ASTM D7157-05
(Test Method)Standard Test Method for Determination of Intrinsic Stability of Asphaltene-Containing Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane Phase Separation; Optical Detection)
Standard Test Method for Determination of Intrinsic Stability of Asphaltene-Containing Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane Phase Separation; Optical Detection)
SCOPE
1.1 This test method covers a procedure for quantifying the intrinsic stability of the asphaltenes in an oil by an automatic instrument using an optical device.
1.2 This test method is applicable to residual products from thermal and hydrocracking processes, to products typical of Specifications D 396 Grades No. 5L, 5H, and 6, and D 2880 Grades No. 3-GT and 4-GT, and to crude oils, providing these products contain 0.5 mass% or greater concentration of asphaltenes (see Test Method D 6560).
1.3 This test method quantifies asphaltene stability in terms of state of peptization of the asphaltenes (S-value), intrinsic stability of the oily medium (So) and the solvency requirements of the peptized asphaltenes (Sa).
1.4 The values stated in SI units are to be regarded as the standard.
1.5 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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An American National Standard
Designation:D7157–05
Standard Test Method for
Determination of Intrinsic Stability of Asphaltene-Containing
Residues, Heavy Fuel Oils, and Crude Oils (n-Heptane Phase
Separation; Optical Detection)
This standard is issued under the fixed designation D 7157; 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 D 4870 TestMethodforDeterminationofTotalSedimentin
Residual Fuels
1.1 This test method covers a procedure for quantifying the
D 6560 Test Method for Determination of Asphaltenes
intrinsic stability of the asphaltenes in an oil by an automatic
(Heptane Insolubles) in Crude Petroleum and Petroleum
instrument using an optical device.
Products
1.2 This test method is applicable to residual products from
D 6792 Guide for a Quality System in Petroleum Products
thermal and hydrocracking processes, to products typical of
and Lubricant Testing Laboratories
Specifications D 396 Grades No. 5L, 5H, and 6, and D 2880
Grades No. 3-GT and 4-GT, and to crude oils, providing these
3. Terminology
products contain 0.5 mass% or greater concentration of as-
3.1 Definitions:
phaltenes (see Test Method D 6560).
3.1.1 For definitions of some terms used in this test method,
1.3 This test method quantifies asphaltene stability in terms
refer to Terminology D 4175.
of state of peptization of the asphaltenes (S-value), intrinsic
3.1.2 asphaltene, n—in petroleum technology, a molecule
stabilityoftheoilymedium(So)andthesolvencyrequirements
of high molecular mass, high carbon/hydrogen ratio, and
of the peptized asphaltenes (Sa).
containing hetero-atoms.
1.4 The values stated in SI units are to be regarded as the
3.1.2.1 Discussion—Asphaltenes are found largely in crude
standard.
oils and in heavy fuel oils containing residual fractions. They
1.5 This standard does not purport to address all of the
are insoluble in alkanes such as n-heptane and cetane, but
safety concerns, if any, associated with its use. It is the
soluble in aromatic solvents such as benzene, toluene, and
responsibility of the user of this standard to establish appro-
1-methylnaphthalene.
priate safety and health practices and determine the applica-
3.1.3 compatibility, n—of crude oils or of heavy fuel oils,
bility of regulatory limitations prior to use
the ability of two or more crude oils or fuel oils to blend
2. Referenced Documents together within certain concentration ranges without evidence
2 of separation, such as the formation of multiple phases.
2.1 ASTM Standards:
3.1.3.1 Discussion—Incompatible heavy fuel oils or crude
D 396 Specification for Fuel Oils
oils, when mixed or blended, result in the flocculation or
D 2880 Specification for Gas Turbine Fuel Oils
precipitation of asphaltenes. Some oils may be compatible
D 4057 Practice for Manual Sampling of Petroleum and
within certain concentration ranges in specific mixtures, but
Petroleum Products
incompatible outside those ranges.
D 4175 Terminology Relating to Petroleum, Petroleum
3.1.4 flocculation, n—of asphaltenes from crude oils or
Products, and Lubricants
heavy fuel oils, the aggregation of colloidally dispersed as-
D 4177 Practice for Automatic Sampling of Petroleum and
phaltenes into visible larger masses which may or may not
Petroleum Products
settle.
3.1.5 peptization, n—of asphaltenes in crude oils or heavy
This test method is under the jurisdiction of Committee D02 on Petroleum
oils, the dispersion of asphaltenes to produce a colloidal
Products and Lubricants and is the direct responsibility of Subcommittee D02.14 on
dispersion.
Stability and Cleanliness of Liquid Fuels.
3.1.6 stability reserve, n—in petroleum technology, the
Current edition approved May 1, 2005. Published May 2005.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
property of an oil to maintain asphaltenes in a peptized state
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and prevent flocculation of asphaltenes.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7157–05
3.1.6.1 Discussion—An oil with a low stability reserve is 4. Summary of Test Method
likelytoundergoflocculationofasphalteneswhenstressed(for
4.1 Thistestmethodusesanintegratedautomatedanalytical
example, extended heated storage) or blended with a range of
measurement system with an optical probe for the detection of
other oils.Two oils each with a high stability reserve are likely
asphaltene precipitation from a toluene solution of the sample.
to maintain asphaltenes in a peptized state and not lead to
4.2 Three test specimens are dissolved in three different
flocculation when blended together.
quantities of toluene. The three specimen/toluene solutions are
3.2 Definitions of Terms Specific to This Standard:
automatically and simultaneously titrated with n-heptane to
3.2.1 intrinsic stability (S-value), n—of refinery residual
cause precipitation of the asphaltenes. The optical probe
streams, residual fuel oils and crude oils, an indication of the
monitors the formation of flocculated asphaltenes during the
stability or available solvency power of an oil with respect to
titration. Flocculated asphaltenes will alter the detected light
precipitation of asphaltenes.
intensity. Start of flocculation is interpreted when the optical
3.2.1.1 Discussion—Since the equation defining S-value is probe detects a significant and sustained decrease in rate-of-
S=(1+ X ), where X is the minimum volume (in mL) of change of the light intensity.
min min
paraffinic solvent, n-heptane, to be added to1gofoilto result
4.3 A computer routine calculates stability parameters and
in flocculation of asphaltenes, the smallest S-value is 1, which subsequently the intrinsic stability of the oil from the added
means the oil is unstable and can precipitate asphaltenes n-heptane at the inversion point, the mass of specimen, and the
without addition of any paraffinic solvent. A higher S-value volume of toluene, for the three specimen/toluene solutions.
indicates that an oil is more stable with respect to flocculation
5. Significance and Use
of asphaltenes. S-value by this test method relates specifically
to toluene and n-heptane as the aromatic and paraffinic sol- 5.1 This test method describes a sensitive method for
vents, respectively. estimatingtheintrinsicstabilityofanoil.Theintrinsicstability
is expressed as S-value. An oil with a low S-value is likely to
3.2.2 inversion point, n—point in the n-heptane titration
undergo flocculation of asphaltenes when stressed (for ex-
curve, where the onset of asphaltene flocculation leads to
ample, extended heated storage) or blended with a range of
inversion of the light intensity.
other oils. Two oils each with a high S-value are likely to
3.2.2.1 Discussion—At the first stage of the addition of
maintain asphaltenes in a peptized state and not lead to
n-heptane to a dilution of specimen and toluene, light intensity
asphaltene flocculation when blended together.
increases through dilution. When asphaltenes start to floccu-
5.2 This test method can be used by petroleum refiners to
late, there will be a point where the increase in light intensity
controlandoptimizetherefineryprocessesandbyblendersand
through dilution matches the light intensity decrease (inver-
marketerstoassesstheintrinsicstabilityofblendedasphaltene-
sion) as a result of coagulated asphaltenes obstructing the light
containing heavy fuel oils.
beam.
3.2.3 Sa, n—the S-value of an asphaltene, which is the
6. Interferences
peptizability or ability of an asphaltene to remain in a colloidal
6.1 High content of insoluble inorganic matter (sediment)
dispersion.
has some interference in this test method. In this case, the
3.2.3.1 Discussion—Sa can also be described as one minus
insoluble matter shall be removed by filtration according to
the ratio of So to S. Sa is linked to the length and number of
Test Method D 4870.
aromatic chains within the asphaltenes.
6.2 Free water present in the oil can cause difficulties with
3.2.4 So, n—the S-value of an oil.
the optical detector and should be removed by any suitable
3.2.4.1 Discussion—So can also be described as the aro-
means (for example, centrifugation) prior to testing.
matic equivalent of the oil expressed as the ratio of the
aromaticsolventtothearomaticplusparaffinicsolventmixture
7. Apparatus
having the same peptizing power as the oil.
7.1 General—(See Fig. 1) This test method uses an inte-
,
3.2.5 solvent aromaticity, n—of a binary mixture of a 3 4
grated automated analytical measurement system comprised
paraffınic and an aromatic solvent, the solvency power of the
of a PC-based computer and three titration stations.
binary mixture.
7.1.1 Computer, PC-based computer with associated soft-
3.2.5.1 Discussion—For the purpose of this test method,
ware, capable of controlling up to three independent titration
solvent aromaticity is defined as a ratio by volume of the
stations, controlling test sequencing, and acquisition of optical
aromaticsolvent(toluene)totheparaffinicsolvent(n-heptane).
3.3 Symbols:
The sole source of supply of the apparatus (Automated Stability Analyser)
known to the committee at this time is Rofa France, 6 Rue Raymond Poincare,
F-25300,LesAllies,France.Ifyouareawareofalternativesuppliers,pleaseprovide
FR = flocculation ratio
this information to ASTM International Headquarters. Your comments will receive
FR = maximum flocculation ratio
max
careful consideration at a meeting of the responsible technical committee, which
S = the intrinsic stability of an oil
you may attend.
Sa = the peptizability of an asphaltene
The Rofa stability analyzer is covered by a patent; INPI, date 18/05/04,
So = the peptizing power of an oil registration number 04.05406. Interested parties are invited to submit information
regarding the identification of an alternative(s) to this patented item to the ASTM
X = paraffinic solvent consumption of undiluted oil,
min
International Headquarters. Your comments will receive careful consideration at a
in mL/g of oil
meeting of the responsible technical committee, which you may attend.
D7157–05
FIG. 1 Schematic Drawing of the Integrated Automated Stability Analyser System
probe signal data. The associated software also provides for such specifications are available. Other grades may be used,
provided it is first ascertained that the reagent is of sufficiently
processing calculations and automatically produces a report of
high purity to permit its use without lessening the accuracy of
important test parameters.
the determination.
7.1.2 Titration Stations:
8.1.1 Toluene.(Warning—Flammable. Health hazard. Va-
7.1.2.1 Titration Unit, automatic computer controlled, ad-
por may cause flash fire.) (See Annex A1.)
justable motor-driven ceramic piston pump, capable of deliv-
8.1.2 n-Heptane.(Warning—Flammable. Vapor harmful.
ering solvent at a rate of 0.01 to 0.5 mL/s, with a volume
Vapor may cause flash fire.) (See Annex A1.)
dispensing accuracy of 60.01 mL.
8.2 Quality Control Sample—A stable and homogeneous
7.1.2.2 Magnetic Stirrer, adjustable from 200 to 400 r/min.
residual fuel oil having physical and chemical properties
7.1.2.3 Optical Probe, consisting of a system of three areas similar to those of typical sample fuels routinely tested.
of light emitters (880 nm) and three areas of light receivers.
9. Sampling and Test Specimens
The analytical measurement system will automatically select
the optimum area, based on the level of translucency of the 9.1 Sampling:
9.1.1 Obtain representative samples in accordance with
sample.
recognized sampling procedures such as Practices D 4057 or
7.1.2.4 Titration Cell, of borosilicate glass, flat bottom,
D 4177.
outside diameter 30 6 2 mm, volume 95 6 15 mL, fitted with
9.1.2 Samples of very viscous materials may be warmed
a tapered ground glass joint (female).
until they are reasonably fluid before they are sampled.
7.2 Balance, capable of reading to 0.1 mg or better.
9.1.3 Store samples prior to taking test specimens at ambi-
7.3 Dispenser, capable of delivering up to 10 mLof toluene
ent temperatures.
with an accuracy of 60.1 mL.
9.2 Test Specimen Preparation:
7.4 Condenser, double surface with a tapered ground-glass
9.2.1 Sample Temperature—If necessary, warm viscous
joint (male) at the bottom to fit the top of the titration cell.
samples until they can be mixed readily before opening the
storage container. For fuels with a high wax content (high pour
7.5 Magnetic Stirrer/Hotplate, stirrer speed adjustable from
point) the temperature must be at least 15°C above the pour
100 to 1000 r/min.
point.
7.6 Stirring Bar, magnetic, PFTE-coated, 20 mm in length.
8. Reagents and Materials
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
8.1 Purity of Reagents—Reagent grade chemicals shall be
listed by the American Chemical Society, see Annual Standards for Laboratory
used in all tests. Unless otherwise indicated, it is intended that
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
all reagents conform to the specifications of the Committee on
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
Analytical Reagents of the American Chemical Society where MD.
D7157–05
9.2.2 Manually shake the sample thoroughly. If the sample 11. Quality Control Monitoring
contains high content of insoluble inorganic matter, filter the
11.1 Confirm the performance of the instrument and test
sample through a 47-mm diameter glass fiber filter medium
procedure by analyzing quality control (QC) samples.
(such as Whatman Grade GF/A), using the Test Method
11.1.1 When quality control/quality assurance (QC/QA)
D 4870 filtration apparatus. Specimen should be representative
protocols are already established in the testing facility, these
of the whole sample.
can be used when they confirm the reliability of the test result.
9.3 Preparation of Specimen Dilutions—Prepare three dilu-
11.1.2 When there is no QC/QA protocol established in the
tions of specimen in toluene in different ratios (see Table 1)as
testing facility, Guide D 6792 can be used for guidance.
follows:
9.3.1 Place a magnetic stirrer bar into a clean titration cell.
12. Procedure
9.3.2 Add the required amount of s
...
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