ASTM D6423-99(2004)
(Test Method)Standard Test Method for Determination of pHe of Ethanol, Denatured Fuel Ethanol, and Fuel Ethanol (Ed75-Ed85)
Standard Test Method for Determination of pHe of Ethanol, Denatured Fuel Ethanol, and Fuel Ethanol (Ed75-Ed85)
SIGNIFICANCE AND USE
The acid strength, as measured by pHe, is a good predictor of the corrosion potential of ethanol fuels. It is preferable to total acidity because total acidity does not measure acid strength; overestimates the contribution of weak acids, such as carbonic acid; and may underestimate the corrosion potential of low concentrations of strong acids, such as sulfuric acid.
SCOPE
1.1 This test method covers a procedure to determine a measure of the acid strength of high ethanol content fuels. These include ethanol, denatured fuel ethanol, and fuel ethanol (Ed75-Ed85). The test method is applicable to fuels containing nominally 70 volume % ethanol, or higher, as described in Specifications D 4806 and D 5798.
1.2 Acid strength as measured in this test method is defined as pHe. A pHe value for alcohol solutions is not directly comparable to pH values of water solutions.
1.3 The value of pHe will depend somewhat on the fuel blend, the stirring rate, and the time the electrode is in the fuel.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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An American National Standard
Designation: D 6423 – 99 (Reapproved 2004)
Standard Test Method for
Determination of pHe of Ethanol, Denatured Fuel Ethanol,
and Fuel Ethanol (Ed75-Ed85)
This standard is issued under the fixed designation D 6423; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.2 denaturants, n—natural gasoline, gasoline compo-
nents,unleadedgasoline,ortoxicornoxiousmaterialsaddedto
1.1 This test method covers a procedure to determine a
fuel ethanol to make it unsuitable for beverage use but not
measure of the acid strength of high ethanol content fuels.
unsuitable for automotive fuel use.
These include ethanol, denatured fuel ethanol, and fuel ethanol
3.1.3 denatured fuel ethanol, n—fuel ethanol made unfit for
(Ed75-Ed85). The test method is applicable to fuels containing
beverage use by the addition of denaturants.
nominally 70 volume % ethanol, or higher, as described in
3.1.4 fuel ethanol (Ed75-Ed85), n—a blend of ethanol and
Specifications D 4806 and D 5798.
hydrocarbons of which the ethanol portion is nominally 75 to
1.2 Acid strength as measured in this test method is defined
85 volume % denatured ethanol.
as pHe. A pHe value for alcohol solutions is not directly
3.2 Definitions of Terms Specific to This Standard:
comparable to pH values of water solutions.
3.2.1 pHe, n—a measure of the acid strength of alcohol
1.3 The value of pHe will depend somewhat on the fuel
fuels defined by this apparatus and procedure.
blend, the stirring rate, and the time the electrode is in the fuel.
1.4 This standard does not purport to address all of the
4. Summary of Test Method
safety concerns, if any, associated with its use. It is the
4.1 The sample is analyzed at room temperature using a
responsibility of the user of this standard to establish appro-
specified electrode system and a pH meter with a sufficiently
priate safety and health practices and determine the applica-
high impedance and recommended for use with ion-specific
bility of regulatory limitations prior to use.
electrodes.
2. Referenced Documents 4.2 Readings are taken at exactly 30 s because the meter
reading will drift throughout the analysis due to solvent effects
2.1 ASTM Standards:
on the electrode.
D 4806 SpecificationforDenaturedFuelEthanolforBlend-
4.3 The electrode is soaked in water-based pH 7 buffer
ing with Gasolines for Use as Automotive Spark-Ignition
between readings to prepare it for the next sample. This
Engine Fuel
rehydrates the glass electrode, a necessary step to preserve the
D 5798 Specification for Fuel Ethanol (Ed75-Ed85) for
electrode’s response characteristics.
Automotive Spark-Ignition Engines
5. Significance and Use
3. Terminology
5.1 The acid strength, as measured by pHe, is a good
3.1 Definitions:
predictor of the corrosion potential of ethanol fuels. It is
3.1.1 ethanol, n—ethyl alcohol, the chemical compound,
preferable to total acidity because total acidity does not
C H OH.
2 5
measure acid strength; overestimates the contribution of weak
acids, such as carbonic acid; and may underestimate the
This test method is under the jurisdiction of ASTM Committee D02 on
corrosion potential of low concentrations of strong acids, such
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee
as sulfuric acid.
D02.A0 on Gasoline and Oxygenated Fuels.
Current edition approved July 1, 2004. Published July 2004. Originally approved
6. Apparatus
in 1999. Last previous edition approved in 1999 as D 6423 - 99.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
6.1 pH meter—All types of commercially available pH
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
meters with a sufficiently high impedance and recommended
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. for use with ion-specific electrodes are acceptable for this test
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 6423 – 99 (2004)
method. Temperature compensation and readability to 0.01 pH 8. Sample Containers
unit are recommended.
8.1 Caremustbeusedinsamplecontainerselectiontoavoid
6.2 Electrode—ORION Ross Sure-Flow combination elec-
reactions that change the pHe of the sample. Do not use steel,
trode with a glass body shall be used. Because the measure-
plated steel, or epoxy-coated steel containers or PVC-coated
ment is (of necessity) not made at equilibrium, it is essential
glass bottles for samples. Avoid closures with a paper seal.
thatthisexactelectrodebeusedtoensurethereproducibilityof
Fluorinated high-density polyethylene and spun aluminum
results. Other electrodes (even those of similar design) will
sample containers with polyethylene closures are acceptable.
likely give different results under some or all conditions due to
Glass bottles without a PVC coating and utilizing TFE-
the use of a different size or type of glass membrane for the pH
fluorocarbon or polyethylene cap seals are also acceptable.
electrode,adifferenttypeofsaltbridgejunction,orothersmall
8.2 Rinse the container with a portion of the fuel to be
differences, which may affect their nonequilibrium response.
sampled before taking the sample.
6.3 Temperature Compensator—The thermocompensator is
a temperature-sensitive resistance element immersed in the
9. Standardization of Assembly
sample with the electrodes. The thermocompensator automati-
9.1 Turn on the pH meter and allow it to warm up
cally corrects for the change in slope of the glass electrode
thoroughly in accordance with the manufacturer’s instructions.
response (with change in temperature) but does not correct for
Note the temperature of the sample to be tested. If temperature
actual changes in sample pH with temperature. Because
compensation is to be manual, adjust the temperature dial of
temperature compensation corrects only for changes in pH
the meter to correspond to the temperature of the sample to be
electroderesponsewithtemperature,thefuelsamplemustbeat
tested and allow time for all buffers, solutions, and the
22 6 2°C.
electrode to equilibrate thermally.
6.4 Beakers, borosilicate glass, 100 mL.
9.2 Clean/rehydrate the electrode after every ten samples
6.5 Magnetic Stirrer—Any laboratory magnetic stirrer can
and new electrodes before first use in alcohol solutions by
be used, along with a TFE-fluorocarbon-coated stirring bar
alternately soaking several times in 1 M NaOH solution and 1
approximately 19 to 25-mm long.
MH SO (or 1 M HCl) for about 30 s each. Remove the
2 4
6.6 Tim
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