SH/T 0234-1992 Determination of Iodine Value and Unsaturated Hydrocarbon Content of Light Petroleum Products (Iodine-Ethanol Method)

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Card type: Test method

1. Method number / Full name / English name / Replacement relationship

• Standard number: SH/T 0234-92
• Full name: Determination of Iodine Value and Unsaturated Hydrocarbon Content of Light Petroleum Products (Iodine-Ethanol Method)
• English name: not provided in the available source
• Replacement relationship: replaces SY 2414-s2 (as in the source, suspected to be SY 2414-82, requires confirmation against the source standard (source-text extraction))
• Other: confirmed in 2004; approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20
• Additional notes: This standard was first published in 1956; it refers to and adopts the former Soviet Union national standard ГОСТ 2070-55 "Determination of Iodine Value and Unsaturated Hydrocarbon Content"

2. Scope of application and non-applicability

• Applicable to aviation gasoline, jet fuel and other light fuels.
• Not applicable: not provided in the available source.

3. Method principle

After reacting the ethanol solution of iodine with the sample, titrate the remaining iodine with a standard sodium thiosulfate titrant; the iodine value is expressed as the number of grams of iodine that can be absorbed by 100 g of sample. The unsaturated hydrocarbon content is calculated from the iodine value and average molecular weight of the sample.

4. Reagents and materials (purity / preparation)

• 5.1 95% ethanol or anhydrous ethanol: analytical reagent.
• 5.2 Iodine: analytical reagent, prepared as an iodine-ethanol solution. During preparation, dissolve 20 g±0.5 g of iodine in 1 L 95% of ethanol.
• 5.3 Potassium iodide: chemical reagent, prepared as a 200 g/L aqueous solution.
• 5.4 Sodium thiosulfate: analytical reagent, prepared as [c(Na₂S₂O₃)=0.1 mol/L] standard sodium thiosulfate titrant.
• 5.5 Starch: freshly prepared 5 g/L indicator solution.
• 4.2 Material: qualitative filter paper.
• Note (note to Section 7): The concentration of the standard sodium thiosulfate titrant is determined by the following method—accurately weigh sublimed pure iodine, dissolve it in potassium iodide solution, use starch solution as indicator, and titrate with the standard sodium thiosulfate titrant (clause 5.4) until the blue-purple color disappears.

5. Apparatus and equipment

• 4.1.1 Dropping bottle: with ground-glass dropper, volume about 20 mL; or glass ampoule, volume about 0.5～1 mL, whose end should be drawn into a capillary.
• 4.1.2 Iodine flask: 500 mL.
• 4.1.3 Graduated cylinder: 25, 250 mL.
• 4.1.4 Burette: 25 or 50 mL.
• 4.1.5 Pipette: 2, 25 mL.

6. Recommended operating conditions

• During shaking and standing, the room temperature should be 20℃±5℃; if higher or lower than this temperature, distilled water pre-cooled or preheated to 20℃±5℃ may be added.
• Shaking mode: rotary shaking, speed about 120～150 r/min; shake for 5 min, let stand for 5 min.

7. Sampling and sample preparation

• 6.1 Filter the sample through qualitative filter paper, and weigh about 0.3～0.4 g.
• Gasoline (to obtain an accurate amount of gasoline): an ampoule may be used. First weigh the mass of the ampoule, then heat the spherical part of the ampoule over a small flame of a gas lamp or alcohol lamp, quickly insert the capillary end of the hot ampoule into the sample, so that the sample drawn into the ampoule can reach 0.3～0.4 g; or, according to the approximate density of the sample, inject a certain volume of sample into the ampoule with a syringe so that it can reach 0.3～0.4 g, then carefully seal the capillary end by welding, and weigh its mass again. Both weighings of the ampoule must be accurate to 0.0004 g. Place the ampoule containing the sample into an iodine flask already containing 5 mL 95% ethanol, break it and the capillary part in the 95% ethanol with a glass rod, and rinse the sample adhering to the glass rod and bottle wall with 10 mL 95% ethanol.
• Jet fuel (to obtain an accurate amount of jet fuel): a dropping bottle may be used. Inject the sample into the dropping bottle and weigh it, draw about 0.5 mL of sample from the dropping bottle, and drop it into an iodine flask already containing 15 mL 95% ethanol. Weigh the dropping bottle; both weighings must be accurate to 0.0004 g, and calculate the amount of sample taken from the difference.

8. Analytical procedure

• 6.2 Use a pipette to inject 25 mL of iodine-ethanol solution into the iodine flask, close the flask mouth tightly with a stopper previously moistened with potassium iodide solution, shake the iodine flask carefully, then add 150 mL of distilled water, and close the flask mouth with the stopper. Shake again for 5 min, using rotary shaking at a speed of about 120～150 r/min, and let stand for 5 min; during shaking and standing, the room temperature should be 20℃±5℃; if higher or lower than this temperature, distilled water pre-cooled or preheated to 20℃±5℃ may be added. Then add 25 mL 200 g/L of potassium iodide solution, immediately rinse the stopper and neck of the flask with distilled water, and titrate with the standard sodium thiosulfate titrant (clause 5.4). When the mixture in the iodine flask appears light yellow, add 5 g/L of starch solution 1～2 mL, and continue titrating with the standard sodium thiosulfate titrant (clause 5.4) until the blue-purple color of the mixture disappears.
• 6.3 Carry out a blank test according to clauses 6.1 and 6.2.

9. Qualitative and quantitative determination and calculation formulas

• Iodine value X₁ (g I/100 g) is calculated according to formula (1):

  X₁ = (V − V₁) × c × 0.1269 × 100 / m

  Where:

  • V—— volume of standard sodium thiosulfate titrant (clause 5.4) consumed in the blank test titration, mL;
  • V₁——volume of standard sodium thiosulfate titrant (clause 5.4) consumed in the sample test titration, mL;
  • c—— actual concentration of the standard sodium thiosulfate titrant (clause 5.4), mol/L;
  • 0.1269—— mass of iodine in grams equivalent to 1.00 mL of standard sodium thiosulfate titrant [c(Na₂S₂O₃)=1.000 mol/L];
  • m—— mass of sample, g.

• Unsaturated hydrocarbon content X₂ [% (m/m)] is calculated according to formula (2):

  X₂ = I × M / 254

  Where:

  • I—— iodine value of the sample, g I/100 g;
  • M—— average molecular weight of unsaturated hydrocarbons in the sample, found from Table 2 (interpolation may be used);
  • 254—— molecular weight of iodine.

• Table 2 (correspondence between sample 50% distillation temperature and average molecular weight M, with 50% distillation temperature determined according to GB/T 255 or GB/T 6536):

  Sample 50% distillation temperature ℃	M	Sample 50% distillation temperature ℃	M
  50	75	175	144
  75	100	200	161
  100	125	250	180
  125	150	—	200

  Note: The above table is the result extracted from source-text extraction; some numerical correspondences have suspected misalignment and require confirmation against the source standard (source-text extraction).

10. Precision

Judge the reliability of the results according to the following provisions (95% confidence level).

• Repeatability: the difference between two results obtained by the same operator in repeated determinations shall not exceed the value in Table 1.
• Reproducibility: the difference between two results submitted by two laboratories shall not exceed the value in Table 1.

Table 1

Note: This precision was obtained in 1981 by using seven samples in nine laboratories to carry out statistical tests, and by processing and analyzing the test results.

11. Report

not provided in the available source.

12. Referenced documents

• GB/T 255 Determination of distillation range of petroleum products
• GB/T 6536 Determination of distillation of 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