A detection and analysis method for lubricating oil degradation based on fluorescent carbon dots

Abstract

The present invention belongs to the technical field of lubricating oil analysis, and specifically relates to a detection and analysis method for lubricating oil degradation based on fluorescent carbon dots. The detection and analysis method provided by the present invention comprises: measuring the fluorescence intensity of a fluorescent carbon dot solution to obtain a blank fluorescence intensity value; mixing the lubricating oil to be tested and the fluorescent carbon dot solution; measuring the fluorescence intensity of the obtained mixed solution of the lubricating oil to be tested to obtain a fluorescence intensity value of the lubricating oil to be tested; substituting the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the lubricating oil to be tested into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested. The analysis method provided by the present invention uses fluorescent carbon dots as probes to analyze the degradation degree of lubricating oil. Compared with the existing analysis methods: infrared absorption spectrum analysis method, X-ray spectrum method and electrical analysis method, the analysis method provided by the present invention not only has a simple analysis process and fast analysis data, but also has accurate analysis results and high sensitivity.

Description

Technical Field

[0001] The invention belongs to the technical field of lubricating oil analysis, and in particular relates to a detection and analysis method for lubricating oil degradation based on fluorescent carbon dots. Background Art

[0002] As a lubricating medium to reduce friction and wear of mechanical equipment, lubricating oil is an important guarantee for the normal operation of equipment. However, due to the influence of frictional heat and external interference, the performance of lubricating oil will degenerate and deteriorate, and it will no longer be able to reduce the damage caused by friction to the equipment, thereby threatening the safe, reliable and economical operation of the equipment. Therefore, in order to realize the diagnosis and monitoring of the tribological state of mechanical equipment, the application of lubricating oil analysis technology, which analyzes various tribological information contained in lubricating oil, was born.

[0003] Specifically, lubricating oil analysis technology is a technology that uses light, electricity, magnetism and other means to analyze the physical and chemical indicators of lubricating oil used in mechanical equipment and the wear and contamination particles it carries, obtain information related to the lubrication and wear status of the equipment, qualitatively and quantitatively describe the wear status of the equipment, evaluate the health status of the equipment, and determine the location, cause and type of the fault. It is the main field of tribological fault diagnosis and one of the products of the continuous development of modern industry. Since the 1940s, lubricating oil analysis technology has gradually developed and been widely used in the fields of transportation, military, production and manufacturing, bringing considerable economic benefits to social development. In particular, the development trend of large-scale, complex, continuous and even intelligent modern industrial machinery and equipment has greatly increased the economic losses caused by equipment failure maintenance and shutdown, and has placed higher and higher requirements on the operation and maintenance of equipment. This has put forward a more immediate demand for the development and application of lubricating oil analysis technology.

[0004] Existing lubricating oil analysis technologies mainly include: infrared absorption spectroscopy analysis technology, X-ray spectroscopy technology and electrical analysis technology. However, the above analysis technologies generally have problems such as complex analysis processes and redundant analysis data, which hinders the further development of analysis technology. Summary of the invention

[0005] The purpose of the present invention is to provide a detection and analysis method for lubricating oil degradation based on fluorescent carbon dots. The detection and analysis method provided by the present invention not only has a simple analysis process and fast data analysis, but also has accurate analysis results and high sensitivity.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for detecting and analyzing lubricating oil degradation based on fluorescent carbon dots, comprising the following steps:

[0008] Under the excitation wavelength condition, the fluorescence intensity of the fluorescent carbon dot solution is measured to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots;

[0009] Mixing the lubricating oil to be tested and the fluorescent carbon dot solution to obtain a lubricating oil mixed solution to be tested;

[0010] Under the same excitation wavelength condition, measuring the fluorescence intensity of the lubricating oil mixed solution to be tested, and obtaining the fluorescence intensity value of the lubricating oil to be tested;

[0011] Substituting the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the lubricating oil to be tested into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested, wherein the degradation degree includes the working time of the lubricating oil or the waste oil content in the lubricating oil;

[0012] The degradation-fluorescence fitting relationship is: the degradation degree of the lubricating oil is used as the independent variable; the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricating oil mixed solution is used as the dependent variable, and the degraded lubricating oil mixed solution is a mixed solution of a lubricating oil with a known degradation degree and a fluorescent carbon dot solution, and the lubricating oil with a known degradation degree is of the same model as the lubricating oil to be tested.

[0013] Preferably, the degradation-fluorescence fitting relationship is a degradation-fluorescence linear regression equation. When the degradation-fluorescence linear regression equation takes the working time of the lubricating oil as an independent variable, the degradation-fluorescence linear regression equation is shown in Formula 1:

[0014] y = 1.07 + 0.008x Formula 1;

[0015] In formula 1, x is the working time of the lubricant, y is the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricant mixed solution; R 2 =0.94201.

[0016] Preferably, the degradation-fluorescence fitting relationship is a degradation-fluorescence fitting curve equation. When the degradation-fluorescence fitting curve equation takes the waste oil content of the lubricating oil as an independent variable, the degradation-fluorescence fitting curve equation is shown in Formula 2:

[0017] y=8.15x 2 -0.84x+1.12 Equation 2;

[0018] In formula 1, x is the waste oil content of the lubricating oil, y is the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricating oil mixed solution; R 2 =0.9920.

[0019] Preferably, the method for establishing the degeneration-fluorescence fitting relationship comprises the following steps:

[0020] Under the excitation wavelength condition, the fluorescence intensity of the fluorescent carbon dot solution is measured to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots;

[0021] Mixing a plurality of degraded lubricating oils with known different degrees of degradation with the fluorescent carbon dot solution respectively to obtain a plurality of mixed solutions of degraded lubricating oils with known different degrees of degradation;

[0022] Under the same excitation wavelength condition, respectively measuring the fluorescence intensity of the mixed solutions of the multiple degraded lubricating oils with different known degradation degrees, to obtain multiple fluorescence intensity values ​​of the degraded lubricating oils with different known degradation degrees;

[0023] The degradation degree of the degraded lubricating oil is used as the independent variable, and the ratio of the blank fluorescence intensity value to the fluorescence intensity values ​​of the multiple degraded lubricating oils with different known degradation degrees is used as the dependent variable, and fitting is performed to obtain the degradation-fluorescence fitting relationship.

[0024] Preferably, when the degradation degree is the working time of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees comprises the following steps:

[0025] The standard lubricating oil is operated for different working time periods under actual working conditions, or is processed for different simulation time periods under simulated degradation conditions that are the same as the actual working conditions of the lubricating oil, to obtain a plurality of degraded lubricating oils with different known working time periods.

[0026] Preferably, when the degradation degree is the waste oil content of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees comprises the following steps:

[0027] The standard lubricating oil and the waste lubricating oil are mixed at different mass percentages to obtain a plurality of degraded lubricating oils with different known waste oil contents.

[0028] Preferably, before the mixing, the degraded lubricating oil is diluted, and the diluted degraded lubricating oil is mixed with the fluorescent carbon dot solution; the dilution solvent is the same as the solvent in the fluorescent carbon dot solution; and the dilution multiple is ≤100 times.

[0029] Preferably, during the mixing, the volume ratio of the diluted degraded lubricating oil to the fluorescent carbon dot solution is ≥1:1.

[0030] Preferably, the solvent in the fluorescent carbon dot solution is toluene.

[0031] Preferably, the mass concentration of the fluorescent carbon dot solution is 0.1 g / L.

[0032] The present invention provides a detection and analysis method for lubricating oil degradation based on fluorescent carbon dots, comprising the following steps: under the condition of an excitation wavelength, measuring the fluorescence intensity of a fluorescent carbon dot solution to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots; mixing the lubricating oil to be tested and the fluorescent carbon dot solution to obtain a mixed solution of the lubricating oil to be tested; under the condition of the same excitation wavelength, measuring the fluorescence intensity of the mixed solution of the lubricating oil to be tested to obtain a fluorescence intensity value of the lubricating oil to be tested; comparing the blank fluorescence intensity value and the The ratio of the fluorescence intensity values ​​of the lubricating oil to be tested is substituted into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested, and the degradation degree includes the working time of the lubricating oil or the waste oil content in the lubricating oil; the degradation-fluorescence fitting relationship is: the degradation degree of the lubricating oil is taken as the independent variable; the ratio of the blank fluorescence intensity value and the fluorescence intensity value of the degraded lubricating oil mixed solution of the degraded lubricating oil is taken as the dependent variable, and the degraded lubricating oil mixed solution is a mixed solution of a lubricating oil with a known degradation degree and a fluorescent carbon dot solution, and the lubricating oil with a known degradation degree is the same as the model of the lubricating oil to be tested. The analysis method provided by the present invention uses fluorescent carbon dots as probes, combines the effects of the generation of various alcohols, aldehydes, ketones, carboxylic acids and other oxidation products on the fluorescence intensity of fluorescent carbon dots during the degradation of lubricating oil, and analyzes the degradation degree of the lubricating oil by monitoring the intensity changes of the fluorescent carbon dot luminescence signal. Compared with the existing analysis methods: infrared absorption spectrum analysis method, X-ray spectrum method and electrical analysis method, the analysis method provided by the present invention not only has a simple analysis process and fast analysis data, but also has accurate analysis results and high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a transmission electron microscope photograph of the fluorescent carbon dots prepared in Example 1;

[0034] Figure 2 is the fluorescence spectrum of the fluorescent carbon dot solution prepared in Example 1;

[0035] Figure 3 is the fluorescence spectra of the fluorescent carbon dots in Example 1 in trimethylolpropane ester (TMP 108A) with different degrees of degradation;

[0036] Figure 4 The degeneration-fluorescence fitting curve and linear regression equation obtained in Example 1;

[0037] Figure 5 The degeneration-fluorescence fitting curve and fitting curve equation obtained in Example 2. DETAILED DESCRIPTION

[0038] The present invention provides a method for detecting and analyzing lubricating oil degradation based on fluorescent carbon dots, comprising the following steps:

[0039] Under the excitation wavelength condition, the fluorescence intensity of the fluorescent carbon dot solution is measured to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots;

[0040] Mixing the lubricating oil to be tested and the fluorescent carbon dot solution to obtain a lubricating oil mixed solution to be tested;

[0041] Under the same excitation wavelength condition, measuring the fluorescence intensity of the lubricating oil mixed solution to be tested, and obtaining the fluorescence intensity value of the lubricating oil to be tested;

[0042] Substituting the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the lubricating oil to be tested into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested, wherein the degradation degree includes the working time of the lubricating oil or the waste oil content in the lubricating oil;

[0043] The degradation-fluorescence fitting relationship is as follows: the degradation degree of the lubricating oil is taken as the independent variable; the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricating oil of the degraded lubricating oil mixed solution is taken as the dependent variable, the degraded lubricating oil mixed solution is a mixed solution of a lubricating oil with a known degradation degree and a fluorescent carbon dot solution, and the lubricating oil with a known degradation degree is of the same model as the lubricating oil to be tested.

[0044] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0045] The present invention measures the fluorescence intensity of a fluorescent carbon dot solution under an excitation wavelength condition to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve lubricating oil; and the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots.

[0046] In the present invention, the method for preparing the fluorescent carbon dots preferably comprises the following steps:

[0047] dispersing carbon and nitrogen organic sources in an organic solvent to perform a solvothermal reaction to obtain a solvothermal reaction liquid;

[0048] The obtained solvent thermal reaction liquid is mixed with n-hexane for precipitation, and the fluorescent carbon dots are obtained by solid-liquid separation.

[0049] In the present invention, the organic source of carbon and nitrogen is preferably p-phenylenediamine.

[0050] In the present invention, the organic solvent is preferably diphenyl ether.

[0051] In the present invention, the mass ratio of the carbon and nitrogen organic sources to the volume ratio of the organic solvent is preferably 0.4 g:30 mL.

[0052] In the present invention, the temperature of the solvothermal reaction is preferably 250° C. The holding time of the solvothermal reaction is preferably 4 hours.

[0053] The present invention preferably mixes the solvent thermal reaction liquid cooled to room temperature with the n-hexane. The present invention has no special requirements on the amount of the n-hexane, and the product in the solvent thermal reaction liquid can be completely precipitated.

[0054] In the present invention, the specific implementation of the solid-liquid separation is preferably centrifugation. In the present invention, the rotation speed of the centrifugation is preferably 10000 rpm. In the present invention, the solid-liquid separation is preferably repeated 3 times, and the time of each solid-liquid separation is preferably 15 minutes.

[0055] In the present invention, the solid-liquid separation obtains a solid product, and the present invention preferably dries the solid product to obtain the fluorescent carbon dots. In the present invention, the drying is preferably performed in air.

[0056] In the present invention, the fluorescent carbon dots are preferably red powder.

[0057] In the present invention, the particle size of the fluorescent carbon dots is preferably 3 nm.

[0058] In the present invention, the optimal excitation wavelength of the fluorescent carbon dots is preferably 468 nm; the emission wavelength of the fluorescent carbon dots under the optimal excitation wavelength condition is preferably 525 nm.

[0059] In the present invention, the solvent in the fluorescent carbon dot solution is preferably toluene.

[0060] In the present invention, the mass concentration of the fluorescent carbon dot solution is 0.1 g / L.

[0061] In the present invention, the excitation wavelength is preferably the optimal excitation wavelength of the fluorescent carbon dot solution.

[0062] The present invention mixes the lubricating oil to be tested and the fluorescent carbon dot solution to obtain the lubricating oil mixed solution to be tested.

[0063] In the present invention, the lubricating oil to be tested is preferably trimethylolpropane ester, model TMP 108A; or commercially available Great Wall GL grade automotive gear oil, model 80W-90; or polyalphaolefin base oil (PAO6); or commercially available SN grade automotive engine oil, model 5W-30.

[0064] In the present invention, before the mixing, the present invention preferably further includes diluting the lubricating oil to be tested, and mixing the diluted lubricating oil to be tested and the fluorescent carbon dot solution; the dilution solvent is preferably the same as the solvent in the fluorescent carbon dot solution; the dilution multiple is preferably ≤100 times, more preferably 20 to 60 times, and specifically preferably 20 times, 50 times or 60 times.

[0065] In the present invention, during the mixing, the volume ratio of the diluted lubricating oil to be tested and the fluorescent carbon dot solution is preferably ≥1:1, more preferably ≥2:1, and further preferably 9:1.

[0066] After obtaining the lubricating oil mixed solution to be tested, the present invention measures the fluorescence intensity of the lubricating oil mixed solution to be tested under the same excitation wavelength condition to obtain the fluorescence intensity value of the lubricating oil to be tested.

[0067] In the present invention, the same excitation wavelength condition is preferably the optimal excitation wavelength of the fluorescent carbon dot solution.

[0068] After obtaining the fluorescence intensity value of the lubricating oil to be tested, the present invention substitutes the ratio of the blank fluorescence intensity value and the fluorescence intensity value of the lubricating oil to be tested into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested, wherein the degradation degree includes the working time of the lubricating oil or the waste oil content in the lubricating oil; the degradation-fluorescence fitting relationship is as follows: the degradation degree of the lubricating oil is used as the independent variable; the ratio of the blank fluorescence intensity value and the fluorescence intensity value of the degraded lubricating oil of the degraded lubricating oil mixed solution is used as the dependent variable, the degraded lubricating oil mixed solution is a mixed solution of a lubricating oil with a known degradation degree and a fluorescent carbon dot solution, and the lubricating oil with a known degradation degree is of the same model as the lubricating oil to be tested.

[0069] In the present invention, the lubricating oil with a known degradation degree and the lubricating oil to be tested are preferably used in the same operating condition.

[0070] In the present invention, the degeneration-fluorescence fitting relationship is preferably a linear fitting curve, a linear regression method, a univariate quadratic fitting curve or a univariate quadratic fitting equation.

[0071] In the present invention, the degradation-fluorescence fitting relationship is a degradation-fluorescence linear regression equation. When the degradation-fluorescence linear regression equation takes the working time of the lubricating oil as an independent variable, the degradation-fluorescence linear regression equation is shown in Formula 1:

[0072] y = 1.07 + 0.008x Formula 1;

[0073] In formula 1, x is the working time of the lubricant, y is the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricant mixed solution; R 2 =0.94201.

[0074] In the present invention, the degradation-fluorescence fitting relationship is a degradation-fluorescence fitting curve equation. When the degradation-fluorescence fitting curve equation takes the waste oil content of the lubricating oil as an independent variable, the degradation-fluorescence fitting curve equation is shown in Formula 2:

[0075] y=8.15x 2 -0.84x+1.12 Equation 2;

[0076] In formula 1, x is the waste oil content of the lubricating oil, y is the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricating oil mixed solution; R 2 =0.9920.

[0077] In the present invention, the method for establishing the degeneration-fluorescence fitting relationship preferably comprises the following steps:

[0078] Under the condition of an excitation wavelength (hereinafter referred to as the first excitation wavelength), the fluorescence intensity of the fluorescent carbon dot solution (hereinafter referred to as the first fluorescent carbon dot solution) is measured to obtain a blank fluorescence intensity value (hereinafter referred to as the first blank fluorescence intensity value); the solvent in the first fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the first fluorescent carbon dot solution are nitrogen-containing carbon dots (hereinafter referred to as the first nitrogen-containing carbon dots);

[0079] Mixing a plurality of degraded lubricating oils with known different degradation degrees with the first fluorescent carbon dot solution respectively (hereinafter referred to as first mixing) to obtain a plurality of mixed solutions of degraded lubricating oils with known different degradation degrees;

[0080] Under the same excitation wavelength (hereinafter referred to as the first same excitation wavelength), the fluorescence intensities of the mixed solutions of the multiple degraded lubricating oils with different known degradation degrees are measured respectively to obtain multiple fluorescence intensity values ​​of the degraded lubricating oils with different known degradation degrees;

[0081] The degradation degree of the degraded lubricating oil is used as the independent variable, and the ratio of the first blank fluorescence intensity value to the fluorescence intensity values ​​of the multiple degraded lubricating oils with different known degradation degrees is used as the dependent variable, and linear fitting is performed to obtain the degradation-fluorescence fitting relationship.

[0082] The present invention measures the fluorescence intensity of a first fluorescent carbon dot solution under a first excitation wavelength to obtain a first blank fluorescence intensity value; the solvent in the first fluorescent carbon dot solution can dissolve lubricating oil; and the fluorescent carbon dots in the first fluorescent carbon dot solution are first nitrogen-containing carbon dots.

[0083] In the present invention, the protection scope of the first nitrogen-containing carbon dots is the same as that of the preparation method of the fluorescent carbon dots described above, and will not be described in detail herein.

[0084] In the present invention, the first fluorescent carbon dots are preferably red powder.

[0085] In the present invention, the particle size of the first fluorescent carbon dots is preferably 3 nm.

[0086] In the present invention, the optimal excitation wavelength of the first fluorescent carbon dots is preferably 468 nm; the emission wavelength of the first fluorescent carbon dots under the optimal excitation wavelength condition is preferably 525 nm.

[0087] In the present invention, the solvent in the first fluorescent carbon dot solution is preferably toluene.

[0088] In the present invention, the mass concentration of the first fluorescent carbon dot solution is 0.1 g / L.

[0089] In the present invention, the first excitation wavelength is preferably the optimal excitation wavelength of the first fluorescent carbon dot solution.

[0090] In the present invention, a plurality of degraded lubricating oils with known different degrees of degradation are first mixed with the first fluorescent carbon dot solution respectively to obtain a plurality of mixed solutions of degraded lubricating oils with known different degrees of degradation.

[0091] In the present invention, when the degradation degree is preferably the working time of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees preferably comprises the following steps:

[0092] The standard lubricating oil is operated for different working time periods under actual working conditions, or is processed for different simulation time periods under simulated degradation conditions that are the same as the actual working conditions of the lubricating oil, to obtain a plurality of degraded lubricating oils with different known working time periods.

[0093] In the present invention, the standard lubricating oil is preferably a lubricating oil that has not been opened and used within the shelf life.

[0094] In the present invention, the actual operating condition is preferably: running at 90° C. in the engine.

[0095] In the present invention, the range of the different working time lengths is preferably 0 to 200 hours.

[0096] In the present invention, the interval between two consecutive working hours of different working hours is preferably 20 hours.

[0097] In a specific embodiment of the present invention, the different working hours are preferably 0h, 20h, 40h, 60h, 80h, 100h, 120h and 140h.

[0098] In the present invention, the simulated degradation condition is preferably: stirring at 150-200° C. in an air environment, and more preferably: stirring at 180° C. in an air environment.

[0099] In the present invention, the range of the different simulation time lengths is preferably 0 to 100 hours.

[0100] In the present invention, the interval between two consecutive simulation time lengths of different simulation time lengths is preferably 5 hours.

[0101] In a specific embodiment of the present invention, the different simulation durations are preferably 0h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h and 50h.

[0102] In the present invention, when the degradation degree is the waste oil content of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees comprises the following steps:

[0103] The standard lubricating oil and the waste lubricating oil are mixed at different mass percentages to obtain a plurality of degraded lubricating oils with different known waste oil contents.

[0104] In the present invention, the mass percentage of waste oil in the plurality of degraded lubricating oils with different known waste oil contents is preferably 0%, 20%, 40%, 60%, 80% and 100%.

[0105] In the present invention, before the first mixing, the present invention preferably also includes diluting the multiple degraded lubricating oils with known different degrees of degradation, and mixing the diluted multiple degraded lubricating oils with known different degrees of degradation with the first fluorescent carbon dot solution respectively; the dilution solvent is preferably the same as the solvent in the first fluorescent carbon dot solution; the dilution multiple is independently preferably ≤100 times, more preferably 20 to 60 times, and specifically preferably 20 times, 50 times or 60 times.

[0106] In the present invention, during the first mixing, the volume ratio of the diluted degraded lubricating oils with different known degrees of degeneration to the fluorescent carbon dot solution is preferably ≥1:1, more preferably ≥2:1, and further preferably 9:1.

[0107] After preparing a plurality of mixed solutions of degraded lubricating oils with different known degrees of degradation, the present invention measures the fluorescence intensities of the mixed solutions of the plurality of mixed solutions of degraded lubricating oils with different known degrees of degradation under the condition of a first same excitation wavelength, and obtains a plurality of fluorescence intensity values ​​of the degraded lubricating oils with different known degrees of degradation.

[0108] In the present invention, the first same excitation wavelength condition is preferably the optimal excitation wavelength of the first fluorescent carbon dot solution.

[0109] After obtaining the first blank fluorescence intensity value and the fluorescence intensity values ​​of the multiple degraded lubricating oils with different known degrees of degradation, the present invention uses the degree of degradation of the degraded lubricating oil as the independent variable and the ratio of the first blank fluorescence intensity value to the fluorescence intensity values ​​of the multiple degraded lubricating oils with different known degrees of degradation as the dependent variable, and performs linear fitting to obtain the degradation-fluorescence fitting relationship.

[0110] The molecular method provided by the present invention uses fluorescent carbon dots as fluorescent probes, combines the generation of various alcohols, aldehydes, ketones, carboxylic acids and other oxidation products during the degradation of lubricating oil, and analyzes the degradation degree of lubricating oil by monitoring the changes in the luminescence signal of fluorescent carbon dots. The analytical method provided by the present invention is simple, sensitive, has high accuracy in predicting the degradation of lubricating oil, and is reliable.

[0111] The present invention uses fluorescent carbon dots as fluorescent probes to detect lubricant degradation products, including oxidation products such as alcohols, aldehydes, ketones, and carboxylic acids, with a total molar concentration preferably ranging from 1 to 900 mmol / L.

[0112] In order to further illustrate the present invention, the technical solution provided by the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0113] Example 1

[0114] In this embodiment, trimethylolpropane ester (TMP 108A) is taken as an example to analyze and determine the degradation degree of the trimethylolpropane ester to be measured. The specific steps include:

[0115] In a three-necked round-bottom flask with a reflux condenser system, 0.40 g of p-phenylenediamine was dispersed in 30 mL of diphenyl ether, mixed, heated to 250 ° C for 4 hours, and then cooled to room temperature. The reaction mixture was poured into an appropriate amount of n-hexane for precipitation, and then centrifuged at 10000 rpm for 15 minutes. The precipitation centrifugation was repeated 3 times, and the solid product obtained by centrifugation was dried in the air to obtain the final red powder as fluorescent carbon dots. The transmission electron microscope photo of the obtained fluorescent carbon dots is shown in the figure. Figure 1 As shown, from Figure 1 It can be seen that the fluorescent carbon dots prepared in this example are uniform in size and in a monodisperse state, with an average size of about 3 nm. A 0.1 g / L fluorescent carbon dot solution was prepared with toluene solution and fluorescence spectrum detection was performed. The spectrum is shown in FIG. Figure 2 As shown, at the optimal excitation wavelength of 468 nm, emission light of 525 nm was obtained, and the blank fluorescence intensity value F0 was obtained.

[0116] Standard trimethylolpropane ester (TMP 108A) was heated in air at 200°C with stirring, and samples were taken every 10 hours. The sampling time periods were: 0h, 10h, 20h, 30h, 40h, 50h, 60h, and 70h. As the heating time increased, the color of trimethylolpropane ester gradually darkened.

[0117] The degenerate trimethylolpropane esters with different degrees of degeneration were diluted 60 times with toluene to obtain diluted degenerate trimethylolpropane ester solutions. 0.2 mL of 0.1 g / L fluorescent carbon dot solution was added to 1.8 mL of the diluted degenerate trimethylolpropane ester solution, and the mixture was allowed to stand for thorough mixing. Then, fluorescence spectrum detection was performed under an excitation wavelength of 468 nm. The spectrum is shown in FIG. Figure 3 As shown by Figure 3 It can be concluded that as the degradation time increases, the fluorescence intensity decreases; the fluorescence intensity values ​​F of degraded trimethylolpropane esters with different degradation degrees are obtained, and F0 / F is calculated; the fluorescence intensity ratio F0 / F is used as the dependent variable, and the degradation time of trimethylolpropane ester is used as the dependent variable, and linear fitting is performed, and the fitting model with the largest correlation coefficient is used as the degradation-fluorescence fitting relationship model. The linear fitting curve and linear regression equation of the degradation-fluorescence fitting relationship obtained in this embodiment are as follows: Figure 4 As shown in formula 1:

[0118] y=ax+bFormula 1;

[0119] Figure 4 In the middle, F0: fluorescence intensity of the fluorescent carbon dot solution without lubricating oil at an excitation wavelength of 468 nm;

[0120] F: fluorescence intensity after adding degenerate trimethylolpropane ester;

[0121] In formula 1: a = 0.008, b = 1.07; R 2 =0.94201.

[0122] The trimethylolpropane ester to be tested was diluted 60 times with toluene to obtain a diluted trimethylolpropane ester solution to be tested. After adding 0.2 mL of 0.1 g / L fluorescent carbon dot solution to 1.8 mL of the diluted trimethylolpropane ester solution to be tested, the mixture was allowed to stand and mixed thoroughly. The fluorescence intensity of the trimethylolpropane ester solution to be tested at an excitation wavelength of 468 nm was measured. The fluorescence intensity of the trimethylolpropane ester solution to be tested at an excitation wavelength of 468 nm was used as the dependent variable and substituted into the linear regression equation of Formula 1 to obtain the working (oxidation) time of the trimethylolpropane ester to be tested.

[0123] Example 2

[0124] This embodiment takes commercially available SN-grade automobile engine oil (5W-30) as an example, and analyzes and determines the degradation degree of the SN-grade 5W-30 oil to be tested. The specific steps include:

[0125] Fluorescent carbon dots were prepared according to the method provided in Example 1, and the blank fluorescence intensity value F0 was measured.

[0126] Different weight percentages of discarded SN-grade 5W-30 oil were added to the commercially available SN-grade automobile engine oil 5W-30 to simulate the actual SN-grade 5W-30 oil with different degradation degrees. The specific process is as follows: the weight percentages of discarded SN-grade 5W-30 oil contained in the lubricating oil standard with different degradation degrees are: 0, 20, 40, 60, 80 and 100%, respectively, to obtain the degraded SN-grade 5W-30 oil with different degradation degrees; diluted 20 times with toluene to obtain the diluted degraded SN-grade 5W-30 oil with different degradation degrees, and diluted 1.8 mL of toluene with different degradation degrees. After adding 0.2 mL of 0.1 g / L fluorescent carbon dot solution to the degraded SN-grade 5W-30 oil, the oil was allowed to stand and mixed thoroughly; the fluorescence intensity value F of the degraded SN-grade 5W-30 oil with different degrees of degeneration after mixing under the condition of 468 nm excitation wavelength was determined according to the method of Example 1, and F0 / F was calculated; the fluorescence intensity ratio F0 / F was used as the dependent variable, and the mass percentage of waste oil in the SN-grade 5W-30 oil was used as the dependent variable, and fitting was performed, and the fitting model with the largest correlation coefficient was used as the degeneration-fluorescence fitting relationship model. The fitting curve equation of the degeneration-fluorescence fitting relationship obtained in this embodiment is as follows: Figure 5 As shown in formula 2:

[0127] y=ax 2 +bx+c formula 2;

[0128] In 2: a = 8.15, b = -0.84, c = 1.12; R 2 =0.9920.

[0129] The SN-grade 5W-30 oil to be tested was diluted 20 times with toluene to obtain a diluted SN-grade 5W-30 oil solution to be tested. After adding 0.2 mL of 0.1 g / L fluorescent carbon dot solution to 1.8 mL of the diluted SN-grade 5W-30 oil solution to be tested, the mixture was allowed to stand and mixed thoroughly. The fluorescence intensity of the SN-grade 5W-30 oil solution to be tested at an excitation wavelength of 468 nm was measured. The fluorescence intensity of the SN-grade 5W-30 oil solution to be tested at an excitation wavelength of 468 nm was used as the dependent variable and substituted into the fitting curve equation of Formula 2 to obtain the mass percentage of waste oil in the SN-grade 5W-30 oil to be tested.

[0130] Example 3

[0131] This embodiment takes polyalphaolefin base oil (PAO6) as an example to analyze and determine the degradation degree of PAO6 to be tested. The specific steps include:

[0132] Fluorescent carbon dots were prepared according to the method provided in Example 1, and the blank fluorescence intensity value F0 was measured.

[0133] The polyalphaolefin base oil (PAO6) was stirred and heated at 180°C in air, and samples were taken every 5 hours, and the sampling time periods were: 0h, 5h, 10h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 50h. As the heating time increases, the color of PAO6 gradually darkens. Obtain degraded PAO6 with different degrees of degradation; dilute the degraded PAO6 with different degrees of degradation according to method 1 of the embodiment, and fully mix it with the fluorescent carbon dot solution according to the method of embodiment 1; determine the fluorescence intensity value F of the degraded PAO6 oil with different degrees of degradation after mixing under the condition of 468nm excitation wavelength according to the method of embodiment 1, and calculate F0 / F; use the fluorescence intensity ratio F0 / F as the dependent variable and the PAO6 degradation time as the dependent variable, perform linear fitting, and use the fitting model with the largest correlation coefficient as the degradation-fluorescence fitting relationship model to obtain the fitting curve and fitting equation of the degradation-fluorescence fitting relationship.

[0134] The PAO6 to be tested was diluted 60 times with toluene to obtain a diluted PAO6 solution to be tested. After adding 0.2 mL of 0.1 g / L fluorescent carbon dot solution to 1.8 mL of the diluted PAO6 solution to be tested, the mixture was allowed to stand and mixed thoroughly. The fluorescence intensity of the PAO6 solution to be tested at an excitation wavelength of 468 nm was measured. The fluorescence intensity of the PAO6 solution to be tested at an excitation wavelength of 468 nm was used as the dependent variable and substituted into the linear regression equation obtained in this example to obtain the simulated oxidation time of the PAO6 to be tested.

[0135] Example 4

[0136] This embodiment takes the commercially available Great Wall GL grade automobile gear oil 80W-90 as an example, and analyzes and determines the degradation degree of the automobile gear oil 80W-90 to be tested. The specific steps include:

[0137] Fluorescent carbon dots were prepared according to the method provided in Example 1, and the blank fluorescence intensity value F0 was measured.

[0138] When the automotive gear oil 80W-90 is running at 90℃ in the engine, samples are taken every 20 hours, and the sampling time periods are: 0h, 20h, 40h, 60h, 80h, 100h, 120h, and 140h. As the heating time increases, the color of the automotive gear oil 80W-90 gradually darkens. Obtain degraded automotive gear oil 80W-90 with different degrees of degradation; dilute the automotive gear oil 80W-90 with different degrees of degradation by 50 times according to the method of Example 1, and fully mix it with the fluorescent carbon dot solution according to the method of Example 1; determine the fluorescence intensity value F of the degraded automotive gear oil 80W-90 with different degrees of degradation after mixing under the condition of 468nm excitation wavelength according to the method of Example 1, and calculate F0 / F; use the fluorescence intensity ratio F0 / F as the dependent variable and the degradation time of the automotive gear oil 80W-90 as the dependent variable to perform linear fitting, and use the fitting model with the largest correlation coefficient as the degradation-fluorescence fitting relationship model to obtain the fitting curve and fitting equation of the degradation-fluorescence fitting relationship.

[0139] The automotive gear oil 80W-90 to be tested was diluted 50 times with toluene to obtain a diluted automotive gear oil 80W-90 solution to be tested. After adding 0.2 mL of 0.1 g / L fluorescent carbon dot solution to 1.8 mL of the diluted automotive gear oil 80W-90 solution to be tested, the mixture was allowed to stand and be fully mixed. The fluorescence intensity of the automotive gear oil 80W-90 solution to be tested at an excitation wavelength of 468 nm was measured. The fluorescence intensity of the automotive gear oil 80W-90 solution to be tested at an excitation wavelength of 468 nm was used as the dependent variable and substituted into the linear regression equation obtained in this embodiment to obtain the working time of the automotive gear oil 80W-90 to be tested in an engine running at 90° C.

[0140] The analysis method for lubricating oil degradation based on fluorescent carbon dots provided by the present invention is suitable for analyzing the degradation degree of lubricating oil. The analysis method established by the present invention uses carbon dots as fluorescent probes, combines the generation of various alcohols, aldehydes, ketones, carboxylic acids and other oxidation products during the degradation process of lubricating oil, and analyzes the degradation degree of lubricating oil by monitoring the changes in the carbon dot luminescence signal. The method is simple to analyze, sensitive to reaction, has high accuracy in predicting the degradation of lubricating oil, and is reliable.

[0141] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for detecting and analyzing lubricating oil degradation based on fluorescent carbon dots, characterized in that: The following steps are involved: Under the excitation wavelength condition, the fluorescence intensity of the fluorescent carbon dot solution is measured to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots; Mixing the lubricating oil to be tested and the fluorescent carbon dot solution to obtain a lubricating oil mixed solution to be tested; Under the same excitation wavelength condition, measuring the fluorescence intensity of the lubricating oil mixed solution to be tested, and obtaining the fluorescence intensity value of the lubricating oil to be tested; Substituting the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the lubricating oil to be tested into the degradation-fluorescence fitting relationship to obtain the degradation degree of the lubricating oil to be tested, wherein the degradation degree includes the working time of the lubricating oil or the waste oil content in the lubricating oil; The degradation-fluorescence fitting relationship is: the degradation degree of the lubricating oil is used as the independent variable; the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricating oil mixed solution is used as the dependent variable, and the degraded lubricating oil mixed solution is a mixed solution of a lubricating oil with a known degradation degree and a fluorescent carbon dot solution, and the lubricating oil with a known degradation degree is of the same model as the lubricating oil to be tested.

2. The analysis method according to claim 1, characterized in that The degradation-fluorescence fitting relationship is a degradation-fluorescence linear regression equation. When the degradation-fluorescence linear regression equation uses the working time of the lubricating oil as an independent variable, the degradation-fluorescence linear regression equation is shown in Formula 1: y = 1.07 + 0.008x Formula 1; In formula 1, x is the working time of the lubricant, y is the ratio of the blank fluorescence intensity value to the fluorescence intensity value of the degraded lubricant mixed solution; R 2 =0.94201.

3. The analysis method according to claim 1, characterized in that The degradation-fluorescence fitting relationship is a degradation-fluorescence fitting curve equation. When the degradation-fluorescence fitting curve equation uses the waste oil content of the lubricating oil as an independent variable, the degradation-fluorescence fitting curve equation is shown in Formula 2: y=8.15x 2 -0.84x+1.12 Equation 2; In formula 2, x is the waste oil content of the lubricating oil, y is the ratio of the fluorescence intensity value of the blank and the fluorescence intensity value of the degraded lubricating oil mixed solution; R 2 =0.9920.

4. The analysis method according to any one of claims 1 to 3, characterized in that The method for establishing the degeneration-fluorescence fitting relationship comprises the following steps: Under the excitation wavelength condition, the fluorescence intensity of the fluorescent carbon dot solution is measured to obtain a blank fluorescence intensity value; the solvent in the fluorescent carbon dot solution can dissolve the lubricating oil; the fluorescent carbon dots in the fluorescent carbon dot solution are nitrogen-containing carbon dots; Mixing a plurality of degraded lubricating oils with known different degrees of degradation with the fluorescent carbon dot solution respectively to obtain a plurality of mixed solutions of degraded lubricating oils with known different degrees of degradation; Under the same excitation wavelength condition, respectively measuring the fluorescence intensity of the mixed solutions of the multiple degraded lubricating oils with different known degradation degrees, to obtain multiple fluorescence intensity values ​​of the degraded lubricating oils with different known degradation degrees; The degradation degree of the degraded lubricating oil is used as the independent variable, and the ratio of the blank fluorescence intensity value to the fluorescence intensity values ​​of the multiple degraded lubricating oils with different known degradation degrees is used as the dependent variable, and fitting is performed to obtain the degradation-fluorescence fitting relationship.

5. The analysis method according to claim 4, characterized in that When the degradation degree is the working time of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees comprises the following steps: The standard lubricating oil is operated for different working time periods under actual working conditions, or is processed for different simulation time periods under simulated degradation conditions that are the same as the actual working conditions of the lubricating oil, to obtain a plurality of degraded lubricating oils with different known working time periods.

6. The analysis method according to claim 4, characterized in that When the degradation degree is the waste oil content of the lubricating oil, the method for preparing the plurality of degraded lubricating oils with different known degradation degrees comprises the following steps: The standard lubricating oil and the waste lubricating oil are mixed at different mass percentages to obtain a plurality of degraded lubricating oils with different known waste oil contents.

7. The analysis method according to claim 4, characterized in that Before the mixing, the degraded lubricating oil is diluted, and the diluted degraded lubricating oil is mixed with the fluorescent carbon dot solution; the dilution solvent is the same as the solvent in the fluorescent carbon dot solution; and the dilution multiple is ≤100 times.

8. The analysis method according to claim 7, characterized in that During the mixing, the volume ratio of the diluted degraded lubricating oil to the fluorescent carbon dot solution is ≥1:

1.

9. The analysis method according to claim 1, characterized in that The solvent in the fluorescent carbon dot solution is toluene.

10. The analysis method according to claim 9, characterized in that The mass concentration of the fluorescent carbon dot solution is 0.1 g / L.

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