SH/T 0253-1992 Determination of total sulfur content in light petroleum products — Coulometric method

Summary page. This page is a compiled excerpt/summary of the standard — it is not the full standard text and does not replace it. Verify every value against the official standard and the product certificate before use.

SH/T 0253-1992 specifies the determination of total sulfur in light petroleum products by oxidative combustion and microcoulometric titration, and this page summarizes its historical identity, scope, principle, apparatus, reagents, operating conditions, calibration, sample introduction, equations, precision and open queries.

Evidence note: historical study material for the 1992 edition, which the 2021 edition explicitly replaces while the old status entry conflicts; not the full standard text or an operating procedure, and technical review is pending. Queries on formula units and multipliers are retained, and no calculator is provided.

Method identity and historical position: Original PDF 1 and the official 1992 record/2021 publication evidence. SH/T 0253-1992, Determination of total sulfur content in light petroleum products (coulometric method). The original header reads SH/T 0253-92; it was approved and implemented on 1992-05-20, replacing SY 2506-83. This page is compiled as historical study of the 1992 edition. The old official entry still shows current, while the 2021 original and the attachment to Energy Administration Publication No. 5 of 2021 explicitly replace this edition and implement on 2022-05-16; the status conflict is retained, current applicability is not established from the old entry, and the 2021 entry point is not overridden. Official metadata and independent technical acceptance are kept separate.

Scope and interference limits: Original PDF 1, Chapter 1. This edition applies to light petroleum products with a boiling point of 40 °C–310 °C and a sulfur content range of 0.5–1000 ppm; above 1000 ppm the original permits determination after dilution, but the dilution and recovery conditions must be checked, and the original range cannot be extended directly. It does not apply to samples with a halogen content greater than 10 times the sulfur content, a total nitrogen content greater than 10% or a heavy metal content exceeding 500 ppm. This page does not call the lower limit of the measuring range the detection limit of a specific instrument or a guaranteed value of a product batch.

Microcoulometric principle and reactions: Original PDF 1, Chapter 2. The sample is vaporized, enters the combustion section with nitrogen and mixes with oxygen, and oxidation produces sulfur dioxide, which enters the titration cell and consumes triiodide ions; the electrode detects the change, electrolysis replenishes the triiodide ions, and the sulfur is obtained from the quantity of electricity consumed. The reactions as printed: I₃⁻ + SO₂ + H₂O → SO₃ + 3I⁻ + 2H⁺; anode: 3I⁻ → I₃⁻ + 2e⁻. SO₃ is transcribed as in the original equation, and the charge omitted by the original author is not guessed or replaced with another reaction. Learning the reaction is not a controlled titration operation.

Apparatus composition: Original PDF 1–3, Chapter 3 and Figures 1–2. The microcoulometer, recorder or coulometric integrator, sectional pyrolysis furnace, quartz pyrolysis tube, titration cell, electromagnetic stirrer, sample injector and gas flow stabilizer together form the analysis system. The recorder sensitivity is 1 mV, and the float-type flow meter is 0–200 mL/min. The two pairs of platinum electrodes in the titration cell serve respectively as indicator-reference and for electrolysis, and their functions must not be combined. Other types of pyrolysis tube and titration cell are permitted provided they ensure the analytical capability specified by this edition; the original dimensional drawings are not fully reconstructed and are not used for manufacture or equipment acceptance.

Gases, solvents and standard materials: Original PDF 2, 3.2 and Chapter 4. The original uses commercially available general-purpose oxygen and nitrogen and requires a blank test to prevent sulfur-containing impurities from entering the system; general-purpose gas does not mean that any gas source is suitable. The sulfur-free oil used for preparing standards is made from refined oil of boiling point 60 °C–180 °C and has a sulfur content below 0.1 ppm as measured by this method. The original lists analytical grade reagents, glacial acetic acid, potassium iodide, sodium azide, iodine and treated water; low-sulfur solvents such as cyclohexane, isooctane and hexadecane and suitable sulfur compounds are used for standards, with no item numbers or supply commitments added. 4.5 calls the water quality conductivity but prints the unit as 10⁶ cm·Ω; the term and dimensions are inconsistent and left for verification, and no water acceptance limit is set on that basis. Activation and reagent safety work must use confirmed procedures.

Electrolyte and standard solutions: Original PDF 4, 5.1–5.2. The original electrolyte formulation lists 0.5 g potassium iodide, 0.6 g sodium azide, 500 mL distilled water and 5 mL glacial acetic acid, diluted to 1000 mL and stored in a brown bottle. This is a method-prepared electrolyte, not proof of product storage or shelf life. Standards must be prepared so that the boiling point of the solution and the type of sulfide are close to those of the sample; the original first prepares 100–1000 ppm and then a dilution series according to the sample range. Original equation 1 prints S₂ = m×S₁×10⁶/(m+m₁) = m×S₁×10⁶/(m+V×ρ). The text before the original equation calls S₂ a % (m/m), while the definition calls S₁ a sulfur percentage, so the input basis against the 10⁶ multiplier requires verification; m and m₁ are in g, V is the solvent in mL and ρ the solvent in g/mL. This page only retains the original equation and does not turn it into an executable standard-preparation calculator.

System preparation and condensation prevention: Original PDF 4, 5.3.1–5.3.7. Replace the heat-resistant silicone rubber septum and connect the gas and pyrolysis systems correctly; remove bubbles from the electrode side arm of the electrolyte so that the liquid level is 3–6 mm above the platinum electrode. The inlet conduit is insulated to prevent water vapour condensation. Stirring is characterized in the learning material by a slight vortex; too fast, unstable or too slow stirring affects equilibrium and determination; avoid bending the electrodes. The complete connection, insulation and high-temperature safety procedure have not been reconstructed, and this page does not replace a controlled operating procedure.

Furnace temperatures, flows and bias voltage: Original PDF 4–5, 5.3.8–5.3.9. The three temperature zones and the two gas paths are listed separately below, and the furnace temperature must not be used as a product storage temperature. The bias voltage is usually 120–160 mV, and a suitable value may also be selected according to the instrument model; the range resistor and amplification must give a symmetrical peak within the recorder range. The range conditions do not prove that any instrument or specific product applies, nor do they replace verification of complete combustion and analytical capability. Item | Original operating condition Inlet section furnace temperature | 600 °C–700 °C Centre section furnace temperature | 800 °C–1000 °C Outlet section furnace temperature | 700 °C–800 °C Oxygen reaction gas flow | 40–200 mL/min Nitrogen carrier gas flow | 40–200 mL/min Usual bias voltage | 120–160 mV

Calibration and recovery: Original PDF 5, 6.1–6.2 equation 2. Select a standard close to the estimated sulfur content of the sample; the difference between the two determination results must not exceed the precision of 8.1 of this edition, and the mean is taken. Original equation 2: C = (S₂/S₃)×100; here S₂ is the mean measured value of the standard in ppm and S₃ the prepared value in ppm. The recovery must be greater than 75% before testing is allowed, and it must not be changed to greater than or equal to; the use and units of S₂ in equations 1 and 2 differ and must be read with their own definitions. The basis and coefficient for entering C as a % in the later equations still require verification and are not guessed as a decimal fraction.

Volumetric and gravimetric sample introduction: Original PDF 5, 6.3–6.5. In the volumetric method, a 10 μL syringe is used to take about 8 μL of sample, and the actual injected amount is determined from the difference between the syringe reading and the residual volume after injection, so 8 μL is not taken directly as the amount actually entering the system each time. The gravimetric method obtains the actual mass from the difference in weighing before and after injection. The original recommends an injection rate within 0.1–1 μL/s to ensure complete combustion, and the procedure for unknown samples is the same as for standards; complete combustion and the measuring capability must be verified. This page publishes no on-machine operation or automatic judgement tool.

Result equations and dimensional queries: Original PDF 5, Chapter 7 equations 3–4 and PDF 7, Annex A. Original equation 3: S = 0.166×Q/(V×ρ×C) = 0.166×Q/(m₂×C). Original equation 4: S = 9948×A×V′×S′/(R×V×ρ×C) = 9948×A×V′×S′/(R×m₂×C). The printed coefficients and grouping are retained and not changed into the 2021 edition formulas. Q is in μC, V the sample in μL, ρ the sample in g/mL, m₂ the sample in mg; A is the peak area in cm², V′ the recorder in mV/cm, R the range resistance in Ω. The body gives S′ in cm/min while Annex A defines min/cm; the textual conflict is retained, and equation 4 cannot be used directly on the basis of this page for calculation. Annex A gives the sulfur equivalent of 16 g/eq and the Faraday constant of 96500 C/eq; this is an equivalent, not a sulfur molar mass of 16 g/mol. The substitution of the percentage recovery C and the standard preparation multiplier still await dimensional verification, and no calculator is published.

Precision curve boundaries: Original PDF 5, Chapter 8 and PDF 6, Figures 4a–b. The difference between repeat results by the same operator must not exceed the repeatability curve value of Figures 4a–b, and the difference between results from different laboratories must not exceed the corresponding reproducibility curve value; the original notes that both figures use logarithmic graph paper. This page does not back-fit a numerical formula from the scanned curves or reconstruct point-by-point limits, nor does it borrow the 2021 exponential expressions. No extrapolation beyond the plotted range; method precision is not batch certificate uncertainty, and this chapter of the edition does not explicitly state a 95% confidence level, which is not guessed.

Source, page order and unverified items: Original PDF 1–8 and Annex A. The eight physical pages run through the body text and figures, with page 1 printed at about 106 and then 107–113; an OCR misreading of 109 must not be used to conclude that a page is missing. Chapters 1–8, Figures 1–4 and the Annex A reference item have been located; the original PDF/OCR is read-only and the scan is not published. The original additional notes refer to ASTM D3120-82, without inferring equivalence. The status entry and the 2021 replacement relationship, the percentage multiplier in equation 1, the input of C, the unit of S′ and the water dimensions are all listed separately for verification; the complete device drawings, controlled safety procedures and the numerical precision curves have not been reconstructed.

Direct answers to common questions: Original PDF 1, 4–7. Can testing start directly at a recovery of 75%? No, the original requires greater than 75%. Is 8 μL always the actual injected amount? No, the injected amount must be obtained from the volume or mass difference before and after. Can the 1992 equations be replaced by the 2021 equations? No; this page keeps the original equations of this edition and marks the queries. Can the logarithmic curves be used to generate a precision judgement automatically? This page has not reconstructed them point by point and provides no such tool. Can the method temperatures and precision replace product storage and uncertainty? No; specific batch values and applicability require separate evidence. Does the old status still showing current mean the 2021 replacement can be ignored? No; the conflict must be verified and is presented as historical study.

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