ASTM D664-95
(Test Method)Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration
SCOPE
1.1 This test method covers procedures for the determination of acidic constituents in petroleum products and lubricants soluble or nearly soluble in mixtures of toluene and propan-2-ol (Note 1). It is applicable for the determination of acids whose dissociation constants in water are larger than 10-9; extremely weak acids whose dissociation constants are smaller than 10-9 do not interfere. Salts react if their hydrolysis constants are larger than 10-9.
Note 1—In new and used oils, the constituents that may be considered to have acidic characteristics include organic and inorganic acids, esters, phenolic compounds, lactones, resins, salts of heavy metals, salts of ammonia and other weak bases, acid salts of polybasic acids, and addition agents such as inhibitors and detergents.
1.2 The test method may be used to indicate relative changes that occur in an oil during use under oxidizing conditions regardless of the color or other properties of the resulting oil. Although the titration is made under definite equilibrium conditions, the test method is not intended to measure an absolute acidic property that can be used to predict performance of an oil under service conditions. No general relationship between bearing corrosion and acid number is known.
Note 2—The acid number obtained by this standard may or may not be numerically the same as that obtained in accordance with Test Methods D974 and D3339.
1.3 The values stated in acceptable SI units are to be regarded as the standard.
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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Designation: D 664 – 95 An American National Standard
British Standard 4457
Designation 177/96
AMERICAN SOCIETY FOR TESTING AND MATERIALS
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Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Acid Number of Petroleum Products by Potentiometric
1
Titration
This standard is issued under the fixed designation D 664; 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.
This test method was adopted as a joint ASTM-IP standard in 1964.
This test method has been adopted for use by government agencies to replace Method 5106 of Federal Test Method Standard No. 791b.
ASTM Test Method D 4739 has been developed as an alternative to the base number portion of D 664.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This test method covers procedures for the determina-
bility of regulatory limitations prior to use.
tion of acidic constituents in petroleum products and lubricants
soluble or nearly soluble in mixtures of toluene and propan-
2. Referenced Documents
2-ol (Note 1). It is applicable for the determination of acids
−9
2.1 ASTM Standards:
whose dissociation constants in water are larger than 10 ;
D 974 Test Method for Acid and Base Number by Color-
extremely weak acids whose dissociation constants are smaller
2
−9
Indicator Titration
than 10 do not interfere. Salts react if their hydrolysis
3
−9
D 1193 Specification for Reagent Water
constants are larger than 10 .
D 3339 Test Method for Acid Number of Petroleum Prod-
NOTE 1—In new and used oils, the constituents that may be considered
4
ucts by Semi-Micro Color Indicator Titration
to have acidic characteristics include organic and inorganic acids, esters,
phenolic compounds, lactones, resins, salts of heavy metals, salts of
3. Terminology
ammonia and other weak bases, acid salts of polybasic acids, and addition
agents such as inhibitors and detergents.
3.1 Definitions:
3.1.1 acid number, n—the quantity of base, expressed as
1.2 The test method may be used to indicate relative
milligrams of potassium hydroxide per gram of sample, re-
changes that occur in an oil during use under oxidizing
quired to titrate a sample to a specified end point.
conditions regardless of the color or other properties of the
3.1.1.1 Discussion—This test method expresses the quantity
resulting oil. Although the titration is made under definite
of base as milligrams of potassium hydroxide per gram of
equilibrium conditions, the test method is not intended to
sample, that is required to titrate a sample in the solvent from
measure an absolute acidic property that can be used to predict
its initial meter reading in millivolts to a meter reading in
performance of an oil under service conditions. No general
millivolts corresponding to a freshly prepared non-aqueous
relationship between bearing corrosion and acid number is
basic buffer solution or a well-defined inflection point as
known.
specified in the test method.
NOTE 2—The acid number obtained by this standard may or may not be
3.1.1.2 Discussion—This test method provides additional
numerically the same as that obtained in accordance with Test Methods
information. The quantity of base, expressed as milligrams of
D 974 and D 3339.
potassium hydroxide per gram of sample, required to titrate a
1.3 The values stated in acceptable SI units are to be
sample in the solvent from its initial meter reading in millivolts
regarded as the standard.
to a meter reading in millivolts corresponding to a freshly
1.4 This standard does not purport to address all of the
prepared nonaqueous acidic buffer solution or a well-defined
safety concerns, if any, associated with its use. It is the
inflection point as specified in the test method shall be reported
as the strong acid number.
1
This test method is under the jurisdiction of ASTM Committee D-2 on
Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee
2
D02.06on Analysis of Lubricants. Annual Book of ASTM Standards, Vol 05.01.
3
Current edition approved Oct. 10, 1995. Published December 1995. Originally Annual Book of ASTM Standards, Vol 11.01.
4
published as D 664 – 42 T. Last previous edition D 664 – 89. Annual Book of ASTM Standards, Vol 05.02.
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D 664
3.1.1.3 Discussion—The causes and effects of the so-called electrodes specified in 6.1.2 and 6.1.3 and when the resistance
strong acids and the causes and effects of the other acids can be between the elec
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