GB/T 7364-2025 Test method for carbonizable substances in paraffin wax

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Card type: Test method

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

• Standard number: GB/T 7364—2025
• Chinese title: Test method for carbonizable substances in paraffin wax
• English title: Test method for carbonizable substance in paraffin wax
• Replacement relationship: replaces GB/T 7364—2006
• Previous versions: first issued in 1987 as GB/T 7364—1987, first revision in 2006, this is the second revision
• Publication/implementation: published on 2025-10-05, implemented on 2026-05-01
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)

2. Scope of application and non-applicability

• This document describes a test method for determining carbonizable substances in paraffin wax.
• Applicable to refined paraffin wax with a melting point of 46 ℃~74 ℃ as determined according to GB/T 2539.
• Not applicable: not provided in the available source.

3. Method principle

At 70 ℃ or a higher temperature, treat the sample melted at 5 mL with 5 mL nitrogen-free concentrated sulfuric acid, compare the color of the treated acid layer with a standard colorimetric solution; if the color is not darker than the standard colorimetric solution, report that the sample passes the test.

4. Reagents and materials (purity / preparation)

• 6.1 Water: meets the grade three water requirements in GB/T 6682—2008.
• 6.2 Sulfuric acid: guaranteed reagent, content (mass fraction) 95%~98%, should be nitrogen-free. Prepare a sulfuric acid solution with a mass fraction of (94.7±0.2)%, and a dilute sulfuric acid solution with a volume ratio of sulfuric acid to water (6.1) of 1:4 (slowly add acid to water, use after cooling 7.1). Nitrogen-free check: dilute a small amount of sulfuric acid with an equal volume of water (6.1) to prepare a sulfuric acid solution, take 10 mL of the cooled solution, carefully add it on top of the diphenylamine sulfuric acid solution (6.11), do not mix, within 1 h the interface should not turn blue. This method can detect a minimum of 0.0002% of NO₃⁻. Note: the sulfuric acid solution with a mass fraction of (94.7±0.2)% is standardized by neutralization titration.
• 6.3 Hydrochloric acid: analytical reagent, content (mass fraction) 36%~38%. Prepare a dilute hydrochloric acid solution with a volume ratio of hydrochloric acid to water (6.1) of 1:39 (slowly add acid to water).
• 6.4 Glacial acetic acid: analytical reagent, content (mass fraction) 99%.
• 6.5 Hydrogen peroxide: analytical reagent. Prepare an aqueous solution with a volume fraction of 3%.
• 6.6 Cobalt chloride: analytical reagent.
• 6.7 Copper sulfate: analytical reagent.
• 6.8 Ferric chloride: analytical reagent.
• 6.9 Sodium hydroxide: analytical reagent. Prepare a sodium hydroxide solution with a mass ratio of sodium hydroxide to water (6.1) of 1:5.
• 6.10 Potassium iodide: analytical reagent.
• 6.11 Diphenylamine sulfuric acid solution: analytical reagent. Dissolve 1.0 g of diphenylamine in 100 mL of sulfuric acid with a mass fraction of 95%~98% to prepare the diphenylamine sulfuric acid solution.
• 6.12 Sodium thiosulfate: analytical reagent. Prepare 0.1 mol/L standard solution according to GB/T 601 and standardize it.
• 6.13 Soluble starch: prepare an aqueous solution with a mass fraction of 1%.
• 6.14 Methyl orange indicator: prepare an aqueous solution with a mass fraction of 0.5%.
• 6.15 White oil: meets the requirements for No. 1 or No. 2 white oil in GB 1886.215—2016.
• 6.16 Cleaning solution: potassium dichromate cleaning solution or glass cleaning solution.

5. Apparatus and equipment

• 5.1 Test tube: as shown in Figure 1, a heat-resistant glass test tube equipped with a ground glass stopper, both the glass stopper and the test tube are engraved with the same number. The test tube is 140 mm±2 mm long, with an outer diameter of 14.5 mm–15.0 mm, a wall thickness of 1.2 mm±0.1 mm, and a volume of 13.6 mL–15.6 mL after the glass stopper is closed. Calibrate the 5 mL and 10 mL liquid level markings, the error should not exceed ±0.2 mL. The tube mouth is flanged so that the test tube can be suspended on the water bath cover.
• 5.2 Water bath: constant temperature range 70 ℃~86 ℃, temperature control accuracy ±0.5 ℃; the water bath can immerse the test tube 10 mL marking 5 mm or more, should be equipped with a cover made of suitable material, with a hole of about 16 mm diameter through which the test tube can be suspended; equipped with a stirrer to make the water temperature uniform.
• 5.3 Colorimeter: used to observe and compare the color of the acid layer with the color of the standard colorimetric solution. The size and shape of the colorimeter are optional, but the shape and size of its window should conform to the dimensions specified in Figure 2.
• 5.4 Thermometer: 50 ℃~100 ℃, minimum division 0.5 ℃.
• 5.5 Constant temperature oven: capable of heating to 105 ℃ and maintaining constant temperature, accuracy 1 ℃.
• 5.6 Burette: 50 mL, accuracy 0.1 mL.
• 5.7 Volumetric flask: 1000 mL.
• 5.8 Pipette: 1 mL, accuracy 0.01 mL; 5 mL, accuracy 0.05 mL; 10 mL, 20 mL and 25 mL, accuracy 0.1 mL.
• 5.9 Iodine flask: 500 mL.
• 5.10 Conical flask: 250 mL.
• 5.11 Balance: accuracy 0.1 mg.

6. Recommended operating conditions

• Test temperature: 70.0 ℃±0.5 ℃; for samples with a melting point higher than 60 ℃, the test temperature should be 10 ℃~12 ℃ higher than their melting point.
• Water bath constant temperature range: 70 ℃~86 ℃, temperature control accuracy ±0.5 ℃.
• Melting sample temperature: at least 8 ℃ above the melting point, but not exceeding 85 ℃, for no more than 1 h.
• Test tube drying: dry in a constant temperature oven at 105 ℃±1 ℃ for 0.5 h~1 h.
• Shaking: rapidly and vigorously shake vertically 3 times, with an amplitude greater than 127 mm, shaking rate 5 times/s; repeat once per minute, for a total of 5 shaking cycles, and the time the test tube stays outside the water bath during each shaking cycle should not exceed 3 s.
• From the first placement of the test tube in the water bath to taking out the test tube for color comparison at 10 min.

7. Sampling and sample preparation

• 8 Sampling: liquid samples are sampled according to GB/T 4756 or GB/T 27867, solid samples are sampled according to SH/T 0229.
• 9.2 Heat and melt a representative sample in a water bath, at a temperature at least 8 ℃ above the melting point, but not exceeding 85 ℃, for no more than 1 h.
• 9.3 Add sulfuric acid with a mass fraction of (94.7±0.2)% to the 5 mL marking of the test tube, then add the melted sample at a temperature not higher than its melting point 5.5 ℃ to the 10 mL marking.

8. Analysis procedure

• 9.1 Clean the test tube with cleaning solution, rinse with tap water and then with water (6.1), dry in a constant temperature oven at 105 ℃±1 ℃ for 0.5 h~1 h.
• 9.2 Heat and melt a representative sample in a water bath, at a temperature at least 8 ℃ above the melting point, but not exceeding 85 ℃, for no more than 1 h.
• 9.3 Add sulfuric acid with a mass fraction of (94.7±0.2)% to the 5 mL marking of the test tube, then add the melted sample at a temperature not higher than its melting point 5.5 ℃ to the 10 mL marking, gently cover with the stopper, and place the test tube in a water bath at test temperature 70.0 ℃±0.5 ℃. For samples with a melting point higher than 60 ℃, the test temperature should be 10 ℃~12 ℃ higher than their melting point.
• 9.4 Heat the test tube containing the sample and sulfuric acid in the water bath for 5 min. Then loosen the stopper to allow sufficient pressure release, re-cover the stopper, quickly remove the test tube from the water bath, press the stopper with a finger, and rapidly and vigorously shake vertically 3 times, with an amplitude greater than 127 mm, shaking rate 5 times/s, and immediately return it to the water bath after shaking. Thereafter repeat the above operation once per minute, for a total of 5 shaking cycles, and the time the test tube stays outside the water bath during each shaking cycle should not exceed 3 s. Note: a shaking machine can also be used, as long as the results obtained are consistent with the manual shaking results specified in the method.
• 9.5 From the first placement of the test tube into the water bath until 10 min when the test tube is removed, immediately place it into the colorimeter, compare the acid layer with the 5 mL standard colorimetric solution in another test tube; this test tube containing the standard colorimetric solution must be vigorously shaken 10 s and allowed to stand for a sufficiently long time so that the contents just separate into two layers.
• 9.6 In some cases, during the test, sulfuric acid will form an emulsion with paraffin that cannot be separated, and the lower acid liquid for comparison with the standard colorimetric solution cannot be obtained. When this occurs, vigorously shake the standard colorimetric solution and white oil into a similar emulsion before comparison; do not wait for separation into two liquid layers.

9. Qualitative and Quantitative and Calculation Formulas

• 10.1 When the color of the acid layer is not darker than the standard colorimetric solution, or the color of the sample and sulfuric acid emulsion is not darker than a similar emulsion formed by vigorously shaking the standard colorimetric solution and white oil in the same proportion, report the sample as "passing" the test.
• 10.2 When the color of the acid layer is darker than the standard colorimetric solution, or the color of the sample and sulfuric acid emulsion is darker than a similar emulsion formed by vigorously shaking the standard colorimetric solution and white oil in the same proportion, report the sample as "failing" the test.
• Preparation of standard colorimetric solution (7.4): Mix cobalt chloride solution, copper sulfate solution, and ferric chloride solution in a volume ratio of 1.5:0.5:3.0 to prepare a light amber standard colorimetric solution. Take 5 mL of the standard colorimetric solution into a test tube (5.1), and cover with 5 mL of white oil.
• Cobalt chloride solution (7.1): Weigh 65.0 g±0.5 g of cobalt chloride (CoCl₂·6H₂O) and place it in a 1000 mL volumetric flask, dissolve with dilute hydrochloric acid (1:39) and dilute to volume to 1000 mL. Use a pipette to accurately transfer 5.0 mL into an iodine flask, add 15 mL sodium hydroxide solution (1:5), 5 mL hydrogen peroxide solution with a volume fraction of 3%, and shake well. Boil for 10 min, cool, then add 2 g potassium iodide and 20 mL dilute sulfuric acid solution (1:4), and shake well. After the precipitate dissolves, using starch solution as indicator, titrate the free iodine with 0.1 mol/L sodium thiosulfate solution; each consumption of 1.0 mL 0.1 mol/L sodium thiosulfate solution is equivalent to 0.0238 g of cobalt chloride (CoCl₂·6H₂O). Add dilute hydrochloric acid (1:39) to adjust the final volume of the cobalt chloride solution so that each milliliter of solution contains 59.5 mg of cobalt chloride (CoCl₂·6H₂O).
• Copper sulfate solution (7.2): Weigh 65.0 g±0.5 g of copper sulfate (CuSO₄·5H₂O) and place it in a 1000 mL volumetric flask, dissolve with dilute hydrochloric acid (1:39) and dilute to volume to 1000 mL. Use a pipette to accurately transfer 10.0 mL into an iodine flask, add 50 mL water (6.1), 4 mL glacial acetic acid, and 3 g potassium iodide, and shake well. After the mixture stands for 5 min, using starch solution as indicator, titrate the free iodine with 0.1 mol/L sodium thiosulfate solution. Each consumption of 1.0 mL 0.1 mol/L sodium thiosulfate solution is equivalent to 0.0250 g of copper sulfate (CuSO₄·5H₂O). Add dilute hydrochloric acid (1:39) to adjust the final volume of the copper sulfate solution so that each milliliter of solution contains 62.4 mg of copper sulfate (CuSO₄·5H₂O).
• Ferric chloride solution (7.3): Weigh 55.0 g±0.5 g of ferric chloride (FeCl₃·6H₂O) and place it in a 1000 mL volumetric flask, dissolve with dilute hydrochloric acid (1:39) and dilute to volume to 1000 mL. Use a pipette to accurately transfer 10.0 mL into an iodine flask, add 5 mL hydrochloric acid, 25 mL water (6.1), and about 3 g potassium iodide, and shake well. After the mixture stands for 5 min, add 50 mL water (6.1) to dilute the mixture, using starch solution as indicator, titrate the free iodine with 0.1 mol/L sodium thiosulfate solution. Each consumption of 1.0 mL 0.1 mol/L sodium thiosulfate solution is equivalent to 0.0270 g of ferric chloride (FeCl₃·6H₂O). Add dilute hydrochloric acid (1:39) to adjust the final volume of the ferric chloride solution so that each milliliter of solution contains 45.0 mg of ferric chloride (FeCl₃·6H₂O).

10. Precision

Since the test results only indicate whether they conform to the judgment criteria specified in the test method, this document makes no statement on precision and bias.

11. Report

• 10.1 When the color of the acid layer is not darker than the standard colorimetric solution, or the color of the sample and sulfuric acid emulsion is not darker than a similar emulsion formed by vigorously shaking the standard colorimetric solution and white oil in the same proportion, report the sample as "passing" the test.
• 10.2 When the color of the acid layer is darker than the standard colorimetric solution, or the color of the sample and sulfuric acid emulsion is darker than a similar emulsion formed by vigorously shaking the standard colorimetric solution and white oil in the same proportion, report the sample as "failing" the test.

12. Referenced Documents

• GB/T 601 Chemical Reagents Preparation of Standard Titration Solutions
• GB 1886.215—2016 National Food Safety Standard Food Additive White Oil (also known as Liquid Paraffin)
• GB/T 2539 Determination of Melting Point of Petroleum Waxes Cooling Curve Method
• GB/T 4756 Manual Sampling of Liquid Petroleum
• GB/T 6682—2008 Specifications and Test Methods for Water Used in Analytical Laboratories
• GB/T 27867 Automatic Sampling of Liquid Petroleum in Pipelines
• SH/T 0229 Sampling Method for Solid and Semi-Solid Petroleum Products

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A