ASTM D4377-00(2006)
(Test Method)Standard Test Method for Water in Crude Oils by Potentiometric Karl Fischer Titration
Standard Test Method for Water in Crude Oils by Potentiometric 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 2 % in crude oils. Mercaptan and sulfide (S or H2S) sulfur are known to interfere with this test method (see Section ).
1.2 This test method is intended for use with standard Karl Fischer reagent or pyridine-free Karl Fischer reagents.
1.3 The values stated in SI units are to be regarded as the standard.
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. Specific precautionary statements are given in Section 7.
General Information
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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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:D4377–00 (Reapproved 2006)
Designation: Manual of Petroleum Measurement Standards (MPMS), Chapter 10.7
Designation: 356/99
Standard Test Method for
Water in Crude Oils by Potentiometric Karl Fischer Titration
This standard is issued under the fixed designation D4377; 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 2.2 API Standards:
MPMS Chapter 8.1 Manual Sampling of Petroleum and
1.1 This test method covers the determination of water in
Petroleum Products (ASTM Practice D4057)
therangefrom0.02to2%incrudeoils.Mercaptanandsulfide
−
MPMS Chapter 8.2 Automatic Sampling of Petroleum and
(S or H S) sulfur are known to interfere with this test method
Petroleum Products (ASTM Practice D4177)
(see Section 5).
MPMS Chapter 10.2 Determination of Water in Crude Oil
1.2 This test method is intended for use with standard Karl
by Distillation (ASTM Test Method D4006)
Fischer reagent or pyridine-free Karl Fischer reagents.
1.3 The values stated in SI units are to be regarded as the
3. Summary of Test Method
standard.
3.1 After homogenizing the crude oil with a mixer, an
1.4 This standard does not purport to address all of the
aliquot of the crude, in a mixed solvent, is titrated to an
safety concerns, if any, associated with its use. It is the
electrometric end-point using Karl Fischer reagent.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Significance and Use
bility of regulatory limitations prior to use. Specific precau-
4.1 A knowledge of the water content of crude oil is
tionary statements are given in Section 7.
important in the refining, purchase, sale, or transfer of crude
oils.
2. Referenced Documents
2.1 ASTM Standards:
5. Interferences
D1193 Specification for Reagent Water
5.1 A number of substances and class of compounds asso-
D4006 Test Method for Water in Crude Oil by Distillation
ciated with condensation or oxidation-reduction reactions in-
D4057 Practice for Manual Sampling of Petroleum and
terfere in the determination of water by Karl Fischer. In crude
Petroleum Products
oils, the most common interferences are mercaptans and
D4177 Practice for Automatic Sampling of Petroleum and
sulfides. At levels of less than 500 µg/g (ppm) (as sulfur) the
Petroleum Products
interference from these compounds is insignificant. For more
E203 TestMethodforWaterUsingVolumetricKarlFischer
informationonsubstancesthatinterfereinthedeterminationof
Titration
waterusingthe(KarlFischerreagent)titrationmethodseeTest
Method E203.
This test method is under the jurisdiction of ASTM Committee D02 on
6. Apparatus
Petroleum Products and Lubricants and theAPI Committee on Petroleum Measure-
ment, and is the direct responsibility of Subcommittee D02.02.10 on Sediment and
6.1 Karl Fischer Apparatus, using electrometric end-point.
Water (API MPMS Chapter 10.0).
A suggested assembly of the apparatus is described in Annex
Current edition approved Nov. 1, 2006. Published December 2006. Originally
´1
approved in 1984. Last previous edition approved in 2000 as D4377–00 . DOI: A2.
10.1520/D4377-00R06.
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 Published as Manual of Petroleum Measurement Standards. Available from
Standards volume information, refer to the standard’s Document Summary page on AmericanPetroleumInstitute(API),1220L.St.,NW,Washington,DC20005-4070,
the ASTM website. http://api-ec.api.org.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
D4377–00 (2006)
6.1.1 Presently there is available on the market commercial Fischer (one-component) reagent (1 mL=5 mg water) to 1
Karl Fischer titration assemblies, some of which automatically part xylene. Fresh Karl Fischer reagent must be used.
stop the titration at the end-point. Instructions for operation of (Warning—See 7.4.1) Must be used with solvent in 7.6.2.
these devices are provided by the manufacturer and not 7.5 Methanol (anhydrous), Maximum 0.1% water but pref-
described herein.This test method is not intended for use with erably less than 0.05% water. (Warning—Flammable. Vapor
coulometric Karl Fischer titrators. harmful. May be fatal or cause blindness if swallowed or
6.2 Mixer, to homogenize the crude sample. inhaled. Cannot be made nonpoisonous.)
6.2.1 Non-Aerating, High-Speed, Shear Mixer, capable of 7.6 Sample Solvent—Use 7.6.1 for standard Karl Fischer
meetingthehomogenizationefficiencytestdescribedinAnnex reagent containing pyridine and 7.6.2 for pyridine-free Karl
A1. The sample size is limited to that suggested by the Fischer reagent.
manufacturer for the size of the probe. 7.6.1 Sample Solvent—Mix 40 mL of 1-ethylpiperidine, 20
6.3 Syringes: mL of methanol, and 40 mL of Karl Fischer reagent in a
6.3.1 Samples and base liquid are most easily added to the sealableglassbottle.Allowthismixturetositovernightbefore
titrationvesselbymeansofaccurateglasssyringeswithLUER adding 200 mL of xylene. Additional methanol may be
fittings and hypodermic needles of suitable length. The bores required in some cases for the proper function of the elec-
of the needles used should be kept as small as possible, but trodes. (Warning—see 7.3.)
large enough to avoid problems arising from back pressure/ 7.6.2 Sample Solvent for Pyridine-Free Reagents—Mix 3
blocking whilst sampling. Suggested syringe sizes are as parts chloroform to 1 part pyridine-free solvent using solvent
follows: part of two-component reagent (contains SO and odorless
6.3.1.1 Syringe, 10 µL, with a needle long enough to dip amine dissolved in methanol) and store in a sealable glass
below the surface of the base solution in the cell during the bottle. An evaluation of a number of crude oils has demon-
standardization procedure (see Section 9). strated that xylene can be substituted for chloroform with no
6.3.1.2 Syringes, 2.5 mL, 5 mL, and 10 mL for crude oil apparent change in accuracy of this test method. (Warning—
samples (see Section 10). Flammable. Vapor harmful.) (Also, see 7.4.1.)
6.3.1.3 Syringe, 20 mL or larger for sample solvent. 7.7 Xylene, reagent grade. Less than 0.05% water.
7.8 Chloroform, reagent grade. (Warning—Harmful if in-
7. Reagents and Materials
haled or swallowed. Carcinogen (animal positive). Skin and
7.1 Purity of Reagents—Reagent grade chemicals shall be
eye irritant. May produce toxic vapors if burned.
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit- 8. Sampling and Test Samples
tee onAnalytical Reagents of theAmerican Chemical Society,
8.1 Sampling,isdefinedasallthestepsrequiredtoobtainan
where such specifications are available. Other grades may be
aliquotrepresentativeofthecontentsofanypipe,tank,orother
used, provided it is first ascertained that the reagent is of
system, and to place the sample into the laboratory test
sufficiently high purity to permit its use without lessening the
container. The laboratory test container and sample volume
accuracy of the determination.
shallbeofsufficientdimensionsandvolumetoallowmixingas
7.2 Purity of Water—Unlessotherwiseindicated,references
described in 8.1.2.1.
to water shall be understood to mean reagent water as defined
8.1.1 Laboratory Sample—Only representative samples ob-
by Type IV of Specification D1193.
tainedasspecifiedinPracticeD4057(API MPMSChapter8.1)
7.3 1-Ethylpiperidine (99+percent). (Warning—Irritant.
andPracticeD4177(API MPMSChapter8.2)shallbeusedfor
Flammable.)
this test method.
7.4 Karl Fischer Reagents, Standard reagent containing
8.1.2 Test Samples—The following sample handling proce-
pyridine (7.4.1) or pyridine-free reagent (7.4.2).
dure shall apply in addition to those covered in 8.1.1.
7.4.1 Karl Fischer Reagent Ethylene Glycol Monomethyl
8.1.2.1 Mixthetestsampleofcrudeoilimmediately(within
Ether Solution, stabilized, containing pyridine, (1 mL=5 mg
15 min) before analysis to insure complete homogeneity. Mix
of water)—Fresh Karl Fischer reagent must be used. Must be
the test sample at room temperature (25°C) in the original
used with solvent in 7.6.1.(Warning—Combustible. Harmful
container.
if swallowed, inhaled, or absorbed through the skin.)
NOTE 1—The sample should be mixed at room temperature (25°C) or
7.4.2 Pyridine-Free Karl Fischer (one-component) reagent
less. Mixing of the sample should not increase the temperature of the
diluted with xylene—Dilute three parts pyridine-free Karl
sample more than 10°C, or a loss of water may occur. The type of mixer
depends on the quantity of crude. Before any unknown mixer is used, the
Thefollowingmixerswereusedinacooperativeprogramandhavebeenfound specifications for the homogenization test, Annex A1, must be met. The
satisfactory for samples under 300 mL; Ultra Turrax Model TP 18/10, available
mixer must be re-evaluated for any changes in the type of crude, quantity
from Tekmar Co., P. O. Box 37202, Cincinnati, OH 45222; Brinkman Polytron
of crude, or shape of the sample container.
ModelPT35,AvailablefromBrinkmanInstrumentsInc.,CantiaguRoad,Westbury,
NY 11590; and Kraft Apparatus Model S-25, SGA, Bloomfield, NJ.
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For suggestions on the testing of reagents not Pyridine-free Karl Fischer reagent and two-component solvent used in the
listed by the American Chemical Society, see Analar Standards for Laboratory cooperative program and found to be satisfactory are available from Crescent
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia ChemicalCo.,Inc.,1324MotorParkway,Hauppauge,NY11788underthenameof
and National Formulary,U.S.PharmacopeialConvention,Inc.(USPC),Rockville, Hydranal a registered trademark of Riedel Dehaen—Composite 5 and Hydranal—
MD. solvent.
D4377–00 (2006)
TABLE 1 Test Sample—% Water Content Based on Sample Size
9.4 Calculate the water equivalence of the Karl Fischer
Expected Water Sample Size, reagent as follows:
Content, % g
F 5 W/T (1)
0–0.3 5
0.3–1 2
where:
1–2 1
F = waterequivalenceoftheKarlFischerreagent,mg/mL,
W = water added, mg, and
T = reagent required for titration of the added water, mL.
8.1.2.1.1 For small sample volumes, 50 to 500 mL, a
9.5 Duplicate values of water equivalence should agree
non-aerating, high speed, shear mixer is required. Use the
within 2% relative. If the variation between the two titrations
mixingtime,mixingspeed,andheightabovethebottomofthe
isgreaterthan2%relative,discardthecontentsofthetitration
container found to be satisfactory toAnnexA1. Clean and dry
vessel. Introduce a further portion of sample solvent into the
the mixer between samples.
vesselandrepeatthestandardizationprocedure.Ifthetitrations
8.1.2.2 ThetestsamplesizeisselectedasindicatedinTable
for two further portions of distilled water still vary by more
1 based on the expected water content.
than 2%, it is likely that either the Karl Fischer reagent or the
sample solvent, or both, have aged. Replace these with fresh
9. Calibration and Standardization
reagents and repeat the procedure for calibration and standard-
9.1 Standardize the Karl Fischer reagent at least once daily.
ization.
9.2 Add enough solvent to the clean, dry titration vessel to
9.6 Determine and record the mean water equivalence
cover the electrodes. The volume of solvent depends on the
value.
size of the titration vessel. Seal all openings to the vessel and
start the magnetic stirrer for a smooth stirring action. Turn on
10. Procedure
the indicating circuit and adjust the potentiometer to give a
reference point with approximately 1 µA of current flowing.
10.1 Addthefreshsamplesolventtothetitrationvesseland
Add Karl Fischer reagent in suitable amounts to the solvent to
bring the solvent to end-point conditions as described in 9.2.
causetheneedletodeflectfromthereferencepoint.Atfirstthe
10.2 Add the crude to the titration vessel immediately after
needle will deflect due to local concentration of the unreacted
themixingstepdescribedin8.1.2.1usingoneofthefollowing
reagent about the electrodes but will fall back to near the
methods:
referencepoint.Astheend-pointisapproached,theneedlewill
10.2.1 Starting with a clean, dry syringe (10 or 5 mL), rinse
fall back more slowly after each addition of Karl Fischer
the syringe two times with the sample and discharge to waste.
reagent. The end-point is reached when, after the addition of a
Withdrawtherequiredamountofsampleanddischargeanyair
single drop of reagent, the needle remains deflected at least 1
bubbles. Weigh the syringe to the nearest 0.1 mg. Inject the
µAfrom the reference point for at least 30 s. Swirl the titration
sample into the titration vessel, clean the needle with a paper
vessel to dry the inside walls of the vessel. Add more Karl
tissue, and reweigh the syringe. Titrate the sample until a
Fischer reagent, if needed, until a steady end-point is reached
steady end-point for at least 30 s is reached and record the
for at least 30 s.
volume of Karl Fischer reagent to the nearest 0.01 mL (see
9.3 StandardizetheKarlFischerreagentwithdistilledwater
Note 2 and Note 4).
by one of the following methods:
9.3.1 From a water filled weighing pipet or syringe previ-
NOTE 4—The solvent should be changed when the sample content
ously weighed to the nearest 0.1 mg, add 1 drop of distilled
exceeds2gof crude per 15 mLof solvent or when 4 mLof titrant per 15
water (about 20 mg) to the sample solvent at end-point
mL of solvent has been added to the titration vessel.
conditions and reweigh the syringe. Record the weight of the
10.2.2 For viscous crudes, add the sample to a clean, dry
water added.Titrate the water with Karl Fischer reagent added
dropperbottleandweighthebottleandcrude.Quicklytransfer
fromtheburetuntilasteadyendpointisreachedforatleast30
the required amount of sample to the titration vessel with the
s.Recordtothenearest0.01mLthevolumeoftheKarlFischer
dropper. Reweigh the bottle. Titrate the sample as in 10.2.1.
reagent needed to reach the end-point.
NOTE 5—After adding the sample do not shake the cell.
NOTE 2—After adding water do not shake the cell.
NOTE 3—Whenwipingtheneedleexercisecare,sonottosiphonliquid
11. Calculations
through the tip of the needle.
9.3.2 Fill a 10-µL syringe with water tak
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