ASTM D7757-12
(Test Method)Standard Test Method for Silicon in Gasoline and Related Products by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry
Standard Test Method for Silicon in Gasoline and Related Products by Monochromatic Wavelength Dispersive X-ray Fluorescence Spectrometry
SIGNIFICANCE AND USE
This test method provides rapid and precise measurement of total silicon in naphthas, gasoline, RFG, ethanol and ethanol-fuel blends, and toluene with minimum sample preparation. Typical analysis time is 5 to 10 min per sample.
Excitation by monochromatic X-rays reduces background, simplifies matrix correction, and increases the signal/background ratio compared to polychromatic excitation used in conventional WDXRF techniques.
Silicone oil defoamer can be added to coker feedstocks to minimize foaming in the coker. Residual silicon in the coker naphtha can adversely affect downstream catalytic processing of the naphtha. This test method provides a means to determine the silicon content of the naphtha.
Silicon contamination of gasoline, denatured ethanol, and their blends has led to fouled vehicle components (for example, spark plugs, exhaust oxygen sensors, catalytic converters) requiring parts replacement and repairs. Finished gasoline and ethanol-fuel blends can come into contact with silicon a number of ways. Waste hydrocarbon solvents such as toluene can be added to gasoline. Such solvents can contain soluble silicon compounds. Silicon-based antifoam agents can be used in ethanol plants, which then pass silicon on to the finished ethanol-fuel blend. This test method can be used to determine if gasoline and ethanol-fuel blends meet specifications with respect to silicon content of the fuel, and for resolution of customer problems.
Some silicon compounds covered by this test method are significantly more volatile than the silicon compounds typically used for the preparation of the calibration standards. Volatile compounds (for example, hexamethyldisiloxane with a boiling point of 101°C), which typically have boiling points below 170°C can give higher silicon sensitivities than the standard.
SCOPE
1.1 This test method covers the determination of total silicon by monochromatic, wavelength-dispersive X-ray fluorescence (MWDXRF) spectrometry in naphthas, gasoline, RFG, ethanol and ethanol-fuel blends, and toluene at concentrations of 3 to 100 mg/kg. The precision of this test method was determined by an interlaboratory study using representative samples of the liquids described in 1.1 and 1.2. The pooled limit of quantitation (PLOQ) was estimated to be 3 mg/kg.
Note 1—Volatile samples such as high-vapor-pressure gasolines or light hydrocarbons might not meet the stated precision because of the evaporation of light components during the analysis.
Note 2—Aromatic compounds such as toluene are under the jurisdiction of Committee D16 on Aromatic Hydrocarbons and Related Chemicals. However, toluene can be a contributor to silicon contamination in gasoline (see 4.4), thus its inclusion in this test method.
1.2 Gasoline samples containing ethanol and other oxygenates may be analyzed with this test method provided the matrix of the calibration standards is either matched to the sample matrices or the matrix correction described in Annex A1 is applied to the results. The conditions for matrix matching and matrix correction are provided Section 5, Interferences.
1.3 Samples with silicon concentrations above 100 mg/kg can be analyzed after dilution with appropriate solvent. The precision and bias of silicon determinations on diluted samples have not been determined and may not be the same as shown for neat samples (Section 16).
1.4 A fundamental assumption in this test method is that the standard and sample matrices are well matched, or that the matrix differences are accounted for (see 13.5). Matrix mismatch can be caused by C/H ratio differences between samples and standards or by the presence of other interfering heteroatoms; observe the cautions and recommendations in Section 5.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, ...
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Standards Content (Sample)
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Designation: D7757 − 12
Standard Test Method for
Silicon in Gasoline and Related Products by Monochromatic
1
Wavelength Dispersive X-ray Fluorescence Spectrometry
This standard is issued under the fixed designation D7757; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of total
responsibility of the user of this standard to establish appro-
silicon by monochromatic, wavelength-dispersive X-ray fluo-
priate safety and health practices and determine the applica-
rescence (MWDXRF) spectrometry in naphthas, gasoline,
bility of regulatory limitations prior to use.
RFG, ethanol and ethanol-fuel blends, and toluene at concen-
trations of 3 to 100 mg/kg. The precision of this test method
2. Referenced Documents
was determined by an interlaboratory study using representa-
2
2.1 ASTM Standards:
tivesamplesoftheliquidsdescribedin1.1and1.2.Thepooled
D4057 Practice for Manual Sampling of Petroleum and
limit of quantitation (PLOQ) was estimated to be 3 mg/kg.
Petroleum Products
NOTE 1—Volatile samples such as high-vapor-pressure gasolines or
D4177 Practice for Automatic Sampling of Petroleum and
light hydrocarbons might not meet the stated precision because of the
Petroleum Products
evaporation of light components during the analysis.
D4806 Specification for Denatured Fuel Ethanol for Blend-
NOTE 2—Aromatic compounds such as toluene are under the jurisdic-
tion of Committee D16 on Aromatic Hydrocarbons and Related Chemi-
ing with Gasolines for Use as Automotive Spark-Ignition
cals. However, toluene can be a contributor to silicon contamination in
Engine Fuel
gasoline (see 4.4), thus its inclusion in this test method.
D5798 Specification for Ethanol Fuel Blends for Flexible-
1.2 Gasoline samples containing ethanol and other oxygen-
Fuel Automotive Spark-Ignition Engines
atesmaybeanalyzedwiththistestmethodprovidedthematrix
D6299 Practice for Applying Statistical Quality Assurance
of the calibration standards is either matched to the sample
and Control Charting Techniques to Evaluate Analytical
matrices or the matrix correction described in Annex A1 is
Measurement System Performance
applied to the results. The conditions for matrix matching and
D6300 Practice for Determination of Precision and Bias
matrix correction are provided Section 5, Interferences.
Data for Use in Test Methods for Petroleum Products and
Lubricants
1.3 Samples with silicon concentrations above 100 mg/kg
can be analyzed after dilution with appropriate solvent. The
3. Summary of Test Method
precision and bias of silicon determinations on diluted samples
have not been determined and may not be the same as shown
3.1 A monochromatic X-ray beam with a wavelength suit-
for neat samples (Section 16).
able to excite the K-shell electrons of silicon is focused onto a
test specimen contained in a sample cell (see Fig. 1). The
1.4 Afundamental assumption in this test method is that the
fluorescent Kα radiation at 0.713 nm (7.13 Å) emitted by
standard and sample matrices are well matched, or that the
silicon is collected by a fixed monochromator (analyzer). The
matrix differences are accounted for (see 13.5). Matrix mis-
intensity (counts per second) of the silicon X-rays is measured
match can be caused by C/H ratio differences between samples
using a suitable detector and converted to the concentration of
and standards or by the presence of other interfering heteroa-
silicon (mg/kg) in a test specimen using a calibration equation.
toms; observe the cautions and recommendations in Section 5.
1.5 The values stated in SI units are to be regarded as
4. Significance and Use
standard. No other units of measurement are included in this
4.1 This test method provides rapid and precise measure-
standard.
ment of total silicon in naphthas, gasoline, RFG, ethanol and
1
This test method is under the jurisdiction of ASTM Committee D02 on
2
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Subcommittee D02.03 on Elemental Analysis. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Jan. 15, 2012. Published March 2012. DOI:10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7757-12. the ASTM website.
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