GB/T 30518-2014 Determination of soluble residues in liquefied petroleum gas — High-temperature gas chromatography

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Card type: Test method

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

• Standard number: GB/T 30518-2014
• Chinese title: Determination of soluble residues in liquefied petroleum gas — High-temperature gas chromatography
• English title: Determination of dissolved residues of liquefied petroleum gases—High temperature gas chromatographic method
• Replacement relationship: not provided in the available source (the foreword only states modified adoption of EN 15470:2007, and does not mention replacement of any national standard)
• Adoption relationship: modified adoption using the redrafting method of the European Standard EN 15470:2007 "Determination of soluble residues in liquefied petroleum gas — High-temperature gas chromatography"
• Publication/implementation: published on 2014-02-19, implemented on 2014-06-01
• Secretariat: Subcommittee on Petroleum Fuels and Lubricants of the National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC 280/SC 1)
• Drafting organization: Sinopec Research Institute of Petroleum Processing

2. Scope of application and exclusions

• Applicable to the determination of soluble residue content in liquefied petroleum gas (LPG).
• Determination range: 40 mg/kg~100 mg/kg; when the residue content is higher, it can be controlled by adjusting the sample amount.
• Note (original text): Samples with residue content outside the range of 40 mg/kg–100 mg/kg may also be determined using this standard, but the precision has not been investigated outside the range of 20 mg/kg–100 mg/kg, and the applicability has not been verified.
• Not applicable: determination of solid samples and high-molecular-weight polymers (>1000 g/mol).
• Method summary (as stated in the scope clause): the sample is evaporated at ambient temperature, dried at 105 °C, and then detected by gas chromatography.

3. Method principle

A glass Erlenmeyer flask is cooled in a cooling bath containing isopropanol and dry ice, and a LPG sample (about 50 g~75 g) is transferred in liquid form from the sample container into the cooled glass Erlenmeyer flask. The sample evaporates naturally; after evaporation is complete, it is placed in an oven at 105 °C for 1 h. After cooling, the residue is diluted with a carbon disulfide solution containing an internal standard, and the diluted mixture is analyzed by gas chromatography, with quantitative calculation by the internal standard method.

4. Reagents and materials (purity / preparation)

• 5.1 Isopropanol: analytical grade.
• 5.2 Dry ice: solid, used for cooling.
• 5.3 Carbon disulfide: analytical grade (content not less than 99.9%).
• 5.4 n-Octane: analytical grade (content not less than 99.9%).
• 5.5 Pentane: analytical grade (content not less than 99.5%).
• 5.6 Helium: content greater than 99.999%.
• 5.7 Hydrogen: content greater than 99.999%.
• 5.8 Air: content greater than 99.999%.
• Preparation of solution A (8.4.2): dilute 40 mg (accurate to 0.1 mg) of n-octane to 100 g in carbon disulfide.

5. Apparatus and equipment

• 6.1 Sample container: total mass within the weighing balance range; stainless steel material is preferred, with two oil-free stainless steel valves, consistent with the discussion in SH/T 0233.
• 6.2 Cooling bath: a Dewar flask or insulated container of 0.5 L~2 L, filled with a suitable cooling liquid (such as a mixture of isopropanol and dry ice), to obtain a low temperature below −60 °C.
• 6.3 Sampling device: see Annex B.
• 6.4 Weighing balance: maximum range determined according to the mass of the sample container (for example 16 kg, 30 kg), with precision of 1 g or smaller.
• 6.5 Analytical balance: precision of 0.1 mg or smaller.
• 6.6 Vent line: stainless steel tube with outer diameter 1.6 mm, length 15 cm, see B.2.
• 6.7 Glass Erlenmeyer flask: 100 mL–150 mL glass Erlenmeyer flask with screw cap; or 100 mL–150 mL stoppered glass Erlenmeyer flask with polytetrafluoroethylene stopper.
• 6.8 Septum: polytetrafluoroethylene (PTFE)-silicone rubber material, for screw-cap glass Erlenmeyer flasks.
• 6.9 Laboratory gloves: PVC material, talc-free.
• 6.10 Gas chromatograph: equipped with an autosampler and integrator.
• 6.11 Capillary chromatographic column: weakly polar high-temperature capillary column (for example, stationary phase 5% phenyl polysiloxane, inner diameter 0.53 mm, film thickness 0.15 μm, length 10 m).
• 6.12 Oven: capable of controlling temperature at 105 °C, with precision of ±1 °C; Note: the oven is used under natural convection conditions.

6. Recommended operating conditions

Table 1 Test conditions:

• Carrier gas: helium, flow rate 4 mL/min
• Inlet: type splitless, temperature 380 °C
• Injector: automatic, injection volume 2 μL
• Detector: FID, temperature 400 °C
• Signals: hydrogen flow rate 30 mL/min, air flow rate 350 mL/min, make-up gas flow rate 30 mL/min
• Column oven temperature: mode compensation; initial temperature 10 °C held for 1 min; final temperature 400 °C; heating rate 15 °C/min

7. Sampling and sample preparation

• Sampling (Chapter 7): sampling of liquefied petroleum gas shall be carried out in accordance with SH/T 0233. The sampler shall be made of suitable grade stainless steel, and may be of single-valve or double-valve type, with or without a discharge tube; the size shall be determined according to the amount required for the test; it shall withstand a pressure of 3.1 MPa or more, and shall be subjected to a 2.0 MPa airtightness test periodically.
• Sample transfer (8.2):
  • 8.2.1 Place the sample container (6.1) on the weighing balance (6.4).
  • 8.2.2 Assemble the apparatus using the equipment in Annex B, connect the bottom valve of the sample container to the sample transfer line as shown in Figure B.1, and connect the vent line at the same time.
  • 8.2.3 Place the transfer line on a support to prevent interference with the balance.
  • 8.2.4 Cooling bath preparation: add dry ice and isopropanol to the insulated container or Dewar flask.
  • 8.2.5 Cleaning of the glass Erlenmeyer flask: clean with analytical grade pentane.
  • 8.2.6 Prepare the screw cap and septum with two holes (6.8) (or a polytetrafluoroethylene stopper with two holes), with hole diameters allowing passage of the 1.6 mm steel tube.
  • 8.2.7 Before sampling, place the clean glass Erlenmeyer flask (with screw cap, septum or stopper, and vent line already installed) in the cooling bath for at least 1 min.
  • 8.2.8 Close the needle valve.
  • 8.2.9 Carefully open the sample container, slowly open the needle valve to fill and flush the connecting line with sample.
  • 8.2.10 When LPG sample flows out uniformly, close the needle valve.
  • 8.2.11 Insert the end of the stainless steel insertion tube into the glass Erlenmeyer flask.
  • 8.2.12 Record the mass of the sample container m1.
  • 8.2.13 Adjust the LPG sample transfer rate by adjusting the needle valve.
  • 8.2.14 When the transferred amount reaches 100 mL, close the needle valve.
  • 8.2.15 Record the mass of the sample container m2.
  • 8.2.16 The LPG sample mass m (g) is calculated according to m=m1−m2.
  • 8.2.17 Obtain the required sample amount by repeating the above process.
• Evaporation process (8.3):
  • 8.3.1 Disconnect the transfer line so that the sample evaporates through the vent line; the lower end of the vent line shall not be inserted below the liquid surface.
  • 8.3.2 The evaporation process has already begun during sample transfer; the glass Erlenmeyer flask containing LPG may be allowed to evaporate naturally at room temperature (not higher than 25 °C), or gradually heated for evaporation using suitable equipment, but the temperature shall not exceed 25 °C.
  • 8.3.3 The evaporation process shall be carried out in a fume hood.
  • 8.3.4 At the end of natural evaporation, open the screw cap or stopper, place in an oven at 105 °C and keep at constant temperature for 1 h; then cover with the cap (stopper), and cool in a desiccator for 30 min. At this point, the glass Erlenmeyer flask contains soluble evaporation residue. At the end of natural evaporation, the glass Erlenmeyer flask should contain no liquid residue or droplets. Warning: when covering with the screw cap, the PTFE side of the septum shall face downward; the glass Erlenmeyer flask shall be placed upright.

8. Analytical procedure

• 8.4.1 Overview: the evaporation residue obtained from 8.3 is cooled and diluted with a carbon disulfide solution containing an internal standard (solution A), and the diluted mixture is analyzed by gas chromatography, with quantification by the internal standard method.
• 8.4.2 Preparation of solution A: dilute 40 mg (accurate to 0.1 mg) of n-octane to 100 g in carbon disulfide.
• 8.4.3 Test conditions: see Table 1 (see Section 6 of this card).
• 8.4.4 Blank test: first fully age the gas chromatographic column. Inject 2 μL of solution A into the chromatographic column, and integrate the area of peaks in the chromatogram from n-C? to the end of the analyte (see Annex C, Figure C.1). The integrated area value of the S₀ region shall not exceed 2% of the area of the n-C? peak, and the integrated area of the S₀ region in the blank test will be subtracted from the integrated area Sₓ of the residue test. (Note: the subscript source-text extraction of n-C in the original text is unclear in the source text, requires confirmation against the source standard (source-text extraction))
• 8.4.5 Sample analysis: Weigh a glass Erlenmeyer flask with a screw cap (or stopper) to the nearest 10 mg. Add approximately 4 mL of solution A to the glass Erlenmeyer flask with cap (or stopper) containing the evaporation residue, and weigh to the nearest 10 mg. Carefully and slowly rinse the inner wall of the glass Erlenmeyer flask with the mixed solution to form solution X for gas chromatographic analysis. If the glass Erlenmeyer flask containing the evaporation residue cannot be analyzed immediately after oven evaporation, store it in a desiccator protected from light until just before analysis, then dissolve the residue with solution A. Under the same operating conditions as the blank test, inject solution X into the gas chromatograph for analysis. The chromatographic integration area (Sₓ) starts from n-C? and ends at the end of the analyte (see Appendix C, Figure C.2).
• Safety (8.1): The test should be conducted in an explosion-proof fume hood; necessary safety measures should be taken to exhaust LPG and carbon disulfide vapor, with particular attention to grounding the instrument to reduce static electricity risks.

9. Qualitative and Quantitative and Calculation Formulas

The soluble evaporation residue content (ER) is expressed as mg/kg and calculated according to formula (1):

ER = [(Sₓ − S₀) × Cᵢ × 1000 × Mₐ] / (Sᵢ × m) …… (1)

Where:

• Sₓ: the integration area of the peak in the chromatogram of the residue test from n-C? to the end of the analyte;
• S₀: the integration area of the peak in the blank test chromatogram from n-C? to the end of the analyte;
• Cᵢ: the concentration of the internal standard n-octane in solution A, in milligrams per gram (mg/g);
• Mₐ: the mass of solution A used to dissolve the soluble evaporation residue, in grams (g);
• Sᵢ: the peak area of the internal standard;
• m: the mass of the LPG sample, in grams (g).

(Note: In the original formula, the symbol subscript source-text extraction has noise; the correspondence of Sₓ/S₀/Cᵢ/Mₐ/Sᵢ is organized according to the original text description; the carbon number of the subscript n-C requires confirmation against the source standard (source-text extraction).)

10. Precision

• 11.1 Overview: The precision verification range is 20 mg/kg~100 mg/kg, determined by statistical analysis of interlaboratory test results according to ISO 4259 method (95% confidence level).
• 11.2 Repeatability (r): For tests conducted by the same operator in the same laboratory using the same instrument on the same sample, the difference between two replicate test results should not exceed the calculated value in Table 2 and the typical value in Table 3.
  • Table 2: r = 0.054X + 3.51 (X is the average of two test results, unit mg/kg)
  • Table 3 Typical values (unit mg/kg):
    • Residue content 20 → r = 5
    • Residue content 50 → r = 6
    • Residue content 75 → r = 8
    • Residue content 100 → r = 9
• 11.3 Reproducibility (R): For tests conducted by different operators in different laboratories using different instruments on the same sample, the difference between two single and independent test results should not exceed the calculated value in Table 2 and the typical value in Table 3.
  • Table 2: R = 0.14X + 9.06 (X is the average of two test results, unit mg/kg)
  • Table 3 Typical values (unit mg/kg):
    • Residue content 20 → R = 12
    • Residue content 50 → R = 16
    • Residue content 75 → R = 20
    • Residue content 100 → R = 23

11. Report

Report the soluble evaporation residue result to the nearest 1 mg/kg.

12. Normative References

• SH/T 0233 Liquefied petroleum gas sampling method (normative reference)
• References: ISO 4259 Determination and application of precision data in relation to methods of test for petroleum products; ISO 13757 Determination of soluble residues in liquefied petroleum gas — High temperature method; EN 15471 Determination of soluble residues in liquefied petroleum gas — High temperature gravimetric method
• Appendix A (informative appendix): Comparison of clause numbers between this standard and EN 15470:2007
• Appendix B (normative appendix): Sample transfer and evaporation equipment
• Appendix C (informative appendix): Gas chromatography test examples

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