1、Designation: D4928 11Designation: Manual 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 designa
2、tion 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 ag
3、encies of the Department of Defense.1. Scope*1.1 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, but at levels of less than500 g/g (ppm), the inte
4、rference 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 This test method is intended for use with standard
5、commercially 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 of thesafety concerns, if any, associated with its use. It is therespo
6、nsibility of the user of this standard to establish appro-priate safety and 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:2D1193 Specification for Reagent WaterD4057 Pra
7、ctice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD5854 Practice for Mixing and Handling of Liquid Samplesof Petroleum and Petroleum ProductsE203 Test Method for Water Using Volumetric Karl FischerTitration2.2 API Stan
8、dards:3MPMS Chapter 8.1 Practice for Manual Sampling of Petro-leum and Petroleum Products (ASTM Practice D4057)MPMS Chapter 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 P
9、etroleum Products(ASTM Practice D5854)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 hasb
10、een titrated, 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 L
11、aw.3.2 The 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 D5854 (APIMPMS Chapter 8.3).3.3 Two procedures are provided for the determi
12、nation ofwater in crude oils. In one procedure, a weighed aliquot ofsample is injected into the titration vessel and the mass % of1This 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 re
13、sponsibility of Subcommittee D02.02.10 on Sediment andWater (API MPMS Chapter 10.0).Current edition approved June 1, 2011. Published August 2011. Originallyapproved in 1989. Last previous edition approved in 2010 as D492800 (2010).DOI: 10.1520/D4928-11.2For referenced ASTM standards, visit the ASTM
14、website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Published as Manual of Petroleum Standards. Available from AmericanPetroleum Institute (API), 1220 L. St.,
15、NW, Washington, DC 20005-4070, http:/www.api.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.water is determined. The other procedure provides for thedirect determ
16、ination of the volume % of water in the crude oilby measuring the volume of crude oil injected into the titrationvessel.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 subst
17、ances 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/g (ppm)(as sulfur), the interfere
18、nce from these compounds is insignifi-cant. Most crude oils, including crude oils classified as “sourcrude,” 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
19、 Method E203).5.2 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 levels
20、 of less than500 g/g (ppm) (as sulfur).6. Apparatus6.1 Karl Fischer Apparatus, using electrometric end-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
21、 not described herein.6.2 Mixer, to homogenize the crude sample.6.2.1 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 manufacturer forthe
22、 size of the mixing probe.6.2.2 Circulating sample mixers, such as those used withautomatic crude oil sampling receivers, are acceptable provid-ing they comply with the principles of Practice D5854 (APIMPMS Chapter 8.3).6.3 Syringes:6.3.1 Samples are most easily added to the titration vesselby means
23、 of accurate glass syringes with LUER fittings andhypodermic needles of suitable length. The bores of 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
24、 L with a needle long enough to dipbelow the surface of the anode solution in the cell wheninserted 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,
25、 and 1000 L (1 mL), forcrude oil samples. For the volumetric determination procedure,the syringes should 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 inten
26、ded thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of 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 witho
27、ut lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water as definedby Type IV of Specification D1193.7.3 Xylene, reagent grade. Less than 0.05 % water.(WarningFlammable. Vapor harmful.)7.4 Karl Fischer R
28、eagentStandard commercially avail-able reagents for coulometric Karl Fischer titrations.7.4.1 Anode 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 expir
29、ation date. Anodesolution should be replaced after 7 days in the titration vessel.(WarningFlammable, 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. Thepreci
30、sion and bias were established using the designated anode solutionand xylene.7.4.2 Cathode Solution, 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. (WarningFla
31、mmable, can befatal if inhaled, swallowed, or absorbed through skin. Possiblecancer hazard.)8. Sampling 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 fo
32、r analysis bya laboratory or test facility. The laboratory sample containerand sample volume shall 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
33、representative samples obtained as specified in PracticeD4057 (API MPMS Chapter 8.1) and Practice D4177 (APIMPMS Chapter 8.2) shall be used to obtain the laboratorysample.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the te
34、sting of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D4928 112NOTE 2Examples of laboratory samples
35、include sample bottles frommanual sampling, receptacles from automatic crude oil samplers, andstorage containers holding a crude oil from a previous analysis.8.3 Test SpecimenThe sample aliquot obtained from thelaboratory sample for analysis by this test method. Oncedrawn, the entire portion of the
36、test specimen will be used inthe analysis. Mix the laboratory sample properly as describedin 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(1
37、5 to 25C) or less in the laboratory sample container andrecord the temperature of the sample 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-enizat
38、ion test, Practice D5854 (API MPMS Chapter 8.3), shallbe met. Reevaluate the mixer for any 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 volume
39、s, 50to 500 mL, a non-aerating, high-speed, shear mixer is required.Use the mixing time, mixing speed, and height of the mixerprobe above the bottom of the container found to be satisfac-tory in Practice D5854 (API MPMS Chapter 8.3). For largercontainers and volumes, appropriate mixing conditions sh
40、all bedefined by following a set of procedures similar to thoseoutlined in Practice D5854 (API MPMS Chapter 8.3) andPractice D4177 (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
41、in degrees Celsiusimmediately after homogenization. The rise in temperaturebetween this 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
42、expected water content.9. Preparation of Apparatus9.1 Follow the manufacturers directions 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
43、mixture ofxylene and Karl Fischer anode solutions which has been foundsuitable for the 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
44、the level ofthe solution in the anode compartment.9.5 Turn on the apparatus and start 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 tom
45、oisture on the inside walls of the titration vessel. Gentle shaking of thevessel (or 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 sinc
46、e thewater titrated is a direct function of the coulombs of electricityconsumed. However, 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 (s
47、ee Section11.1.3). If the result is outside 10 000 6 200 g, replace boththe anode and 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 describ
48、ed in Section 9.11.1.2 Add an aliquot of the crude oil test specimen to thetitration 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 sa
49、mple and discard to waste. Immediatelywithdraw a further portion of sample, clean the 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, i
