ISO 13757:1996

Overview

ISO 13757:1996 - Liquefied petroleum gases - Determination of oily residues (high‑temperature method) defines a laboratory procedure to quantify the residual oily matter left in LPG after evaporation at 105 °C. The standard describes sampling, solvent extraction, concentration, oven drying and gravimetric determination of oily residues and includes safety cautions for hazardous materials and equipment. Results are reported in mg/kg (milligrams per kilogram) LPG.

Key topics and requirements

• Purpose and principle: Concentrate a filtered LPG sample by evaporation, extract the concentrate into dichloromethane (methylene chloride), evaporate the solvent using a rotary evaporator, dry the residue at 105 °C (1 h) and weigh the oily residue gravimetrically.
• Reagents: Analytical-grade dichloromethane (or pentane as an alternative where dichloromethane is restricted), acetone, ammonium peroxodisulfate/sulfuric acid (for cleaning), and solid CO2 for deep cooling baths.
• Apparatus and sampling: Stainless-steel sample cylinder with valves and dip tube, in-line filter with 0.8 μm membrane, stainless cooling coil (coiled tubing), rotary evaporator, 200 cm3 round-bottom evaporation flask (tare requirements), oven (105 °C), precision balances, desiccator and appropriate needle valves. Typical sample mass taken: ~800–1 200 g.
• Procedure controls: Rinse lines with solvent and LPG, perform blank measurements, avoid vacuum on the evaporator during solvent removal, and ensure glassware cleaning and tare procedures as specified.
• Safety: Work under explosion-proof hood or open-air with earthing to prevent static; handle dichloromethane and oxidizing cleaning solutions with appropriate PPE and fume extraction.
• Precision: Interlaboratory precision reported for samples with oily residues 70–100 mg/kg: repeatability r = 15 mg/kg and reproducibility R = 50 mg/kg.
• Reporting: Report result to nearest 1 mg/kg and include method reference, product identification, solvent used, any deviations, and test date.

Applications

• Routine quality control and acceptance testing of LPG batches to detect deposit-forming residues.
• Regulatory compliance and product specification verification for LPG producers, distributors and importers.
• Laboratory analysis in industrial testing labs, refineries and third‑party testing services assessing LPG cleanliness for burners, vaporizers and customer delivery.
• Supporting equipment manufacturers and maintenance teams concerned with fouling of vaporizers and heat exchangers due to oily deposits.

Related standards

• ISO 3696:1987 - Water for analytical laboratory use (referenced for water quality).
• ISO 4257:1988 - Method of sampling LPG (normative sampling reference).
• Annex A of ISO 13757 provides examples of commercially available equipment and cleaning agents.

Keywords: ISO 13757:1996, LPG oily residues, high‑temperature method, dichloromethane, rotary evaporator, gravimetric determination, LPG testing, quality control.