ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels
ASTM D6296 Standard Test Method for Total Olefins in Spark-ignition Engine Fuels by Multi-dimensional Gas Chromatography
4. Summary of Test Method
4.1 A reproducible 0.2-µL volume of a representative sample, or a dilution thereof, is introduced into a computer controlled gas chromatographic system consisting of a series of columns, traps, and switching valves operating at various temperatures. The valves are actuated at pre-determined times to direct portions of the sample to appropriate columns and traps. The sample first passes through a polar column that retains C12+ hydrocarbons, all aromatics, C11+ olefins, and some alcohols, all of which are subsequently backflushed to vent. The fraction eluting from the polar column, which contains C11 and lower boiling saturated hydrocarbons as well as decene and lower boiling olefins, enters an ether/alcohol trap where the ethers and alcohols are selectively retained and also subsequently backflushed. The fraction eluting from the ether/alcohol trap, which consists of C11 and lower boiling saturated hydrocarbons and the olefins, enters an olefin trap. The olefins are selectively retained while the saturated hydrocarbons elute, pass through a non-polar column, and are detected by a flame ionization detector (FID). When the saturated hydrocarbons have completely eluted to the FID, the non-polar column oven is cooled and the olefins, which have been retained on the olefin trap, are desorbed by heating. The desorbed olefins enter and elute from the non-polar column, which is temperature programmed to separate the olefins by boiling point, and are detected by the FID.
NOTE 2 - Separation of olefins by boiling point is necessary for the calculation of the volume % of the olefins because the density of low boiling olefins differs from that of high boiling olefins and, therefore, a density correction must be applied.
4.2 Quantitation of the detected olefin peak areas to provide volume % or mass %, or both, is accomplished through the use of an external standard followed by the application of flame ionization detector response factors. The quantitation also takes into consideration the baseline compensation, sample dilution, and density corrections.
5. Significance and Use
5.1 The quantitative determination of olefins in spark-ignition engine fuels is required to comply with government regulations.
5.2 Knowledge of the total olefin content provides a means to monitor the efficiency of catalytic cracking processes.
5.3 This test method provides better precision for olefin content than Test Method D1319. It also provides data in a much shorter time, approximately 20 min following calibration, and maximizes automation to reduce operator labor.
5.4 This test method is not applicable to M85 or E85 fuels, which contain 85 % methanol and ethanol, respectively.
6. Interferences
6.1 Some types of sulfur-containing compounds are irreversibly absorbed in the olefin and oxygenate traps ultimately reducing the trap capacity. However, a variety of spark-ignition engine fuels have been analyzed without significant performance deterioration of these traps.
6.2 Commercial dyes used to distinguish between grades and types of spark-ignition engine fuels have not been found to interfere with this test method.
6.3 Commercial detergent additives utilized in spark-ignition engine fuels have not been found to interfere with this test method.
6.4 Dissolved water in spark-ignition engine fuels has not been found to interfere with this test method. Free water must be removed using anhydrous sodium sulfate or other drying agent to permit injection of accurate sample volumes.
