SH/T 0398-2007 Determination of Molecular Weight of Petroleum Waxes and Petrolatums

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Card type: Test method

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

• Standard number: SH/T 0398-2007
• Chinese title: Determination of Molecular Weight of Petroleum Waxes and Petrolatums
• English title: Standard test method for molecular weight of petroleum wax and petrolatum
• Replacement relationship: replaces SH/T 0398—1992 "Determination of Molecular Weight of Petroleum Waxes and Petrolatums"
• Adoption relationship: modified adoption of "Determination of Average Molecular Weight" (English version) in the United States Food Chemicals Codex FCC V 2002
• Issued/implemented: issued on 2007-08-01, implemented on 2008-01-01
• Issuing authority: National Development and Reform Commission of the People's Republic of China
• Technical committee: Fushun Research Institute of Petroleum and Petrochemicals, China Petroleum & Chemical Corporation
• Drafting organization: Fushun Research Institute of Petroleum and Petrochemicals, China Petroleum & Chemical Corporation
• Main drafters: Zhang Huicheng, Wang Lijun

2. Scope of application and non-applicability

• 1.1 specifies a method for determining the molecular weight of petroleum waxes and petrolatums by vapor pressure osmometry (abbreviated as the VPO method).
• 1.2 is applicable to paraffin wax, microcrystalline wax, liquid paraffin, white oil, petrolatum, and special waxes that can be dissolved in o-dichlorobenzene or toluene solvent.
• 1.2 is not applicable to substances that readily associate or dissociate.
• 1.3 includes the standard curve method and the instrument constant method; the standard curve method is only applicable to samples with molecular weight <800, while the instrument constant method is applicable to the entire measurement range.
• 1.4 This standard does not address all safety issues associated with its use; before use, the user should establish appropriate safety and protective measures and formulate corresponding management systems.

3. Method principle

According to Raoult's law for ideal solutions, in a constant-temperature system below the boiling point of the solvent, the thermal effect caused by the decrease in vapor pressure of the solution is measured to calculate the average molecular weight of the test sample.

4. Reagents and materials (purity / preparation)

• 4.1 o-Dichlorobenzene: analytical reagent. Warning: toxic, flammable.
• 4.2 Toluene: analytical reagent. Warning: toxic, flammable.
• 4.3 Dehydrating agent: magnesium perchlorate (granular or lump) or 5A molecular sieve (granular).
• 4.4 Standard sample: benzil or other chromatographically pure n-alkanes.
• Preparation of standard solutions: use the standard samples specified in clause 4.4 to prepare any several (not fewer than 4) standard solutions with molality in the range of 0.005 mol/kg to 0.05 mol/kg (the original text of this paragraph has noise at source-text extraction, and the unit of the upper concentration limit requires confirmation against the source standard (source-text extraction)).

5. Apparatus and equipment

• 3.1 VPO molecular weight analyzer.
• 3.2 Volumetric flask: 5 mL or 10 mL.
• 3.3 Syringe: needle with spring, 1 mL.
• 5.1.1 Involves: thermistor probe, syringe, thermometer, aluminum block housing, measuring cell, glass cup (with filter paper wick), cell cover, power supply, voltage stabilizer, aluminum block heating system, helical potentiometer, bridge, recorder, heating aluminum block (containing hole No. 0 and holes No. 1, 2, 3, 4).
• 5.1 Mentions German KNAURR type instrument (debug and calibrate according to the instrument manual; if this type of instrument is used, debug according to steps 5.1.1 to 5.1.3).

6. Recommended operating conditions

• Solvent and temperature: use o-dichlorobenzene as solvent, set temperature at 100 ℃; use toluene as solvent, set temperature at 60 ℃.
• Keep constant temperature for 1.5 hours; the temperature difference between the measuring cell temperature and the top syringe heater is allowed to be less than 2 (the unit in the original text is not marked, requires confirmation against the source standard (source-text extraction)).
• 5.1.3 Use two 1 mL syringes to take the same pure solvent and place it into hole No. 0 of the heating aluminum block for preheating; rinse the thermistor with pure solvent, and suspend one droplet on each of the two thermistor beads; after the instrument state stabilizes, adjust the zero point; press the "%" advance button, and adjust the bridge voltage to 100%.
• 5.2.1 Place the standard solutions in order from low to high concentration into holes No. 1, 2, 3, 4 of the instrument heater aluminum block for preheating.
• Reading: after a few minutes, when the meter or recorder reaches a stable reading or reaches the given retention time, read ΔV; repeat the reading until (ΔV 0.2 mV) (the original wording requires confirmation against the source standard (source-text extraction)).

7. Sampling and sample preparation

• 5.3.1 Standard curve method: prepare two sample solutions with different mass fractions (the original text is interrupted at source-text extraction here, and the specific mass fractions require confirmation against the source standard (source-text extraction)), and operate according to 5.2.1.
• 5.3.2 Instrument constant method: prepare four or more sample solutions with different (mass fractions, the original text is interrupted at source-text extraction, requires confirmation against the source standard (source-text extraction)), operate according to 5.2.3, and measure their ΔV values respectively.
• The remaining content on sampling and sample preparation is not provided in the available source.

8. Analytical procedure

• 5.1 Calibrate the instrument: debug and calibrate according to the instrument manual; if a German KNAURR type instrument is used, debug according to steps 5.1.1 to 5.1.3.
• 5.2 Drawing of the standard curve and determination of the instrument constant: due to heat loss from the temperature sensor and other components of the instrument, the molecular weight of the test sample cannot be obtained using the voltage difference displayed by the recorder and the formula derived from the method principle; instead, comparison measurement is performed using standard samples of known molecular weight and the test sample; the comparison measurement methods are the standard curve method and the instrument constant method.
• 5.2.1 Drawing of the standard curve: use the standard samples specified in clause 4.4 to prepare any several (not fewer than 4) standard solutions with molality in the range of 0.005 mol/kg to 0.05 mol/kg, place them in order from low to high concentration into holes No. 1, 2, 3, 4 of the heater aluminum block for preheating; rinse the thermistor with the solution to be measured, and suspend 1 drops of the solution to be measured on it; after a few minutes, read the stable reading ΔV; draw the standard curve with the corresponding molality C as the abscissa (Figure 1). After the curve is prepared, use two substances of known molecular weight to verify the reliability of the curve; when the relative error between the measured molecular weight and the theoretical value (the numerical value in the original text is missing at source-text extraction, requires confirmation against the source standard (source-text extraction)), the curve is considered usable.
• 5.2.2 (marked in the original text as 5.4.20, suspected to be noise at source-text extraction, requires confirmation against the source standard (source-text extraction)) Determination of the instrument constant: use standard substances to prepare standard solutions of several concentrations with molality in the range of 0.005 mol/kg to 0.03 mol/kg, and measure their potential difference ΔV values respectively; draw a straight line with molality Cw as the abscissa and ΔV/Cw as the ordinate and extrapolate to Cw=0; the (ΔV/Cw) value at this time is the instrument constant; after the instrument constant is measured, two substances of known molecular weight should also be used to verify the instrument constant; only when the relative error between the measured molecular weight and the theoretical value is less than 2% can this instrument constant be used (Figure 2).
• 5.3 Determination of the molecular weight of the test sample:
  • 5.3.1 Standard curve method: prepare two sample solutions with different mass fractions, operate according to 5.2.1, measure their ΔV values respectively, and find their corresponding molality from the standard curve.
  • 5.3.2 Instrument constant method: prepare four or more sample solutions with different mass fractions, operate according to 5.2.3, measure their ΔV values respectively, and calculate the ΔV/Cw value; draw a straight line with Cw as the abscissa and ΔV/Cw as the ordinate and extrapolate to ΔV/Cw=0; the value at this time is the sample constant value (Figure 3).

9. Qualitative and quantitative determination and calculation formulas

• 6.2 Standard curve method: the molecular weight of the test sample is calculated according to formula (1).
  • Where: M—— molecular weight of the test sample; w—— mass fraction of the test sample (mg/g); C—— molality found from the standard curve. (The formula symbol in the original text has noise at source-text extraction, requires confirmation against the source standard (source-text extraction))
• Instrument constant method: the molecular weight of the test sample is calculated according to formula (2).
  • Where: M—— molecular weight of the test sample; K—— instrument constant; the remaining symbols are missing in the original text at source-text extraction, requires confirmation against the source standard (source-text extraction).
• Take a single measurement result (the original text is interrupted at source-text extraction here, requires confirmation against the source standard (source-text extraction)).
• 7 Report: express the measurement result to the nearest integer.

10. Precision

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

• 8.1 Repeatability: for the same operator, in the same laboratory, using the same instrument, according to the procedure specified in the method, within a continuous period of time, the allowable difference between repeated measurement results for the same test sample is found from Figure 4 (Figure 4 contains two curves, the standard curve method and the instrument constant method, with molecular weight range on the abscissa from 200 to 800).
• 8.2 Reproducibility: for different operators, in different laboratories, using instruments of the same type, according to the procedure specified in the method, the allowable difference between measurement results for the same test sample is found from Figure 5 (Figure 5 contains two curves, the standard curve method and the instrument constant method, with molecular weight range on the abscissa from 200 to 800).
• The specific allowable difference values are given in the original text in the form of figures; the main text does not list numerical values, not provided in the available source.

11. Report

• 7 Report: express the measurement result to the nearest integer.

12. Referenced documents

• United States Food Chemicals Codex FCC V 2002 "Determination of Average Molecular Weight" (English version) (source of modified adoption).
• SH/T 0398—1992 "Determination of Molecular Weight of Petroleum Waxes and Petrolatums" (replaced).
• The remaining normative referenced documents are 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 Q&A