Method for testing the acid value of rust preventive oils

Abstract

This invention provides a method for testing the acid value of rust-preventive oil, comprising: S100, titration of the sample, including: weighing the sample into a container, adding a titrating solvent, and dissolving it by sonication; adding water to the dissolved sample, mixing, and preparing a titration solution; adding phenolphthalein indicator to the titration solution, titrating with a standard hydrochloric acid solution until colorless, and recording the volume V of the standard hydrochloric acid solution consumed; S200, titration of a blank sample, including: adding the same amount of titrating solvent as in step S110 and the same amount of water as in step S120 to a container, mixing, and preparing a blank sample; adding phenolphthalein indicator, titrating with the standard hydrochloric acid solution until colorless, and recording the volume V0 of the standard hydrochloric acid solution consumed; S300, calculating the acid value of the rust-preventive oil using formula I; wherein, the titrating solvent is selected from a potassium hydroxide aqueous solution and a mixed solution of tetramethylammonium hydroxide in 2-phenyl-2-propanol and methanol. The test method of this invention provides highly accurate results and is simple to operate.

Description

Technical Field

[0001] This invention belongs to the field of acid value testing technology, specifically relating to a method for determining the acid value of rust-preventive oils. Background Technology

[0002] Metal corrosion is a widespread problem across all sectors of the national economy, and using rust-preventive oil to protect metal products is one of the most common methods of rust prevention. Rust inhibitors, as a common additive in lubricating oil formulations, are an indispensable component of rust-preventive oils, effectively enhancing their rust-preventive properties. When oils containing rust inhibitors come into contact with metal, the polar groups in the rust inhibitor molecules have a strong adsorption force on the metal surface, forming a tight monomolecular or multimolecular protective layer that prevents oxygen, moisture, or other corrosive media from contacting the metal, thus preventing rust. Acid value is an important characteristic indicator of rust-preventive oils and rust inhibitors, indicating the amount of acidic substances in them. For some lubricating oils (rust-preventive oils) containing acidic additives (such as the rust inhibitor alkenyl succinic acid), their acid value needs to be controlled within a certain range. If the acid value is below this range, it indicates that the dosage added to the oil is insufficient.

[0003] Currently, the main national standard method for the rapid determination of acid value in petroleum products is GB / T 7304, "Determination of Acid Value of Petroleum Products and Lubricants (Voltage Titration Method)". This method involves dissolving the sample in a titrant and performing potentiometric titration using potassium hydroxide and isopropanol as the titrant. The acid value is expressed as the number of milligrams of alkali (mgKOH / g) required to reach the specified endpoint. In this method, the titrant is a mixture of water, isopropanol, and toluene (v:v:v = 5:495:500). 125 mL of the titrant is added to a pre-weighed conical flask and stirred until the sample dissolves.

[0004] However, rust-preventive oils typically have high viscosity. The GB / T 7304 method, when measuring viscous and heavy oils, suffers from insufficient solubility for these oils and cannot completely dissolve poorly soluble rust inhibitors. Consequently, the measured acid value of rust-preventive oils is generally lower than the actual value, and repeatability is poor. Therefore, a suitable method for determining the acid value of viscous and heavy oils (especially rust-preventive oils) is needed. Summary of the Invention

[0005] In view of this, and in response to the above-mentioned problems in the prior art, the present invention provides a method for testing the acid value of rust-preventive oil. The test method of the present invention has high accuracy and is simple to operate.

[0006] The objective of this invention is achieved through the following approach.

[0007] This invention provides a test method for the acid value of rust-preventive oil with improved accuracy, wherein the test method includes the following steps:

[0008] S100, titration of the sample, including:

[0009] S110. Weigh the sample into a container, add the titration solvent, and dissolve it by sonication to obtain the dissolved sample.

[0010] S120. Add water to the dissolved sample, mix, and prepare the titration solution.

[0011] S130. Add phenolphthalein indicator to the solution to be titrated, and titrate with hydrochloric acid standard solution until colorless. Record the volume V of hydrochloric acid standard solution consumed.

[0012] S200, titration of blank sample, including:

[0013] S210. Add the same amount of titration solvent as in step S110 and the same amount of water as in step S120 to the container, mix, and obtain a blank sample.

[0014] S220. Add phenolphthalein indicator to the blank sample and titrate with the hydrochloric acid standard solution until colorless, and record the volume V0 of hydrochloric acid standard solution consumed.

[0015] S300, calculate the rust-preventive oil acid value using formula I.

[0016]

[0017] In Formula I, AN is the acid value of the rust-preventive oil, in mgKOH / g;

[0018] C represents the concentration of the hydrochloric acid standard solution, in mol·L⁻¹. -1 ;

[0019] V is the volume of standard solution consumed during the titration of the sample, in mL;

[0020] V0 is the volume of standard solution consumed in the titration of the blank sample, in mL;

[0021] m is the mass of the sample, in grams;

[0022] 56.1 represents the molar mass of KOH, in g / mol;

[0023] The titration solvent is selected from potassium hydroxide aqueous solution and tetramethylammonium hydroxide standard solution, wherein the tetramethylammonium hydroxide standard solution is a mixed solution of tetramethylammonium hydroxide in 2-phenyl-2-propanol and methanol.

[0024] The inventors of this application discovered that by using potassium hydroxide aqueous solution and tetramethylammonium hydroxide standard solution as titration solvents to dissolve the rust inhibitor in the rust-preventive oil under ultrasonic conditions, followed by dilution and volume adjustment with water, back titration with hydrochloric acid standard solution, and titration of a blank sample under the same conditions, the measured acid value of the rust-preventive oil is higher than the measured value in GB / T 7304, demonstrating high accuracy.

[0025] According to the test method provided by the present invention, the rust-preventive oil contains a rust inhibitor. The rust inhibitor contains an organic acid as an acidic substance. Examples of the organic acid include, but are not limited to: polycarboxylic acids, tricarboxylic acids, dodecenylsuccinic acid, and unsaturated fatty acids.

[0026] In some embodiments, the rust-preventive oil is a viscous and heavy oil containing polycarboxylic acids, ternary polycarboxylic acids, and / or dodecenyl succinic acid.

[0027] According to the testing method provided by the present invention, step S100 further includes: drying the sample before weighing it into the container.

[0028] In some embodiments, the drying process includes drying the sample at 90-120°C, for example, 105°C, for 2-4 hours.

[0029] According to the test method provided by the present invention, the mass of the sample weighed in step S110 can be 0.1-0.2g. To improve accuracy, the sample is accurate to 0.0002g.

[0030] According to the test method provided by the present invention, the concentration of the titration solvent can be 0.01-0.5 mol / L, for example, 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L or a range thereof, preferably 0.04-0.3 mol / L.

[0031] In some embodiments, the titration solvent is a tetramethylammonium hydroxide standard solution with a concentration of 0.04-0.06 mol / L; and in other embodiments, the titration solvent is a tetramethylammonium hydroxide standard solution with a concentration of 0.1-0.3 mol / L. For example, a 0.2 mol / L aqueous solution of potassium hydroxide or a 0.05 mol / L tetramethylammonium hydroxide standard solution can be used as the titration solvent.

[0032] In this invention, the amount of titrating solvent used is sufficient to neutralize the acidic substances (rust inhibitors) in the rust-preventive oil, especially in excess. In some embodiments, the amount of titrating solvent used in steps S110 and S210 is the same, 5-20 ml. For example, the amount of titrating solvent used in steps S110 and S210 can be 5 ml, 6 ml, 7 ml, 8 ml, 9 ml, 10 ml, 11 ml, 12 ml, 15 ml, 16 ml, 18 ml, 20 ml, or a range thereof. In some specific embodiments, the amount of titrating solvent used in steps S110 and S210 is 10 ml.

[0033] According to the test method provided by the present invention, in step S100, acidic substances in the sample are dissolved and neutralized using a titration solvent, and then, for the purpose of facilitating titration, the dissolved sample is diluted and brought to volume with water. The inventors of this application unexpectedly discovered that a higher acid value was measured when using a tetramethylammonium hydroxide standard solution compared to using an aqueous potassium hydroxide solution as the titration solvent. Not wanting to be limited by theory, it is believed that a tetramethylammonium hydroxide standard solution is more conducive to the dissolution and salt formation of acidic substances in rust-preventive oils, and that tetramethylammonium hydroxide is more alkaline. Furthermore, after its standard solution is mixed with water, tetramethylammonium hydroxide can be well dispersed, resulting in a faster titration reaction rate and facilitating the confirmation of the titration endpoint.

[0034] In some embodiments, the titration solvent is a tetramethylammonium hydroxide standard solution.

[0035] This invention allows for the preparation of a tetramethylammonium hydroxide standard solution using methods known in the art. Furthermore, this invention does not specifically limit the ratio of 2-phenyl-2-propanol to methanol in the tetramethylammonium hydroxide standard solution. In some embodiments, the volume ratio of 2-phenyl-2-propanol to methanol can be 1-5:1. For example, the volume ratio of 2-phenyl-2-propanol to methanol can be 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 5:1, or a range thereof, preferably 2-4:1.

[0036] According to the testing method provided by the present invention, the ultrasound time in step S110 can be 5-30 min. For example, the ultrasound time in step S110 can be 5 min, 8 min, 10 min, 12 min, 15 min, 20 min, 25 min, 30 min or a range thereof, preferably 10-20 min.

[0037] According to the testing method provided by the present invention, the amount of water added in steps S120 and S210 can be 40-100 ml, for example, 40 ml, 50 ml, 60 ml, 70 ml, 80 ml, 90 ml, 100 ml or a range thereof.

[0038] According to the test method provided by the present invention, the concentration of the phenolphthalein indicator solution is 10 g / L. In some embodiments, the phenolphthalein indicator solution is a phenolphthalein-ethanol indicator solution. The preparation method of such a phenolphthalein indicator solution is as follows: weigh 1 g of phenolphthalein, dissolve it in 95% ethanol, and then dilute it to 100 mL with 95% ethanol.

[0039] According to the test method provided by the present invention, the concentration of the hydrochloric acid standard solution can be 0.01-0.2 mol / L. For example, the concentration of the hydrochloric acid standard solution can be 0.01 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, 0.05 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / L, or a range thereof, preferably 0.05-0.1 mol / L.

[0040] The testing method of this invention has the following advantages: It facilitates the determination of acid values ​​in poorly soluble rust-preventive oils, solves the problem of incomplete sample dissolution during titration leading to lower results, and provides high accuracy and reliability in acid value determination. It meets the requirements for determining the acid value of rust-preventive oils and is particularly suitable for addressing the insufficient solubility of viscous and heavy oils. Furthermore, the rust-preventive oil can be either a finished product or a raw material. This testing method effectively improves analytical efficiency, providing a new detection method for the selection and judgment of raw materials and the control of finished oil quality, and has high application prospects. Detailed Implementation

[0041] The preferred embodiments of the present invention will now be described in detail.

[0042] The samples and types used in the following embodiments are shown in Table 1.

[0043] Table 1 Sample Types

[0044]

[0045]

[0046] Sample pretreatment

[0047] Weigh 10 ± 0.5 g of sample and place it in a clean petri dish. Place the petri dish in an oven and dry at 105 °C for 4 hours. Cool to room temperature and set aside.

[0048] Potassium hydroxide aqueous solution

[0049] Weigh 1.12 g of potassium hydroxide into a beaker, add distilled water to dissolve it, pour the solution along a glass rod into a volumetric flask, pour the water used to wash the beaker into the volumetric flask, and make up to 100 mL to obtain a 0.2 mol / L potassium hydroxide aqueous solution (KOH aqueous solution).

[0050] Tetramethylammonium hydroxide standard solution

[0051] Weigh 4.55 g of tetramethylammonium hydroxide and dissolve it in a mixed solution of 2-phenyl-2-propanol and methanol in a volume ratio of 3:1. Dilute the mixture to 1 L to prepare a standard solution of tetramethylammonium hydroxide (TMAH solution) with a concentration of 0.05 mol / L.

[0052] Phenolphthalein indicator solution

[0053] Weigh 1g of phenolphthalein, dissolve it in 95% ethanol, and dilute it to 100mL with 95% ethanol to prepare a phenolphthalein ethanol indicator solution with a concentration of 10g / L.

[0054] standard hydrochloric acid solution

[0055] The concentration of the hydrochloric acid standard solution is 0.05 mol / L, and it should be used within 2 months after calibration.

[0056] Example 1

[0057] 1. Titration of the sample

[0058] (1) Weigh 0.1570g of sample No. 1 into a 250mL conical flask, add 10mL of potassium hydroxide aqueous solution, and place it in an ultrasonic cleaner to dissolve for 10 minutes to obtain the dissolved sample.

[0059] (2) Add 50 mL of water to the conical flask, mix, and obtain the titration solution.

[0060] (3) Add 1 drop of phenolphthalein ethanol indicator to the solution to be titrated, and titrate with hydrochloric acid standard solution until colorless. Record the volume V of hydrochloric acid standard solution consumed, which is 19.48 mL.

[0061] 2. Titration of blank sample

[0062] (1) Add 10 mL of potassium hydroxide aqueous solution to the conical flask, add 50 mL of water, mix, and prepare a blank sample.

[0063] (2) Add 1 drop of phenolphthalein ethanol indicator to the blank sample, titrate with hydrochloric acid standard solution until colorless, and record the volume of hydrochloric acid standard solution consumed, V0, which is 38.74 mL.

[0064] 3. Calculate the acid value of the sample.

[0065] The acid value was calculated using formula I, and the results are shown in Table 2.

[0066]

[0067] In Formula I, AN is the acid value of the rust-preventive oil, in mgKOH / g;

[0068] C represents the concentration of the hydrochloric acid standard solution, in mol·L⁻¹. -1 ;

[0069] V is the volume of standard solution consumed during the titration of the sample, in mL;

[0070] V0 is the volume of standard solution consumed in the titration of the blank sample, in mL;

[0071] m is the mass of the sample, in grams;

[0072] 56.1 represents the molar mass of KOH, in g / mol.

[0073] Using the titration solvents listed in Table 2, the acid values ​​of samples 1, 2, and 3 were measured using the same method, and the results are shown in Table 2.

[0074] Acid value results for samples No. 21-3

[0075]

[0076] As can be seen from Table 2, the acid values ​​measured by the method of the present invention are all within the product index range. The test method of the present invention has high accuracy, and the acid values ​​measured by using TMAH solution as titration solvent are significantly higher than those measured by using KOH aqueous solution as titration solvent, achieving better results. Subsequent examples all use TMAH solution as titration solvent.

[0077] Example 2

[0078] The repeatability of samples 1-3 was tested using the same method as in Example 1, and the results are shown in Table 3.

[0079] Table 3 Results of Repeatability Tests

[0080]

[0081]

[0082] As can be seen from Table 3, for samples 1-3, the acid value is in the range of 230-352 mgKOH / g. The difference between the three parallel tests of the test method of the present invention is less than 6 mgKOH / g, and the relative standard deviation is less than 2.45%. The test method of the present invention has good repeatability.

[0083] Example 3

[0084] The acid value of sample No. 4 was measured using the method described in Example 1, repeated three times, and the average value was taken. The measurement results are shown in Table 4. Additionally, the acid values ​​of samples No. 1-4 were determined using GB / T 7304, as shown in Table 4.

[0085] Table 4 Results of acid value determination by different methods

[0086]

[0087] As can be seen from Table 4, the test results obtained by the method of the present invention better reflect the acid value of the rust-preventive oil, and the test method of the present invention is feasible. In addition, for sample 4, oleic acid, which is an oily liquid, the test results obtained by the present invention are basically consistent with GB / T7304, indicating that the present invention is particularly suitable for solving the problem of insufficient dissolving capacity for viscous and heavy oils.

[0088] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A method for testing the acid value of rust preventive oil, wherein, The test method comprises the following steps: S100, titration of the sample, comprising: S110, weighing the sample in a container, adding a titration solvent, ultrasonic dissolution to obtain a dissolved sample; S120, adding water to the dissolved sample, mixing to prepare a sample to be titrated; S130, adding a phenolphthalein indicator to the sample to be titrated, titrating to colorless with a hydrochloric acid standard solution, and recording the volume V of the hydrochloric acid standard solution consumed; S200, titration of the blank sample, comprising: S210, adding the same amount of titration solvent as in step S110 and the same amount of water as in step S120 to the container, mixing to prepare a blank sample; S220, adding a phenolphthalein indicator to the blank sample, titrating to colorless with the hydrochloric acid standard solution, and recording the volume V0 of the hydrochloric acid standard solution consumed; S300, calculating the acid value of the rust-proof oil by formula I, In formula I, AN is the acid value of the rust-proof oil, unit: mgKOH / g; C is the concentration of the standard solution of hydrochloric acid, unit: mol L -1 ; V is the volume of the standard solution consumed when titrating the sample, unit: mL; V0 is the volume of the standard solution consumed when titrating the blank sample, unit: mL; m is the mass of the sample, unit: g; 56.1 represents the molar mass of KOH, unit: g / mol; The titration solvent is selected from a potassium hydroxide aqueous solution and a tetramethylammonium hydroxide standard solution, and the tetramethylammonium hydroxide standard solution is a 2-phenyl-2-propanol and methanol mixed solution of tetramethylammonium hydroxide.

2. The test method of claim 1, wherein, The rust-proof oil contains an organic acid; the organic acid is preferably a polycarboxylic acid, a trivalent polycarboxylic acid, a dodecenyl succinic acid, and an unsaturated fatty acid.

3. The test method of claim 1 or 2, wherein, Step S100 further comprises: before weighing the sample in the container, drying the sample; And / or, the mass of the sample weighed in step S110 can be 0.1-0.2g.

4. The test method of any one of claims 1-3, wherein, The concentration of the titration solvent can be 0.01-0.5mol / L, preferably 0.04-0.3mol / L.

5. The test method of claim 4, wherein, The titration solvent is a tetramethylammonium hydroxide standard solution with a concentration of 0.04-0.06mol / L.

6. The test method of claim 4, wherein, The volume ratio of 2-phenyl-2-propanol to methanol in the tetramethylammonium hydroxide standard solution is 1-5:1, preferably 2-4:

1.

7. The test method of any one of claims 1-6, wherein, The amount of titration solvent used in steps S110 and S210 is the same, which is 5-20ml.

8. The test method of any one of claims 1-7, wherein, The ultrasonic time in step S110 can be 5-30min, preferably 10-20min.

9. The test method of any one of claims 1-8, wherein, The amount of water added in steps S120 and S210 is 40-100ml.

10. The test method of any one of claims 1-9, wherein, The phenolphthalein indicator is a phenolphthalein-ethanol indicator; And / or, the concentration of the hydrochloric acid standard solution can be 0.01-0.2mol / L, preferably 0.05-0.1mol / L.

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