ISO 13759:1996

Overview

ISO 13759:1996 is an internationally recognized standard that specifies a spectrometric method for determining the concentration of alkyl nitrate in diesel fuels. It is applicable for measuring alkyl nitrate within the volume fraction range of 0.03% to 0.30%. Alkyl nitrates are additives typically used to enhance the cetane number in diesel fuels, thereby improving ignition quality and engine performance. This standard outlines precise laboratory procedures to accurately quantify alkyl nitrate content, ensuring fuel quality and compliance with industry requirements.

The method involves the hydrolysis of alkyl nitrates to release nitric acid, which then reacts with 2,4-dimethylphenol to form a colored compound. The intensity of this color, measured spectrometrically at 452 nm, correlates to the alkyl nitrate concentration based on a calibrated curve. Note that the presence of nitrate esters, inorganic nitrate ions, or nitrogen oxides can interfere with the test results, requiring careful sample handling.

Key Topics

• Scope and Application
  Measures alkyl nitrate in diesel fuel within 0.03% to 0.30% volume fraction. Calibration depends on knowing the specific alkyl nitrate; if unknown, a reference such as 2-ethylhexyl nitrate is used for indicative results.

• Testing Principle
  Hydrolysis in sulfuric acid releases nitric acid, which forms a yellow salt with 2,4-dimethylphenol and sodium hydroxide. The yellow salt’s absorbance at 452 nm quantifies alkyl nitrate concentration.

• Reagents and Equipment
  Requires analytical-grade reagents including sulfuric acid, sodium hydroxide, 2,4-dimethylphenol, propan-2-ol, and diesel fuel standards. Precise volumetric glassware and spectrometric instruments with 10 mm path length cells are necessary.

• Calibration Curve Preparation
  Involves creating a series of standard solutions, measuring absorbance, and plotting corrected values to establish a linear calibration curve for accurate quantification.

• Precision and Reliability
  Demonstrates high repeatability (difference within 0.017% volume fraction) and reproducibility across laboratories (difference within 0.036% volume fraction), underpinning the method’s robustness.

• Result Expression and Reporting
  Concentration results are reported as a volume percentage [% (v/v)] of alkyl nitrate, with test reports documenting product identification, test conditions, and deviations from the standard where applicable.

Applications

ISO 13759:1996 serves as a critical tool in the petroleum products industry, particularly in:

• Quality Control of Diesel Fuels
  Ensuring correct alkyl nitrate dosage achieves optimal cetane number enhancement without exceeding safety or regulatory limits.

• Additive Performance Verification
  Fuel manufacturers and additive suppliers use this method to verify alkyl nitrate efficacy and stability in formulated diesel fuels.

• Regulatory Compliance
  Governments and testing agencies employ this standard to enforce limits on alkyl nitrate content in fuels, mitigating environmental and safety risks.

• Research and Development
  Laboratories use these procedures to develop new diesel fuel formulations with improved ignition qualities and lower emissions.

Related Standards

ISO 13759:1996 complements and references other key standards that govern diesel fuel properties and testing:

• ISO 5165 – Determination of ignition quality (cetane number) of diesel fuels by the engine method, impacted by alkyl nitrate additives.

• ISO 4264 – Calculation of cetane index for middle-distillate fuels, unaffected by alkyl nitrate content.

• ISO 3696 – Specifications for water used in analytical laboratories, relevant for reagent preparation.

• ISO 385-1, ISO 835-1, ISO 1042 – Standards governing laboratory glassware critical for accurate volumetric measurements in testing.

By adhering to ISO 13759:1996, laboratories and fuel producers can accurately and reliably determine alkyl nitrate content in diesel fuels, supporting optimized fuel performance and regulatory adherence.

Keywords: ISO 13759, alkyl nitrate determination, diesel fuel analysis, spectrometric method, petroleum standards, cetane number additive, diesel fuel quality control, chemical analysis of fuels, nitrogen oxides interference, alkyl nitrate calibration.