ASTM D4928-00(2005)
(Test Method)Standard Test Methods for Water in Crude Oils by Coulometric Karl Fischer Titration
Standard Test Methods for Water in Crude Oils by Coulometric Karl Fischer Titration
SIGNIFICANCE AND USE
A knowledge of the water content of crude oil is important in the refining, purchase, sale, or transfer of crude oils.
SCOPE
1.1 This test method covers the determination of water in the range from 0.02 to 5 mass or volume % in crude oils. Mercaptan (RSH) and sulfide (S- or H2S) as sulfur are known to interfere with this test method, but at levels of less than 500 μg/g (ppm), the interference from these compounds is insignificant (see Section 5).
1.2 This test method can be used to determine water in the 0.005 to 0.02 mass % range, but the effects of the mercaptan and sulfide interference at these levels has not been determined.
1.3 This test method is intended for use with standard commercially available coulometric Karl Fischer reagent.
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. For specific hazard statements, see Section 7.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:D4928–00 (Reapproved 2005)
Designation: Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9
Designation: 386/99
Standard Test Methods for
Water in Crude Oils by Coulometric Karl Fischer Titration
This standard is issued under the fixed designation D4928; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope of Petroleum and Petroleum Products
E203 TestMethodforWaterUsingVolumetricKarlFischer
1.1 This test method covers the determination of water in
Titration
the range from 0.02 to 5 mass or volume % in crude oils.
−
2.2 API Standards:
Mercaptan (RSH) and sulfide (S or H S) as sulfur are known
MPMS Chapter 8.1 Practice for Manual Sampling of Petro-
to interfere with this test method, but at levels of less than
leum and Petroleum Products (ASTM Practice D4057)
500µg/g (ppm), the interference from these compounds is
MPMS Chapter 8.2 Practice for Automatic Sampling of
insignificant (see Section 5).
Petroleum and Petroleum Products (ASTM Practice
1.2 This test method can be used to determine water in the
D4177)
0.005 to 0.02 mass % range, but the effects of the mercaptan
MPMS Chapter 8.3 Practice for Mixing and Handling of
and sulfide interference at these levels has not been deter-
Liquid Samples of Petroleum and Petroleum Products
mined.
(ASTM Practice D5854)
1.3 This test method is intended for use with standard
commercially available coulometric Karl Fischer reagent.
3. Summary of Test Method
1.4 This standard does not purport to address all of the
3.1 After homogenizing the crude oil with a mixer, an
safety concerns, if any, associated with its use. It is the
aliquot is injected into the titration vessel of a Karl Fischer
responsibility of the user of this standard to establish appro-
apparatus in which iodine for the Karl Fischer reaction is
priate safety and health practices and determine the applica-
generatedcoulometricallyattheanode.Whenallthewaterhas
bility of regulatory limitations prior to use. For specific hazard
been titrated, excess iodine is detected by an electrometric
statements, see Section 7.
end-point detector and the titration is terminated. Based on the
2. Referenced Documents stoichiometry of the reaction, one mole of iodine reacts with
2 one mole of water, thus the quantity of water is proportional to
2.1 ASTM Standards:
the total integrated current according to Faraday’s Law.
D1193 Specification for Reagent Water
3.2 The precision of this test method is critically dependent
D4057 Practice for Manual Sampling of Petroleum and
ontheeffectivenessofthehomogenizationstep.Theefficiency
Petroleum Products
of the mixer used to achieve a homogeneous sample is
D4177 Practice for Automatic Sampling of Petroleum and
determined by the procedure given in Practice D5854 (API
Petroleum Products
MPMS Chapter 8.3).
D5854 PracticeforMixingandHandlingofLiquidSamples
3.3 Two procedures are provided for the determination of
water in crude oils. In one procedure, a weighed aliquot of
This test method is under the jurisdiction of ASTM Committee D02 on
sample is injected into the titration vessel and the mass % of
Petroleum Products and Lubricants and theAPI Committee on Petroleum Measure-
water is determined. The other procedure provides for the
ment, and is the direct responsibility of Subcommittee D02.02/COMQ, the joint
direct determination of the volume % of water in the crude oil
ASTM-API Committee on Static Petroleum Measurement.
bymeasuringthevolumeofcrudeoilinjectedintothetitration
Current edition approved June 1, 2005. Published October 2005. Originally
´1
approved in 1989. Last previous edition approved in 2000 as D4928–00 . DOI:
vessel.
10.1520/D4928-00R05.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Published as Manual of Petroleum Standards. Available from the American
the ASTM website. Petroleum Institute (API), 1220 L St., NW, Washington, DC 20005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4928–00 (2005)
4. Significance and Use 7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals shall be
4.1 A knowledge of the water content of crude oil is
used in all tests. Unless otherwise indicated, it is intended that
important in the refining, purchase, sale, or transfer of crude
all reagents shall conform to the specifications of the Commit-
oils.
tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available. Other grades may be
5. Interferences
used, provided it is first ascertained that the reagent is of
5.1 A number of substances and classes of compounds
sufficiently high purity to permit its use without lessening the
associated with condensation or oxidation-reduction reactions
accuracy of the determination.
interfereinthedeterminationofwaterbyKarlFischer.Incrude
7.2 Purity of Water—Unlessotherwiseindicated,references
oils, the most common interferences are mercaptans and
to water shall be understood to mean reagent water as defined
sulfides(nottotalsulfur).Atlevelsoflessthan500µg/g(ppm)
by Type IV of Specification D1193.
(as sulfur), the interference from these compounds is insignifi-
7.3 Xylene, reagent grade. Less than 0.05 % water.
cant. Most crude oils, including crude oils classified as “sour
(Warning—Flammable. Vapor harmful.)
crude,”havemercaptanandsulfidelevelsoflessthan500µg/g
7.4 Karl Fischer Reagent—Standard commercially avail-
(ppm) as sulfur. For more information on substances that
able reagents for coulometric Karl Fischer titrations.
interfereinthedeterminationofwaterbyKarlFischertitration
7.4.1 Anode Solution, shall be 6 parts of commercial Karl
method (see Test Method E203).
Fischer anode solution with 4 parts of reagent grade xylene.
5.2 The significance of the mercaptan and sulfide interfer-
Fresh Karl Fischer anode solution shall be used. Anode
ence on the Karl Fischer titration for water levels in the 0.005
solution shall not be used past its expiration date. Anode
to 0.02 mass % range has not been determined experimentally.
solution should be replaced after 7 days in the titration vessel.
At these low water levels, however, the interference may be
(Warning—Flammable, toxic by inhalation and if swallowed,
significant for mercaptan and sulfide levels of less than
avoid contact with skin.)
500µg/g (ppm) (as sulfur).
NOTE 1—Other proportions of anode solution and xylene can be used
and should be determined for a particular reagent and apparatus. The
6. Apparatus
precision and bias were established using the designated anode solution
6.1 Karl Fischer Apparatus, using electrometric end-point.
and xylene.
Presently there are available on the market a number of
7.4.2 Cathode Solution, use standard commercially avail-
commercial coulometric Karl Fischer titration assemblies.
able Karl Fischer cathode solution. Cathode solution shall not
Instructions for operation of these devices are provided by the
beusedaftertheexpirationdateandshouldbereplacedafter7
manufacturer and not described herein.
days in the titration vessel. (Warning—Flammable, can be
6.2 Mixer, to homogenize the crude sample.
fatal if inhaled, swallowed, or absorbed through skin. Possible
6.2.1 Non-Aerating, High-Speed, Shear Mixer—The mixer
cancer hazard.)
shall be capable of meeting the homogenization efficiency test
8. Sampling and Test Specimens
described in Practice D5854 (API MPMS Chapter 8.3). The
samplesizeislimitedtothatsuggestedbythemanufacturerfor 8.1 Samplingisdefinedasallthestepsrequiredtoobtainan
aliquotrepresentativeofthecontentsofanypipe,tank,orother
the size of the mixing probe.
system and to place the sample into a container for analysis by
6.2.2 Circulating sample mixers, such as those used with
a laboratory or test facility. The laboratory sample container
automatic crude oil sampling receivers, are acceptable provid-
and sample volume shall be of sufficient dimensions and
ing they comply with the principles of Practice D5854 (API
volume to allow mixing as described in 8.4.
MPMS Chapter 8.3).
8.2 Laboratory Sample—The sample of crude oil presented
6.3 Syringes:
tothelaboratoryortestfacilityforanalysisbythistestmethod.
6.3.1 Samples are most easily added to the titration vessel
Only representative samples obtained as specified in Practice
by means of accurate glass syringes with LUER fittings and
D4057 (API MPMS Chapter 8.1) and Practice D4177 (API
hypodermic needles of suitable length. The bores of the
MPMS Chapter 8.2) shall be used to obtain the laboratory
needles used should be kept as small as possible but large
sample.
enough to avoid problems arising from back pressure and
blocking while sampling. Suggested syringe sizes are as
NOTE 2—Examples of laboratory samples include sample bottles from
follows: manual sampling, receptacles from automatic crude oil samplers, and
storage containers holding a crude oil from a previous analysis.
6.3.1.1 Syringe, 10 µL with a needle long enough to dip
below the surface of the anode solution in the cell when 8.3 Test Specimen—The sample aliquot obtained from the
inserted through the inlet port septum. This syringe is used in laboratory sample for analysis by this test method. Once
the calibration step (Section 10). It should be of suitable
graduations for readings to the nearest 0.1 µL or better.
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not
6.3.1.2 Syringes, 250 µL, 500 µL, and 1000 µL (1 mL), for
listed by the American Chemical Society, see Analar Standards for Laboratory
crudeoilsamples.Forthevolumetricdeterminationprocedure,
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
the syringes should be accurate to 5 µL, 10 µL, and 20 µL
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
(0.02mL), respectively. MD.
D4928–00 (2005)
TABLE 1 Approximate Test Specimen Size Based on Expected NOTE 3—Highbackgroundcurrentforaprolongedperiodcanbedueto
Water Content
moisture on the inside walls of the titration vessel. Gentle shaking of the
vessel (or more vigorous stirring action) will wash the inside with
Expected Water Sample Size,
Water Titrated, µg
electrolyte.Keepthetitratorontoallowstabilizationtoalowbackground
Content, % gormL
current.
0.02–0.1 1.0 200–1000
0.1–0.5 0.5 500–2500
10. Standardization
0.5–5.0 0.25 1250–12500
10.1 In principle, standardization is not necessary since the
water titrated is a direct function of the coulombs of electricity
drawn, the entire portion of the test specimen will be used in
consumed. However, reagent performance deteriorates with
the analysis. Mix the laboratory sample properly as described
use and shall be regularly monitored by accurately injecting
in 8.4 before drawing the test specimen.
10µLofpurewater.Suggestedintervalsareinitiallywithfresh
8.4 Mix the laboratory sample of crude oil immediately
reagent and then after every ten determinations (see Section
(within 15 min) before drawing the test specimen to ensure
11.1.3). If the result is outside 10000 6 200 µg, replace both
complete homogeneity. Mix the sample at room temperature
the anode and cathode solutions.
(15 to 25°C) or less in the laboratory sample container and
record the temperature of the sample in degrees Celsius
11. Procedure
immediately before mixing. The type of mixer depends on the
11.1 Mass Determination of Sample Size:
quantityofcrudeoilinthelaboratorysamplecontainer.Before
11.1.1 Add fresh solvents to the anode and cathode com-
any unknown mixer is used, the specifications for the homog-
partments of the titration vessel and bring the solvent to
enization test, Practice D5854 (API MPMS Chapter 8.3), shall
end-point conditions as described in Section 9.
be met. Reevaluate the mixer for any changes in the type of
11.1.2 Add an aliquot of the crude oil test specimen to the
crude, volume of crude in the container, the shape of the
titration vessel immediately after the mixing step described in
container, or the mixing conditions (such as mixing speed and
8.4 using the following method.
time of mixing).
11.1.2.1 Starting with a clean, dry syringe of suitable
8.5 Forsmalllaboratorysamplecontainersandvolumes,50
capacity (see Table 1 and Note 4), withdraw at least three
to500mL,anon-aerating,high-speed,shearmixerisrequired.
portions of the sample and discard to waste. Immediately
Use the mixing time, mixing speed, and height of the mixer
withdraw a further portion of sample, clean the needle with a
probe above the bottom of the container found to be satisfac-
paper tissue, and weigh the syringe and contents to the nearest
tory in Practice D5854 (API MPMS Chapter 8.3). For larger
0.1mg.Inserttheneedlethroughtheinletportseptum,startthe
containersandvolumes,appropriatemixingconditionsshallbe
titration and with the tip of the needle just below the liquid
defined by following a set of procedures similar to those
surface, inject the sample. Withdraw the syringe and reweigh
outlined in Practice D5854 (API MPMS Chapter 8.3) and
the syringe to the nearest 0.1 mg. After the end-point is
Practice D4177 (API MPMS Chapter 8.2) but modified for
reached, record the titrated water from the digital readout on
applicationtothelargercontainersandvolumes.Cleananddry
the instrument.
the mixer between samples.
8.6 RecordthetemperatureofthesampleindegreesCelsius NOTE 4—If the concentration of water in the sample is completely
unknown, it is advisable to start with a small trial portion of sample to
immediately after homogenization. The rise in temperature
avoid excessive titration time and depletion of the reagents. Further
betweenthisreadingandtheinitialreadingbeforemixing(8.4)
adjustment of the aliquot size can then be made as necessary.
is not to exceed 10°C, otherwise loss of water can occur or the
11.1.2.2 When the background current or titration rate
emulsion can become unstable.
returns to a stable reading at the end of the titration as
8.7 Select the test specimen size as indicated in Table 1
discussed in 9.5, additional samples can be added in accor-
based on the expected water content.
dance with 11.1.2.1.
9. Preparation of Apparatus
11.1.3 Replace the solutions when one of the following
9.1 Follow
...
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