1、Designation: D4928 11D4928 12Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9Designation: 386/99Standard 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
2、indicates 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 agencie
3、s of the Department of Defense.1. Scope*1.1 This test method covers the determination of water in the range from 0.02 to 55.00 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 g/g(ppm),ppm(m),
4、 the interference from these compounds is insignificant (see Section 56).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 andsulfide interference at these levels has not been determined. For the range 0.005 to 0.02 mass %, there
5、is no precision or biasstatement.1.3 This test method is intended for use with standard commercially available coulometric Karl Fischer reagent.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.5 This standard does not pur
6、port to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. For specific hazardwarning statements, see Sec
7、tion 78.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum and Petroleum Products (API MPMS Chapter 8.1)D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products (API MPMS Chapter 8.2)D5854 Practice for Mixi
8、ng and Handling of Liquid Samples of Petroleum and Petroleum Products (API MPMS Chapter 8.3)E203 Test Method for Water Using Volumetric Karl Fischer Titration2.2 API Standards:3MPMS Chapter 8.1 Practice for Manual Sampling of Petroleum and Petroleum Products (ASTM Practice D4057)MPMS Chapter 8.2 Pra
9、ctice for Automatic Sampling of Petroleum and Petroleum Products (ASTM Practice D4177)MPMS Chapter 8.3 Practice for Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products (ASTM PracticeD5854)3. Terminology3.1 The following terms are used with respect to sampling (see Section 9).3.
10、2 Definitions of Terms Specific to This Standard:3.2.1 aliquot, na small portion of a larger sample which is analyzed and assumed to represent the whole sample.1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricants and the API Committee on Petroleum M
11、easurement and isthe direct responsibility of Subcommittee D02.02 /COMQ on Hydrocarbon Measurement for Custody Transfer (Joint ASTM-API).Current edition approved June 1, 2011Dec. 1, 2012. Published August 2011April 2013. Originally approved in 1989. Last previous edition approved in 20102011 asD4928
12、00 (2010). 11. DOI: 10.1520/D4928-11.10.1520/D4928-12.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Publi
13、shed as Manual of Petroleum Standards. Available from American Petroleum Institute (API), 1220 L. St., NW, Washington, DC 20005-4070, http:/www.api.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to t
14、he previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary
15、 of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 sample, nportion extracted from the contents of any pipe, tank, or other system, and intended to be representative of thatsys
16、tem, placed in a primary sample container for analysis.3.2.3 test specimen, nthe representative sample taken from the primary or intermediate sample (aliquot) container for analysis.The entire test specimen is used in the analysis.4. Summary of Test Method4.1 After homogenizing the crude oil with a
17、mixer, an aliquot sample, a test specimen of that sample is injected into the titrationvesselcell of a Karl Fischer apparatus in which iodine for the Karl Fischer reaction is generated coulometrically at the anode. Whenall the water has been titrated, excess iodine is detected by an electrometric en
18、d-pointendpoint detector and the titration isterminated. Based on the stoichiometry of the reaction, one mole of iodine reacts with one mole of water,water thus the quantityof water is proportional to the total integrated current according to Faradays Law.can be determined.4.2 The precision of this
19、test method is critically dependent on the effectiveness of the homogenization step. Theefficiencyacceptability of the mixermixing used to achieve a homogeneous sample is determined by the procedure given in PracticeD5854 (API MPMS Chapter 8.3). In addition, if the test method is performed on a volu
20、me basis, the precision of the test methodis critically dependent on the accuracy and repeatability of the volume injected.4.3 Two procedures are provided for the determination of water in crude oils. In one procedure, a weighed aliquot of sampletest specimen is injected into the titration vesselcel
21、l and the mass % of water is determined. The other procedure provides for thedirect determination of the volume % of water in the crude oil by measuring the volume of crude oil injected into the titrationvessel.cell.5. Significance and Use5.1 A knowledge of The accurate analysis of a crude oil sampl
22、e to determine the water content of crude oil is important in therefining, purchase, sale, or transfer of crude oils.6. Interferences6.1 A number of substances and classes of compounds associated with condensation or oxidation-reduction reactions interferein the determination of water by Karl Fische
23、r. In crude oils, the most common interferences are mercaptans and sulfides (not totalsulfur). At levels of less than 500 g/g (ppm)ppm(m) (as sulfur), the interference from these compounds is insignificant. Mostcrude oils, including crude oils classified as “sour crude,” have mercaptan and sulfide l
24、evels of less than 500 g/g (ppm)ppm(m)as sulfur. For more information on substances that interfere in the determination of water by Karl Fischer titration method(seemethod, see Test Method E203)6.2 The significance of the mercaptan and sulfide interference on the Karl Fischer titration for water lev
25、els in the 0.005 to 0.02mass % range has not been determined experimentally.At these low water levels, however, the interference may be significant formercaptan and sulfide levels of less than 500 g/g (ppm)ppm(m) (as sulfur).7. Apparatus7.1 Karl Fischer Apparatus, using electrometric end-point. Pres
26、ently there are available on the market a number of commercialcoulometric Karl Fischer titration assemblies. endpoint detector. The instrument must have anode and cathode reagents in separatecompartments. Instructions for operation of these Karl Fischer titration devices are provided by the manufact
27、urer and not describedherein.7.2 Mixer, to homogenize the crude sample.7.2.1 Non-Aerating, High-Speed, Shear MixerThe mixer shall be capable of meeting the homogenization efficiency testdescribed in Practice D5854 (API MPMS Chapter 8.3). The sample size is limited to that suggested by the manufactur
28、ermanufacturers specifications for the size of the mixing probe.mixer.7.2.2 Circulating Sample MixerCirculating sample mixers, A device such as those used with automatic crude oil samplingreceivers, areis acceptable providing they complyit complies with the principles of Practice D5854 (API MPMS Cha
29、pter 8.3).7.3 Syringes: SyringesTest specimens are most easily added to the titration cell by means of accurate glass syringes with LuerLok fittings and hypodermic needles of suitable length. The bores of the needles used should be kept as small as possible but largeenough to avoid problems arising
30、from back pressure and blocking while injecting a test specimen. The syringe size should beselected such that the test specimen is not less than half the total volume contained by the syringe, the needle should be long enoughto permit the injection of the test specimen into the fluid, below the surf
31、ace of the fluid in the titration cell.7.3.1 Syringes for Gravimetric DeterminationSamples are most easily added to the titration vessel by means of accurate glasssyringes with LUER fittings and hypodermic needles of suitable length. The bores of the needles used should be kept as small aspossible b
32、ut large enough to avoid problems arising from back pressure and blocking while sampling. Suggested syringe sizes areas follows:For gravimetric determination, any type of syringe that does not leak is appropriate. Syringe should have physicaldimensions to fit on the balance appropriately.D4928 1226.
33、3.1.1 Syringe, 10 Lwith a needle long enough to dip below the surface of the anode solution in the cell when inserted throughthe inlet port septum. This syringe is used in the calibration step (Section 10). It should be of suitable graduations for readings tothe nearest 0.1 L or better.6.3.1.2 Syrin
34、ges, 250 L, 500 L, and 1000 L (1 mL), for crude oil samples. For the volumetric determination procedure, thesyringes should be accurate to 5 L, 10 L, and 20 L (0.02 mL), respectively.7.3.2 Syringe for Volumetric DeterminationFor volumetric determination a certified syringe capable of delivering thev
35、olumetric quantity with an accuracy 0.5% of the contained volume is required.7.4 Balance for Mass DeterminationAny analytical balance 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 test specimen injected i
36、nto the titration cell shall be calibrated.NOTE 1The use of balances on structures that are in motion may not be appropriate.7.5 Titration CellSunlight can cause disassociation of the iodine in the Karl Fischer reagent, resulting in false results. Atitration cell made of opaque material may reduce t
37、his effect.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals Chemicals of reagent grade or higher purity shall be used in all tests. Unlessotherwise indicated, it is intended that all reagents shall conform to the specifications of the Committee on Analytical Reagentsof the Amer
38、ican Chemical Society, where such specifications are available.4 Other grades may be used, provided it is firstascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.8.2 Purity of WaterUnless otherwise indicated, references t
39、o water shall be understood to mean reagent water as defined byType IV of Specification D1193.8.3 XyleneXylene, reagent Reagent grade. Less than 0.05 % water. (WarningFlammable. Vapor harmful.)8.4 Karl Fischer ReagentStandard commercially available reagents for coulometric Karl Fischer titrations.8.
40、4.1 Anode and cathode reagents shall not be used past the manufacturers expiration date.8.4.2 The need to replace the anode and cathode reagent is a function of number of tests run and the amount of water previouslytitrated. An abnormally slow titration is an indication that the reagents should be r
41、eplaced.8.4.3 Anode Solution, Reagent shall be 6 partsAmixture of commercial coulometric Karl Fischer anode solution with 4 partsof reagent grade xylene. Fresh Karl Fischer anode solution shall be used.Anode solution shall not be used past its expiration date.Anode solution should be replaced after
42、7 days in the titration vessel. reagent and reagent grade xylene, typically in a 6:4 mixture.Other proportions of anode reagent and xylene can be used and should be determined for a particular reagent and apparatus. Theprecision and bias were established using a 6 parts Karl Fischer reagent and 4 pa
43、rts xylene. (WarningFlammable, toxic byinhalation and if swallowed, avoid contact with skin.)skin.)NOTE 1Other proportions of anode solution and xylene can be used and should be determined for a particular reagent and apparatus. The precisionand bias were established using the designated anode solut
44、ion and xylene.8.4.4 Cathode Solution, Reagent use Use standard commercially available coulometric Karl Fischer cathode solution.Cathode solution shall not be used after the expiration date and should be replaced after 7 days in the titration vessel. reagent.(WarningFlammable, can be fatal if inhale
45、d, swallowed, or absorbed through skin. Possible cancer hazard.)hazard.)8.4.5 Check SolutionNIST Traceable check solution used for verifying the calibration of the Karl Fischer instrument. In theabsence of an available check solution, pure water may be used.9. Sampling and Test Specimens9.1 Sample C
46、ontainerSampling is defined as all the steps required to obtain an aliquot representative of the contents of anypipe, tank, or other system and to place the sample into a container for analysis by a laboratory or test facility. The laboratorysample container and sample volume shall be of sufficient
47、dimensions and volume to allow mixing as described inIt shall beconstructed of a material to which water does not adhere 8.4.with a sealable lid or other mechanism to prevent rain or humidityfrom contaminating the sample.9.1.1 If a non-aerating high-speed shear mixer is to be used, the sample contai
48、ner shall be of sufficient dimensions to allowmixing as described in 9.6 and consistent with the sample container used in any mixer efficiency testing.9.1.2 If a circulating sample mixer is to be used, the primary sample container shall be designed for direct connection to themixing system without t
49、ransfer to an intermediate sample container. Internals should be constructed to ensure fluid circulationresults in efficient homogenization of the sample. This can be accomplished with spray nozzles, dispersion tubes or otherproprietary designs.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed bythe American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States P
