SH/T 0239-1992 Determination of C₆~C₉ alkanes, cycloalkanes and aromatics in reformer feedstocks and reformates (porous-layer packed-column chromatography)

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. Standard designation, title, English title and supersession

• Standard designation: SH/T 0239-92 (confirmed in 2004 according to the source card)
• Title translated from Chinese: Determination of C₆~C₉ alkanes, cycloalkanes and aromatics in reformer feedstocks and reformates (porous-layer packed-column chromatography)
• Official English title: not found in the available source.
• Supersession: replaces SY 2126-83.
• First publication: 1978 (see supplementary information in the source).
• Approval and implementation: approved by China Petrochemical Corporation on 1992-05-20; implemented on 1992-05-20.

2. Scope and exclusions

• Applies to reformer feedstocks and their reformates in the 60~145℃ distillation range. [The source card flags uncertainty in the transcription of these values; verify them against the original before use.]
• Exclusions: not found in the available source.

3. Principle

A porous-layer packed chromatographic column made with 13X molecular sieve and 101 support is used with temperature-programmed gas chromatography and flame ionization detection. The sample components are separated into cycloalkanes, alkanes and aromatics by carbon number. Each peak area is multiplied by its correction factor; area normalization gives the percentage of each component. These percentages are then summed to obtain total alkanes, total cycloalkanes and total aromatics in the sample.

4. Reagents and materials: purity and preparation

• Sodium hydroxide: chemically pure; prepare a 30 g/L sodium hydroxide solution. [The source card flags uncertainty in the transcription of these values; verify them against the original before use.]
• Hydrogen: electrolytic hydrogen (purity ＞99.5%), dehydrated and purified using 5A molecular sieve.
• Compressed air: dehydrated and purified using 5A molecular sieve.
• 13X molecular sieve: 40–60 mesh or 60–80 mesh, for chromatography. Historical source note: obtainable from Shanghai Molecular Sieve Factory; current availability is not established here.
• Support: white 101 support, 40~60 mesh. Historical source note: obtainable from Shanghai First Reagent Factory; current availability is not established here.
• 5A molecular sieve: for drying, approximately 20 mesh.
• Distilled water.
• pH indicator paper.

5. Apparatus

• Gas chromatograph: with temperature programming and a flame ionization detector. The column oven can operate up to 400℃.
• Chromatographic column: stainless-steel tubing, 2 m long, internal diameter 3~4 mm.
• Microsyringe: 1 μL.
• Centrifuge.
• Muffle furnace: for heating 5A molecular sieve (see 5.1 of the source).
• Agate mortar (see 5.2.2 of the source).
• Centrifuge tubes (see 5.2.2 of the source).
• Oven (see 5.2.3 of the source).

6. Recommended operating conditions

• Inlet pressure at the constant-flow valve: 294.2–392.3 kPa (3–4 kgf/cm²).
• Carrier gas flow: hydrogen (or helium), 60~80 mL/min.
• Air flow: 600~800 mL/min.
• Chart speed: 300 mm/h.
• Injection volume: 0.02~0.50 μL. [The source card flags uncertainty in the transcription of these values; verify them against the original before use.]
• Detector temperature: 200℃.
• Injector temperature: 200~250℃. [The source card flags uncertainty in the transcription of these values; verify them against the original before use.]
• Column operating temperature: inject at 150–180℃; increase at 5–10℃/min to a final temperature of 380~395℃ and hold until all components have eluted. [The source card flags uncertainty in the transcription of these values; verify them against the original before use.]

7. Sampling and sample preparation

Not found in the available source.

8. Procedure

• Treatment of 5A molecular sieve: heat approximately 20-mesh 5A molecular sieve in a muffle furnace at 500℃ for 2 h. Place it in the chromatograph drying tube to dry and purify the carrier gas and air.
• Preparation of the chromatographic column:
  • Soak a suitable quantity of 13X molecular sieve in 30 g/L sodium hydroxide solution for half an hour. Remove the alkaline liquid, then wash repeatedly with distilled water until pH paper indicates neutrality.
  • Transfer the alkali-treated 13X molecular sieve to an agate mortar and grind with distilled water. Transfer to a beaker and add distilled water to form a suspension. Allow to settle for 1 h, then decant the upper suspension into centrifuge tubes. Centrifuge for 10 min at 3500 r/min and discard the water above the sediment. The molecular-sieve particles at the bottom of the tubes can then be used for coating.
  • Weigh the wet molecular sieve and add enough distilled water to form a suspension that will immerse the support. Add the weighed support at a molecular-sieve-to-support mass ratio of 4:100. Stir gently and remove excess water. Dry in an oven at 150℃, then use the usual column-packing procedure to prepare the porous-layer packed chromatographic column.
• Column activation: install the prepared column in the column oven. Before each use, activate at 350℃ for 1 h under carrier gas flow.
• Column performance check: the peak-height resolution Rh between C₆ alkanes and benzene must exceed 60% for the column to be considered suitable (see Figure 1 of the source). Otherwise, prepare a new column using fresh 13X molecular sieve. The source transcription of this acceptance threshold is unclear and requires verification.
  • Formula: Rh = (h − hm) / h × 100% ＞ 60% (the source extraction reads “>U.b l”; the threshold remains unverified).
  • Where h is the height of the smaller of the two peaks and hm is the height of their intersection.
• Start the chromatograph under the specified separation conditions. Once stable, inject the sample. Typical chromatograms are shown in Figures 2 and 3 of the source.

9. Identification, quantification and calculations

• Calculate each component content Xi [% (m/m)] by area normalization using equation (2):

  Xi = (fi · Ai) / Σ(fi · Ai) × 100 ……(2)

  Where Ai is the peak area of component i and fi is its relative mass correction factor.

• Recommended correction factors: benzene 0.86; toluene 0.865; xylenes 0.93; ethylbenzene 0.90 (with nC₆ as the reference substance). The correction factor for other aromatics and hydrocarbons is 1.00. Each laboratory must verify these recommended factors with its own instrument and known samples. If substantial errors arise, determine the correction factors using that instrument.

• Sum the cycloalkane, alkane and aromatic contents across carbon numbers to obtain the total content of each hydrocarbon class.

• Note: peak areas may be measured using an electronic integrator, a computer, or peak height multiplied by peak width at half height.

10. Precision

Use the following provisions to assess the reliability of results at a 95% confidence level. They apply to reformates with total aromatics of 30%~85% and reformer feedstocks with total cycloalkanes of 15%~55%.

• 8.1 Repeatability: the difference between two repeated results must not exceed 1.0% (m/m) for total cycloalkanes in reformer feedstocks, or 1.5% (m/m) for total aromatics in reformates.
• 8.2 Reproducibility: the difference between results reported by two laboratories must not exceed 1.5% (m/m) for total cycloalkanes in reformer feedstocks, or 2.0% (m/m) for total aromatics in reformates.

11. Reporting

Report the arithmetic mean of two repeated determinations.

12. Referenced documents

Not found 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 reference