Rapid detection method for content of free water in aviation fuel

Abstract

The invention discloses a method for rapidly detecting the content of free water in aviation fuel, and belongs to the technical field of analysis and detection. The rapid detection method for the free water content in the aviation fuel comprises the following steps: filtering the aviation fuel by adopting a fluorescent film; and carrying out fluorescence test on the filtered fluorescent film, and determining the content of free water in the aviation fuel through fluorescence intensity. The relational expression between the fluorescence intensity and the free water content in the aviation fuel is y = e (6.6907 + 0.01275 x <-0.000022 > x < 2 >), and R is 0.9994; wherein y is the fluorescence intensity, x is the free water content in the aviation fuel, and R is a correlation coefficient. The specific content of the free water in the aviation fuel is quantitatively determined by measuring the fluorescence intensity on the filtered fluorescent film, quantitative detection of the content of 1-100 ppm of the free water in the aviation fuel can be achieved within 10 min, good sensitivity, accuracy and correlation are achieved, good repeatability and reproducibility are achieved, and the detection method is convenient, rapid, easy to operate and low in cost. The test speed is high.

Description

Technical Field

[0001] The present application belongs to the technical field of analysis and detection, and in particular relates to a method for rapid detection of free water content in aviation fuel. Background Art

[0002] The free water in aviation fuel will not only increase the freezing point of aviation fuel, deteriorate the low-temperature flow performance, and may form ice particles to block the oil pipeline, resulting in interruption of fuel supply and engine flameout, but also cause the failure of additives such as antistatic agents and antioxidants, thereby reducing combustion efficiency and increasing corrosiveness. At the same time, it may reduce the lubricity of the fuel, increase mechanical wear, accelerate mechanical corrosion, and cause downtime accidents, which are directly related to flight safety. Therefore, it is necessary to detect the water content in aviation fuel to ensure flight safety.

[0003] There are two methods for detecting free water in aviation fuel: one is the observation method, which is to observe whether there is free water in the aviation fuel by shaking a transparent sampling bottle containing aviation fuel under strong light. However, the detection results are severely limited by the quality of personnel and the representativeness of the samples. Only a rough judgment can be made, and the free water content cannot be determined. The other is the quantitative detection method of free water content, including GB / T260 "Determination of Water Content in Petroleum Products" and GB / T1133 "Determination of Water Content in Liquid Petroleum Products (Karl Fischer Method)". The test results are calculated through instrument testing, but there are problems such as long detection time, harsh conditions, non-portable instruments, and poor reproducibility of test results. Summary of the invention

[0004] The present application discloses a rapid detection method for free water content in aviation fuel, aiming to solve technical problems in existing detection methods such as individual errors in detection results, harsh detection conditions and poor reproducibility of test results.

[0005] In order to achieve the above purpose, the technical solution of this application is:

[0006] The first aspect of the present application provides a method for rapid detection of free water content in aviation fuel, the method comprising:

[0007] Using fluorescent membranes to filter aviation fuel;

[0008] The filtered fluorescent membrane is subjected to a fluorescence test, and the free water content in the aviation fuel is confirmed by the fluorescence intensity.

[0009] In combination with the first aspect, preferably, the relationship between the fluorescence intensity and the free water content in the aviation fuel is an exponential function relationship with the natural logarithm e as the base.

[0010] In combination with the first aspect, preferably, the relationship between the fluorescence intensity and the free water content in the aviation fuel is:

[0011] y=e^(6.6907+0.01275x-0.000022x 2 ), R is 0.9994;

[0012] Where y is the fluorescence intensity, x is the free water content in aviation fuel, and R is the correlation coefficient.

[0013] In combination with the first aspect, preferably, the fluorescent film includes a filter paper substrate and a sodium fluorescein colloidal solution compounded on one side of the filter paper substrate.

[0014] In combination with the first aspect, preferably, the filter paper substrate has a thickness of 600 μm.

[0015] In combination with the first aspect, preferably, the penetration thickness of the sodium fluorescein colloid in the filter paper substrate is 300 μm.

[0016] In combination with the first aspect, preferably, the colloidal solution of sodium fluorescein is a divalent anionic structure having a structural form of formula (1):

[0017]

[0018] In combination with the first aspect, preferably, the method for preparing the fluorescent film includes:

[0019] Dissolve fluorescein sodium and sodium hydroxide in methanol, adjust the pKa to 6.39 or above, let stand, take the supernatant and add hydroxypropyl methylcellulose to obtain a colloidal solution of fluorescein sodium;

[0020] The colloidal solution of sodium fluorescein is applied to one side of a filter paper substrate to obtain the fluorescent film.

[0021] In combination with the first aspect, preferably, the coating method includes one of spraying and printing.

[0022] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application include at least:

[0023] The rapid detection method provided in the present application reacts the fluorescent film with the free water in the aviation fuel, and quantitatively determines the specific content of free water in the aviation fuel by measuring the fluorescence intensity on the fluorescent film after filtration. It can achieve quantitative detection of 1-100ppm free water content in aviation fuel within 10 minutes, has good sensitivity, accuracy and correlation, and has good repeatability and reproducibility. The detection method is convenient, fast, simple to operate and low in cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 A physical picture of the filter paper substrate provided in the embodiments of the present application under sunlight and ultraviolet light;

[0026] Wherein, a) is under sunlight; b) is under ultraviolet light;

[0027] Figure 2 Actual pictures of the A1-fluorescent film provided in the embodiments of the present application under sunlight and ultraviolet light;

[0028] Wherein, a) is under sunlight; b) is under ultraviolet light;

[0029] Figure 3 Scanning electron microscope images of the filter paper substrate and the Al-fluorescent film provided in the examples of the present application;

[0030] Wherein, a) is a filter paper substrate; b) is an A1-fluorescent film;

[0031] Figure 4 This is a fluorescence spectrum of the A1-fluorescent film provided in the embodiment of the present application after detecting free water;

[0032] Figure 5 This is a fitting curve diagram of the fluorescence intensity and free water content in the A1-fluorescent film provided in the examples of the present application. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0034] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time. A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0035] In the following description of this embodiment, the term "at least one" refers to one or more, and "plurality" refers to two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b or c", or "at least one of a, b and c", can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0036] Those skilled in the art should understand that in the following description of the embodiments of the present application, the order of serial numbers does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0037] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

[0038] It should be noted that all raw materials and reagents in the examples of the present application were purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0039] In a first aspect, an embodiment of the present application provides a method for rapid detection of free water content in aviation fuel, the method comprising:

[0040] Using fluorescent membranes to filter aviation fuel;

[0041] The filtered fluorescent membrane is subjected to a fluorescence test, and the free water content in the aviation fuel is confirmed by the fluorescence intensity.

[0042] Among them, the fluorescent film is reacted with the free water in the aviation fuel, and the specific content of free water in the aviation fuel is quantitatively determined by measuring the fluorescence intensity on the fluorescent film after filtration. The quantitative detection of 1-100ppm free water content in aviation fuel can be achieved within 10 minutes, with good sensitivity, accuracy and correlation, and good repeatability and reproducibility. This detection method is convenient, fast, simple to operate and low in cost.

[0043] In the embodiment of the present application, the relationship between the fluorescence intensity and the free water content in the aviation fuel is an exponential function relationship with the natural logarithm e as the base. The relationship between the fluorescence intensity and the free water content in the aviation fuel is: y = e^(6.6907 + 0.01275x - 0.000022x 2), R is 0.9994; where y is the fluorescence intensity, x is the free water content in aviation fuel, and R is the correlation coefficient. 500mL of 3# jet fuel containing different ppm free water content is passed through the dry fluorescent film in turn under a peristaltic pump. After the sodium fluorescein on the surface of the membrane fully reacts with the free water in the oil, yellow-green fluorescent spots are left on the surface. As the free water content gradually increases, the number of fluorescent spots continues to rise, and the fluorescent area of ​​the membrane also slowly expands. The filtered fluorescent film is placed in a fluorescence spectrometer, and light with a wavelength of 360nm is used as the excitation light source. The sum of the intensities of all fluorescent areas on the surface of the membrane is collected, and the fluorescence emission spectrum and luminescence intensity are plotted. It can be seen that the optimal emission wavelength of all fluorescent membranes after encountering water is about 560nm, and will not shift due to changes in water content, indicating that there is a unique and definite relationship between the fluorescence properties of the membrane and the substance to be measured (free water). As the free water content increases, the fluorescence intensity of the membrane increases, and there will be no phenomenon of fluorescence intensity decreasing due to too little solid fluorescein sodium attached to the surface and a decrease in the concentration of fluorescein sodium in solution. The free water content in aviation fuel and the luminescence intensity at the best emission wavelength of the membrane are plotted and fitted. It can be seen that there is a strong correlation between the fluorescence intensity of the membrane and the free water content in the fuel oil. The fitted correlation expression is y=e^(6.6907+0.01275x-0.000022x 2 ), the correlation coefficient reached (R-Square) 0.9994.

[0044] In the embodiment of the present application, the fluorescent film includes a filter paper substrate and a colloidal solution of sodium fluorescein compounded on one side of the filter paper substrate. The filter paper substrate has good hydrophilicity, and the thickness of the filter paper substrate is preferably 600 μm, which can ensure the smooth passage of aviation fuel. Sodium fluorescein can react chemically with free water and emit fluorescence under the action of ultraviolet light. Therefore, it is possible to judge whether there is free water in the aviation fuel by observing whether fluorescence occurs, and the detection result will no longer produce errors due to individual discrimination differences, thereby improving the accuracy of the detection result. In addition, there is a strong correlation between the fluorescence intensity and the free water content in the fuel oil, and the specific content of free water in the aviation fuel can be quantitatively determined by measuring the fluorescence intensity, thereby realizing the quantitative determination of the free water content in the aviation fuel.

[0045] It should be noted that the fluorescent film used in this application is a filter paper surface modified on one side by a colloidal solution of sodium fluorescein. When determining the free water in aviation fuel, the aviation fuel is filtered through the side containing the colloidal solution of sodium fluorescein. If the fluorescent film is prepared into a double-sided one, the free water is evenly dispersed in the oil sample when filtering the oil sample. When a water drop passes through the membrane, the sodium fluorescein changes color and the effective fluorescent spots increase; but when the subsequent water droplets pass through the same position of the membrane, no effective fluorescent spots will be added, which is equivalent to the free water that passes later not being detected. Therefore, in order to make each drop of free water produce an effective fluorescent spot, sodium fluorescein must be present on both sides of the filter paper, and the fluorescence intensity of both sides must be detected when statistics are performed. However, the double-sided detection time is greatly increased, but the single-sided one can detect most of the free water in the range of 1-100ppm. Therefore, choosing a single-sided fluorescent film can save costs and reduce detection time.

[0046] It should be noted that the free water fluorescent indicator material prepared in the present application can achieve quantitative detection of 1-100 ppm free water in aviation fuel within 10 minutes, and the detection limit achieved is far lower than the standard requirement (30 ppm) of my country's petroleum products industry that the free water in aviation fuel should not exceed 30 ppm.

[0047] It should be noted that sodium fluorescein is a sodium salt derivative of fluorescein and has good solubility in water. The polycyclic molecular structures of fluorescein itself, such as benzene ring, thiophene ring, pyridine ring, etc., give sodium fluorescein excellent photoluminescent properties. Its dilute solution can emit bright yellow-green fluorescence under ultraviolet light, and the optimal emission wavelength is about 560nm. With the increase of solution concentration, the molecular aggregation phenomenon is obvious, the fluorescence intensity is greatly weakened, and even fluorescence quenching occurs in the solid state. Under normal circumstances, the structure of sodium fluorescein in solution is relatively stable. In a neutral environment, it often exists in the form of quinone type, zwitterion type and ester type molecules. When the pH of the solution changes, sodium fluorescein participates in acid-base balance and the molecular structure changes accordingly. In an acidic environment, sodium fluorescein is often mainly in the form of cations; while in an alkaline environment, the concentrations of monovalent anions and divalent anions increase successively. In addition, the luminescence intensity of the sodium fluorescein solution also changes accordingly with the change of the molecular structure. When sodium hydroxide is continuously added to the neutral solution of sodium fluorescein, the pH value of the solution increases, the monoanionic and divalent anionic sodium fluorescein increases continuously, and the fluorescence intensity of the solution increases immediately. After the neutral sodium fluorescein is completely converted into a divalent anionic state, the fluorescence intensity of the solution reaches the highest. After the dianionic sodium fluorescein solution is dried, the sodium fluorescein can remain in the divalent anionic state. After contacting water, the fluorescence is activated again. This is the key basis for ensuring that the fluorescent film can respond sensitively to free water in the fuel. The structural formulas of the sodium fluorescein molecule in different solutions are shown below:

[0048]

[0049] It should be noted that the pKa of the solution when the cationic sodium fluorescein changes to the neutral state is 2.24, the pKa of the solution when the neutral state changes to the monovalent anion state is 4.20, and the pKa of the solution when the monovalent anion state changes to the divalent anion state is 6.39. Adjusting the pKa of the sodium fluorescein colloidal solution to above 6.39 is the key to preparing the fluorescent indicator material.

[0050] It should be noted that the pKa of the sodium fluorescein colloidal solution is adjusted to be above 6.39, and the sodium fluorescein colloidal solution is a divalent anionic structure having a structural form of formula (1):

[0051]

[0052] In an embodiment of the present application, the preparation method of the fluorescent film includes: dissolving sodium fluorescein and sodium hydroxide in methanol, adjusting the pKa to 6.39 or above, taking the supernatant after standing, adding hydroxypropyl methylcellulose, and obtaining a colloidal solution of sodium fluorescein; applying the colloidal solution of sodium fluorescein on the surface of the substrate to obtain the fluorescent film. In order to adjust the pKa to 6.39 or above, sodium hydroxide is used to adjust the pH to 12-14, so that the sodium fluorescein can be controlled to be a divalent anionic structure.

[0053] It should be noted that hydroxypropyl methylcellulose is added to prepare the colloidal solution of sodium fluorescein. Hydroxypropyl methylcellulose is alcohol-soluble, which can, on the one hand, make the colloidal solution of sodium fluorescein deposited on one side of the filter paper basement membrane, which is beneficial to control the penetration thickness of the filter paper basement membrane, and on the other hand, it is beneficial to shorten the distance between the sodium fluorescein molecules, so that it can be stably and evenly distributed on the filter paper basement membrane, thereby presenting an aggregation-induced quenching state in a dry state.

[0054] In the embodiment of the present application, the coating method is preferably one of spraying and printing. Among them, by spraying or printing, the colloidal solution of sodium fluorescein is deposited on one side of the filter paper base film, which can effectively control the penetration thickness, thereby realizing the quantitative detection of the free water content in the aviation fuel, and improving the accuracy of the detection result.

[0055] It should be noted that the quantitative detection results in the rapid detection method provided in the present application are greatly improved in reliability and repeatability compared with the traditional Karl Fischer method, which is of great significance for the design of a portable free water detection instrument based on fluorescent membrane.

[0056] The technical solution of the present application will be further described below in conjunction with specific embodiments.

[0057] Example 1

[0058] This embodiment provides a method for preparing an Al-fluorescent film, which specifically includes:

[0059] S101: dissolving sodium fluorescein in methanol to prepare a sodium fluorescein-methanol saturated solution, and after standing, taking the clarified liquid and continuously adding sodium hydroxide particles to adjust the pKa of the solution to 6.39. After standing, taking the supernatant and adding hydroxypropyl methylcellulose and stirring until dissolved to obtain a colloidal solution of sodium fluorescein;

[0060] S102: Spraying the colloidal solution of sodium fluorescein onto the filter paper substrate to obtain an A1-fluorescent film.

[0061] The filter paper substrate of Example 1 was tested under sunlight and ultraviolet light respectively. Figure 1 As shown, the selected filter paper substrate has a flat and smooth surface, has no obvious fluorescence under ultraviolet light, and is about 600 μm thick, which can ensure that the fluorescent membrane has strong resistance to damage and bending during use.

[0062] The colloidal solution of sodium fluorescein was sprayed onto the filter paper substrate, and the A1-fluorescent film was tested under sunlight and ultraviolet light, respectively. Figure 2 As shown, in the dry state, it appears orange in sunlight and has no fluorescence under ultraviolet light. When it comes into contact with water, the fluorescence is activated and the surface turns yellow. At the same time, it emits yellow-green fluorescence after being irradiated with ultraviolet light.

[0063] The filter paper substrate and A1-fluorescent film were examined by scanning electron microscopy. Figure 3 As shown, Figure 3 (a) is the SEM photo of the filter paper substrate before and after coating with solid sodium fluorescein. It can be seen from the figure that the pore diameter of the filter paper substrate before coating is about 5μm, and (b) the pore size of the membrane after coating has not changed, which is smaller than the particle size of free water in aviation dye (>14μm), laying a foundation for effectively intercepting free water particles in fuel oil, prolonging the reaction time of free water and solid sodium fluorescein, and improving the detection accuracy of free water by the membrane.

[0064] Example 1 of the present application investigates the application of the A1-fluorescent film in the quantitative determination of the free water content in 3# jet fuel. The specific method is as follows: 4L of aviation kerosene containing saturated dissolved water is used as a standard oil sample, 1ppm, 10ppm, 20ppm, 30ppm, 40ppm, 50ppm, and 100ppm of free water are added to the standard oil sample respectively, and the mixture is stirred and mixed at a constant temperature to obtain 7 water-containing aviation kerosene samples. The 3# jet fuel containing free water is pumped through the fluorescent film. After the test, the membrane is placed in a fluorescence spectrometer, and light with a wavelength of 360nm is used as an excitation light source. The total intensity of all fluorescent areas on the surface of the membrane is collected, and the fluorescence emission spectrum and luminescence intensity are tested. The results are shown in Table 1 below:

[0065] Table 1 Fluorescence intensity of the fluorescent film after testing the standard oil sample and 5 water-containing aviation kerosene samples

[0066] sample Optimal emission wavelength Fluorescence intensity (au) Standard oil sample 560nm 0 Standard oil sample + 1ppm free water 560nm 815.2 Standard oil sample + 10ppm free water 560nm 927.5 Standard oil sample + 20ppm free water 560nm 1025 Standard oil sample + 30ppm free water 560nm 1168 Standard oil sample + 40ppm free water 560nm 1288 Standard oil sample + 50ppm free water 560nm 1441 Standard oil sample + 100ppm free water 560nm 2321

[0067] According to Table 1 and Figure 4 The results show that the optimal emission wavelength of all fluorescent films after contact with water is about 560nm, and will not shift due to changes in water content, indicating that there is a unique and definite relationship between the fluorescence properties of the membrane and the substance to be tested (free water). And as the free water content increases, the fluorescence intensity of the membrane increases, and there will be no phenomenon of fluorescence intensity decrease due to too little solid fluorescein sodium attached to the surface and a decrease in the concentration of fluorescein sodium in solution.

[0068] This application uses the least squares method to fit the correlation between fluorescence intensity and free water content in fuel oil, and uses binomial fitting to obtain the following functional relationship:

[0069] y=e^(6.6907+0.01275x-0.000022x 2 ), the correlation coefficient R-Square reached 0.9994.

[0070] Among them, y is the fluorescence intensity generated by the corresponding fluorescent film, x is the free water content in the fuel oil, and the fitting curve is as follows Figure 5 shown.

[0071] The functional relationship was used to verify the free water content in 3# jet fuel with different contents, and the actual test was carried out using a fluorescent film. The results are shown in Table 2:

[0072] Table 2 Actual test results of free water content in aviation kerosene samples with different water contents and calculation results based on fitting curves

[0073]

[0074] As can be seen from Table 2, the present invention has high sensitivity, high accuracy and good repeatability in testing the free water content in aviation kerosene. Therefore, the fluorescent film prepared in the present invention can achieve quantitative detection of 1-100 ppm free water content in aviation fuel within 10 minutes, has good sensitivity, accuracy and correlation, and has good repeatability and reproducibility. The detection method is convenient and fast, simple to operate, and has a fast test speed.

[0075] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0076] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit the present application. Although the present application has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions recorded in the aforementioned embodiments may still be modified, or some or all of the technical features therein may be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A method for rapid detection of free water content in aviation fuel, characterized in that: The method comprises: Using fluorescent membranes to filter aviation fuel; The filtered fluorescent membrane is subjected to a fluorescence test, and the free water content in the aviation fuel is confirmed by the fluorescence intensity.

2. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The relationship between the fluorescence intensity and the free water content in the aviation fuel is an exponential function relationship with the natural logarithm e as the base.

3. The method for rapid detection of free water content in aviation fuel according to claim 2, characterized in that: The relationship between the fluorescence intensity and the free water content in the aviation fuel is: y=e^(6.6907+0.01275x-0.000022x 2 ), R is 0.9994; Where y is the fluorescence intensity, x is the free water content in aviation fuel, and R is the correlation coefficient.

4. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The fluorescent film comprises a filter paper substrate and a sodium fluorescein colloid solution compounded on one side of the filter paper substrate.

5. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The thickness of the filter paper substrate is 600 μm.

6. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The penetration thickness of the sodium fluorescein colloidal solution in the filter paper substrate is 300 μm.

7. The rapid detection method for free water content in aviation fuel according to claim 1, characterized in that: The fluorescein sodium colloidal solution is a divalent anionic structure having a structural form of formula (1):

8. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The preparation method of the fluorescent film comprises: Dissolve fluorescein sodium and sodium hydroxide in methanol, adjust the pKa to 6.39 or above, let stand, take the supernatant and add hydroxypropyl methylcellulose to obtain a colloidal solution of fluorescein sodium; The colloidal solution of sodium fluorescein is applied to one side of a filter paper substrate to obtain the fluorescent film.

9. The method for rapid detection of free water content in aviation fuel according to claim 1, characterized in that: The coating method includes spraying and printing.

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