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D4864-14 – Standard Test Method Technical Guide
📋 Scope and Significance
This test method covers the determination of methanol in propylene concentrates in the range of approximately 4 mg/kg to 40 mg/kg (parts-per-million by mass). The values stated in SI units are regarded as standard, with other values provided in parentheses for information only. Methanol is a common impurity in propylene concentrates and can have a deleterious effect on various processes that use this feedstock. Users must establish appropriate safety and health practices per regulatory limitations, with specific warnings given in sections 11.1.1, 11.2.1, and 12.11 of the standard.
⚙️ Test Procedure and Methodology
A known mass of water is pressured into a sample cylinder containing a known amount of liquified propylene concentrate. After shaking, the water/methanol phase is withdrawn. A reproducible volume of this extract is injected into a gas chromatograph (GC) equipped with either a thermal conductivity detector or a flame ionization detector. The methanol concentration is calculated from the peak area using calibration and extraction factors obtained from synthetic blends of known methanol content.
The apparatus includes a GC with overall sensitivity sufficient to detect at least 4 mg/kg of methanol. The column must separate methanol from water, other alcohols, and any co-extracted hydrocarbons. Refer to Table 1 for suitable columns and Practice E260 for preparation instructions. The sample cylinder should include an outage tube designed to allow a vapor space of 15% to 20% of the cylinder volume for safety in storage, handling, and transportation.
📊 Key Test Parameters
| 🟦 Parameter | 📏 Specification |
|---|---|
| Methanol Concentration Range | 4 mg/kg to 40 mg/kg |
| Gas Chromatograph Sensitivity | Sufficient to detect 4 mg/kg methanol |
| Detector Options | Thermal Conductivity or Flame Ionization |
| Column Requirement | Separation of methanol from water and other alcohols |
| Sample Cylinder Ullage (Vapor Space) | 15% to 20% of cylinder volume |
Technical Note: The outage tube is a critical safety feature that ensures a consistent vapor space of 15–20% for safe handling of volatile samples. Always verify the outage tube length before sampling.
Safety Warning: Consult sections 11.1.1, 11.2.1, and 12.11 of the standard for specific safety statements. This test method involves high-pressure liquefied gas and requires proper precautions.
❓ Frequently Asked Questions
🔍 What is the concentration range for methanol detection?
The test method is designed for methanol concentrations ranging from 4 mg/kg to 40 mg/kg (parts-per-million by mass).
💡 How is the methanol extraction performed?
Methanol is extracted by adding water to the propylene sample in a cylinder, shaking it, and then withdrawing the water/methanol phase for GC injection.
⚡ What detectors are suitable for this analysis?
Both thermal conductivity detectors (TCD) and flame ionization detectors (FID) are suitable, provided they have adequate sensitivity for the methanol concentration range.
📌 What is the function of the outage tube?
The outage tube creates a vapor space (15–20% of cylinder volume) to manage pressure and ensure safety during storage and handling of the sample.