Method for evaluating performance of synthetic ester antioxidant based on free dynamics and apparent activation energy of model

Abstract

The invention discloses a synthetic ester antioxidant performance evaluation method based on model free dynamics and apparent activation energy, and belongs to the technical field of antioxidant performance analysis. According to the method, a model free dynamics method is utilized, and the apparent activation energy is calculated, so that rapid screening and performance prediction of the lubricating oil antioxidant system are realized. The antioxidant evaluation method can quickly, accurately and quantitatively evaluate the efficiency and synergistic effect of the synthetic ester antioxidant, has good consistency compared with the traditional long-term oxidation test result, and can greatly shorten the research and development period and reduce the research and development cost. The method disclosed by the invention can be widely applied to the fields of lubricating oil, lubricating grease, hydraulic oil, conduction oil and the like which take synthetic ester as base oil, and is used for developing novel antioxidants, comparing the performance of the existing antioxidants and optimizing a compound formula; the method has important significance in promoting the development of high-end synthetic lubricating materials and in the technical field of performance analysis of lubricating oil antioxidants.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of antioxidant performance analysis, and particularly relates to a synthetic ester antioxidant performance evaluation method based on model free kinetics and apparent activation energy. BACKGROUND

[0002] Synthetic ester base oil has important applications in high-temperature lubrication fields such as aviation and high-end equipment due to its excellent high and low temperature performance, viscosity-temperature characteristics and thermal oxidation stability. With increasingly harsh working conditions of equipment, higher requirements are put forward for the antioxidant capacity of lubricants at a high temperature of 200 DEG C or above. Adding an antioxidant is one of the most effective means to improve the service life of lubricating oil.

[0003] At present, the performance of antioxidants is mainly evaluated by traditional methods such as a rotary oxygen bomb test and an oven oxidation test. These methods take tens to hundreds of hours, and can only provide a single end-point index such as an induction period and an acid value change, so it is difficult to quickly and quantitatively compare the performance differences of different antioxidant formulations from the nature of reaction kinetics, and it is also difficult to effectively reveal the synergistic mechanism between antioxidants. Therefore, it is of great significance to develop a new method for quickly, scientifically and quantitatively screening synthetic ester antioxidants, which can accelerate the development of high-performance lubricants. SUMMARY

[0004] The application provides a synthetic ester antioxidant performance evaluation method, which comprises the following steps: (1) Sample preparation The antioxidant to be evaluated is added to synthetic ester base oil, and stirred until completely dissolved to obtain a sample to be tested; (2) Thermal analysis test The sample is heated under an oxygen-containing atmosphere at at least three different constant heating rates β, and a thermal analysis test is performed, and a curve of mass or heat flow versus temperature is recorded; (3) Kinetic parameter calculation From the thermal analysis curves of each sample obtained in step (2), the same conversion rate α is selected, and the absolute temperature Tα corresponding to the conversion rate under different constant heating rates is recorded; the data is processed by a model free kinetics method, and the apparent activation energy Ea is calculated; (4) Performance evaluation and screening The apparent activation energy Ea value of the sample to be tested at the same conversion rate or the average apparent activation energy Ea value thereof is compared; the higher the apparent activation energy Ea of the sample, the better the thermal oxidation stability thereof, and the better the performance of the corresponding antioxidant system.

[0005] In the performance evaluation method of the synthetic ester antioxidant, in the step (1), the synthetic ester base oil comprises at least one of polyol ester, diester, and complex ester; and the antioxidant comprises hindered phenol, aromatic amine, thioester, phosphite, or a complex system of the antioxidants.

[0006] In the performance evaluation method of the synthetic ester antioxidant, in the step (1), the addition amount of the antioxidant is 0.1% to 5% of the synthetic ester base oil.

[0007] In the performance evaluation method of the synthetic ester antioxidant, in the step (2), the oxygen-containing atmosphere is air or oxygen.

[0008] In the performance evaluation method of the synthetic ester antioxidant, in the step (2), the different constant heating rates are selected from at least three of 5 K / min, 10 K / min, 15 K / min, 20 K / min, 25 K / min, 30 K / min, 35 K / min, 40 K / min, 45 K / min, 50 K / min, 55 K / min, and 60 K / min.

[0009] In the performance evaluation method of the synthetic ester antioxidant, in the step (3), the conversion rate a is selected from any value in the range of 0.1 to 0.9.

[0010] In the performance evaluation method of the synthetic ester antioxidant, in the step (3), the model free kinetics method comprises Flynn-Wall-Ozawa method (FWO method) and Kissinger-Akahira-Sunose method (KAS method).

[0011] In the above technical solution, the Flynn-Wall-Ozawa method (FWO method) is as follows: log(β) is plotted against 1 / Ta, and linear fitting is performed; the apparent activation energy at the conversion rate a is calculated by the formula Ea = - (m × R) / 0.4567 according to the slope m of the fitting straight line, wherein R is a universal gas constant.

[0012] In the above technical solution, the Kissinger-Akahira-Sunose method (KAS method) is as follows: ln(β / Ta 2 ) is plotted against 1 / Ta, and linear fitting is performed; the apparent activation energy at the conversion rate a is calculated by the formula Ea = -m × R according to the slope m of the fitting straight line.

[0013] In the above synthetic ester antioxidant performance evaluation method, in step (3), Kissinger method can also be used to calculate the average activation energy by using the change of peak temperature Tp of thermal analysis curve at different heating rates for rapid preliminary screening; as preferred, the high activation energy formula screened based on the method is verified by traditional oven oxidation test and / or PDSC induction period test to confirm its long-term oxidation stability.

[0014] The above synthetic ester antioxidant performance evaluation method realizes rapid ordering and screening of performances of various antioxidants or compounded antioxidants by comparing the relative sizes of Eas of various to-be-tested samples, and also realizes identification of synergistic effects between various antioxidants in a compounded scheme.

[0015] Based on this, the application also provides an application of the above synthetic ester antioxidant performance evaluation method; the application includes: (1) realizing rapid ordering and screening of performances of antioxidants or compounded antioxidants thereof; (2) realizing identification of synergistic effects between various single antioxidants in a compounded antioxidant.

[0016] The application has the following beneficial effects: (1) fast and efficient: the entire test and data analysis can be completed within 1-2 days, which greatly shortens the research and development period compared with the oven test lasting for hundreds of hours. (2) quantitative and accurate: the apparent activation energy Ea is a quantitative kinetic parameter, which can accurately reflect the difference in the ability of antioxidants to improve the oxidation stability of oil products, and is more scientific than a single temperature or time point. (3) mechanism correlation: Ea is directly related to the reaction energy barrier, which helps to understand the effect of antioxidants from the mechanism (such as whether it effectively increases the difficulty of chain initiation or chain propagation steps). (4) revealing synergistic effect: the method can sensitively detect the synergistic or antagonistic effect between different antioxidants. For example, if the Ea of a compounded system is significantly higher than that of a single antioxidant system, it proves that there is a synergistic effect. (5) less sample and low cost: thermal analysis test only needs milligram-level samples, which is suitable for early screening of valuable samples. (6) strong predictability: high Ea formulas screened based on the method all show excellent oxidation stability when verified by traditional methods, which proves that the method has good prediction reliability.

[0017] The antioxidant evaluation method of the application can quickly, accurately and quantitatively evaluate the performance and synergistic effect of synthetic ester antioxidants, which has good consistency compared with the results of traditional long-term oxidation test, can greatly shorten the research and development period, and reduce the research and development cost. The method of the application can be widely applied in the fields of synthetic ester-based lubricating oil, grease, hydraulic oil and heat conducting oil, and used for development of new antioxidants, performance comparison of existing antioxidants and optimization of compounded formula, which has important significance for promoting the development of high-end synthetic lubricating materials and in the field of lubricating oil antioxidant performance analysis technology. Attached Figure Description

[0018] Figure 1 Thermogravimetric (TG / DTG) curves of different samples at different heating rates are shown.

[0019] Figure 2 The results of the analysis of different samples using the FWO method are shown; where a, c, e, and g are kinetic curves, and b, d, f, and h are activation energies.

[0020] Figure 3 The results of the KAS method on different samples are shown; where a, c, e, and g are kinetic curves, and b, d, f, and h are activation energies.

[0021] Figure 4 The images show the FTIR spectra of the PE5 sample before and after oxidation in the oven, where a represents the sample before oxidation and b represents the sample after oxidation. Detailed Implementation

[0022] In this invention, the aromatic amine antioxidant L57 is a liquid octylbutyldiphenylamine antioxidant, and the hindered phenolic antioxidant 1010 is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], both of which are purchased from BASF.

[0023] The performance indicators of the pentaerythritol ester PE5 used in this invention are shown in Table 1: Table 1 Performance Indicators of Pentaerythritol Ester (PE5) Thermal analysis kinetic methods, particularly model-free kinetic methods (such as the Flynn-Wall-Ozawa method and the Kissinger-Akahara-Sanos method), have proven to be effective tools for studying the thermal decomposition behavior of materials. By calculating the apparent activation energy, the energy barrier required to overcome for the reaction to occur can be directly reflected. However, current techniques have not applied such methods to the rapid screening and performance prediction of lubricating oil antioxidant systems.

[0024] This invention provides a method for evaluating the performance of synthetic ester antioxidants, comprising the following steps: (1) Sample preparation The antioxidant to be evaluated is added to the synthetic ester base oil at a certain mass percentage (preferably 0.1%~5%) and stirred at 60~80°C until completely dissolved to obtain the lubricant sample to be tested. At the same time, a blank base oil sample without antioxidant is prepared as a control.

[0025] (2) Thermal analysis test Under an oxygen-containing atmosphere (such as air or oxygen), perform thermal analysis tests on the sample at at least three different constant heating rates (β, such as 5, 10, 15, 20 K / min) and record the curves of mass or heat flow as a function of temperature. (3) Calculation of dynamic parameters From the thermal analysis curves obtained in step (2), a series of identical conversion rates α (from 0.1 to 0.9) are selected. Preferably, the conversion rates α are selected at three characteristic points: 0.1, 0.5, and 0.9, representing the initial, middle, and late stages of the reaction, respectively. For each fixed conversion rate α, the absolute temperature Tα corresponding to reaching that conversion rate at different constant heating rates β is recorded. The data is processed using the model free kinetics method to calculate the apparent activation energy Ea.

[0026] Preferably, one or a combination of the following two methods is used to process the data: Flynn-Woll-Ozawa method (FWO method): Plot log(β) against 1 / Tα and perform linear fitting; calculate the apparent activation energy at the conversion rate α based on the slope m of the fitted line using the formula Ea = - (m × R) / 0.4567, where R is the universal gas constant.

[0027] Kissinger-Akahala-Tanos method (KAS method): using ln(β / Tα) 2 Plot 1 / Tα and perform linear fitting; calculate the apparent activation energy at the conversion rate α using the formula Ea = -m × R based on the slope m of the fitted line.

[0028] The two methods described above can calculate Ea at each conversion rate and examine the trend of Ea with α, or calculate the average Ea of the entire decomposition process.

[0029] (4) Performance evaluation and screening Compare the apparent activation energy (Ea) values ​​or their average values ​​for different test samples (including different antioxidants) at the same conversion rate. Samples with higher apparent activation energy (Ea) have better thermal oxidation stability and corresponding antioxidant systems with better performance.

[0030] In the above-mentioned method for evaluating the performance of synthetic ester antioxidants, the conversion rate α in the thermal analysis is defined and calculated through mass loss, which is a standard and routine process, as shown below: (1) Definition and Formula α=(m0−m T ) / (m0−m f ); Where, m0: initial mass, i.e., the mass of the sample at the start of the experiment (usually at room temperature); m TThe instantaneous mass at temperature T (or time t) is the data point recorded in real time by the thermogravimetric analyzer; m f : Final residual mass, i.e., the mass of the sample at the end of the experiment (usually after decomposition or complete reaction); m0−m f : Represents the total mass change, that is, the maximum mass that can be lost during the entire reaction process.

[0031] (2) Calculation steps Under the set atmosphere and heating program, a complete mass-temperature (or time) curve is obtained. Then, three key mass values ​​are determined: m0 is read from the start of the curve, m is read from the end of the curve (plateau region), and m... f The mass corresponding to each data point on the curve is m. T For each temperature point T, the corresponding m T Substituting into the above formula, we can obtain the conversion rate α corresponding to that temperature point.

[0032] (3) Output results Through the above calculations, the original mass-temperature curve is transformed into a conversion rate (α)-temperature curve. This new curve serves as the direct input data for model-free dynamic analysis (such as the FWO method and the KAS method).

[0033] Other materials used in this invention, unless otherwise stated, are commercially available. Other terms used in this invention, unless otherwise specified, generally have the meanings commonly understood by those skilled in the art. The invention is further described in detail below with reference to specific embodiments and data. The following embodiments are merely illustrative and not intended to limit the scope of the invention in any way.

[0034] Example 1 The following samples were prepared using pentaerythritol ester (PE5) as the base oil: (A) Pure PE5 (control); (B) PE5 + 2 wt% aromatic amine antioxidant L57; (C) PE5 + 2 wt% hindered phenolic antioxidant 1010; (D) PE5 + 1 wt% hindered phenolic antioxidant 1010 + 1 wt% aromatic amine antioxidant L57.

[0035] Thermogravimetric analysis (TGA) was performed on the above samples in air at heating rates of 10, 20, 30, and 40 K / min. The TGA data were processed using the FWO and KAS methods, and the apparent activation energy Ea of each sample at a conversion rate of α=0.5 was calculated.

[0036] The experimental results are shown in Table 2: Table 2 Apparent activation energies (Ea kJ / mol) of different lubricant samples Table 2 shows the following screening conclusions: Based on Ea, the order is D > B > C ≈ A. This indicates that antioxidant L57 significantly improves the Ea of PE5, outperforming antioxidant 1010. The combination system of antioxidant L57 and antioxidant 1010 (D) has the highest Ea, demonstrating a significant synergistic effect and suggesting it may possess the best thermal oxidative stability.

[0037] Example 2 The following samples were prepared using pentaerythritol ester (PE5) as the base oil: (A) Pure PE5 (control); (B) PE5 + 2 wt% aromatic amine antioxidant L57; (C) PE5 + 2 wt% hindered phenolic antioxidant 1010; (D) PE5 + 1 wt% hindered phenolic antioxidant 1010 + 1 wt% aromatic amine antioxidant L57.

[0038] Thermogravimetric analysis (TGA) was performed on the above samples in air atmosphere at heating rates of 10, 20, 30, and 40 K / min. The TGA data were processed using the FWO and KAS methods, and the apparent activation energy Ea of each sample at a conversion rate of α=0.1 was calculated.

[0039] The experimental results are shown in Table 3: Table 3 Apparent activation energies (Ea kJ / mol) of different lubricant samples Table 3 shows the following screening conclusions: Based on Ea, the order is D > B > C ≈ A. This indicates that antioxidant L57 significantly improves the Ea of PE5, showing better results than antioxidant 1010. The combination system of antioxidant L57 and antioxidant 1010 (D) has the highest Ea, exhibiting a significant synergistic effect and suggesting it may possess the best thermal oxidative stability. These results are consistent with the conclusions of Example 1.

[0040] Example 3 The following samples were prepared using pentaerythritol ester (PE5) as the base oil: (A) Pure PE5 (control); (B) PE5 + 2 wt% aromatic amine antioxidant L57; (C) PE5 + 2 wt% hindered phenolic antioxidant 1010; (D) PE5 + 1 wt% hindered phenolic antioxidant 1010 + 1 wt% aromatic amine antioxidant L57.

[0041] Thermogravimetric analysis (TGA) was performed on the above samples in air atmosphere at heating rates of 10, 20, 30, and 40 K / min. The TGA data were processed using the FWO and KAS methods, and the apparent activation energy Ea of each sample at a conversion rate of α=0.9 was calculated.

[0042] The experimental results are shown in Table 4: Table 4 Apparent activation energies (Ea kJ / mol) of different lubricant samples Table 4 shows the following screening conclusions: Based on Ea, the order is D > B > C ≈ A. This indicates that antioxidant L57 significantly improves the Ea of PE5, showing better results than antioxidant 1010. The combination system of antioxidant L57 and antioxidant 1010 (D) has the highest Ea, exhibiting a significant synergistic effect and suggesting it may possess the best thermal oxidative stability. These results are consistent with the conclusions of Example 1.

[0043] In the above embodiments, the thermogravimetric (TG / DTG) curves of different samples at different heating rates are as follows: Figure 1 As shown; the analytical results of different samples using the FWO method are as follows. Figure 2 As shown; the analytical results of different samples using the KAS method, such as... Figure 3 As shown.

[0044] I. Verification Experiment Viscosity and acid value are important indicators reflecting the degree of oxidation of lubricating oil. Continuous monitoring of these parameters can ensure the safe and reliable operation of the formulated lubricating oil. The four samples mentioned above were subjected to oxidation tests in a 200℃ oven for 8 hours. The changes in total acid value (ΔTAN) and viscosity increase (ΔKV40) before and after oxidation were measured. Simultaneously, PDSC testing was performed to obtain the oxidation induction temperature.

[0045] The experimental results are shown in Table 5: Table 5. Changes in acid value and viscosity of different samples after oven oxidation. Table 5 shows that after baking at 200℃ for 8 hours, the total acid number (TAN) and kinematic viscosity at 40℃ increased for all oil samples. Clearly, all formulations showed varying degrees of increase in TAN and kinematic viscosity after the hot oil oxidation test, indicating that the samples underwent different degrees of oxidation during high-temperature heating in the presence of air. After 8 hours of oxidation, the PE5 base oil showed a higher degree of oxidation, resulting in a large amount of acidic compounds and polymerization oxidation products. The PE5 formulation containing 1% antioxidant 1010 + 1% antioxidant L57 showed the smallest changes in TAN and kinematic viscosity, followed by the PE5 formulation containing 2% antioxidant L57. These results indicate that L57 is effective in inhibiting the increase in TAN and kinematic viscosity. Furthermore, the PE5 formulation containing 1% antioxidant 1010 + 1% antioxidant L57 showed better control over oil oxidation than the PE5 containing only 2% antioxidant 1010. This is consistent with the trend of activation energy changes in the PE5 samples.

[0046] To monitor the changes in the composition of the four PE5 samples, their FTIR spectra before and after oxidation in the oven were measured, as follows: Figure 4 As shown.

[0047] Figure 4 The Fourier transform infrared spectra of the above oil samples before and after oven oxidation treatment are shown. The carbonyl group (located at 1743 cm⁻¹) -1 The absorption peak at the C=O group (as expected) is very strong, observed in both PE5 and PE5 containing 2% antioxidant 1010. This indicates that the main oxidation product is a carboxylate. For PE5 containing 2% antioxidant L57 and PE5 containing 1% antioxidant 1010 + 1% antioxidant L57, the absorption intensity of the carbonyl group becomes narrower and lower. This indicates that the introduction of antioxidant L57 or a mixture thereof can significantly slow down the oxidation process of PE5. This is consistent with the changes in acid value and viscosity of the PE5 samples.

[0048] In summary, the antioxidant evaluation method based on model free kinetics and apparent activation energy provided by this invention can rapidly, accurately, and quantitatively evaluate the efficacy and synergistic effects of synthetic ester antioxidants. It exhibits good consistency with traditional long-term oxidation test results, significantly shortening the R&D cycle and reducing R&D costs. This method can be widely applied in fields such as lubricating oils, greases, hydraulic oils, and heat transfer oils that use synthetic esters as base oils. It can be used for the development of novel antioxidants, performance comparisons of existing antioxidants, and optimization of compound formulations, which is of great significance for promoting the development of high-end synthetic lubricating materials.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for evaluating the performance of synthetic ester antioxidants, characterized in that, Includes the following steps: (1) Sample preparation The antioxidant to be evaluated was added to the synthetic ester base oil and stirred until completely dissolved to obtain the sample to be tested. (2) Thermal analysis test Under an oxygen-containing atmosphere, the sample was heated at at least three different constant heating rates β, and thermal analysis tests were performed to record the curves of mass or heat flow as a function of temperature. (3) Calculation of dynamic parameters From the thermal analysis curves of each sample obtained in step (2), select the same conversion rate α and record the absolute temperature Tα corresponding to the conversion rate at different constant heating rates; use the model free dynamics method to process the data and calculate the apparent activation energy Ea; (4) Performance evaluation and screening Compare the apparent activation energy (Ea) values ​​of the test samples at the same conversion rate or their average apparent activation energy (Ea) values; the higher the apparent activation energy (Ea) of the sample, the better its thermal oxidation stability and the better the performance of the corresponding antioxidant system.

2. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (1), the synthetic ester base oil includes at least one of polyol esters, diesters, and complex esters; the antioxidant includes hindered phenols, aromatic amines, thioesters, phosphites, or their compound antioxidant systems.

3. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (1), the amount of antioxidant added is 0.1% to 5% of the synthetic ester base oil.

4. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (2), the oxygen-containing atmosphere is air or oxygen.

5. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (2), the different constant heating rates are selected from at least three of the following: 5 K / min, 10 K / min, 15 K / min, 20 K / min, 25 K / min, 30 K / min, 35 K / min, 40 K / min, 45 K / min, 50 K / min, 55 K / min, and 60 K / min.

6. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (3), the conversion rate α is selected from any value between 0.1 and 0.

9.

7. The method for evaluating the performance of synthetic ester antioxidants according to claim 1, characterized in that, In step (3), the model free dynamics method includes the Flynn-Woll-Ozawa method (FWO method) and the Kissinger-Akahara-Sanos method (KAS method).

8. The method for evaluating the performance of synthetic ester antioxidants according to claim 7, characterized in that, The Flynn-Woll-Ozawa (FWO) method is as follows: plot log(β) against 1 / Tα and perform linear fitting; calculate the apparent activation energy at the conversion rate α using the formula Ea = - (m × R) / 0.4567 based on the slope m of the fitted line, where R is the universal gas constant.

9. The method for evaluating the performance of synthetic ester antioxidants according to claim 7, characterized in that, The Kissinger-Akahala-Thanos method (KAS method) is as follows: ln(β / Tα) 2 Plot 1 / Tα and perform linear fitting; calculate the apparent activation energy at the conversion rate α using the formula Ea = -m × R based on the slope m of the fitted line.

10. The application of the performance evaluation method for synthetic ester antioxidants according to claim 1, characterized in that, The applications include: (1) To achieve rapid ranking and screening of the properties of antioxidants or their compound antioxidants; and / or, (2) To identify the synergistic effect among individual antioxidants in compound antioxidants.

Images