SH/T 0171-1992 Determination of Nitrogen in Petroleum and Petroleum Products (Thymol Colorimetric Method)

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Card type: Test method

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

• Standard number: SH/T 0171-92
• Chinese title: Determination of Nitrogen in Petroleum and Petroleum Products (Thymol Colorimetric Method)
• English title: not provided in the available source
• Replacement relationship: replaces ZB E30 012-88
• Other: approved by 1992-05-20, implemented by 1992-05-20; confirmed in (200] year (original text as such, year requires confirmation against the source standard (source-text extraction))
• Technical responsibility: technical responsibility by the Research Institute of Petroleum Processing
• Drafting: drafted under the responsibility of the Refining Research Institute of Luoyang Petrochemical Engineering Company
• First issued: 1977 year 2 month

2. Applicable scope and non-applicability

• Applicable to petroleum and petroleum products with nitrogen content greater than 0.00002% (m/m).
• Not applicable: not provided in the available source.

3. Method principle

The sample is digested in sulfuric acid with selenious acid catalyst added, and the digestion product ammonium sulfate is directly determined by the sodium hypochlorite-thymol colorimetric method.

4. Reagents and materials (purity / preparation)

• 4.1 Sodium hypochlorite: analytical reagent.
• 4.2 Ammonium chloride: guaranteed reagent.
• 4.3 Sodium hydroxide: guaranteed reagent. Prepare 40 g/L, 60 g/L and 200 g/L solutions.
• 4.4 Sodium bicarbonate: guaranteed reagent.
• 4.5 Sodium carbonate: guaranteed reagent.
• 4.6 Thymol: chemical reagent.
• 4.7 Potassium sulfate: analytical reagent. In a porcelain evaporating dish, ignite in a high-temperature furnace at 560℃ for 8 h and set aside.
• 4.8 Disodium ethylenediaminetetraacetate: analytical reagent.
• 4.9 Selenious acid: chemical reagent.
• 4.10 Sulfuric acid: guaranteed reagent and analytical reagent.
• 4.11 Acetone: analytical reagent.
• 4.12 Sodium thiosulfate: analytical reagent, prepare c(Na₂S₂O₃)=0.1 mol/L sodium thiosulfate standard titration solution.
• 4.13 Petroleum ether: 90～120℃, analytical reagent.
• 4.14 Phenolphthalein indicator: prepare 0.5 g/L ethanol indicator solution.
• 4.15 Distilled water: doubly distilled.

Reagent preparation in the preparatory work:

• 5.2 Denitrified petroleum ether: extract nitrogen compounds from petroleum ether twice with sulfuric acid (analytical reagent). The volume ratio of sulfuric acid to petroleum ether is 1:2, shake the mixture vigorously for 15 min, allow to stand for layering, discard the sulfuric acid, and denitrified petroleum ether is obtained.
• 5.3.1 Sodium hypochlorite: prepare a solution with available chlorine content of 0.10% (solutions prepared from commercially available sodium hypochlorite need to be standardized once every two months).
  • Standardization: use a pipette to take 1.0 mL sodium hypochlorite solution, add 20 mL water, shake well, add 2 g potassium iodide, finally add 5 mL hydrochloric acid, with starch as indicator, titrate with sodium thiosulfate standard titration solution, determine available chlorine content X₁ (%) according to formula (1):
    • X₁ = 1.8 c·V ………………(1)
    • Where: c— the actual concentration of the sodium thiosulfate standard titration solution, mol/L; V— the volume of sodium thiosulfate standard titration solution consumed during titration, mL.
• 5.3.2 Ammonium chloride standard solution: during preparation, dry ammonium chloride at 110℃ for 1 h, weigh 0.7638 g into a 1000 mL volumetric flask, dilute to the mark with water, and a standard solution of 200 μg N/mL is obtained. Take 25.00 mL of this solution into a 500 mL volumetric flask, dilute to the mark, and a standard solution of 10 μg N/mL is obtained.
• 5.3.3 Sodium hypochlorite buffer mixed solution: take 5 g sodium bicarbonate, 8 g sodium carbonate, dissolve in 750 mL water, then add 250 mL sodium hypochlorite solution with chlorine content of 0.10%.
• 5.3.4 Thymol-acetone solution: weigh 15 g thymol, dissolve in 100 mL acetone, store in a brown bottle. Take care to prevent loss of acetone by evaporation.
• 5.3.5 Thymol-sodium hydroxide solution: mix equal volumes of the thymol-acetone solution and 60 g/L sodium hydroxide solution before use.
• 5.3.6 Sulfuric acid-selenious acid mixed solution: 100 mL sulfuric acid (guaranteed reagent), add 0.3 g selenious acid. When preparing and using this solution, special attention must be paid to preventing absorption of ammonia from the air.
• 5.3.7 Sulfuric acid-selenious acid mixed solution (1:1): add the sulfuric acid-selenious acid mixed solution prepared in 5.3.6 to an equal volume of water.
• 5.3.8 Disodium ethylenediaminetetraacetate solution: weigh 15 g disodium ethylenediaminetetraacetate, dissolve in 250 mL water, prepare 75 g/L solution.
• 5.3.9 Doubly distilled water: take once-distilled water, add a few drops of sulfuric acid and 10 g/L potassium permanganate aqueous solution in a ground-glass stoppered flask and distill to prepare doubly distilled water. This standard uses doubly distilled water throughout.

5. Instruments and equipment

• 3.1 Digestion apparatus, composed of the following parts:
  • 3.1.1 Heating furnace: power about 2 kW, capable of ensuring complete reaction of the digestion liquid. The top of the heating furnace has test tube insertion holes; after insertion, the test tubes should form an angle of 45° with the horizontal plane (original text is “[garbled angle value]”, requires confirmation against the source standard (source-text extraction)) (the test tube mouth must not face the operator).
  • 3.1.2 Insulation layer: thickness about 100 mm, the front part can be removed to observe the reaction phenomenon of the digestion liquid in the test tube.
  • 3.1.3 Test tube: hard glass test tube with inner diameter 15 mm and length 250 mm, marked with 10 mL and 30 mL graduation lines, and with a ground-glass stopper.
• 3.2 72 type spectrophotometer.
• 3.3 Test tube rack.
• 3.4 Small glass cup: outer diameter 5 mm, inner diameter 4 mm, cup height 2.5 mm, cup depth 2.0 mm.
• 3.5 Glass tube: for aeration and stirring, inner diameter 1 mm, outer diameter 3 mm.
• 3.6 Volumetric flask: 500, 1000 mL.
• 3.7 Microburette: 4, 10 mL.
• 3.8 Graduated cylinder: 25, 100 mL.
• 3.9 Pipette: 2, 25 mL.
• 3.10 Separatory funnel: 50 mL.
• 3.11 Porcelain evaporator: 250 mL.
• 3.12 Syringe: 0.25, 1, 5 mL.

6. Recommended operating conditions

• Digestion: control the voltage so that the digestion liquid level in the test tube does not exceed the 30 mL graduation line; when the digestion liquid begins to turn yellow, increase the voltage and put the front insulation layer in place, so that sulfuric acid refluxes upward and carries down the sample on the test tube; when the digestion liquid is colorless and transparent, continue digestion for 30 min.
• Colorimetry: use a 1 cm liquid cell, select a wavelength of 665 nm, and measure absorbance with distilled water as reference solution.
• Standing time for the standard working curve: cover, shake well, and measure after standing for 1 h.
• Frequency of standard working curve check: under normal circumstances, check the standard working curve once every six months.
• Frequency of sodium hypochlorite solution standardization: solutions prepared from commercially available sodium hypochlorite need to be standardized once every two months.

7. Sampling and sample preparation

• 6.1 Samples with nitrogen content greater than 0.003% (m/m): take 10～200 mg of sample (see the table below for sample amount, the original table content requires confirmation against the source standard (source-text extraction)); for flowing samples, use a 0.25 mL syringe to sample; for viscous samples, use a small glass cup to sample.
• 6.2 Samples with nitrogen content of 0.003% (m/m) and less than 0.003% (m/m): weigh 1～20 g of sample into a separatory funnel, add sulfuric acid-selenious acid (1:1) mixed solution 1 mL, shake for 15 min, after standing and layering, put the extract into a test tube containing potassium sulfate 400 mg, repeat the extraction once more, and combine the extracts in the same test tube. Then carry out digestion and colorimetric determination according to the procedure in clause 6.1. If a sample is difficult to layer when directly extracted with sulfuric acid, the sample may be diluted in advance with denitrified petroleum ether.
• A blank test shall be carried out each time.
• The content of the original “Table of provisions for sample nitrogen content and sample amount” requires confirmation against the source standard (source-text extraction).

8. Analytical procedure

• 5.4 Draw the standard working curve: In seven test tubes, use a microburette to respectively add 0, 5, 10, 15, 20, 25 and 30 μg nitrogen standard solution, and add water to 10 mL. To each add 0.5 g/L phenolphthalein ethanol indicator solution 1 drops, disodium ethylenediaminetetraacetate solution 1 drops, then insert a stirring glass tube with an air flow of about 50 mL/min into the test tube, neutralize with 40 g/L sodium hydroxide solution until the solution turns red, immediately add sodium hypochlorite buffer mixed solution 2.0 mL, thymol-sodium hydroxide solution 2.0 mL. If a precipitate forms, immediately add several drops of 40 g/L sodium hydroxide solution to make the precipitate disappear, take out the stirring glass tube, rinse it clean with water, add water to the 30 mL mark, cover and shake well, after standing for 1 h, use a 1 cm liquid cell, select 665 nm wavelength, measure absorbance with distilled water as reference solution, subtract the blank absorbance, and plot the standard working curve with nitrogen content as the abscissa and absorbance as the ordinate.
• 6.1 Analysis of samples with nitrogen content greater than 0.003% (m/m): Add potassium sulfate 400 mg to the test tube, use a 1 mL syringe without a needle to take sulfuric acid-selenious acid mixed solution 1 or 1.6 mL, take sample 10～200 mg, place at the bottom of the test tube, shake vigorously, and then digest. Control the voltage so that the liquid level of the digestion solution in the test tube does not exceed the 30 mL mark. When the digestion solution begins to turn yellow, increase the voltage and put on the front insulation layer so that the sulfuric acid refluxes upward and carries down the sample on the test tube. When the digestion solution is colorless and transparent, continue digestion for 30 min, remove the test tube, after slight cooling, add water along the wall around the tube to the 10 mL mark, shake well, and perform colorimetric determination according to the operating steps for drawing the standard working curve, but during neutralization place the test tube in cold water, neutralize with 200 g/L sodium hydroxide solution until the digestion solution is about to turn red, rinse the tube wall and air tube with water, then neutralize with 40 g/L sodium hydroxide solution until the digestion solution turns red. A blank test shall be done each time.
• 6.2 Analysis of samples with nitrogen content of 0.003% (m/m) and less than 0.003% (m/m): After sample preparation according to Section 7, carry out digestion and colorimetric determination according to the steps in Clause 6.1. A blank test shall be done each time.

9. Qualitative and Quantitative and Calculation Formula

• The nitrogen content in the sample X[% (m/m)] is calculated according to formula (2):
  • X = (A / (m × 1000)) × 100 = 0.1 × A / m
  • Where: A— is the nitrogen content found from the standard working curve, μg; m— is the mass of the sample, mg.
  • Note: The original formula layout is “one X two A m x 1000 x 100= 0.Ix A knife t”, arranged according to context, requires confirmation against the source standard (source-text extraction).

10. Precision

Repeatability: The difference between two results of repeated determinations shall not be greater than the following values.

Note: The original table layout is “60.0001” “> 0.0001[unreadable separator]0.001”, in which “60.0001” is suspected to be “≤0.0001”, requires confirmation against the source standard (source-text extraction).

11. Report

Take the arithmetic mean of two results of repeated determinations as the determination result of the sample.

12. Reference Documents

not provided in the available source.

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 for Questions and Answers