high reproducibility, reduced response to disturbances, and improved stability.

Summary of The Invention

In one aspect, the invention relates to a method of determining the concentration of an anionic polymer or oligomer in industrial water, the method comprising mixing a buffer solution and a cationic dye solution, measuring the absorbance of the buffer-dye mixture at a selected wavelength and determining the polymer or oligomer concentration by a predetermined absorbance value.

In alternative embodiments of the present invention, the buffer solution may be a multifunctional buffer solution, and may contain a variety of buffers, masking agents and/or stabilizers, and combinations thereof. Other embodiments provide that a plurality of dyes may be used.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and benefits obtained by its uses, reference is made to the accompanying drawings and descriptive matter. The drawings are intended to depict examples of the invention in its various forms. The drawings are not intended to limit all of the ways in which the invention can be made and used. Various components of the present invention may be modified and substituted. The invention also resides in sub-combinations and sub-systems of the elements described and methods of using them.

Brief Description of Drawings

FIG. 1 depicts the change in absorbance of 1, 9-dimethylmethylene blue at 530, 593 and 647nm as a function of polymer HPS-I concentration.

FIG. 2 depicts the change in absorbance of azure B at 593nm as a function of polymer HPS-I concentration.

FIG. 3 depicts the change in absorbance of Brilliant Crystal Blue (Brilliant Crystal Blue) as a function of the concentration of HPS-I in the polymer.

FIG. 4 depicts the change in absorbance at 585nm of Bright Crystal Blue (BCB) as a function of solution conductivity for a concentration of 2ppm of polymer HPS-I.

FIG. 5 depicts the precipitation of DMMB dye after the addition of HPS-1.

Fig. 6 depicts the same experiment as fig. 5, but with 40ppm gum arabic added.

FIG. 7 depicts the use of Mn²⁺As a masking agent for AEC.

Fig. 8 depicts a calibration curve for the DCA 247.

Detailed Description

Although the present invention has been described with reference to preferred embodiments, various modifications or substitutions may be made by those skilled in the art to which the present invention pertains without departing from the technical scope of the present invention. Therefore, the technical scope of the present invention encompasses not only those embodiments described but also all embodiments falling within the scope of the claims.

Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as "about," is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Range limitations may be combined and/or interchanged with ranges identified and including all the sub-ranges contained therein unless context or language indicates otherwise. Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term "about".

The terms "comprises," "comprising," "including," "contains," "having," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

Embodiments of the present invention include improved methods for determining the concentration of anionic polymers and/or oligomers in a sample of industrial water. The methods disclosed and claimed herein are particularly useful for rapidly and accurately determining the concentration of anionic polymer corrosion or scale inhibitors in aqueous systems, including but not limited to boilers, cooling towers, evaporators, gas wash towers, kilns, and desalters. This method includes using a predetermined calibration curve for optimal efficiency and effectiveness. Polymers that can be detected by the method of the present invention include, but are not limited to, water soluble anionic polymers containing anionic groups such as carboxylate, sulfonate, sulfate, phosphonate, phosphate. The same examples are polyacrylic acid partial polymers, polysulfonated polymers and maleic anhydride polymers. Some specific examples of anionic polymers that are contemplated are HPS-1, AEC and APES (GE Betz, Trevose, Pa.).

One factor to be evaluated for any particular polymer is the degree of interaction of the polymer with the dye. This factor can be determined by plotting the change in absorbance of the dye as a function of the particular polymer. To determine the absorbance change of the dye composition, the initial absorbance of the dye composition is measured at any wavelength of the visible spectrum from 300 to 700nm at a set time after mixing the composition. In the present application, these measurements are repeated as a function of the concentration of the particular polymer. FIG. 1 shows, as an example, the variation in the absorbance of 1, 9-dimethylmethylene blue (DMMB) at 530, 593 and 647nm as a function of the polymer HPS-I (acrylic acid/1-allyloxy, 2-hydroxypropanesulfonate) and its concentration. FIG. 2 shows the absorbance change at 593nm as a function of HPS-I for the alternative dye Azure B (AB). Thus, the degree of interaction of a particular dye with any polymer (such as, but not limited to, HPS-I) can be quantified. For those skilled in the art, FIGS. 1 and 2 clearly show that DMMB interacts much more strongly with HPS-I than AB interacts with HPS-I.

Another factor to be considered in embodiments of the present invention is the ionic strength effect. FIG. 3 shows the absorbance of Bright Crystal Blue (BCB) dye at 585nm as a function of HPS-I polymer concentration. Comparing FIG. 3 and FIG. 2, it is shown that BCB interacts with HPS-I even more weakly than AB interacts with HPS-I. Accordingly, the weaker the interaction, the less desirable the dye and polymer combination.

FIG. 4 depicts another factor that may be considered in an embodiment of the present invention. Specifically, FIG. 4 shows the change in absorbance of BCB at 585nm as a function of solution conductivity for a HPS-I polymer concentration of 2 ppm. Conductivity values are a quantitative indicator of ionic strength. BCB has an ionic strength effect, thus indicating that BCB is not a good dye for HPS-I determination in real water samples, since it is too difficult to control the ionic strength of the sample. The information from fig. 4, in conjunction with the information identified in fig. 1 and 2, illustrates the need to select the appropriate dye to obtain the most accurate value for the polymer or oligomer in the aqueous solution. In particular, the dyes used need to have a strong interaction with the polymer in question in order to minimize possible interference from the aqueous matrix. To date, methods that take into account the combined effects of factors such as polymer/dye interactions, ionic strength, and solution conductivity are not known. The data obtained from studying these interactions led to the claimed method of the present invention.

Cationic and anionic dyes and polymers are water soluble due to the charge; i.e. they carry a positive or negative charge. When the dye forms a complex with the polymer, the total ionic charge carried by the complex is reduced because the charges neutralize each other. One example is the interaction of a negatively charged dye with a positively charged polymer. As a result of this interaction, it is possible to precipitate the dye-polymer complex from the test system. This effect can be problematic, particularly in cases where the aqueous system is the factor with high hardness. In one embodiment of the present invention, a multifunctional buffer may be added to address some of the factors that limit the ability to rapidly and accurately measure the presence of polymers and/or oligomers in aqueous solutions. Multifunctional buffers are compositions or solutions that include, but are not limited to, stabilizers, sequestering agents, and/or pH buffers, and combinations thereof. Such multifunctional buffers are unknown and not used in the prior art and provide a great role in the interference problem with accurately measuring the polymer/oligomer concentration in a solution. The use of this multifunctional buffer solves the problems of selectivity and stability by minimizing or eliminating factors that affect the efficient and effective determination of polymer concentration and makes the process of the present invention practical for use in today's industrial facilities.

One embodiment of the present invention includes the addition of a stabilizer to more accurately determine the concentration of polymer/oligomer in the aqueous solution. The addition of stabilizers can help solve the problems of precipitation and experimental instability. FIG. 5 shows that after addition of the polymer (in this case HPS-I), DMMB rapidly precipitated from the test solution. Figure 6 shows the same experiment with polymer interaction, but with the addition of a stabilizer, showing reduced precipitation. In particular, figure 6 shows that DMMB did not precipitate as much or as fast after addition of the polymer HPS-1 due to the presence of the stabilizer (gum arabic in this case). On-line or automated applications require stability tests without precipitation, which can lead to e.g. fluid clogging and deposition at the optical window. The stabilizer may be added in various amounts, for example, from about 10ppm to about 100ppm, or from about 30ppm to about 50 ppm.

Another embodiment of the present invention provides for masking surfactants that may be present with the polymer and/or oligomer. Anionic surfactants can be effectively masked by the addition of a masking agent to the multifunctional buffer. By adding such masking agents, the reading of the polymer concentration is more accurate. FIG. 7 shows that 490ppm of Mn is present in the buffer²⁺At this time, 5ppm of polyepoxysuccinic acid (PESA) did not respond to the dye. Dodecylbenzene sulfonate is an example of another anionic surfactant that can be masked by the addition of cationic surfactants to an aqueous system. The amount of masking agent is from 20ppm to about 2000ppm, further from about 100ppm to about 1000 ppm. Masking agents include, but are not limited to, divalent manganese salts, ferrous salts, calcium salts, zinc salts, quaternary amine surfactants, or combinations thereof.

Certain components are naturally present in water and aqueous systems. For example, tannic acid is a natural component present in surface water. Tannic acid can cause serious interference with metachromatic dye-based colorimetry when measuring anionic polymer (e.g., synthetic anionic polymer) concentrations. It has been found that the polymers HPS-I and PESA are not responsive to cationic dyes such as, but not limited to, basic blue 17 when high hardness concentrations of water are present. However, tannic acid exhibits a sensitive response to dyes such as basic blue 17(BB17) in the presence of high hardness concentration aqueous systems. Thus, an alternative embodiment of the present invention requires a two-dye method to determine the anionic polymer concentration (e.g., HPS-I) and the tannic acid concentration. This can be accomplished by first measuring the total response of an aqueous system to a cationic dye such as DMMB, where the aqueous system comprises tannic acid and an anionic polymer such as HPS-I. A second cationic dye, such as BB17, is then exposed to the aqueous system and the absorbance response from the exposure is measured. Since the second dye (in this case BB17) is not responsive to the anionic polymer (in this case HPS-I), the absorbance measured with this second dye is clearly correlated with the other components (e.g. tannic acid). Thus simply subtracting the second component or concentration of component measured with the second dye from the initial reading of the total response gives a measure of the anionic polymer in the system (i.e. in this case the HPS-I concentration).

In one embodiment of the invention, a method of determining the concentration of an anionic polymer or oligomer in an industrial water sample comprises adding a multifunctional buffer solution to the industrial water sample, then adding a cationic dye solution to the buffered water sample to obtain a mixture, measuring the absorbance of the mixture at a selected wavelength, and determining the concentration of the polymer or oligomer from the absorbance values based on a predetermined calibration equation. Calibration of a particular polymer is determined by plotting the absorbance at a set wavelength as a function of polymer concentration.

A portion or sample of the industrial water sample may be any convenient amount of an aqueous solution containing a polymer or oligomer compound. Additionally, pretreatment of the water sample may be desirable, such as filtering the sample to remove particulates, adding an effective amount of a reducing agent to reduce chlorine and/or ferric ions (if present), thereby minimizing interference from these components.

The dyes are selected from metachromatic dyes, which are dyes that change color upon interaction with a polyionic compound. Cationic dyes include, but are not limited to, dimethyl methylene blue, basic blue 17, new methylene blue, and combinations thereof. One embodiment of the present invention calls for the use of 1, 9-dimethylmethylene blue as the cationic dye. The cationic dye is added in an effective amount, typically about 0.5 to about 3.0 times the molar concentration of the polymer in the test.

Alternative embodiments of the present invention require the use of a second or additional multifunctional buffer. In this embodiment, a method for determining the concentration of an anionic polymer or oligomer in an industrial water sample using differential masking comprises adding a first multifunctional buffer solution to a portion of the sample, followed by adding a cationic dye solution to the sample-buffer mixture to obtain a mixture; measuring the absorbance of the mixture at the selected wavelength, then adding a second multifunctional buffer to a second portion of the industrial water sample to obtain a second buffer-water mixture, adding a cationic dye solution to the second buffer-water mixture, measuring the absorbance of the mixture obtained from the second mixture, and determining the concentration of the polymer and oligomer from the two absorbance values according to a predetermined calibration equation. In one embodiment, the use of two multifunctional buffer solutions is included, the multifunctional buffer including at least one masking agent, which may be the same or different in each buffer solution, and present in the same or different amounts in the buffer solutions, and any combination thereof.

Another embodiment of the present invention follows the above steps, but differs in that the sample is determined by deriving a background correction, using a second or alternative cationic dye mixed with a second water-buffer mixture to form a second mixture. In this case, therefore, the method includes adding a multifunctional buffer solution to a portion of the water sample, adding a first cationic dye solution to the initial sample-buffer mixture, measuring the absorbance of the initial mixture at a selected wavelength, and then repeating these steps, wherein the first cationic dye solution is replaced with a second cationic dye solution. The polymer and oligomer concentrations were then derived from the absorbance values obtained in the above method and using a predetermined calibration equation.

The absorbance used in the present invention can be determined using the Lambert-Beer law as follows:

A＝abc

wherein a is absorbance; a ═ absorbance of the dye (absorbance); b is the optical path length; c is the concentration of the colored substance. The dye used has a maximum absorbance in the range of 300 to 1000nm, and the absorbance is desirably measured at a wavelength in the range of the maximum absorbance.

The absorbance may be measured using any suitable device known in the art for measuring absorbance. Suitable devices include, but are not limited to, colorimeters, spectrophotometers, color wheels, and other types of well-known color comparison measurement tools. One embodiment provides for measuring the optical response using an optical system that includes a white light source (e.g., a tungsten lamp available from Ocean Optics, Inc of Dunalin, FL) and a portable spectrometer (e.g., Model ST2000 available from Ocean Optics, Inc. of Dunalin, FL). Desirably, the spectrometer used covers a spectral range of about 250nm to about 1100 nm.

To determine the concentration or amount of anionic polymer present in an industrial water system, a calibration curve needs to be first generated for each target polymer. Calibration curves were generated by preparing different samples of water containing known amounts of polymer, preparing appropriate reactant solutions and measuring the absorbance of the samples using the reactant solutions. In one embodiment of the invention, the absorbance is reported as the difference in absorbance. The absorbance difference is the difference between the absorbance of the reactant solution itself and the absorbance of the mixture of the reactant solution and the tested water sample. The calibration curve is thus a plot of this absorbance difference versus the known concentration of polymer in the sample. Once the calibration curve is generated, the calibration curve can be used to indicate how much polymer is present in the sample by comparing the sample measured absorbance difference to the curve and reading the amount of corresponding polymer on the curve. An example of this curve is shown in fig. 8, which depicts a calibration curve for the DCA 247.

It should be understood that various changes and modifications to the embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.

The present invention is illustrated in the following non-limiting examples, which are for illustrative purposes only and are not to be construed as limiting the scope of the invention. All parts and percentages in the examples are by weight unless otherwise indicated.

Examples

A calibration curve for DCA 247(GE Betz, Trevose, PA) was determined. A solution of 1, 9-dimethylmethylene blue (DMMB) containing 100ppm of DMMB in deionized water was prepared. The buffer had a pH of 4.2 and was prepared from 0.1M acetic acid and 1M sodium hydroxide in deionized water. The buffer solution contained 100ppm of gum arabic as a stabilizer and 5000ppm of manganese sulfate monohydrate as a masking agent to eliminate interference of polyepoxysuccinic acid (PESA). The absorbance was measured at 525nm and plotted as a function of the concentration of DCA 247. The calibration equation is y ═ 0.0311x +0.207, and R²0.9984. The results are shown in FIG. 12.

Claims (14)

1. A method of determining the concentration of an anionic polymer or oligomer in an industrial water sample, the method comprising:

(a) adding a multifunctional buffer solution to the sample, wherein the multifunctional buffer solution contains at least one masking agent selected from the group consisting of divalent manganese salts, ferrous salts, calcium salts, zinc salts, quaternary amine surfactants, or combinations thereof;

(b) adding a cationic dye solution to the buffer-sample mixture of step (a);

(c) measuring the absorbance of the mixture of step (b) above at one or more selected wavelengths; and

(d) determining the polymer or oligomer concentration from the absorbance values measured in step (c) according to a predetermined calibration equation.

2. The method of claim 1, wherein said multifunctional buffer of step (a) further comprises a stabilizer or a pH buffer.

3. The method of determining the concentration of an anionic polymer or oligomer in an industrial water sample of claim 1 by differential masking, the method comprising:

(a) adding a first multifunctional buffer solution to a portion of said sample;

(b) adding a cationic dye solution to the sample-buffer mixture of step (a);

(c) measuring the absorbance of the mixture of step (b) at one or more selected wavelengths;

(d) adding a second multifunctional buffer to a second portion of said sample;

(e) adding the cationic dye solution to the sample-buffer mixture of step (d);

(f) measuring the absorbance of the mixture obtained in step (e);

(g) determining polymer and oligomer concentrations from the absorbance values obtained in step (c) and step (f) according to a predetermined calibration equation, wherein the first and second multifunctional buffers each contain at least one masking agent selected from divalent manganese salts, ferrous salts, calcium salts, zinc salts, quaternary amine surfactants, or combinations thereof.

4. The method of claim 3, wherein said first multifunctional buffer of step (a) further comprises a stabilizer or a pH buffer.

5. The method of claim 3, wherein said second multifunctional buffer of step (d) further comprises a stabilizer or a pH buffer.

6. The method of claim 3, wherein said first multifunctional buffer comprises at least one masking agent, wherein said masking agent is different from the masking agent of the second multifunctional buffer.

7. The method of claim 3, wherein said first multifunctional buffer contains a masking agent that is present in an amount that is not the same as the amount of masking agent present in the second multifunctional buffer.

8. The method of claim 1 or 3, wherein the cationic dye is selected from the group consisting of dimethyl methylene blue, basic blue 17 and new methylene blue N and combinations thereof.

9. The method of any one of claims 2, 4 or 5, wherein the stabilizing agent is gum arabic.

10. The method of determining the concentration of an anionic polymer or oligomer in an industrial water sample of claim 1 by interference background correction using a second dye solution, the method comprising:

(a) adding a multifunctional buffer solution to a portion of said sample, wherein said multifunctional buffer solution comprises at least one masking agent selected from the group consisting of divalent manganese salts, ferrous salts, calcium salts, zinc salts, quaternary amine surfactants, or combinations thereof;

(b) adding a first cationic dye solution to the sample-buffer mixture of (a);

(c) measuring the absorbance of the mixture of step (b) at one or more selected wavelengths;

(d) repeating steps (a), (b) and (c), wherein the first dye solution is replaced with a second dye solution;

(e) obtaining polymer and oligomer concentrations from the absorbance values obtained in step (c) and step (d) and using a predetermined calibration equation.

11. The method of claim 10, wherein the first cationic dye is selected from the group consisting of dimethyl methylene blue, basic blue 17, and new methylene blue N, and combinations thereof.

12. The method of claim 10, wherein the second cationic dye is selected from the group consisting of dimethyl methylene blue, basic blue 17, and new methylene blue N, and combinations thereof.

13. The method of claim 10, wherein the first cationic dye and the second cationic dye are selected from the group consisting of dimethyl methylene blue, basic blue 17, and new methylene blue N, and combinations thereof, but the first cationic dye is different from the second cationic dye.

14. The method of claim 10, wherein said multifunctional buffer of step (a) further comprises a stabilizer, a pH buffer, and combinations thereof.