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D1157-23 – Standard Test Method Technical Guide
ASTM D1157-23 specifies the standard procedure for determining the total concentration of p-tertiary-butylcatechol (TBC) in light hydrocarbons, specifically butadiene and mixed C₄ streams. This inhibitor is critical for preventing oxidation during storage and transport. The method provides reliable quantification within a defined range, suitable for both production and quality control laboratories.
📐 Scope and Principle of the Method
This test method is explicitly designed for the determination of total TBC inhibitor added to polymerization and recycle grades of butadiene or other C₄ hydrocarbon mixtures. It applies strictly to samples containing no other phenolic materials besides catechol. The standard is applicable over a range of 50 mg/kg to 500 mg/kg.
The core principle is a colorimetric reaction. The catechol is first separated from the butadiene matrix through evaporation. The resulting residue is dissolved in water, and an excess of ferric chloride (FeCl₃) is added. The intensity of the resulting yellow-colored complex is measured using a photoelectric colorimeter.
⚠️ Critical Safety Precaution: Section 1.3.1 of the standard explicitly requires the user to obtain LPG safety training prior to conducting this test. The handling of volatile hydrocarbons necessitates strict safety and ventilation practices.
⚙️ Required Apparatus and Test Procedure
Successful execution of D1157-23 requires specific laboratory equipment, most notably a sensitive photometer capable of isolating a narrow spectral range in the blue region (425 nm). Standard volumetric glassware is also essential for preparing standards and sample solutions.
| 🛠️ Apparatus / Reagent | 📏 Specification / Requirement |
|---|---|
| Photoelectric Photometer | Capable of narrow band isolation at 425 nm (blue) |
| Graduates / Volumetric Flasks | 100 mL capacity |
| Erlenmeyer Flasks | 250 mL capacity |
| Funnels | 75 mm diameter |
| Pipets | 5 mL capacity |
| Reagents | Reagent grade chemicals; Ferric Chloride (FeCl₃) |
The test procedure involves careful sampling per Practice D1265, evaporation of the light hydrocarbon matrix, and subsequent photometric analysis of the colored complex formed by the inhibitor with ferric chloride.
📊 Interpretation, Significance, and Interferences
Per the significance statement in Section 4, TBC is commonly added to commercial butadiene in amounts of 50 mg/kg to 250 mg/kg as an oxidation inhibitor. This method allows both producers and users to verify the inhibitor concentration meets specifications.
💡 Technical Note on Interferences: While small amounts of polymer do not interfere, the test method is limited to samples containing no phenolic material other than catechol. All phenols and their quinone oxidation products are included in the calculated catechol content.
| 🔬 Parameter | 📐 Value / Condition Constraint |
|---|---|
| Standard Designation | ASTM D1157-23 |
| Measured Analyte | Total p-tertiary-butylcatechol (TBC) Inhibitor |
| Applicable Matrix | Light Hydrocarbons, C₄ streams, Butadiene |
| Quantitation Range | 50 mg/kg to 500 mg/kg |
| Detection Wavelength | 425 nm (Blue Light) |
| Referenced Sampling Standard | ASTM D1265 (Practice for Sampling LP Gases) |
The method demonstrates robust accuracy for its intended purpose, forming a cornerstone of quality assurance for monomer production and handling.
❓ Frequently Asked Questions
🔍 What is the specific standard for measuring TBC in butadiene?
ASTM D1157-23 is the designated standard test method for determining total inhibitor content (TBC) in light hydrocarbons like butadiene.
💡 What is the working range for the ASTM D1157-23 test method?
This test method is applicable over a range of 50 mg/kg to 500 mg/kg of TBC.
⚡ What training does the standard require for safety?
Section 1.3.1 of D1157-23 mandates that the user obtain specific LPG safety training to ensure the safe handling of light hydrocarbons during the procedure.
📌 What chemical reaction forms the basis of this test?
The isolated catechol residue reacts with an excess of ferric chloride to form a yellow-colored complex, the intensity of which is measured at 425 nm with a photoelectric photometer.