Standard Test Method for Acid Number of Crude Oils and Petroleum Products by Catalytic Thermometric Titration

SIGNIFICANCE AND USE
5.1 Crude oils and oil sands bitumen contain naturally occurring acidic species. Acidity of crude oil has been implicated in corrosion of distribution and process systems. The relative amount of these materials can be determined by titrating with bases. The acid number is a measure of this amount of acidic substance in the oil under the conditions of the test.  
5.2 Acid number of crude and distilled petroleum fractions has been measured by Test Method D664. Test Method D664 was developed for the analysis of lubricants and biodiesel. The titration solvent used in Test Method D664 does not properly address dissolving difficult samples such as crude oil, bitumen, and high wax samples addressed in this test method. Refer to Appendix X1.  
5.3 Test Method D974 is also not applicable to measuring acidity of crudes and highly colored samples because the indicator is not visible or it is difficult to discern a color change to detect the end point of the titration.
SCOPE
1.1 This test method covers the determination of acidic components in crude oil and petroleum products including waxes, bitumen, base stocks, and asphalts that are soluble in mixtures of xylenes and propan-2-ol. 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. The values obtained by this test method may not be numerically equivalent to other acid value measurements. The range of KOH acid numbers included in the precision statement is 0.1 mg/g to 16 mg/g.  
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.3 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. Some specific hazards statements are given in Section 7 on Safety Precautions.

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Publication Date
30-Jun-2016
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ASTM D8045-16 - Standard Test Method for Acid Number of Crude Oils and Petroleum Products by Catalytic Thermometric Titration
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D8045 − 16
Standard Test Method for
Acid Number of Crude Oils and Petroleum Products by
1
Catalytic Thermometric Titration
This standard is issued under the fixed designation D8045; 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 D4175 Terminology Relating to Petroleum Products, Liquid
Fuels, and Lubricants
1.1 This test method covers the determination of acidic
D4177 Practice for Automatic Sampling of Petroleum and
components in crude oil and petroleum products including
Petroleum Products
waxes, bitumen, base stocks, and asphalts that are soluble in
D5854 Practice for Mixing and Handling of Liquid Samples
mixtures of xylenes and propan-2-ol. It is applicable for the
of Petroleum and Petroleum Products
determination of acids whose dissociation constants in water
–9 D6299 Practice for Applying Statistical Quality Assurance
are larger than 10 ; extremely weak acids whose dissociation
–9 and Control Charting Techniques to Evaluate Analytical
constants are smaller than 10 do not interfere. The values
Measurement System Performance
obtainedbythistestmethodmaynotbenumericallyequivalent
to other acid value measurements. The range of KOH acid
3. Terminology
numbers included in the precision statement is 0.1 mg⁄g to
16 mg⁄g.
3.1 For general terminology, refer to Terminology D4175.
1.2 The values stated in SI units are to be regarded as
3.2 Definitions:
standard. No other units of measurement are included in this
3.2.1 acid number, n—the quantity of a specified base,
standard.
expressed in milligrams of potassium hydroxide per gram of
sample, required to titrate a sample in a specified solvent to a
1.3 This standard does not purport to address all of the
specified endpoint using a specified detection system.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3.2.2 catalytic thermometric titration, n—a method to de-
priate safety and health practices and determine the applica-
termine the end point of a chemical reaction through the use a
bility of regulatory limitations prior to use. Some specific
temperaturemeasuringdeviceandtheadditionofachemicalto
hazards statements are given in Section 7 on Safety Precau-
enhance the detection of the endpoint.
tions.
3.2.3 crude oil, n—a naturally occurring hydrocarbon
mixture, generally in a liquid state, which may also include
2. Referenced Documents
compounds of sulfur, nitrogen, oxygen, metals, and other
2
2.1 ASTM Standards:
elements.
D664 Test Method for Acid Number of Petroleum Products
by Potentiometric Titration
4. Summary of Test Method
D974 Test Method for Acid and Base Number by Color-
4.1 The sample and a fixed mass of paraformaldehyde are
Indicator Titration
dissolvedinamixtureofxylenesandpropan-2-ol.Themixture
D1193 Specification for Reagent Water
is then titrated with potassium hydroxide using a constant rate
D4057 Practice for Manual Sampling of Petroleum and
of titrant addition. A plot of the temperature of the reaction
Petroleum Products
mixture versus the volume of titrant is generated. An exother-
mic reaction between the titrant and sample occurs simultane-
ously with the endothermic depolymerization of paraformalde-
1
This test method is under the jurisdiction of ASTM Committee D02 on
hyde.After all of the acidic material in the sample has reacted,
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
the slope of the plot changes due to the absence of the
Subcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.
competitive exothermic acid-base reaction. The change in
Current edition approved July 1, 2016. Published August 2016. DOI: 10.1520/
D8045-16.
slope is the inflection point. The depolymerization of para-
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
formaldehyde is catalytically initiated and does not consume a
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
significant quantity of potassium hydroxide. The net change
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. (positive or negative) in temperature prior to the consumption
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

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D8045 − 16
of the acidic sample will be dependent upon the relative 8.6 Titration Beaker, with sufficient volume and made of a
magnitude of the heats of reaction and environmental influ- material that does not interact with
...

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