ASTM D4928-2012(2018) Standard Test Method for Water in Crude Oils by Coulometric Karl Fischer Titration.pdf

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1、Designation: D4928 12 (Reapproved 2018)Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9Standard Test Method forWater in Crude Oils by Coulometric Karl Fischer Titration1This standard is issued under the fixed designation D4928; the number immediately following the designation indicates

2、 the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the

3、U.S. Department of Defense.1. Scope1.1 This test method covers the determination of water inthe range from 0.02 to 5.00 mass or volume % in crude oils.Mercaptan (RSH) and sulfide (Sor H2S) as sulfur are knownto interfere with this test method, but at levels of less than500 gg ppm(m), the interferenc

4、e from these compounds isinsignificant (see Section 6).1.2 This test method can be used to determine water in the0.005 to 0.02 mass % range, but the effects of the mercaptanand sulfide interference at these levels has not been deter-mined. For the range 0.005 to 0.02 mass %, there is noprecision or

5、bias statement.1.3 This test method is intended for use with standardcommercially available coulometric Karl Fischer reagent.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This standard does not purport to address all o

6、f thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.For specific warning statements, see Section 8.1.6

7、 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Tr

8、ade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum Products (API MPMS Chapter 8.1)D4177 Practice for Automatic Sampling of Petroleum andPetroleum Products (API MPMS Chapter 8.2)D5854 Practic

9、e for Mixing and Handling of Liquid Samplesof Petroleum and Petroleum Products (API MPMS Chap-ter 8.3)E203 Test Method for Water Using Volumetric Karl FischerTitration2.2 API Standards:3MPMS Chapter 8.1 Practice for Manual Sampling of Petro-leum and Petroleum Products (ASTM Practice D4057)MPMS Chapt

10、er 8.2 Practice for Automatic Sampling ofPetroleum and Petroleum Products (ASTM PracticeD4177)MPMS Chapter 8.3 Practice for Mixing and Handling ofLiquid Samples of Petroleum and Petroleum Products(ASTM Practice D5854)3. Terminology3.1 The following terms are used with respect to sampling(see Section

11、 9).3.2 Definitions of Terms Specific to This Standard:3.2.1 aliquot, na small portion of a larger sample which isanalyzed and assumed to represent the whole sample.3.2.2 sample, nportion extracted from the contents of anypipe, tank, or other system, and intended to be representative ofthat system,

12、placed in a primary sample container for analysis.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and the API Committee onPetroleum Measurement, and is the direct responsibility of Subcommittee D02.02/COMQ, the joint ASTM-API Commi

13、ttee on Hydrocarbon Measurement forCustody Transfer (Joint ASTM-API). This test method has been approved by thesponsoring committees and accepted by the Cooperating Societies in accordancewith established procedures.Current edition approved July 1, 2018. Published August 2018. Originallyapproved in

14、1989. Last previous edition approved in 2012 as D4928 12. DOI:10.1520/D4928-12R18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary pag

15、e onthe ASTM website.3Published as Manual of Petroleum Standards. Available from AmericanPetroleum Institute (API), 1220 L. St., NW, Washington, DC 20005-4070, http:/www.api.org. Jointly copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, USA and

16、the American Petroleum Institute (API), 1220 L Street NW, Washington DC 20005, USAThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and

17、Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.3 test specimen, nthe representative sample takenfrom the primary or intermediate sample (aliquot) container foranalysis. The entire test specimen is used in the analysis.4. Summary of Test Method

18、4.1 After homogenizing the crude oil sample, a test speci-men of that sample is injected into the titration cell of a KarlFischer apparatus in which iodine for the Karl Fischer reactionis generated coulometrically at the anode. When all the waterhas been titrated, excess iodine is detected by an ele

19、ctrometricendpoint detector and the titration is terminated. Based on thestoichiometry of the reaction, one mole of iodine reacts withone mole of water thus the quantity of water can be deter-mined.4.2 The precision of this test method is critically dependenton the effectiveness of the homogenizatio

20、n step. The accept-ability of the mixing used to achieve a homogeneous sample isdetermined by the procedure given in Practice D5854 (APIMPMS Chapter 8.3). In addition, if the test method is per-formed on a volume basis, the precision of the test method iscritically dependent on the accuracy and repe

21、atability of thevolume injected.4.3 Two procedures are provided for the determination ofwater in crude oils. In one procedure, a weighed test specimenis injected into the titration cell and the mass % of water isdetermined. The other procedure provides for the direct deter-mination of the volume % o

22、f water in the crude oil bymeasuring the volume of crude oil injected into the titrationcell.5. Significance and Use5.1 The accurate analysis of a crude oil sample to determinethe water content is important in the refining, purchase, sale, ortransfer of crude oils.6. Interferences6.1 A number of sub

23、stances and classes of compoundsassociated with condensation or oxidation-reduction reactionsinterfere in the determination of water by Karl Fischer. In crudeoils, the most common interferences are mercaptans andsulfides (not total sulfur). At levels of less than 500 g/gppm(m) (as sulfur), the inter

24、ference from these compounds isinsignificant. Most crude oils, including crude oils classified as“sour crude,” have mercaptan and sulfide levels of less than500 g/g ppm(m) as sulfur. For more information on sub-stances that interfere in the determination of water by KarlFischer titration method, see

25、 Test Method E203.6.2 The significance of the mercaptan and sulfide interfer-ence on the Karl Fischer titration for water levels in the 0.005to 0.02 mass % range has not been determined experimentally.At these low water levels, however, the interference may besignificant for mercaptan and sulfide le

26、vels of less than500 gg ppm(m) (as sulfur).7. Apparatus7.1 Karl Fischer Apparatus, using electrometric endpointdetector. The instrument must have anode and cathode reagentsin separate compartments. Instructions for operation of KarlFischer titration devices are provided by the manufacturer andnot de

27、scribed herein.7.2 Mixer, to homogenize the crude sample.7.2.1 Non-Aerating, High-Speed, Shear MixerThe mixershall be capable of meeting the homogenization efficiency testdescribed in Practice D5854 (API MPMS Chapter 8.3). Thesample size is limited to that suggested by the manufacturersspecification

28、s for the size of the mixer.7.2.2 Circulating Sample MixerA device such as usedwith automatic crude oil sampling receivers, is acceptableproviding it complies with the principles of Practice D5854(API MPMS Chapter 8.3).7.3 SyringesTest specimens are most easily added to thetitration cell by means of

29、 accurate glass syringes with Luer Lokfittings and hypodermic needles of suitable length. The boresof the needles used should be kept as small as possible butlarge enough to avoid problems arising from back pressure andblocking while injecting a test specimen. The syringe sizeshould be selected such

30、 that the test specimen is not less thanhalf the total volume contained by the syringe, the needleshould be long enough to permit the injection of the testspecimen into the fluid, below the surface of the fluid in thetitration cell.7.3.1 Syringes for Gravimetric DeterminationFor gravi-metric determi

31、nation, any type of syringe that does not leak isappropriate. Syringe should have physical dimensions to fit onthe balance appropriately.7.3.2 Syringe for Volumetric DeterminationFor volumet-ric determination a certified syringe capable of delivering thevolumetric quantity with an accuracy 0.5% of t

32、he containedvolume is required.7.4 Balance for Mass DeterminationAny analytical bal-ance with an accuracy and resolution of 0.1 mg, and capable ofweighing up to 100 g can be used.7.4.1 The balance for determining the weight of the testspecimen injected into the titration cell shall be calibrated.NOT

33、E 1The use of balances on structures that are in motion may notbe appropriate.7.5 Titration CellSunlight can cause disassociation of theiodine in the Karl Fischer reagent, resulting in false results. Atitration cell made of opaque material may reduce this effect.8. Reagents and Materials8.1 Purity o

34、f ReagentsChemicals of reagent grade orhigher purity shall be used in all tests. Unless otherwiseindicated, it is intended that all reagents shall conform to thespecifications of the Committee on Analytical Reagents of theAmerican Chemical Society, where such specifications areavailable.4Other grade

35、s may be used, provided it is first4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K

36、., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D4928 12 (2018)2ascertained that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.8.2 Purity of WaterUnless otherwise

37、indicated, referencesto water shall be understood to mean reagent water as definedby Type IV of Specification D1193.8.3 XyleneReagent grade. Less than 0.05 % water.(WarningFlammable. Vapor harmful.)8.4 Karl Fischer ReagentStandard commercially avail-able reagents for coulometric Karl Fischer titrati

38、ons.8.4.1 Anode and cathode reagents shall not be used past themanufacturers expiration date.8.4.2 The need to replace the anode and cathode reagent isa function of number of tests run and the amount of waterpreviously titrated. An abnormally slow titration is an indica-tion that the reagents should

39、 be replaced.8.4.3 Anode ReagentA mixture of commercial coulomet-ric Karl Fischer anode reagent and reagent grade xylene,typically in a 6:4 mixture. Other proportions of anode reagentand xylene can be used and should be determined for aparticular reagent and apparatus. The precision and bias wereest

40、ablished using a 6 parts Karl Fischer reagent and 4 partsxylene. (WarningFlammable, toxic by inhalation and ifswallowed, avoid contact with skin.)8.4.4 Cathode ReagentUse standard commercially avail-able coulometric Karl Fischer cathode reagent. (WarningFlammable, can be fatal if inhaled, swallowed,

41、 or absorbedthrough skin. Possible cancer hazard.)8.4.5 Check SolutionNIST Traceable check solution usedfor verifying the calibration of the Karl Fischer instrument. Inthe absence of an available check solution, pure water may beused.9. Sampling and Test Specimens9.1 Sample ContainerIt shall be cons

42、tructed of a materialto which water does not adhere with a sealable lid or othermechanism to prevent rain or humidity from contaminating thesample.9.1.1 If a non-aerating high-speed shear mixer is to be used,the sample container shall be of sufficient dimensions to allowmixing as described in 9.6 an

43、d consistent with the samplecontainer used in any mixer efficiency testing.9.1.2 If a circulating sample mixer is to be used, the primarysample container shall be designed for direct connection to themixing system without transfer to an intermediate samplecontainer. Internals should be constructed t

44、o ensure fluidcirculation results in efficient homogenization of the sample.This can be accomplished with spray nozzles, dispersion tubesor other proprietary designs.9.1.3 Sample Container PreparationThe sample containershall be clean and dry prior to use. Inspect the integrity ofsample container li

45、d seals.9.2 Sample VolumeThe volume required for a test speci-men to be analyzed is very small (typically 1 mLor less) so theprimary constraint for sample volume is that it be sufficient toallow mixing as described in 9.6, and withdrawal of multipletest specimens for repeat testing.9.3 Sampling Appa

46、ratusSample lines and other samplingapparatus that comes into contact with the fluid being sampledshall be constructed of a material to which water does notadhere. The apparatus shall be constructed so that water doesnot collect in deadlegs and low spots. There may be uniquerequirements specified in

47、 the sampling method listed in 9.5.Prior to extracting a sample, sample apparatus should beappropriately purged or cleaned to prevent contamination.9.4 Sample Storage and HandlingSamples should beproperly labeled and secured as appropriate to prevent tamper-ing. Samples can be stored indefinitely as

48、 long as the containeris constructed to prevent ingress or egress of vapors, and thefluid being tested can be rehomogenized. No additional envi-ronmental constraints apply to properly sealed containers.9.5 Sampling MethodRepresentative samples obtained asspecified in Practice D4057 (API MPMS Chapter

49、 8.1) andPractice D4177 (API MPMS Chapter 8.2) should be used toobtain the sample.9.5.1 Sampling Viscous Crude OilApplication of thismethod of viscous crude oils may present challenges in twodifferent areas; sample mixing and test specimen extraction.Mixing apparatus may operate less efficiently. It may bedifficult or impossible to extract and deliver an exact quantityof test specimen (see Section 15). Equipment or proceduremodifications if required may invalidate the precision state-ment in this method. Validation of any modifications ar