1、Designation: D6550 10 (Reapproved 2015)D6550 15Standard Test Method forDetermination of Olefin Content of Gasolines bySupercritical-Fluid Chromatography 1This standard is issued under the fixed designation D6550; the number immediately following the designation indicates the year oforiginal adoption
2、 or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers the determination of the total amount of olef
3、ins in blended motor gasolines and gasoline blendingstocks by supercritical-fluid chromatography (SFC). Results are expressed in terms of mass % olefins. The application range isfrom 1 mass % to 25 mass % total olefins.1.2 This test method can be used for analysis of commercial gasolines, including
4、those containing varying levels of oxygenates,such as methyl tert/butyl ether (MTBE), diisopropyl ether (DIPE), methyl tert/amyl ether (TAME), and ethanol, withoutinterference.NOTE 1This test method has not been designed for the determination of the total amounts of saturates, aromatics, and oxygena
5、tes.1.3 This test method includes a relative bias section based on Practice D6708 accuracy assessment between Test Method D6550and Test Method D1319 for total olefins in spark-ignition engine fuels as a possible Test Method D6550 alternative to Test MethodD1319 for U.S. EPA regulations reporting. Th
6、e Practice D6708 derived correlation equation is only applicable for fuels in theconcentration range from 0.2 % to 26.2 % by mass as reported by Test Method D6550. The applicable Test Method D1319concentration range for total olefins is 0.2 % to 27.7 % by volume as reported by Test Method D1319.1.4
7、The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appro
8、priate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1319 Test Method for Hydrocarbon Types in Liquid Petroleum Products by Fluorescent Indicator AdsorptionD4052 Test Method for Density, Relative Density,
9、 and API Gravity of Liquids by Digital Density MeterD5186 Test Method for Determination of theAromatic Content and PolynuclearAromatic Content of Diesel Fuels andAviationTurbine Fuels By Supercritical Fluid ChromatographyD6296 Test Method for Total Olefins in Spark-ignition Engine Fuels by Multidime
10、nsional Gas ChromatographyD6299 Practice for Applying Statistical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System PerformanceD6708 Practice for Statistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purportto Measure th
11、e Same Property of a MaterialD6839 Test Method for Hydrocarbon Types, Oxygenated Compounds and Benzene in Spark Ignition Engine Fuels by GasChromatography3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 critical pressure, nthe pressure needed to condense a gas to a liquid at th
12、e critical temperature.1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.04.0C on Liquid Chromatography.Current edition approved April 1, 2015Dec. 1, 2015. Published June 2015Decem
13、ber 2015. Originally approved in 2000. Last previous edition approved in 20102015 asD6550 10.D6550 10 (2015). DOI: 10.1520/D6550-10R15.10.1520/D6550-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Sta
14、ndardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possibl
15、e to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyri
16、ght ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 critical temperature, nthe highest temperature at which a gaseous fluid can be condensed to a liquid by means ofcompression.3.1.3 supercritical fluid, na fluid maintained above its criti
17、cal temperature and critical pressure.3.1.4 supercritical-fluid chromatography (SFC), na type of chromatography that employs a supercritical fluid as the mobilephase.4. Summary of Test Method4.1 Asmall aliquot of the fuel sample is injected onto a set of two chromatographic columns connected in seri
18、es and transportedusing supercritical carbon dioxide (CO2) as the mobile phase. The first column is packed with high-surface-area silica particles.The second column contains either high-surface-area silica particles loaded with silver ions or strong-cation-exchange materialloaded with silver ions.4.
19、2 Two switching valves are used to direct the different classes of components through the chromatographic system to thedetector. In a forward-flow mode, saturates (normal and branched alkanes, cyclic alkanes) pass through both columns to thedetector, while the olefins are trapped on the silver-loade
20、d column and the aromatics and oxygenates are retained on the silicacolumn.Aromatic compounds and oxygenates are subsequently eluted from the silica column to the detector in a back-flush mode.Finally, the olefins are back-flushed from the silver-loaded column to the detector.4.3 A flame-ionization
21、detector (FID) is used for quantitation. Calibration is based on the area of the chromatographic signalfor olefins, relative to standard reference materials, which contain a known mass % of total olefins as corrected for density.5. Significance and Use5.1 Gasoline-range olefinic hydrocarbons have be
22、en demonstrated to contribute to photochemical reactions in the atmosphere,which result in the formation of photochemical smog in susceptible urban areas.5.2 The California Air Resources Board (CARB) has specified a maximum allowable limit of total olefins in motor gasoline.This necessitates an appr
23、opriate analytical test method for determination of total olefins to be used both by regulators andproducers.5.3 This test method compares favorably with Test Method D1319 (FIA) for the determination of total olefins in motorgasolines. It does not require any sample preparation, has a comparatively
24、short analysis time of about 10 min, and is readilyautomated. Alternative methods for determination of olefins in gasoline include Test Methods D6839 and D6296.6. Apparatus6.1 Supercritical-fluid Chromatograph (SFC)Any SFC instrumentation can be used that has the following characteristics andmeets t
25、he performance requirements specified in Section 8.NOTE 2The SFC instruments suitable for Test Method D5186 are suitable for this test method, if equipped with two switching valves, as describedunder 6.1.7.6.1.1 PumpThe SFC pump shall be able to operate at the required pressures (typically up to abo
26、ut 30 MPa) and deliver asufficiently stable flow to meet the requirements of retention-time precision (better than 0.3 %) and detection background (seeSection 8). The characteristics of the pump will largely determine the optimum column diameter. The use of 4.6 mm internaldiameter (i.d.) columns req
27、uires a pump capacity of at least 1 mLmin of liquid CO2. Columns with an inside diameter of 2 mmand 1 mm require minimum pump capacities of 200 Lmin and 50 Lmin, respectively.6.1.2 DetectorsA FID is required for quantitation. A flow restrictor shall be installed immediately before the FID. Thisrestr
28、ictor serves to maintain the required pressure in the column, while allowing the pump and detector to perform as specified.A (diode-array or variable wavelength) UV detector for establishing optimum switching times (see Sections 8 and 9) is optional.Such a detector can be incorporated in two differe
29、nt manners.6.1.2.1 A UV detector with a very small dead volume can be inserted between the column and the FID and operated in series.6.1.2.2 Apost-column splitting device, consisting of a T-junction with an appropriate flow restrictor to the FID, can be insertedbetween the column and the UV detector
30、. Using the T-junction, the two detectors can be operated in parallel. The combination ofrestrictors (before the FID and after the UV detector) shall allow the pump and detector to perform as specified.TABLE 1 Typical ColumnsSilica Column Silver-loaded ColumnVendor Merck Vendor Hypersil, Phenomenex,
31、 SelerityPacking material Lichrospher SI 60 Packing material Hypersil SCX, Selectosil SCX, Ag+ formParticle size, m 5 Particle size, m 5Length, mm 250 Length, mm 100 or 50Internal diameter, mm 4.6 Internal diameter, mm 4.6D6550 1526.1.3 Sample-inlet SystemA liquid-sample injection valve3 is required
32、, capable of introducing (sub-)microlitre volume witha precision better than 0.5 %. A 1 L injection volume was found to be adequate in combination with 4.6 mm inside diametercolumns. Corresponding injection volumes are 200 nL and 50 nL for columns with inside diameters of 2 mm and 1 mm,respectively.
33、 The sample inlet system shall be installed and operated in a manner such that the chromatographic separation is notnegatively affected.6.1.4 ColumnsTwo columns of equal inside diameter are required:6.1.4.1 A high-surface-area-silica column, capable of separating alkanes and olefins from aromatics a
34、s specified in Section 8.Typically, one or several 250 mm long columns are used. These columns are packed with particles having an average diameter of5 m or less, 600 nm (60 ) pores, and a surface area of 350 m2/g.NOTE 3Columns suitable for Test Method D5186 are also suitable for the present method.
35、 A typical example is shown in Table 1.6.1.4.2 A silver-loaded-silica column or a cation-exchange column in the silver form. Cation-exchange columns are claimed4to yield more stable columns. Typically, one 50 mm or 100 mm long column packed with particles with an average diameter of5 m is used for t
36、he analysis.NOTE 4Some columns that have been used successfully are shown in Table 1.6.1.5 Column-temperature ControlThe chromatograph shall be capable of column temperature control to within 0.5 C orless.6.1.6 Computor or Electronic IntegratorMeans shall be provided for the determination of accumul
37、ated peak areas. This canbe done by means of a computer or electronic integrator. The computer or integrator shall have the capability of correcting forbaseline shifts during the run.6.1.7 Switching ValvesTwo six-way switching valves are configured in accordance with the scheme shown in Fig. 1. This
38、configuration allows four different valve positions, defined as follows:6.1.7.1 Position ASilica column (forward-flush mode) and silver-loaded column (forward-flush mode) connected in series.This position is used (1) to inject the sample on the two columns, (2) to elute the saturates, (3) to trap th
39、e olefins on thesilver-loaded column, and (4) to retain the aromatics and oxygenates on the silica column.6.1.7.2 Position BSilica column (backflush mode) connected in-line; silver-loaded column not in flow path. This position isused to elute the aromatics and polar compounds.6.1.7.3 Position CSilic
40、a column not in flow path; silver-loaded column (backflush mode) connected in-line. This position isused to elute the olefins.6.1.7.4 Position DSilica column (forward-flush mode) connected in-line; silver-loaded column not in flow path. This positionis used to optimize the separation. Also, this pos
41、ition allows Test Method D5186 to be performed without changing the system.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform to the specifications of the Committee on Analytical Reage
42、nts of the American Chemical Society where such3 Sample valves with loop volumes down to 50 nL are commercially available from Valco (Houston, TX).4 Anderson, P. E., Demirbueker, M., and Blomberg, L. G., Journal of Chromatography, 596, 1991, pp. 301-311.FIG. 1 Configuration of Switching Valves (Show
43、n in Position A)D6550 153specifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the determination.7.2 AirZero-grade (hydrocarbon-free) air is used as the FID oxidant.
44、 (Warning Air is usually supplied as a compressed gasunder high pressure, and it supports combustion.)7.3 Calibration SolutionA mixture of hydrocarbons with a known mass % of olefins of the type and concentration found intypical gasolines. This olefin mixture can be diluted by weight with olefin-fre
45、e components, such as alkylate, toluene, xylenes, andoxygenates, such as MTBE, as appropriate to approximate the composition of the fuels being tested.7.4 Carbon Dioxide (CO2) Supercritical-fluid-chromatographic grade, 99.99 % minimum purity, supplied pressurized in acylinder with a dip tube for rem
46、oval of liquid CO2. (WarningLiquid at high pressure. Release of pressure results in productionof extremely cold, solid CO2 and gas, which can dilute available atmospheric oxygen.)7.5 HydrogenHydrogen of high quality (hydrocarbon-free) is used as the fuel for the FID. (WarningHydrogen is usuallysuppl
47、ied under high pressure and is extremely flammable.)7.6 Loading-time MixtureA mixture of a typical alkane and an olefin, which can be used to determine the loading time (see8.2.2.3 ( 1) and 8.2.2.3 (2) while protecting the silver-loaded column from exposure to aromatic compounds.7.7 Performance Mixt
48、ureA mixture of a typical alkane, a mono-aromatic (usually toluene), and a typical mono-olefin can beused to fine-tune this test method and to check its performance.Amixture of n-heptane, toluene, and 3-methyl-2-pentene has beensuccessfully used for this purpose.7.8 Quality Control SampleA motor gas
49、oline containing olefins to be used to establish and monitor the precision of theanalytical measurement system.8. Preparation of Apparatus8.1 Install the SFC instrumentation in accordance with the manufacturers instructions. System operating conditions will dependon the column used and optimization of performance. The conditions listed in Table 1 have been used successfully. If theperformance characteristics in terms of retention and resolution, specified in 8.2, are not achieved, the temperature, pressure, ormobile-phase flow rate
