GB/T 3145-2023 Determination of Crystallizing Point of Benzene

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Card type: Test method

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

• Standard number: GB/T 3145—2023
• Chinese full title: Determination of Crystallizing Point of Benzene
• English name: Determination of benzene crystallizing point
• Replacement relationship: replaces GB/T 3145—1982 "Determination of Crystallizing Point of Benzene"
• Publication/implementation: published on 2023-11-27, implemented on 2024-03-01
• First publication and revision status: first published in 1982, this is the first revision
• Proposing and administering body: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280)
• Drafting unit: Sinopec Jinling Company
• Main drafters: Zhou Guoxiao, Li Zhixing, Jiang Cailin, Chen Huawei

2. Scope of application and non-applicability

• This document describes the test method for determining the crystallizing point of benzene.
• This document is applicable to the determination of the crystallizing point of benzene.
• Not applicable: not provided in the available source.

3. Method principle

When cooled under specified conditions, after the liquid-phase benzene sample is cooled to a certain temperature and a solid phase appears, the temperature rises again; the highest temperature reached is the crystallizing point of benzene. (See Chapter 4 Method summary)

4. Reagents and materials (purity / preparation)

• 6.1 Water/crushed ice: shall meet the requirements for grade three water in GB/T 6682—2008.
• 6.2 Thermal insulation material: dry absorbent cotton or glass wool.
• Other reagents: not provided in the available source.

5. Apparatus and equipment

• 5.1 Air-jacketed test tube
  • 5.1.1 Inner tube: test tube, length 125 mm, outer diameter 15 mm.
  • 5.1.2 Air sleeve: test tube, length 150 mm, outer diameter 25 mm.
• 5.2 Thick-walled test tube: glass test tube, length 150 mm, outer diameter 18 mm, inner diameter 14 mm. Only to be used when measurement is performed with a temperature sensor.
• 5.3 Test tube stopper
  • 5.3.1 Two-hole stopper: cork or polytetrafluoroethylene material, with the two holes respectively used for fixing the temperature measuring device and the stirrer shaft.
  • 5.3.2 Ring stopper: cork or polytetrafluoroethylene material, used for sealing between the inner tube (5.1.1) and the air sleeve (5.1.2), and capable of fixing the inner tube vertically in the center of the air sleeve. On the premise of ensuring the sealing effect, the ring stopper may also be replaced by other forms.
• 5.4 Cooling bath: a beaker with a volume of 1000 mL, or other similar suitable container, whose effective depth is not less than 127 mm, filled with crushed ice as the refrigerant, or refrigeration equipment that meets the volume and depth requirements and can control the temperature at 0 ℃.
• 5.5 Stirrer: metal (copper or stainless steel) wire with a diameter of 1 mm, one end bent into a spiral shape, with the ring and shaft perpendicular, so that the spiral ring can move freely in the annular space between the inner tube or thick-walled test tube and the temperature measuring device. Stirring rate is 60 times/min.
• 5.6 Temperature measuring device
  • 5.6.1 Thermometer: scale division value 0.02 ℃, shall meet the requirements of GB-41 in GB/T 514—2005. It is recommended to store the thermometer at 0 ℃~6 ℃.
  • 5.6.2 Temperature sensor: accuracy not lower than 0.01 ℃. The verification or calibration of the temperature sensor shall be performed at least once a year and cover its range of use.
• 5.7 Stirring device (optional): the stirring device shown in Figure 1 may replace manual stirring of the benzene liquid.
  • Figure 1 index number explanation: 1—— rotary stirring motor; 2—— reciprocating motor displacement; 3—— temperature measuring device; 4—— test tube stopper; 5—— air-jacketed test tube or thick-walled test tube; 6—— stirrer; 7—— cooling bath; 8—— cooling bath base.

6. Recommended operating conditions

• Cooling bath temperature: 0 ℃ (crushed ice or refrigeration equipment capable of controlling temperature at 0 ℃, see 5.4).
• Stirring rate: 60 times/min (see 5.5).
• Thermometer storage conditions: recommended 0 ℃~6 ℃ (see 5.6.1).
• Other operating conditions: not provided in the available source.

7. Sampling and sample preparation

• Sampling and sample handling shall be carried out in accordance with the requirements of GB/T 4756. (See Chapter 8 Sampling)
• Sample preparation details: not provided in the available source.

8. Analysis procedure

• 9.1 Fit a two-hole stopper to the inner tube of the air-jacketed test tube or to the thick-walled test tube. Insert the temperature measuring device vertically into the central hole of the two-hole stopper; if the measuring device is a thermometer, it shall be inserted to the position where the 4.00 ℃ scale line is flush with the upper edge of the two-hole stopper; if the measuring device is a temperature sensor, the insertion depth shall ensure that the sensor can fully contact the benzene liquid. Insert the stirrer shaft into the other hole of the two-hole stopper and allow it to move freely up and down.
• 9.2 If an air-jacketed test tube is used, a layer of thermal insulation material with a thickness of about 3 mm shall be placed at the bottom of the air sleeve. When the inner tube is inserted into the air sleeve, the mouth of the inner tube shall be flush with the ring stopper or seal matched with the air sleeve, and the inner tube shall be fixed vertically in the center of the air sleeve.
• 10.1 Add 7 mL~8 mL of benzene sample into the inner tube or thick-walled test tube, and add 1 drops of water, shake thoroughly to make the benzene sample reach a saturated state.
• 10.2 Insert the two-hole stopper prepared according to 9.1 into the inner tube or thick-walled test tube.
• 10.3 If an air-jacketed test tube is used, place the inner tube containing the sample into the cooling bath, and while stirring continuously, rapidly cool the sample in the inner tube to about 6 ℃, then wipe dry the outer wall of the inner tube and place it into the air sleeve prepared according to 9.2, then place the assembled air-jacketed test tube into the cooling bath and continue cooling. If a thick-walled test tube is used, it shall be placed directly into the cooling bath.
• 10.4 Stir the benzene sample continuously and observe the temperature indication. During this process, the temperature will drop to a minimum point, then rise to a maximum point, remain constant at the maximum point for at least 15 s, and then continue to drop again. Record the constant temperature at the maximum point, reading accurately to 0.01 ℃, and record it as the crystallizing point of the water-containing sample (t0). If a thermometer is used for temperature measurement, the difference between the minimum point temperature and the maximum point temperature shall not exceed 0.7 ℃. If the difference between the minimum point temperature and the maximum point temperature is not obvious, or the time for which the temperature remains constant at the maximum point does not reach 15 s, the test shall be repeated.
• Note: The minimum point temperature is formed due to supercooling before benzene crystallization.

9. Qualitative and quantitative determination and calculation formulas

• 11.1 Calculation
  • Calculate the crystallizing point of the water-free sample (t) according to formula (1):
    • t = t0 + Δt + 0.09 …………………………(1)
    • Where:
      • t0—— crystallizing point of the water-containing sample, in degrees Celsius (℃);
      • Δt—— correction value of the thermometer or temperature sensor, in degrees Celsius (℃);
      • 0.09—— correction value for converting the water-containing sample to a water-free sample, in degrees Celsius (℃).
  • The observed or calculated values shall be rounded in accordance with GB/T 8170, to the nearest 0.01 ℃.
• 11.2 Expression of results
  • Report the crystallizing point of the water-free sample, to the nearest 0.01 ℃.

10. Precision

• 13.1 General: judge the reliability of test results according to the following rules (95% confidence level).
• 13.2 Precision of benzene crystallizing point when using a thermometer
  • Repeatability: the difference between 2 consecutive test results obtained by the same operator, in the same laboratory, using the same thermometer, according to the same method, on the same sample shall not exceed 0.04 ℃.
• 13.3 Precision of benzene crystallizing point when using a temperature sensor
  • 13.3.1 Repeatability: the difference between 2 consecutive test results obtained by the same operator, in the same laboratory, using the same instrument, according to the same method, on the same sample shall not exceed 0.04 ℃.
  • 13.3.2 Reproducibility: the difference between 2 single, independent test results obtained by different operators, in different laboratories, using different instruments, according to the same method, on the same sample shall not exceed 0.05 ℃.

11. Report

• Report the crystallizing point of the water-free sample, to the nearest 0.01 ℃. (See 11.2)
• Report format or other reporting requirements: not provided in the available source.

12. Referenced documents

• GB/T 514—2005 Technical conditions for glass liquid thermometers for petroleum product testing
• GB/T 4756 Manual sampling method for petroleum liquids
• GB/T 6682—2008 Specifications and test methods for water for analytical laboratory use
• GB/T 8170 Rules for rounding off numerical values and expression and determination of limiting values
• References: [1] ASTM D6809 Standard guide for quality control and quality assurance procedures for aromatic hydrocarbons and related materials

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 Q&A