1、Designation: D 4928 00 (Reapproved 2005)Designation: Manual of Petroleum Measurement Standards (MPMS), Chapter 10.9Designation: 386/99An American National StandardStandard Test Methods forWater in Crude Oils by Coulometric Karl Fischer Titration1This standard is issued under the fixed designation D
2、4928; the number immediately following the designation 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 (e) indicates an editorial change since the last revision or reapp
3、roval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers the determination of water inthe range from 0.02 to 5 mass or volume % in crude oils.Mercaptan (RSH) and sulfide (Sor H2S) as sulfur are knownto interfere with this test method,
4、 but at levels of less than500 g/g (ppm), the interference from these compounds isinsignificant (see Section 5).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.1.3
5、This test method is intended for use with standardcommercially available coulometric Karl Fischer reagent.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety an
6、d health practices and determine the applica-bility of regulatory limitations prior to use. For specific hazardstatements, see Section 7.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 4057 Practice for Manual Sampling of Petroleum andPetroleum Products (API MPMS C
7、hapter 8.1)D 4177 Practice for Automatic Sampling of Petroleum andPetroleum Products (API MPMS Chapter 8.2)D 5854 Practice for Mixing and Handling Liquid Samplesof Petroleum and Petroleum Products (API MPMS Chapter8.3)E 203 Test Method for Water Using Karl Fischer Titration2.2 API Standards:3MPMS Ch
8、apter 8.1 Practice for Manual Sampling of Petro-leum and Petroleum Products (ASTM Practice D 4057)MPMS Chapter 8.2 Practice for Automatic Sampling ofPetroleum and Petroleum Products (ASTM PracticeD 4177)MPMS Chapter 8.3 Practice for Mixing and Handling ofLiquid Samples of Petroleum and Petroleum Pro
9、ducts(ASTM Practice D 5854)3. Summary of Test Method3.1 After homogenizing the crude oil with a mixer, analiquot is injected into the titration vessel of a Karl Fischerapparatus in which iodine for the Karl Fischer reaction isgenerated coulometrically at the anode. When all the water hasbeen titrate
10、d, excess iodine is detected by an electrometricend-point 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 is proportional tothe total integrated current according to Faradays Law.3.2 The
11、precision of this test method is critically dependenton the effectiveness of the homogenization step. The efficiencyof the mixer used to achieve a homogeneous sample isdetermined by the procedure given in Practice D 5854 (APIMPMS Chapter 8.3).3.3 Two procedures are provided for the determination ofw
12、ater in crude oils. In one procedure, a weighed aliquot ofsample is injected into the titration vessel and the mass % ofwater is determined. The other procedure provides for thedirect determination of the volume % of water in the crude oilby measuring the volume of crude oil injected into the titrat
13、ionvessel.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and the API Committee on Petroleum Measure-ment, and is the direct responsibility of Subcommittee D02.02/COMQ, the jointASTM-API Committee on Static Petroleum Measurement.Current edition a
14、pproved June 1, 2005. Published October 2005. Originallyapproved in 1989. Last previous edition approved in 2000 as D 492800e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information
15、, refer to the standards Document Summary page onthe ASTM website.3Published as Manual of Petroleum Standards. Available from the AmericanPetroleum Institute (API), 1220 L St., NW, Washington, DC 20005.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-295
16、9, United States.4. Significance and Use4.1 A knowledge of the water content of crude oil isimportant in the refining, purchase, sale, or transfer of crudeoils.5. Interferences5.1 A number of substances and classes of compoundsassociated with condensation or oxidation-reduction reactionsinterfere in
17、 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/g (ppm)(as sulfur), the interference from these compounds is insignifi-cant. Most crude oils, including crude oils classified as “sourcr
18、ude,” have mercaptan and sulfide levels of less than 500 g/g(ppm) as sulfur. For more information on substances thatinterfere in the determination of water by Karl Fischer titrationmethod (see Test Method E 203).5.2 The significance of the mercaptan and sulfide interfer-ence on the Karl Fischer titr
19、ation 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 levels of less than500 g/g (ppm) (as sulfur).6. Apparatus6.1 Karl Fischer Apparatus, using electrometric end
20、-point.Presently there are available on the market a number ofcommercial coulometric Karl Fischer titration assemblies.Instructions for operation of these devices are provided by themanufacturer and not described herein.6.2 Mixer, to homogenize the crude sample.6.2.1 Non-Aerating, High-Speed, Shear
21、MixerThe mixershall be capable of meeting the homogenization efficiency testdescribed in Practice D 5854 (API MPMS Chapter 8.3). Thesample size is limited to that suggested by the manufacturer forthe size of the mixing probe.6.2.2 Circulating sample mixers, such as those used withautomatic crude oil
22、 sampling receivers, are acceptable provid-ing they comply with the principles of Practice D 5854 (APIMPMS Chapter 8.3).6.3 Syringes:6.3.1 Samples are most easily added to the titration vesselby means of accurate glass syringes with LUER fittings andhypodermic needles of suitable length. The bores o
23、f theneedles used should be kept as small as possible but largeenough to avoid problems arising from back pressure andblocking while sampling. Suggested syringe sizes are asfollows:6.3.1.1 Syringe, 10 L with a needle long enough to dipbelow the surface of the anode solution in the cell wheninserted
24、through the inlet port septum. This syringe is used inthe calibration step (Section 10). It should be of suitablegraduations for readings to the nearest 0.1 L or better.6.3.1.2 Syringes, 250 L, 500 L, and 1000 L (1 mL), forcrude oil samples. For the volumetric determination procedure,the syringes sh
25、ould be accurate to 5 L, 10 L, and 20 L(0.02 mL), respectively.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of
26、 the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referen
27、cesto water shall be understood to mean reagent water as definedby Type IV of Specification D 1193.7.3 Xylene, reagent grade. Less than 0.05 % water.(WarningFlammable. Vapor harmful.)7.4 Karl Fischer ReagentStandard commercially avail-able reagents for coulometric Karl Fischer titrations.7.4.1 Anode
28、 Solution, shall be 6 parts of commercial KarlFischer anode solution with 4 parts of reagent grade xylene.Fresh Karl Fischer anode solution shall be used. Anodesolution shall not be used past its expiration date. Anodesolution should be replaced after 7 days in the titration vessel.(WarningFlammable
29、, toxic by inhalation and if swallowed,avoid contact with skin.)NOTE 1Other proportions of anode solution and xylene can be usedand should be determined for a particular reagent and apparatus. Theprecision and bias were established using the designated anode solutionand xylene.7.4.2 Cathode Solution
30、, use standard commercially avail-able Karl Fischer cathode solution. Cathode solution shall notbe used after the expiration date and should be replaced after 7days in the titration vessel. (WarningFlammable, can befatal if inhaled, swallowed, or absorbed through skin. Possiblecancer hazard.)8. Samp
31、ling and Test Specimens8.1 Sampling is defined as all the steps required to obtain analiquot representative of the contents of any pipe, tank, or othersystem and to place the sample into a container for analysis bya laboratory or test facility. The laboratory sample containerand sample volume shall
32、be of sufficient dimensions andvolume to allow mixing as described in 8.4.8.2 Laboratory SampleThe sample of crude oil presentedto the laboratory or test facility for analysis by this test method.Only representative samples obtained as specified in PracticeD 4057 (API MPMS Chapter 8.1) and Practice
33、D 4177 (APIMPMS Chapter 8.2) shall be used to obtain the laboratorysample.NOTE 2Examples of laboratory samples include sample bottles frommanual sampling, receptacles from automatic crude oil samplers, andstorage containers holding a crude oil from a previous analysis.4Reagent Chemicals, American Ch
34、emical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S.
35、Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D 4928 00 (2005)28.3 Test SpecimenThe sample aliquot obtained from thelaboratory sample for analysis by this test method. Oncedrawn, the entire portion of the test specimen will be used inthe analysis. Mix the laboratory sample properly as describe
36、din 8.4 before drawing the test specimen.8.4 Mix the laboratory sample of crude oil immediately(within 15 min) before drawing the test specimen to ensurecomplete homogeneity. Mix the sample at room temperature(15 to 25C) or less in the laboratory sample container andrecord the temperature of the sam
37、ple in degrees Celsiusimmediately before mixing. The type of mixer depends on thequantity of crude oil in the laboratory sample container. Beforeany unknown mixer is used, the specifications for the homog-enization test, Practice D 5854 (API MPMS Chapter 8.3), shallbe met. Reevaluate the mixer for a
38、ny changes in the type ofcrude, volume of crude in the container, the shape of thecontainer, or the mixing conditions (such as mixing speed andtime of mixing).8.5 For small laboratory sample containers and volumes, 50to 500 mL, a non-aerating, high-speed, shear mixer is required.Use the mixing time,
39、 mixing speed, and height of the mixerprobe above the bottom of the container found to be satisfac-tory in Practice D 5854 (API MPMS Chapter 8.3). For largercontainers and volumes, appropriate mixing conditions shall bedefined by following a set of procedures similar to thoseoutlined in Practice D 5
40、854 (API MPMS Chapter 8.3) andPractice D 4177 (API MPMS Chapter 8.2) but modified forapplication to the larger containers and volumes. Clean and drythe mixer between samples.8.6 Record the temperature of the sample in degrees Celsiusimmediately after homogenization. The rise in temperaturebetween th
41、is reading and the initial reading before mixing (8.4)is not to exceed 10C, otherwise loss of water can occur or theemulsion can become unstable.8.7 Select the test specimen size as indicated in Table 1based on the expected water content.9. Preparation of Apparatus9.1 Follow the manufacturers direct
42、ions for preparationand operation of the titration apparatus.9.2 Seal all joints and connections to the vessel to preventatmospheric moisture from entering the apparatus.9.3 Add to the anode (outer) compartment the mixture ofxylene and Karl Fischer anode solutions which has been foundsuitable for th
43、e particular reagent and apparatus being used.Add the solutions to the level recommended by the manufac-turer.9.4 Add to the cathode (inner) compartment the Karl Fis-cher cathode solution to a level 2 to 3 mm below the level ofthe solution in the anode compartment.9.5 Turn on the apparatus and start
44、 the magnetic stirrer fora smooth stirring action. Allow the residual moisture in thetitration vessel to be titrated until the end-point is reached.NOTE 3High background current for a prolonged period can be due tomoisture on the inside walls of the titration vessel. Gentle shaking of thevessel (or
45、more vigorous stirring action) will wash the inside withelectrolyte. Keep the titrator on to allow stabilization to a low backgroundcurrent.10. Standardization10.1 In principle, standardization is not necessary since thewater titrated is a direct function of the coulombs of electricityconsumed. Howe
46、ver, reagent performance deteriorates withuse and shall be regularly monitored by accurately injecting10 Lof pure water. Suggested intervals are initially with freshreagent and then after every ten determinations (see Section11.1.3). If the result is outside 10 000 6 200 g, replace boththe anode and
47、 cathode solutions.11. Procedure11.1 Mass Determination of Sample Size:11.1.1 Add fresh solvents to the anode and cathode com-partments of the titration vessel and bring the solvent toend-point conditions as described in Section 9.11.1.2 Add an aliquot of the crude oil test specimen to thetitration
48、vessel immediately after the mixing step described in8.4 using the following method.11.1.2.1 Starting with a clean, dry syringe of suitablecapacity (see Table 1 and Note 4), withdraw at least threeportions of the sample and discard to waste. Immediatelywithdraw a further portion of sample, clean the
49、 needle with apaper tissue, and weigh the syringe and contents to the nearest0.1 mg. Insert the needle through the inlet port septum, start thetitration and with the tip of the needle just below the liquidsurface, inject the sample. Withdraw the syringe and reweighthe syringe to the nearest 0.1 mg. After the end-point isreached, record the titrated water from the digital readout onthe instrument.NOTE 4If the concentration of water in the sample is completelyunknown, it is advisable to start with a small trial portion of sample toavoid excessive titratio
