A method for determining the total acid value of aviation kerosene

Abstract

This invention discloses a method for determining the total acid value of jet fuel. It adopts the same endpoint determination principle as GB / T 12574-2023, based on a general-purpose automatic potentiometric titration platform with photometric titration function. Under a nitrogen atmosphere, the alkaline titrant is added at a constant or near-constant rate of 0.5–2.0 mL / min, with a photometric electrode at 490–620 nm for determination. This allows for a single titration endpoint and automatic detection of the total acid value of jet fuel. This constant or near-constant rate photometric titration method reduces interference from carbon dioxide and overcomes endpoint errors caused by subjective judgment in manual indicator methods, particularly the tendency for over-tipping. It also eliminates the need for specialized instrument methods that require machine vision technology to construct and intelligently train a dataset of titration endpoint color images. Furthermore, this invention significantly shortens the determination time for the total acid value of jet fuel, is simple to operate, economical, and practical, and can improve the quality control and detection level of jet fuel.

Description

Technical Field

[0001] This invention relates to the field of oil analysis and testing technology, specifically to a method for determining the total acid value of jet fuel. Background Technology

[0002] Total acid value is a crucial and mandatory test item for evaluating the physicochemical properties of jet fuel (i.e., aviation kerosene, hereinafter referred to as jet fuel). It significantly impacts the process conditions and quality control of jet fuel plants, the use of anti-wear additives, the development of new production processes, and storage stability. It is characterized by high requirements, trace amounts of acid (not exceeding 0.015 mg KOH / g), and high testing frequency. Currently, my country's jet fuel product standard (No. 3 jet fuel, GB 6537-2018) clearly stipulates that the acid value determination adopts the GB / T12574-2023 method for determining the total acid value of jet fuel. Therefore, rapid and accurate analysis and evaluation of acid value is one of the important guarantees for effectively controlling the quality of jet fuel. Total acid value refers to the number of milligrams of alkali (KOH) required to neutralize all acidic components in 1g of sample, expressed as mgKOH / g. Acidic substances in aviation kerosene include naphthenic acids, other organic acids (fatty carboxylic acids, phenolic compounds, thiols, etc.), and inorganic acids (carbon dioxide, hydrogen sulfide, etc.). These substances are either inherent in crude oil or generated under storage and usage conditions, and even include additives and their byproducts. During the storage, transportation, and use of aviation kerosene, these corrosive substances can cause corrosion, swelling, or ablation of contacted metal materials, rubber materials, and coatings. This not only affects the oxidation stability and cleanliness of the aviation kerosene itself but also the service life of equipment using the fuel. For example, excessive acidity can increase engine carbon deposits, leading to piston wear and nozzle coking. Therefore, accurate determination of the acid value of aviation kerosene, especially the determination of trace total acid value, is of great significance for ensuring the quality and safety of fuel products, the quality of fuels in use, and the safe operation of mechanical equipment.

[0003] Currently, the domestic standard for determining the total acid value of jet fuel is GB / T 12574-2023, while the international standard is ASTM D3242-2017, the standard test method for acidity of aviation turbine fuels. Both methods specify the use of p-naphthol benzene as a color indicator to determine the titration endpoint. When determining the total acid value of jet fuel, the endpoint color changes from orange-yellow to bright green. The manual titration method in GB / T 12574-2023 is susceptible to human error due to varying color sensitivity. Furthermore, manual titration involves factors such as fixed drop volume, manual adjustment of titration speed, and manual control of titration termination, often leading to over-tipping, which affects the accuracy and precision of the results. In particular, the large quantities of toxic and harmful reagents such as toluene used pose a risk of injury. The automatic titration method in GB / T 12574-2023 uses machine vision technology to acquire, transmit, recognize, process and analyze digital images, enabling the determination of the endpoint color of the indicator method and the automatic determination of the total acid value of aviation kerosene. It has strong real-time performance and high accuracy. This technology requires the use of industrial-grade high-fidelity high-speed cameras and high-speed micro industrial control computers, and requires the establishment of mathematical models. The price of the instruments and maintenance costs are relatively high.

[0004] Potentiometric titration can also be used to determine the acid value of jet fuel. It has good accuracy and a high degree of automation. In particular, the droplet volume is determined by the magnitude of the potential change during potentiometric titration. A large potential change requires a small droplet volume, and a small potential change requires a large droplet volume. By interpolation, the point with the largest potential change rate is found as the equivalence point (titering endpoint). For oils containing trace amounts of polybasic weak acids, the potential change is weak during acid-base neutralization titration, resulting in no abrupt jump at the titration endpoint. There may also be multiple jump points, leading to endpoint misjudgment. Moreover, potentiometric titration is not the standard method for jet fuel production, and the repeatability of the determination is difficult to meet the requirement that the total acid value of jet fuel be less than 0.015 mgKOH / g. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the total acid value of jet fuel. This method combines a photometric electrode of appropriate wavelength and adopts the same endpoint determination principle as GB / T 12574-2023 to accurately determine the trace total acid value content of jet fuel. Moreover, the method of this invention can achieve constant rate or small volume millisecond-level interval titration function through simulation on a general potentiometric titrator, without the need for special instruments, and the test results can be used as factory data.

[0006] In one aspect of the invention, a method for determining the total acid value of jet fuel is provided. According to an embodiment of the invention, based on a universal automatic potentiometric titration platform with photometric titration function, under a nitrogen atmosphere, an alkaline titrant is added at a constant or near-constant rate of 0.5–2.0 mL / min, and a photometric electrode at 490–620 nm is used to determine the titration endpoint, automatically detecting the total acid value of the jet fuel. The alkaline titrant can also be added at near-constant rates with small volumes and millisecond intervals.

[0007] This invention employs the same endpoint determination principle as GB / T 12574-2023, adding the alkali titrant at a constant rate and using a suitable wavelength photometric electrode to accurately determine the trace total acid value of jet fuel. Under a nitrogen atmosphere, 0.01 mol / L potassium hydroxide titrant is added dropwise at a volume of 0.5–2.0 mL / min, and a single abrupt change point can be obtained as the titration endpoint when using a 490–620 nm photometric electrode.

[0008] In addition, the method for determining the total acid value of jet fuel according to the above embodiments of the present invention may also have the following additional technical features:

[0009] In some embodiments of the present invention, the method includes the following steps:

[0010] (1) Using a potentiometric titrator as the experimental platform, set up photometric titration conditions;

[0011] (2) Using a simulated constant-rate dropping method or a small-volume (0.005-0.01 mL) millisecond (0.01-0.1 s) interval constant-rate dropping method, weigh the jet fuel sample to be tested in the titration cup under the above photometric titration conditions, place it on the titration stage, start the potentiometric titrator, move the porous titration cup lid to the upper edge of the titration cup, automatically add the toluene-isopropanol-water mixed titration solvent, then add the p-naphthol benzene indicator, introduce nitrogen gas into the bottom of the titration cup, and then switch the nitrogen gas to the top of the liquid surface in the titration cup. At this time, while stirring, add the alkaline titrant at a constant rate, and use the matching photometric electrode to automatically determine the titration endpoint based on the photometric change, and measure the total acid value of the jet fuel.

[0012] Specifically, the steps for determining the acid value of jet fuel are as follows: First, weigh approximately 100±5g of jet fuel sample, accurate to 0.01g, and place it in a titration cell. Add 100mL of titration solvent (toluene, isopropanol, and water in a volume ratio of 100:99:1) and 0.1mL of 10 g / L p-naphthol indicator. While stirring continuously, bubble nitrogen gas at a flow rate of 600-800mL / min for 3 minutes. Continue bubbling and stirring. At this point, the solution usually appears orange. Titrate with potassium hydroxide isopropanol standard solution. When the solution first appears green / greenish-brown, reduce the volume increment of the titrant to dropwise and half-dropwise until the green / greenish-brown color remains unchanged for 15 seconds, which is the titration endpoint.

[0013] In some embodiments of the present invention, in step (1), the photometric titration conditions are set as follows: signal drift in the titration conditions is turned off; the minimum and maximum titration interval times are both set to 0. Some potentiometric titrators can only be set to non-zero values, which can be set according to their limit values, such as 0.01 s; the minimum and maximum titrant volume increments are the same, and the set values ​​are 0.01 to 0.05 mL; the jump point evaluation parameter ERC is set to 30 to 50.

[0014] In some embodiments of the present invention, in step (2), the porous titration cup lid is equipped with a paddle stirrer, a photometric electrode, four infusion tubes of different diameters (which respectively deliver standard alkali titrant, toluene-isopropanol-water mixed titration solvent, p-naphthol benzene indicator, and for waste liquid extraction), and two nitrogen tubes, one of which extends to the bottom of the titration cup and the other extends above the liquid surface of the titration cup.

[0015] In some embodiments of the present invention, in step (2), the volume ratio of toluene, isopropanol and water in the toluene-isopropanol-water mixed titration solvent is (98-100):(95-99):(1-3).

[0016] In some embodiments of the present invention, in step (2), the concentration of the p-naphthol benzene indicator is 8-12 g / L.

[0017] In some embodiments of the present invention, in step (2), the flow rate of nitrogen gas introduced into the bottom of the titration cup is 600-800 mL / min, and the introduction time is not less than 3 min.

[0018] In some embodiments of the present invention, in step (2), the alkaline titrant is a potassium hydroxide titrant.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] (1) This invention does not require specialized instruments. It can achieve constant-rate or small-volume millisecond-level interval quasi-constant-rate titration on a potentiometric titrator through simulation, such as intervals of 0.01 to 0.1 s and 0.005 to 0.01 mL / time. The endpoint jump is obvious, and the test results can be used as factory data. This constant-rate or quasi-constant-rate photometric titration method reduces the interference of carbon dioxide and overcomes the endpoint error caused by subjective judgment in the manual indicator method, especially the easy over-tipping phenomenon. At the same time, it eliminates the need for the construction and intelligent training of titration endpoint color image datasets required by machine vision technology in specialized instrument methods. Secondly, this invention is simple to operate, economical and practical, and can improve the quality control and detection level of aviation kerosene.

[0021] (2) The determination of the acid value of jet fuel is a non-aqueous acid-base titration, which is sensitive to carbon dioxide in the air. In dynamic photometric titration, the titration is intermittent, and the maximum volume (0.2-0.10 mL) and minimum volume (0.02-0.01 mL) of each titration, as well as the interval, are determined by the signal drift reaching a stable range, and the volume of each titration is determined by the difference in the signal before and after stabilization. Near the endpoint, the titration volume is small, the signal drift is large, and the signal stabilization time will inevitably increase. Near the endpoint, a slight excess of alkali is easily penetrated by carbon dioxide, resulting in a slight acidity, which manifests as indicator color reversion. This inevitably leads to the continued addition of alkali titrant, which can easily cause over-tipping, create multiple abrupt jump points that can easily lead to misjudgment of the endpoint, and also result in a longer titration time. In the constant-rate photometric titration of this invention, the alkali titrant is added to the test solution at a constant rate of 0.5-2.0 mL / min with high precision, at a rate of 0.05-0.02 mL / min per drop. After the endpoint color change, the alkali titrant is still added at a uniform rate. Even if there is carbon dioxide interference, there will be no color return phenomenon. It is especially suitable for application scenarios where the titrant concentration is low and the titrant consumption is low when the acid value of jet fuel is low.

[0022] (3) In the constant-rate photometric titration of aviation kerosene acid value of the present invention, even without nitrogen protection, no color return phenomenon will occur near the endpoint. At the same time, a single and obvious abrupt endpoint can be obtained, and the analysis time is greatly shortened. The constant-rate photometric titration data under nitrogen protection and nitrogen-free environments show that the difference between the volume of titrant consumed in the blank and the volume of titrant consumed in the sample is basically the same. According to the acid value calculation formula, the determination results of aviation kerosene acid value without nitrogen protection and aviation kerosene acid value with nitrogen protection are almost the same. This indicates that the interference of carbon dioxide in the ambient air on the constant-rate photometric titration of acid value is almost negligible, and at the same time, it solves the problem of repeated endpoints in conventional dynamic titration.

[0023] (4) The method of the present invention has good repeatability because during constant-rate uninterrupted titration, the alkali titrant is added at a constant rate of 0.5-2.0 mL / min with high precision until the endpoint color change. Even after the endpoint color change, the alkali titrant is still added at a uniform rate. Even if there is carbon dioxide interference, there will be no color return phenomenon. It is especially suitable for application scenarios where the titrant concentration is low and the titrant consumption is low when the acid value of jet fuel is low. As can be seen from the measurement steps, constant-rate titration does not have the conventional dynamic titration interval and waiting time. The titration time is also significantly shortened compared with the dynamic titration time. At the same time, it solves the problem of misjudging the endpoint of multiple abrupt jump points in conventional dynamic titration. Attached Figure Description

[0024] Figure 1 This is a titration curve and a first-order guide curve for determining the total acid value of jet fuel using the constant-rate titration spectrophotometric method in Example 1 of this invention. In the figure, the total acid value titration curve is represented by a light blue line, corresponding to the left coordinate value, with the unit being (mV); the yellow-green line is the first-order guide curve, corresponding to the right coordinate value (△mV / △mL).

[0025] Figure 2 This is a titration curve and a first-order guide curve for determining the total acid value of jet fuel using the normal dynamic titration photometric method in Comparative Example 1 of this invention. In the figure, the total acid value titration curve is represented by the dark blue line, corresponding to the left coordinate value, in units of (mV); the yellow-green line is the first-order guide curve, corresponding to the right coordinate value (△mV / △mL).

[0026] Figure 3 This is a comparison of the superimposed photometric titration curves of the total acid value of a certain aviation kerosene sample under the conditions of constant rate (blue line) and dynamic (red line) titration under the conditions of Comparative Example 1 of this invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] The platform used in the following examples is a Metrohm 888 Titrando potentiometric titrator, equipped with an 8-wavelength selectable Optrode photometric electrode (470nm, 502nm, 520nm, 574nm, 590nm, 610nm, 640nm, 660nm), an 800 Dosino dispensing apparatus, and Tiamo 3.5 titration software. Operational requirements are in accordance with GB / T 12574-2023, "Determination of Total Acid Number of Jet Fuel." The invention will be described in detail below with reference to the examples.

[0029] Example 1

[0030] A method for determining the total acid value of jet fuel includes the following steps:

[0031] (1) Under dynamic titration (DET), the wavelength of the photometric electrode is selected as 574nm, and the constant rate titration mode is simulated: signal drift (potential stability) is set to "off", the minimum and maximum titration interval time are both set to "0", the minimum and maximum volume increment of titrant are the same, set to "0.04mL", the constant rate titrant addition is 2.4mL / min, and the jump point evaluation parameter ERC (similar to the first level) is set to "30".

[0032] (2) Weigh 101.1 g (accurate to 0.1 g) of the aviation kerosene A sample to be tested into a 300 mL titration cup, place it on the titration table (pan), start the potentiometric titrator, move the multi-hole titration cup lid (with paddle stirrer, photometric electrode, four different diameter infusion tubes, and two nitrogen tubes (one to the bottom of the cup, one above the liquid surface) to the top edge of the titration cup, automatically add 100 mL of toluene-isopropanol-water mixed titration solvent with a volume ratio of 100:99:1, then add 0.1 mL of p-naphthol benzene indicator with a concentration of 10 g / L, and introduce nitrogen gas through the nitrogen tube leading to the bottom of the cup at a flow rate of 700. The titration rate is 0.01012 mol / L, and the time is no less than 3 minutes. After that, the nitrogen gas is switched to the channel above the liquid surface. Then, the alkaline titrant (potassium hydroxide titrant) is added dropwise at a constant rate while stirring. The photometric electrode is used, and the titration endpoint is automatically determined based on the change in photometric intensity (under 574 nm conditions, as the light changes from orange at the initial titration to green near the titration endpoint, the absorbance of the photometric electrode changes, and the digital-to-analog conversion is converted into a millivolt potential signal. The point with the largest change in absorbance (the largest change in the millivolt potential signal) (i.e., the largest first derivative) is determined as the titration endpoint). The concentration of potassium hydroxide titrant is 0.01012 mol / L, and the volume of titrant consumed at the endpoint is 2.235 mL. Under the same conditions, the blank endpoint consumes 0.287 mL of titrant. According to the calculation formula of GB / T 12574-2023 standard method, the acid value of the jet fuel is calculated to be 0.0109 mgKOH / g.

[0033] Total acid number is calculated using the following formula:

[0034] Total acid value AN=C KOH ×(V1-V0)×56.1 / m, where: AN is the acid value of the sample, mgKOH / g; V1 is the volume of titrant consumed at the titration endpoint, mL; V0 is the solvent blank value, mL; C KOH ρ is the titrant concentration, mol / L; m is the oil sample mass, g.

[0035] Comparative Example 1

[0036] A method for determining the total acid value of jet fuel includes the following steps:

[0037] (1) Dynamic titration (DET) titrant addition method: the photometric electrode wavelength is selected as 610nm, the signal drift (potential stability) is selected as "50 mV / min", the minimum titration interval is set to "5s", the maximum interval is set to "40s", the minimum titrant volume increment is set to "0.01mL", the maximum titrant volume increment is set to "0.10mL", and the jump point evaluation parameter ERC (similar to the first-order number) is set to "30".

[0038] (2) The typical dynamic photometric titration procedure is the same as the constant-rate photometric titration procedure. The main differences in parameter settings are shown in the table below. The photometric probe wavelength is 610 nm, the stirring speed is 1100±100 r / min, the nitrogen gas speed is 600~800 mL / min, the nitrogen flow time is ≥3 min, the data acquisition density is 4, the indicator addition is 0.5 mL, the endpoint threshold is 55 ERC, the endpoint evaluation is based on the maximum change rate of color, and the minimum addition volume for constant titration is the same as that for dynamic method, which is set to 0.01 mL to ensure that the discrimination accuracy of the titration volume near the endpoint is the same for constant-rate method and dynamic method.

[0039] In dynamic photometric titration mode, the addition rate and amount of alkali titrant are automatically adjusted according to changes in color (potential). As the titration proceeds, the rate of change in potential (color) near the endpoint gradually increases and then rapidly jumps near the endpoint. Because it is a non-aqueous titration, it is susceptible to interference from carbon dioxide when detecting low-content acid values.

[0040] Table 1. Parameters for constant-rate photometric titration and dynamic photometric titration

[0041]

[0042] Figure 1 In Example 1, the constant-rate titration was simulated using dynamic titration (DET) mode, with the following titration parameters: photometric electrode wavelength selected as 610 nm, signal drift (potential stability) set to "off", minimum and maximum titration intervals both set to "0", minimum and maximum titrant volume increments set to "0.02 mL", and the jump point evaluation parameter ERC (similar to the first derivative) set to "30". A single jump endpoint was obtained, with a jump value ERC > 185. The automatic endpoint determination (EP1) consumed 2.235 mL of 0.01012 mol / L potassium hydroxide titrant.

[0043] Figure 2 In Comparative Example 1, the titrant was added under normal dynamic titration (DET) mode. The titration curve was flat. The acidic substance in jet fuel was a mixture of trace amounts of strong and weak acids in the sample. In addition, the carbon dioxide in the air near the endpoint caused some acid-base buffering. The first-order lead wire increased the difficulty of measurement in determining the endpoint.

[0044] Figure 1 and Figure 2 The experiment showed that although the automatic endpoint determination (EP1) consumed 2.803 mL of 0.01012 mol / L potassium hydroxide titrant, the endpoint jump value ERC was approximately 93. The result indicated that the endpoint was clearly over-titrated, and the jump value was also lower than that of constant-rate spectrophotometric titration. Figure 1 Small, and from Figure 2As can be seen, the titration curve is flat, and the actual endpoint should be the manually determined endpoint (BP1), with an endpoint volume of 1.791 mL and an endpoint jump value (ERC) of approximately 23. The titration curve and first-order guide curve of the constant-rate titration spectrophotometric method for determining the total acid value of jet fuel in this invention are superior to those of the normal dynamic titration spectrophotometric method, resulting in better data repeatability and accuracy.

[0045] Figure 3 The image shows the overlay of the dynamic titration curve (red line) and the constant rate titration curve (blue line) for the same jet fuel sample. It is clear that the constant rate titration curve (blue line) is steeper, indicating that the jump near the endpoint is greater. In other words, the rate of change of the blue line is greater than the first derivative of the dynamic titration curve (red line), which is superior to the dynamic titration curve (red line).

[0046] Example 2

[0047] A method for determining the total acid value of jet fuel includes the following steps:

[0048] (1) Under dynamic titration (DET), the wavelength of the photometric electrode is selected as 610nm, and the constant rate titration mode is simulated: signal drift (potential stability) is set to "off", the minimum and maximum titration interval time are both set to "0", the minimum and maximum volume increment of titrant are the same, set to "0.02mL", the constant rate titrant addition is 1.2mL / min, and the jump point evaluation parameter ERC (similar to the first level) is set to "25".

[0049] (2) Weigh 100.5 g (accurate to 0.1 g) of the jet fuel B sample to be tested into a 300 mL titration cup, place it on the titration table (pan), start the potentiometric titrator, move the multi-hole titration cup lid (with paddle stirrer, photometric electrode, 4 infusion tubes of different diameters, and two nitrogen tubes (one to the bottom of the cup, one above the liquid surface) to the top edge of the titration cup, automatically add 100 mL of toluene-isopropanol-water mixed titration solvent with a volume ratio of 100:99:1, then add 0.1 mL of p-naphthol benzene indicator with a concentration of 10 g / L, and introduce nitrogen gas through the nitrogen tube leading to the bottom of the cup at a flow rate of 700. The nitrogen flow rate was increased to mL / min for at least 3 minutes. Then, the nitrogen flow was switched to the stream above the liquid surface. Subsequently, the alkali titrant was added dropwise at a constant rate while stirring. A photometric electrode was used, and the titration endpoint was automatically determined based on the change in photometric intensity. The concentration of potassium hydroxide titrant was 0.01012 mol / L, and the volume of titrant consumed at the endpoint was 1.302 mL. Under the same conditions, the blank endpoint consumed 0.288 mL of titrant. According to the calculation formula of GB / T 12574-2023 standard method, the acid value of jet fuel was found to be 0.0053 mgKOH / g.

[0050] Example 3

[0051] A method for determining the total acid value of jet fuel includes the following steps:

[0052] (1) Under equal volume titration (MET), the wavelength of the photometric electrode is selected as 610 nm. The simulated constant rate titration method is: signal drift (potential stability) is set to "off", titration interval is set to "0.01s", titrant volume increment is set to "0.03mL", titrant constant rate titration is ≈1.62mL / min, and the jump point evaluation parameter ERC (similar to the first level) is set to "25".

[0053] (2) Weigh 102.0 g (accurate to 0.1 g) of the jet fuel B sample to be tested into a 300 mL titration cup, place it on the titration table (pan), start the potentiometric titrator, move the multi-hole titration cup lid (with paddle stirrer, photometric electrode, 4 infusion tubes of different diameters, and two nitrogen tubes (one to the bottom of the cup, one above the liquid surface) to the top edge of the titration cup, automatically add 100 mL of toluene-isopropanol-water mixed titration solvent with a volume ratio of 100:99:1, then add 0.1 mL of p-naphthol benzene indicator with a concentration of 10 g / L, and introduce nitrogen gas into the nitrogen tube leading to the bottom of the cup at a flow rate of 700. The nitrogen flow rate was increased to mL / min for at least 3 minutes. Then, the nitrogen flow was switched to the stream above the liquid surface. Subsequently, the alkali titrant was added dropwise at a constant rate while stirring. The photometric electrode automatically determined the titration endpoint based on the change in photometric intensity. The concentration of potassium hydroxide titrant was 0.01012 mol / L, and the volume of titrant consumed at the endpoint was 1.300 mL. Under the same conditions, the blank endpoint consumed 0.288 mL of titrant. According to the calculation formula of GB / T 12574-2023 standard method, the acid value of jet fuel was found to be 0.0056 mgKOH / g.

[0054] Example 4

[0055] A method for determining the total acid value of jet fuel includes the following steps:

[0056] (1) Under equal volume titration (MET), the wavelength of the photometric electrode is selected as 520nm, and the simulated constant rate titration mode is used: signal drift (potential stability) is set to "off", titration interval is set to "0.01s", titrant volume increment is set to "0.02mL", titrant constant rate titration is approximately 1.08mL / min, and the jump point evaluation parameter ERC (similar to the first level) is set to "30".

[0057] (2) Weigh 100.2 g (accurate to 0.1 g) of the aviation kerosene C sample to be tested into a 300 mL titration cup, place it on the titration table (pan), start the potentiometric titrator, move the multi-hole titration cup lid (with paddle stirrer, photometric electrode, four infusion tubes of different diameters, and two nitrogen tubes (one to the bottom of the cup, one above the liquid surface) to the top edge of the titration cup, automatically add 100 mL of toluene-isopropanol-water mixed titration solvent with a volume ratio of 100:99:1, then add 0.1 mL of p-naphthol benzene indicator with a concentration of 10 g / L, and introduce nitrogen gas through the nitrogen tube leading to the bottom of the cup at a flow rate of 700. The nitrogen flow rate was increased to mL / min for at least 3 minutes. Then, the nitrogen flow was switched to the stream above the liquid surface. Subsequently, the alkali titrant was added dropwise at a constant rate while stirring. A photometric electrode was used, and the titration endpoint was automatically determined based on the change in photometric intensity. The concentration of potassium hydroxide titrant was 0.01003 mol / L, and the volume of titrant consumed at the endpoint was 0.583 mL. Under the same conditions, the blank endpoint consumed 0.283 mL of titrant. According to the calculation formula of GB / T 12574-2023 standard method, the acid value of jet fuel was found to be 0.0017 mgKOH / g.

[0058] Example 5

[0059] A method for determining the total acid value of jet fuel includes the following steps:

[0060] (1) Under equal volume titration (MET), the wavelength of the photometric electrode was selected as 590 nm, and the constant rate titration method was simulated: the signal drift (potential stability) was set to a large value of "1500 mV / min", the minimum and maximum titration interval time were both set to "0", the minimum and maximum volume increment of the titrant were the same, and the value was set to "0.03 mL", the constant rate titrant addition was 1.8 mL / min, and the jump point evaluation parameter ERC (similar to the first level) was set to "35".

[0061] (2) Weigh 100.4 g (accurate to 0.1 g) of the jet fuel B sample to be tested into a 500 mL titration cup, place it on the titration table (pan), start the potentiometric titrator, move the multi-hole titration cup lid (with paddle stirrer, photometric electrode, 4 infusion tubes of different diameters, and two nitrogen tubes (one to the bottom of the cup, one above the liquid surface) to the top edge of the titration cup, automatically add 100 mL of toluene-isopropanol-water mixed titration solvent with a volume ratio of 100:99:1, then add 0.1 mL of p-naphthol benzene indicator with a concentration of 10 / L, and introduce nitrogen gas into the nitrogen tube leading to the bottom of the cup at a flow rate of 700. The nitrogen flow rate was increased to mL / min for at least 3 minutes. Then, the nitrogen flow was switched to the stream above the liquid surface. Subsequently, the alkali titrant was added dropwise at a constant rate while stirring. The photometric electrode automatically determined the titration endpoint based on the change in photometric intensity. The concentration of potassium hydroxide titrant was 0.01012 mol / L, and the volume of titrant consumed at the endpoint was 0.506 mL. Under the same conditions, the blank endpoint consumed 0.286 mL of titrant. According to the calculation formula of GB / T 12574-2023 standard method, the acid value of jet fuel was found to be 0.0012 mgKOH / g.

[0062] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the present invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A method for determining the total acid number of marine gas oil, characterized by: Based on a general-purpose automatic potentiometric titration platform with photometric titration function, the alkaline titrant is added at a constant or near-constant rate of 0.5–2.0 mL / min under a nitrogen atmosphere. The titration endpoint is determined by a photometric electrode of 490–620 nm, and the total acid value of jet fuel is automatically detected.

2. The method for determining the total acid value of aviation kerosene according to claim 1, characterized in that, Includes the following steps: (1) Using a potentiometric titrator as the experimental platform, set up photometric titration conditions; (2) Weigh the jet fuel sample to be tested into the titration cup under the above photometric titration conditions, place it on the titration stage, start the potentiometric titrator, move the porous titration cup lid to the upper edge of the titration cup, automatically add the toluene-isopropanol-water mixed titration solvent, then add the p-naphthol benzene indicator, and introduce nitrogen gas into the bottom of the titration cup. Then switch the nitrogen gas to the top of the liquid surface in the titration cup. At this time, add the alkaline titrant at a constant rate while stirring. With the matching photometric electrode, the titration endpoint is automatically determined according to the photometric change, and the total acid value of the jet fuel is measured.

3. The method for determining the total acid number of marine gas oil according to claim 2, characterized in that: In step (1), the photometric titration conditions are set as follows: turn off signal drift in the titration conditions; set both the minimum and maximum titration interval time to 0; set the minimum and maximum titrant volume increment to the same value of 0.01 to 0.05 mL; and set the jump point evaluation parameter ERC to 30 to 50.

4. The method for determining the total acid number of marine gas oil according to claim 2, characterized in that: In step (2), a paddle stirrer, a photometric electrode, four infusion tubes of different diameters, and two nitrogen tubes are inserted into the lid of the porous titration cup. One nitrogen tube extends to the bottom of the titration cup, and the other nitrogen tube extends above the liquid surface of the titration cup.

5. The method for determining the total acid number of marine gas oil according to claim 2, characterized in that: In step (2), the volume ratio of toluene, isopropanol and water in the toluene-isopropanol-water mixed titration solvent is (98-100):(95-99):(1-3).

6. The method for determining the total acid number of marine gas oil according to claim 2, characterized in that: In step (2), the concentration of the p-naphthol benzene indicator is 8-12 g / L.

7. The method according to claim 2, characterized in that: In step (2), the flow rate of nitrogen gas introduced into the bottom of the titration vessel is 600-800 mL / min, and the introduction time is not less than 3 min.

8. The method for determining the total acid number of marine gas oil according to claim 2, characterized in that: In step (2), the alkaline titrant is potassium hydroxide titrant.

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