NB/SH/T 0174-2015 Detection of mercaptans and other sulfur compounds in petroleum products and hydrocarbon solvents — Doctor test method

AI-translated method card — human verification pending. This is not an official translation of the standard. Unclear source values remain unverified; check the original standard and product certificate before use.

Card type: Test method

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

• Standard number: NB/SH/T 0174—2015
• Chinese full title: Detection of mercaptans and other sulfur compounds in petroleum products and hydrocarbon solvents — Doctor test method
• English name: Petroleum products and hydrocarbon solvents—Detection of thiols and other sulfur species—Doctor test
• Replacement relationship: replaces SH/T 0174—1992 "Qualitative test method for mercaptans in aromatic hydrocarbons and light petroleum products (Doctor test method)"
• Adoption relationship: modified adoption by redrafting method of ISO 5275:2003 (MOD)
• Publication/implementation: published on 2015-10-27, implemented on 2016-03-01
• Issuing authority: National Energy Administration

2. Scope of application and non-applicability

• This standard specifies a test method for the qualitative detection of mercaptans, hydrogen sulfide and elemental sulfur using Doctor reagent.
• Applicable to hydrocarbon solvents and petroleum fractions (including intermediate products and products).
• The preliminary test of this standard can also detect the presence of peroxides and phenolic substances, but it is not applicable when peroxides and phenolic substances are greater than trace amounts.
• When the carbon disulfide content is too high (its sulfur content mass fraction greater than 0.4%), it will cause the aqueous phase to darken and interfere with this test.
• Method application (Chapter 4): This standard is a pass/fail test method based on the detection threshold of mercaptan concentration, where the detection threshold varies with different test samples. It is usually used as an alternative method to quantitative determination of mercaptans.

3. Method principle

Shake the sample with sodium plumbite solution added, and observe the mixed solution to infer from its appearance whether mercaptans, hydrogen sulfide, elemental sulfur or peroxides are present. Then further determine whether mercaptans are present by adding sulfur powder, shaking and observing changes in the appearance of the final mixed solution.

4. Reagents and materials (purity / preparation)

• 5.1 General: Unless otherwise specified, analytical grade reagents shall be used. Water shall meet the requirements for grade three water in GB/T 6682—2008.
• 5.2 Lead acetate trihydrate (CH₃COO)₂Pb·3H₂O: analytical grade, used to prepare sodium plumbite solution.
• 5.3 Sodium hydroxide (NaOH): analytical grade, used to prepare sodium hydroxide solution with mass fraction 10%.
• 5.4 Sodium plumbite solution (Doctor reagent):
  • 5.4.1 Dissolve 25 g lead acetate trihydrate in 200 mL water, filter and add the filtrate to 100 mL aqueous solution in which 60 g sodium hydroxide has been dissolved. Heat this mixed solution in a boiling water bath for 30 min±5 min, and after cooling dilute with water to 1000 mL.
  • 5.4.2 This solution should be stored in a closed container. If not clear, it should be filtered before use.
• 5.5 Cadmium chloride: analytical grade. Warning: cadmium chloride is toxic and should be disposed of as environmentally toxic waste.
• 5.6 Hydrochloric acid (HCl): mass fraction about 36%.
• 5.7 Cadmium chloride solution:
  • 5.7.1 Dissolve cadmium chloride in water, add 10 mL hydrochloric acid, then dilute to 1000 mL. (The reagent amount figures in this clause require confirmation against the source standard (source-text extraction))
  • 5.7.2 For routine analysis, 50 g/L sodium bicarbonate aqueous solution may be used instead of cadmium chloride solution. However, because the sulfur produced by the reaction of sodium bicarbonate with hydrogen sulfide is colorless, lead acetate test paper is required to verify whether hydrogen sulfide has been removed.
• 5.8 Sulfur (sublimed sulfur): sublimed sulfur powder. Should be stored in a closed container.
• 5.9 Potassium iodide solution (KI): Dissolve potassium iodide in 10 mL water to prepare potassium iodide solution of 100 g/L, and it should be prepared before use each day. (The weighed amount of potassium iodide in the source text requires confirmation against the source standard (source-text extraction))
• 5.10 Acetic acid solution (CH₃COOH): Dissolve glacial acetic acid in 10 mL water to prepare acetic acid solution of 100 g/L, and it should be prepared before use each day. (The weighed amount of glacial acetic acid in the source text requires confirmation against the source standard (source-text extraction))
• 5.11 Starch solution: Dissolve 0.05 g starch in 10 mL water to prepare starch solution of 5 g/L, and it should be prepared before use each day.
• 5.12 Sodium bicarbonate (NaHCO₃): analytical grade.
• 5.13 Lead acetate test paper: prepare 50 g/L sodium bicarbonate... (the content of this clause in the source text is incomplete, requires confirmation against the source standard (source-text extraction))

5. Apparatus and equipment

• 6.1 Mixing cylinder: glass, capacity 50 mL, used for mixing solutions during the test.
• 6.2 Graduated cylinders: glass, capacities 5 mL and 10 mL respectively, used for measuring reagents. (The capacity figures in the source text require confirmation against the source standard (source-text extraction))
• 6.3 Separatory funnel: glass, with stopper.

6. Recommended operating conditions

Not provided in the available source.

7. Sampling and sample preparation

• 7.1 Unless otherwise specified, sampling shall be in accordance with the provisions of GB/T 4756 or GB/T 27867, and the test sample used for analysis shall be representative.
• 7.2 Before the test, the sample should be shaken thoroughly to mix fully. At room temperature, if the vapor pressure of the sample exceeds 30 kPa, pressure should be released frequently to ensure safety.

8. Analytical procedure

• 8.1 Preliminary test
  • 8.1.1 Phenolic substances — If it is suspected that the test sample contains phenolic substances used as oxidation inhibitors, which may interfere with the color of the aqueous phase in the test result, use a mixing cylinder (6.1) to take 10 mL test sample, add 5 mL sodium hydroxide solution with mass fraction 10% (5.3), and shake the mixing cylinder vigorously for 15 s. Then observe the color development. If no meaningful color development appears, continue the test as specified in 8.1.2. If meaningful color development appears, stop the test.
    • Note: Any color development deeper than yellow is meaningful color development. If yellow is produced, depending on the color development, the 4th type in Table 1 may be modified.
  • 8.1.2 Mercaptans, elemental sulfur, hydrogen sulfide, peroxides — Place 10 mL test sample and 5 mL sodium plumbite solution (5.4) in a mixing cylinder (6.1), and shake the mixing cylinder vigorously for 15 s. Then observe the mixed solution and judge according to the provisions of Table 1.

Table 1 Judgment of preliminary test

• 8.2 Peroxides: Take 10 mL test sample and place it in a mixing cylinder (6.1), add 2 mL potassium iodide solution (5.9), a few drops of acetic acid solution (5.10) and a few drops of starch solution (5.11). Shake the mixing cylinder vigorously for 15 s, and after the mixed solution becomes clear, observe the color of the aqueous layer. If the aqueous layer appears blue, it proves the presence of peroxides sufficient to invalidate the test result.
• 8.3 Hydrogen sulfide
  • 8.3.1 If a black precipitate forms after performing step 8.1.2, use a separatory funnel (6.3) to take a new 20 mL test sample, add 1 mL cadmium chloride solution (5.7), and shake vigorously for 15 s. After layering is stable, slowly pour out 10 mL non-aqueous layer into a mixing cylinder (6.1), and repeat the operating steps of 8.1.2. If there is no black precipitate after the first washing, add the washed test sample to sodium plumbite solution (5.4) and continue the operating steps of 8.1.2; if black precipitate still appears, remove the aqueous layer in the separatory funnel, then add 0.5 mL cadmium chloride solution (5.7), and repeat the washing and test. If sodium bicarbonate solution is used to remove hydrogen sulfide, the specific requirements are detailed in 5.7.2.
  • 8.3.2 Usually after two washings the test sample will no longer form black precipitate. If precipitate still forms, the hydrogen sulfide washing step should be continued until the test sample no longer forms black precipitate. However, it must be ensured that the final volume of the test sample is greater than 10 mL, so that the operating steps of clauses 8.1.2 and 8.4 can be completed.
• 8.4 Mercaptans: To the mixed solution of test sample and sodium plumbite obtained according to clause 8.1.2 or 8.3, add a small amount of sulfur (5.8). The amount added should not be too much, just enough to cover the interface of the mixed solution of test sample and sodium plumbite. Shake the mixing cylinder vigorously for 15 s, and let stand for 60 s±5 s. Observe whether brown or black precipitate appears in the mixed solution. If precipitate forms, mercaptans above the detection threshold of this standard are considered present.

9. Qualitative and quantitative determination and calculation formulas

• 9.1 If, according to the steps of 8.1.1, it is determined that interfering substances are present and the test cannot continue, report as "Test invalid — interfering substances present".
• 9.2 If, according to the steps of clause 8.2, it is determined that peroxides are present, report as "Test invalid — peroxides present".
• 9.3 If, after testing according to the provisions of 8.1.2, a black precipitate appears immediately after the test sample and sodium plumbite solution are mixed and shaken, report as "Fail (positive) — hydrogen sulfide present". If, after removing hydrogen sulfide, a black or brown precipitate is produced after adding sulfur according to the provisions of clause 8.4, report as "Positive (fail) — hydrogen sulfide and mercaptans present".
• 9.4 If, according to the provisions of 8.1.2, the mixed solution of test sample and sodium plumbite becomes milky white after shaking, and then the color gradually darkens, report as "Positive (fail) — mercaptans and/or elemental sulfur present".
• 9.5 If, as specified in 8.1.2, the mixed solution of the test sample and sodium plumbite turns milky white after shaking, and as specified in 8.4, after adding sulfur, a brown or black precipitate forms in the mixed solution, report as "positive (fail)—mercaptans present".
• 9.6 If, as specified in 8.1.2, the mixed solution of the test sample and sodium plumbite shows no precipitate, no color change, or only turns light yellow after shaking, and as specified in 8.4, after adding sulfur, the mixed solution does not produce a precipitate, report as "negative (pass)"; if the mixed solution produces a precipitate, report as "positive (fail)—mercaptans present".
• Calculation formula: not provided in the available source.

10. Precision

Because this method only determines whether active sulfur is present in a sample by comparing the active sulfur content of a single sample under specified test conditions with the detection threshold specified in this method, precision cannot be determined.

11. Report

The test report shall include at least the following:

• a) reference to this standard;
• b) the type and complete identification or certificate of the sample tested;
• c) test results (see Chapter 9);
• d) any differences from the specified test procedure, noting agreement or other reasons;
• e) date of test.

12. Normative References

• GB/T 4756 Petroleum liquids—Manual sampling (GB/T 4756—1998, eqv ISO 3170:1988)
• GB/T 6682—2008 Water for analytical laboratory use—Specification and test methods (ISO 3696:1987 MOD)
• GB/T 27867 Petroleum liquids—Automatic pipeline sampling (GB/T 27867—2011, ISO 3171:1988 IDT)
• ISO 5275:2003 Petroleum products and hydrocarbon solvents—Detection of thiols and other sulfur species—Doctor test (modified adoption)

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