GB/T 262-2010 Standard Test Method for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents

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1. Method number / full title / English title / replacement relationship

• Standard number: GB/T 262-2010
• Chinese title: Standard Test Method for Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents
• English title: Petroleum products and hydrocarbon solvents — Determination of aniline point and mixed aniline point
• Replacement relationship: replaces GB/T 262-1988 "Test Method for Aniline Point of Petroleum Products"; previous versions are GB/T 262-1964, GB/T 262-1977, GB/T 262-1988
• Adoption relationship: modified adoption of ISO 2977:1997 (MOD)
• Method division: Method One (manual method, light-colored transparent samples), Method Two (automated instrument method, light-colored and dark-colored samples), Method Three (volatile sample method)
• Publication/implementation: published by 2011-01-10, implemented by 2011-05-01

2. Scope of application and non-applicability

• 1.1 specifies the determination method for aniline point of petroleum products and hydrocarbon solvents, and the determination method for mixed aniline point of the above products when the sample aniline point is lower than the aniline crystallization temperature in the aniline-sample mixture.
• 1.2 Method One is applicable to the determination of transparent samples whose initial boiling point is higher than room temperature, and whose aniline point is lower than the bubble point of the aniline-sample mixture but higher than its condensation point.
• 1.3 Method Two is applicable to the determination, using an automated instrument, of samples to which Method One is applicable as well as extremely dark-colored samples that Method One cannot determine.
• 1.4 Method Three is applicable to the determination of samples that volatilize significantly at the aniline point temperature, such as aviation gasoline.
• Non-applicability: the source text does not list a separate "non-applicability" clause; 10.2 specifies that if the continuously observed temperature shows an increasing (decreasing) change, or the observed temperature variation range is greater than 0.2 ℃ for light-colored transparent specimens and greater than 0.3 ℃ for dark-colored specimens, then this method is reported as not applicable.
• Note 1: The aniline point (or mixed aniline point) has an auxiliary role in characterizing the properties of pure hydrocarbons and in the analysis of hydrocarbon mixtures. Aromatic hydrocarbons have the lowest aniline point, chain paraffins the highest, and naphthenes and olefins have aniline points between those of aromatics and chain paraffins. Within a homologous series, the aniline point increases with increasing relative molecular mass of the hydrocarbons.
• Note 2: The aniline point is most commonly used to estimate the aromatic hydrocarbon content in hydrocarbon mixtures.

3. Method principle

A specified volume of aniline and the test specimen, or aniline and the test specimen plus n-heptane, is placed in a test tube, and the mixture is stirred. The mixture is heated at a controlled rate until the two phases in the mixture are completely miscible. Then the mixture is cooled at a controlled rate, and the temperature at which the two phases separate is recorded as the aniline point or mixed aniline point of the test specimen. (Chapter 4)

4. Reagents and materials (purity / preparation)

• 5.1 Aniline: analytical reagent. Warning: Aniline is a highly toxic substance even in very small amounts and is absorbed through the skin. Special care must be taken when handling it. All operators should wear safety goggles and aniline-impermeable gloves when directly handling aniline.
  • 5.1.1 Dry the aniline with potassium hydroxide pellets, distill it on the day of use, and discard the first and last 10% (volume fraction) fractions. When the aniline thus prepared is tested with n-heptane (see 5.3) according to the procedure in 7.3, the difference between the n-heptane aniline points measured in two tests shall not be greater than 0.1 ℃, and their average value shall be 69.3 ℃±0.2 ℃ (the source text here has source-text extraction doubt: the value "69.3 CC±0.", requires confirmation against the source standard (source-text extraction)).
  • 5.1.2 Another method for treating aniline: instead of distilling the aniline on the day of use, the aniline may be distilled as described above, the distillate collected in ampoules, the ampoules then sealed under vacuum or dry nitrogen, and stored in a cool, dark place until use.
  • 5.1.3 With either of the above methods, appropriate measures shall be taken to prevent contamination of the aniline by moisture from the atmosphere (see 7.2.2). Note 1: Experience has shown that aniline treated by 5.1.2 can be stored for at least six months without deterioration. Note 2: In routine analysis, as long as the aniline meets the requirements of the n-heptane aniline point test, it is not necessarily required to distill the aniline.
  • 5.1.4 The aniline point of aniline-n-heptane measured with an automated instrument, after correction according to the formula in 8.4.1, shall be 69.3 ℃±0.2 ℃.
• 5.2 Desiccant: industrial anhydrous sodium sulfate or calcium sulfate, calcined and cooled in a desiccator. (The source text "industrial longli water sodium sulfate" is source-text extraction noise, requires confirmation against the source standard (source-text extraction))
• 5.3 n-Heptane: purity not less than 99.75%.
• 5.4 Potassium hydroxide: chemical grade, used for drying aniline.

5. Apparatus and equipment

• 7.2.1 Aniline point tester for light-colored transparent samples: as shown in Figure 1, including the following components.
  • 7.2.1.1 Test tube: diameter 25 mm±1 mm, length 150 mm±3 mm, made of heat-resistant glass.
  • 7.2.1.2 Jacket: diameter 40 mm±2 mm, length 170 mm±3 mm, made of heat-resistant glass.
  • 7.2.1.3 Stirrer: made of soft iron wire, diameter about 2 mm, with a concentric ring of diameter about 19 mm at the bottom. The length from the bottom of the stirrer to its top right-angle bend is about 200 mm, and the length of the right-angle bent portion of the stirrer is about 55 mm. A glass sleeve about 65 mm long with an inner diameter of 3 mm may be used as a guide tube for the stirrer. The stirrer may be operated manually or mechanically.
• 7.2.2 Heating bath and cooling bath: including a suitable air bath, a non-aqueous, non-volatile transparent liquid bath, or an infrared lamp (250 W~375 W); the heating bath shall be equipped with a heating control device.
  • 7.2.2.1 Since aniline readily absorbs water, and moist aniline will give erroneous test results, water shall not be used as the medium for the heating bath or cooling bath. Note: For example, if the aniline contains a volume fraction of 0.1% water, the measured n-heptane aniline point will be about 0.5 ℃ higher than the n-heptane aniline point measured with dry aniline.
  • 7.2.2.2 If the aniline point of the test specimen is lower than the atmospheric dew point, dry inert gas shall be slowly passed into the aniline point test tube to blanket the aniline-test specimen mixture.
• 7.2.3 Thermometer: meets the technical requirements for thermometers No. GB-75, No. GB-76, and No. GB-77 in GB/T 514. No. GB-75 is a low-temperature range thermometer, with a temperature measurement range of −38 ℃~42 ℃ and a scale division of 0.2 ℃; No. GB-76 is a medium-temperature range thermometer, with a temperature measurement range of 25 ℃~105 ℃ and a scale division of 0.2 ℃; No. GB-77 is a high-temperature range thermometer, with a temperature measurement range of 90 ℃~170 ℃ and a scale division of 0.2 ℃. The immersion depth of all three thermometers is 50 mm.
• 7.2.4 Pipettes: capacities of 5.0 mL and 10.0 mL.
• 7.2.5 Balance: capable of weighing to 0.01 g, used for weighing the test tube and test specimen when it is inconvenient to use a pipette to transfer the test specimen.
• 7.2.6 Safety goggles.
• 7.2.7 Safety gloves: impermeable to aniline.
• 8.2 Automated aniline point tester: shall be equipped with a device for detecting changes in sample turbidity, a heating device for the test specimen-aniline mixture, and a thermometer or temperature sensor meeting the temperature measurement precision and accuracy specified in 7.2.3.
• 9.2.1 Aniline point tester for volatile samples: including the following components.
  • 9.2.1.1 Test tube: made of heat-resistant glass, shape and dimensions as shown in Figure 2, containing a thin-walled glass thermometer tube with a sealed bottom end. This tube is fitted with a tight stopper for inserting the thermometer, made of cork or other suitable material. The thermometer sensing bulb rests on a cork ring or disc at the bottom of the tube, and the tube contains enough light-colored transformer oil to cover the thermometer sensing bulb. The thermometer tube is fixed to the top of the test tube with a tight stopper, and the stopper position is fixed with a clamp to prevent escape of test specimen vapor. Note: Any other suitable device may be used, for example, a threaded plastic cap for inserting the thermometer, to prevent vapor from escaping from the apparatus. In this case, the thermometer tube may be omitted, and the thermometer sensing bulb is immersed in the aniline-test specimen mixture.
  • 9.2.1.2 Protective device: a sturdy metal mesh guard to enclose the test tube, preferably connected together with the clamp that holds the thermometer tube.
• 9.2.2 For other apparatus, see 7.2.2~7.2.7.

6. Recommended operating conditions

• Heating rate (Method One): when necessary, the jacket may be heated directly at a rate of about 1 ℃/min~3 ℃/min until the mixture is completely miscible (7.3.2).
• Stirring: stir the aniline-test specimen mixture rapidly with a 50 mm stroke, but avoid stirring up bubbles (7.3.2).
• Cooling rate (Method One): allow the mixture to cool slowly at a rate of 0.5 ℃/min~1.0 ℃/min (7.3.3).
• Cooling endpoint: continue cooling to 1 ℃~2 ℃ below the temperature at which turbidity first appears (7.3.3).
• Method Three: when approaching the aniline point, if the temperature change rate is greater than 1 ℃/min, place the test tube in an outer jacket preheated or precooled to a suitable temperature (9.3.2).
• Thermometer immersion depth: 50 mm (7.2.3).

7. Sampling and test specimen preparation

• 6.1 Shake the test specimen vigorously with a volume fraction of about 10% desiccant (see 5.2) for 3 min~5 min to dry the test specimen. Warm viscous or waxy test specimens to a temperature that will not cause loss of light components or dehydration of the desiccant in order to reduce the viscosity of the test specimen. If visible suspended water is present in the test specimen, first dehydrate the test specimen by centrifugation, and then carry out final drying with desiccant.
• 6.2 Remove suspended desiccant by centrifugation or filtration. Heat test specimens containing wax crystals to a homogeneous phase, and maintain the heated state during the centrifugation or filtration operation.
• 7.1 Applicable sample selection (Method One): This method can determine transparent petroleum product and hydrocarbon solvent samples whose color, determined according to GB/T 6540, is not greater than 6.5, and whose initial boiling point is far higher than the expected aniline point.
• 8.1.1 (Method Two): This method uses automatic apparatus and can determine the samples applicable to Method One and dark samples that Method One cannot determine.
• 9.1 (Method Three): This method can determine transparent samples whose color, determined in accordance with GB/T 6540, is not greater than 6.5, and whose initial boiling point is so low that Method One cannot give a correct aniline point result. Note: For example, aviation gasoline may be determined by this method.

8. Analytical Procedure

Method One (7.3)

• 7.3.1 Clean and dry the apparatus. Pipette 10 mL aniline and 10 mL dried test sample into a test tube equipped with a stirrer and a thermometer and placed in a jacket. If the sample is too viscous to be pipetted, weigh a sample equivalent to 10 mL±0.02 mL at room temperature, to the nearest 0.01 g. Fix the thermometer in the test tube with a cork so that the immersion line of the thermometer is at the level of the aniline-sample mixture, and ensure that the thermometer bulb does not touch the wall of the test tube. Fix the test tube with a cork at the center of the jacket.
• 7.3.2 If the aniline-sample mixture is not completely miscible at room temperature, heat the aniline-sample mixture with a heating bath. Stir the aniline-sample mixture rapidly with a stroke of 50 mm, but avoid entraining air bubbles. If necessary, heat the jacket directly at a rate of about 1 ℃/min~3 ℃/min until the mixture is completely miscible. If the aniline-sample mixture is completely miscible at room temperature, use a non-aqueous cooling bath instead of the heat source.
• 7.3.3 Continue stirring the miscible aniline-sample mixture in a room-temperature air bath or non-aqueous cooling bath, and allow the mixture to cool slowly at a rate of 0.5 ℃/min~1.0 ℃/min, continuing cooling to 1 ℃~2 ℃ below the temperature at which turbidity first appears, and record the temperature when the mixture suddenly becomes completely turbid (see Note) as the aniline point of the sample, to the nearest 0.1 ℃. This temperature (rather than the temperature at which a small amount of material separates) is the minimum equilibrium solution temperature. Note: The characteristic of truly reaching the aniline point is that as the temperature decreases, the turbidity of the mixture increases sharply, and the degree of turbidity is such that the thermometer bulb becomes blurred under reflected light.
• 7.3.4 Repeat the heating and cooling, and repeat the observation of the aniline point temperature, until the result specified in 10.1 can be obtained.
• 7.4 Mixed aniline point determination procedure: For samples whose aniline point is lower than the crystallization temperature of aniline in the aniline-sample mixture, pipette 10 mL aniline, 5 mL sample, and 5 mL n-heptane (see 5.3) into a clean, dry apparatus, and determine the mixed aniline point of the sample as described in 7.3.1~7.3.4.

Method Two (8.3)

• Prepare the apparatus according to the manufacturer's instructions, and ensure that the apparatus is clean and dry. Using the specified total volume of aniline and sample (plus n-heptane), according to the corresponding ratio specified in 7.3.1 or 7.4, carry out the determination according to the apparatus operating instructions. The results of three determinations shall meet the requirements in 10.1.
• 8.1.2 Automatic aniline point testers are commercially available and have been verified to give results that meet the requirements of this standard. Users of the apparatus shall ensure that the manufacturer's instructions are fully followed with respect to standardization, correction, and apparatus operation. Some automatic apparatus are not suitable for all sample types covered by this standard. In case of dispute, only manual apparatus shall be used for the determination.

Method Three (9.3)

• 9.3.1 Clean and dry the apparatus. Pipette 5 mL aniline and 5 mL dried test sample into a test tube, both cooled to a temperature at which there will be no evaporation loss during the determination of the sample. Close the test tube tightly with a stopper, install the thermometer tube at the center of the test tube, and make its bottom 5 mm from the bottom of the test tube. Fix the stopper in place with a clamp, and install a guard.
• 9.3.2 Operate according to the procedures described in 7.3.2 and 7.3.3, but mixing of the sample and aniline is performed by shaking the test tube. When approaching the aniline point, if the rate of temperature change is greater than 1 ℃/min, place the test tube in an outer jacket preheated or precooled to a suitable temperature.
• 9.3.3 Repeatedly heat and cool the mixture, and repeatedly observe the aniline point temperature, until the result specified in 10.1 can be obtained.

9. Qualitative and Quantitative Calculation Formulas

• Evaluation and expression of results (Chapter 10):
  • 10.1 If the range of variation of the aniline point or mixed aniline point temperature from three consecutive observations is not greater than 0.1 ℃ for light-colored transparent samples or not greater than 0.2 ℃ for dark samples, report the average of these three observed temperatures, after correction of the thermometer reading, to the nearest 0.1 ℃, as the aniline point or mixed aniline point of the sample.
  • 10.2 If, after five observations, the range of variation of the aniline point or mixed aniline point temperature of the sample does not meet the above requirements, repeat the test with a fresh portion of aniline and sample in a clean, dry apparatus; if the consecutively observed temperatures show an increasing (decreasing) trend, or the range of variation of the observed temperatures is greater than 0.2 ℃ for light-colored transparent samples or greater than 0.3 ℃ for dark samples, report that this method is not applicable.
• Correction formula for automatic apparatus (8.4.1):
  • Xa = (Xs − A) / B ⋯ (1)
  • Where: Xa— is the aniline point of the sample obtained with the automatic apparatus after correction, ℃; Xs— is the aniline point of the sample actually measured with the automatic apparatus, ℃; A— is the temperature correction value, ℃; B— is a constant.
  • A and B are obtained for each automatic apparatus as described in 8.4.2.
  • Note: It has been confirmed by cooperative testing that the observed aniline points obtained with some automatic apparatus are lower than the results determined by Method One. When a higher sample cooling rate is used, the difference between the results determined with the automatic apparatus and those determined by Method One becomes larger, and increases as the aniline point increases.
• Method for determining the constants A and B (8.4.2): Using Method One and the automatic apparatus, determine the aniline points of three or more samples each in the ranges of aniline point 43 ℃~50 ℃, 60 ℃~65 ℃, and 75 ℃~80 ℃. Using the least squares method, solve the following simultaneous equations, and calculate the constants A and B according to equation (2) and equation (3):
  • Σ (Xs) = NA + BΣ (Xa) ⋯ (2)
  • N (XaXs) = AΣ (Xa) + BΣ (Xa²) ⋯ (3)
  • Where: Σ (Xs) — the sum of the aniline points of all samples measured with the automatic apparatus; Σ (Xa) — the sum of the aniline points of all samples measured by Method One; Σ (Xa²) — the sum of the squares of the aniline points of all samples measured by Method One; Σ (XaXs) — the sum of the products of the aniline point of each sample measured with the automatic apparatus and the aniline point measured by Method One; N— is the number of samples.
  • Note: In an example of test results obtained from a cooperative test by five laboratories on five samples with an aniline point range of 34 ℃~87 ℃, the constants A and B were calculated to be 0.79 and 0.991, respectively. Although this method specifies a minimum of nine samples for the determination, if test data from more samples are used, the precision of the constants A and B obtained from the above equations can be improved. (The symbols Xa and Xs in the original formula are inconsistent with the text description in source-text extraction, requires confirmation against the source standard (source-text extraction))

10. Precision

• 11.1 Use the following provisions to judge the reliability of test results (95% confidence level).
• 11.2 Repeatability (r): The difference between two results obtained by the same operator in the same laboratory, using the same apparatus, on the same sample shall not be greater than the value specified below.
  • Aniline point or mixed aniline point: light-colored transparent samples r=0.2 ℃; dark samples r=0.3 ℃
• 11.3 Reproducibility (R): The difference between two single and independent results obtained by different operators in different laboratories, using different apparatus, on the same sample shall not be greater than the value specified below.
  • Aniline point: light-colored transparent samples R=0.5 ℃; dark samples R=1.0 ℃
  • Mixed aniline point: light-colored transparent samples R=0.7 ℃; dark samples R=1.0 ℃

11. Report

The test report shall include at least the following contents (Chapter 12):

• a) Note the reference to this standard;
• b) Type and identification of the sample tested;
• c) Test results (see Chapter 10);
• d) Note any differences from the specified test procedure by agreement or for other reasons;
• e) Date of test.

12. Reference Documents

• GB/T 514 Specification for glass liquid thermometers for petroleum product testing
• GB/T 6540 Determination of color of petroleum products
• ISO 2977:1997 (modified adoption, non-normative reference document)

13. Source and verification

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