SH/T 0303-1992 Determination of sulfur content in additives (coulometric method)

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Card type: Test method

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

• Standard number: SH/T 0303-92
• Chinese name: Determination of sulfur content in additives (coulometric method)
• English name: not provided in the available source
• Replacement relationship: replaces SY 2688-83
• Other: marked “(20 confirmed in ×× year)” (the original text is source-text extraction noise, the specific year requires confirmation against the source standard (source-text extraction))
• Approval/implementation: approved by China Petrochemical Corporation 1992-05-20, implemented on 1992-05-20

2. Scope of application and non-applicability

• Applicable to non-volatile lubricating oil additives with sulfur content in the range of 0.5%～50%(m/m).
• Elements such as phosphorus, chlorine, nitrogen, zinc, calcium, and barium contained in the additive do not interfere with the determination results.
• Non-applicable scope: not provided in the available source.

3. Method principle

• This standard uses the coulometric method to determine the total sulfur content of additives.
• The sample is burned and decomposed at a high temperature of 1000℃ in an oxygen stream, during which sulfur burns to form SO₂ and SO₃.
• SO₂ enters the electrolytic cell with the combustion gas stream and reacts with I₃⁻ in the electrolyte, causing a change in the concentration of I₃⁻ in the electrolyte.
• At this time, the electrolysis anode reacts to generate I₃⁻; the electrolysis cathode reacts.
• The titration endpoint is indicated and controlled by a dual platinum plate electrode. After reaching the endpoint, electrolysis stops, and the microcoulometer records the amount of electricity consumed.
• Before determining the sulfur content of the sample, the instrument must first be calibrated with di-n-butyl disulfide standard reagent to determine its sulfur recovery rate, and then the sulfur content of the additive sample is determined, and the sulfur content of the sample is calculated based on the amount of electricity consumed and the sulfur recovery rate.

4. Reagents and materials (purity / preparation)

• 4.1 di-n-butyl disulfide: standard substance.
• 4.2 potassium iodide: analytical grade.
• 4.3 glacial acetic acid: analytical grade.
• 4.4 sodium azide: chemical grade.
• 4.5 vanadium pentoxide: chemical grade.
• 4.6 nitric acid: chemical grade, prepared by volume ratio into 1:1 nitric acid solution.
• 4.7 hydrochloric acid: chemical grade, prepared by volume ratio into 1:1 hydrochloric acid solution.
• Electrolyte preparation (5.1): weigh 10g potassium iodide, 5g sodium azide, measure 10mL glacial acetic acid, dissolve in 1L deionized water or distilled water, and store in a brown bottle for later use.
• Materials (3.2): magnet; ordinary oxygen (the content after “ordinary oxygen” in the original text requires confirmation against the source standard (source-text extraction)).

5. Instruments and equipment

• 3.1.1 Microcoulometer: YS-2A type microcoulometer or other microcoulometer of the same type. It should have a given bridge circuit matched with a dual platinum plate indicating electrode and with an adjustable current of 0～10μA; be able to provide an electrolysis current of 1～10μA; measurement and electrolysis should be isolated from each other; the current-time integration error should not exceed 1% (the original text “11%o” requires confirmation against the source standard (source-text extraction)).
• 3.1.2 Electrolytic cell: as shown in Figure 1. The electrolytic cell is a glass cylinder of φ60mm and height 70mm, with one 19 standard ground joint insertion hole, two 14 standard ground joint insertion holes, and one gas inlet tube insertion hole on the upper part, for installing electrodes and the gas inlet tube. Below the 19 female ground joint is connected a cathode compartment with a diameter of about 18mm, in which a cathode chamber is placed. The cathode chamber is a cylinder of φ12mm×40mm, with a semipermeable membrane made of ground glass or ion exchange membrane at the bottom, to prevent iodine from diffusing into the cathode chamber and only allow H⁺ to pass through. The electrolysis cathode is a platinum wire electrode. The electrolysis anode is a 7mm×10mm platinum plate electrode. The indicating electrode is a dual platinum plate electrode, each with an area of 7mm×10mm, and a spacing of 4～7mm. The two electrodes should be well insulated. The lower part of the gas inlet tube should be drawn into a capillary of φ1～2mm, so that the combustion gas can be dispersed in the electrolyte as fine bubbles.
• 3.1.3 Magnetic stirrer.
• 3.1.4 High-temperature furnace: furnace chamber diameter is φ40mm, length 550～600mm. The temperature distribution in the furnace is uniform; when ensuring the combustion section temperature is 1000℃, the maximum temperature in the furnace must not exceed 1150℃. The thermocouple placement hole for the combustion section should go straight through the furnace chamber, at a distance of 150mm from the furnace mouth.
• 3.1.5 Temperature controller.
• 3.1.6 Quartz tube: as shown in Figure 2 (the original text dimension data source-text extraction is severely noisy, requires confirmation against the source standard (source-text extraction)).
• 3.1.7 Quartz sample boat: as shown in Figure 3.
• 3.1.8 Quartz sample cup: a flat-bottomed quartz cup with dimensions φ6mm×6mm.
• 3.1.9 Gas flow controller or regulating valve.
• 3.1.10 Rotameter: range 0～500mL/min.
• 3.1.11 Semi-micro analytical balance: sensitivity 0.01mg.

6. Recommended operating conditions

• Combustion temperature: 1000℃ (high-temperature furnace held constant at 1000℃).
• Oxygen flow rate: 150mL/min±10mL/min (5.6).
• Microcoulometer settings (taking YS-2A type as an example, 5.7): set the “work—delay” selector to “work”; set the “auto—manual” selector to “auto”; set the “time selection” to “25s”; turn the “gain” to maximum; turn the “compensation” to “expand” (original text requires confirmation against the source standard (source-text extraction)); set the given value to “4”.
• Electrolytic cell equilibrium requirements (5.8): set the electrolysis current range to “1” μA (the original text “1"A” requires confirmation against the source standard (source-text extraction)), equilibrate the electrolytic cell until the microcoulometer counts no more than 0.2mC per minute on average, and the meter pointer must not drift in the iodine direction.
• Electrolysis time: not less than 1min (6.3).

7. Sampling and sample preparation

• 6.1 Weigh the sample into a quartz sample cup using a semi-micro balance, accurate to 0.01mg. Weigh the sample as follows to match the electrolysis current range:

• 6.9 If the sample contains alkaline earth metals such as calcium and barium, it is necessary to cover the sample with vanadium pentoxide at 1～2 times the sample amount.
• Quartz sample cup treatment (6.7): place the quartz sample cup in a beaker, add 1:1 hydrochloric acid solution, boil for 5～10min, after cooling rinse carefully with tap water and distilled water, dry and set aside.

8. Analytical procedure

• 5.2 Soak the two pairs of electrodes in 1:1 nitric acid for 1～2min, then rinse clean with distilled water and insert them into the corresponding positions in the electrolytic cell.
• 5.3 Add 40～50mL electrolyte to the electrolytic cell; the amount should be sufficient to immerse each pair of electrodes but not exceed the upper opening of the cathode chamber. The cathode chamber should be filled with electrolyte.
• 5.4 Assemble the instrument as shown in Figure 4, connect the oxygen path and the high-temperature furnace to the temperature controller, and connect each pair of electrodes to the microcoulometer.
• 5.5 Turn on the temperature controller switch, raise the temperature of the high-temperature furnace and hold it constant at 1000℃.
• 5.6 Turn on the oxygen, adjust the oxygen flow rate to 150mL/min±10mL/min.
• 5.7 Turn on the microcoulometer switch, set each selector switch as required (see Section 6).
• 5.8 Start the magnetic stirrer (note to adjust the stirring speed and position so that bubbles can be dispersed in the electrolytic cell and must not escape directly). Press the “start” button, set the electrolysis current range to “1” μA, and equilibrate the electrolytic cell. The electrolytic cell should be fully equilibrated until the microcoulometer counts no more than 0.2mC per minute on average, and the meter pointer must not drift in the iodine direction. Otherwise, check each pair of electrodes, or carefully burn the indicating electrode with an alcohol lamp, or clean the electrolytic cell and replace the electrolyte. Then re-equilibrate the electrolytic cell until it meets the requirements.
• 6.2 Open the rubber stopper at the mouth of the quartz tube, place the weighed sample in the quartz sample cup in the quartz sample boat, then put them together into the quartz tube, close the rubber stopper, and use a magnet to send the sample boat to the combustion position.
• 6.3 Immediately after sample introduction is completed, press the “start” button; counting begins after 25s (note to select the electrolysis current range as above so that the electrolysis time is not less than 1min).
  • Note ①: Before the formal determination begins, two to four sulfur-containing samples that do not contain metals should first be burned to bring the adsorption of the quartz tube to equilibrium.
  • Note ②: After each change of the electrolysis current range, it is also necessary to first burn one to two sulfur-containing samples that do not contain metals, so that the electrolytic cell re-establishes equilibrium, to avoid erroneous results due to different over-iodine phenomena.
• 6.4 When counting stops and the “measurement” meter pointer returns to the equilibrium position, record the electricity quantity. Then open the rubber stopper, use a magnet to take out the quartz sample boat, and close the rubber stopper again.
• 6.5 After the determination is completed, turn off the temperature controller and microcoulometer switches, continue to pass oxygen to purge the quartz tube for 10min, and close the flow controller and oxygen cylinder.
• 6.6 Turn off the magnetic stirrer switch. Pour out the electrolyte in the electrolytic cell, rinse the electrolytic cell and electrodes carefully with distilled water, then fill with distilled water and soak the electrodes in distilled water.
• 6.8 According to clauses 6.2～6.4, run three to five di-n-butyl disulfide standard substances, record the electricity quantity Q₀ respectively, calculate their sulfur recovery rate T, and take the arithmetic mean as the instrument’s average sulfur recovery rate Tₐ.
• 6.9 According to clauses 6.2～6.4, determine the sulfur content in the additive, record the electricity quantity Q, and calculate its sulfur content. If the sample contains alkaline earth metals such as calcium and barium, it is necessary to cover the sample with vanadium pentoxide at 1～2 times the sample amount.
  • Note: During the initial period of using vanadium pentoxide, the sulfur recovery rate drops rapidly and then tends to stabilize. At this time, when determining the sulfur content of samples containing calcium and barium, di-n-butyl disulfide standard substance should be inserted from time to time during the determination process to correct the sulfur recovery rate.

9. Qualitative and quantitative and calculation formula

• 7.1 The sulfur recovery rate T(%) is calculated according to formula (1): T = Q₀ / (15.62 × m₁) Where: Q₀—microcoulometer electricity count, mC; m₁—mass of di-n-butyl disulfide, mg; 15.62— conversion coefficient, mC/mg.
• 7.2 Sulfur content of the sample S[%(m/m)] is calculated according to formula (2): S = Q / (60 × m₂ × T) × 100 (the original formula source-text extraction is severely noisy, requires confirmation against the source standard (source-text extraction)) Where: Q— microcoulometer electric quantity count, mC; m₂—sample mass, mg (the original text “g” requires confirmation against the source standard (source-text extraction)); 60— conversion coefficient, mC/mg; T— average sulfur conversion rate, %.

10. Precision

• Use the following provisions to judge the reliability of test results (95% confidence level).
• 8.1 Repeatability: the difference between two results obtained by the same operator from repeated determinations shall not exceed the following values:

• 8.2 Reproducibility: the difference between two results submitted by two laboratories shall not exceed the following values:

• Note: The precision of this standard was obtained in 1982 through statistical experiments conducted by five laboratories on ten samples, and through data processing and analysis of the experimental results.

11. Report

• Take the arithmetic mean of two repeated determination results as the sulfur content of the sample.

12. Referenced documents

• not provided in the available source (apart from the replaced standard SY 2688-83, no other normative referenced documents are listed).

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 reference