ASTM D7923-2017ae1 5625 Standard Test Method for Water in Ethanol and Hydrocarbon Blends by Karl Fischer Titration.pdf

1、Designation: D7923 17a1Standard Test Method forWater in Ethanol and Hydrocarbon Blends by Karl FischerTitration1This standard is issued under the fixed designation D7923; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of

2、last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEThe title of Table 3 was corrected editorially in July 2018.1. Scope*1.1 This test method covers the determination of water f

3、rom0.05 % to 5.0 % by mass in blends of ethanol, hydrocarbon,and corresponding blends. It is intended for measuring watercontent of gasoline or other hydrocarbon blendstock, denaturedfuel ethanol as cited in Specification D4806, and ethanol fuelblends such as those cited in Specification D5798 and P

4、racticeD7794. This test method is not applicable to samples that arephase separated.1.1.1 Procedure AFor measurement of water up to 2 % bymass in ethanol and hydrocarbon blends using coulometricKarl Fischer titration. This is the referee method for samplescontaining up to 2 % water.1.1.2 Procedure B

5、For measurement of water up to 5.4 %by mass in ethanol and hydrocarbon blends using volumetricKarl Fischer titration.1.2 This method measures mass percent water and allowsfor the alternative reporting of volume percent. This testmethod recommends the use of pyridine-free reagents.1.3 The values stat

6、ed in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.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, he

7、alth, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.Specific precautionary statements are given in Section 8.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established i

8、n the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1152 Specification for Methanol (Methyl Alcohol)D1193 Specification fo

9、r Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4175 Terminology Relating to Petroleum Products, LiquidFuels, and LubricantsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blend-ing with G

10、asolines for Use as Automotive Spark-IgnitionEngine FuelD5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System PerformanceD6708 Pr

11、actice for Statistical Assessment and Improvementof Expected Agreement Between Two Test Methods thatPurport to Measure the Same Property of a MaterialD7794 Practice for Blending Mid-Level Ethanol FuelBlends for Flexible-Fuel Vehicles withAutomotive Spark-Ignition EnginesE203 Test Method for Water Us

12、ing Volumetric Karl FischerTitrationE1064 Test Method for Water in Organic Liquids by Coulo-metric Karl Fischer Titration3. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Definitions:1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liqui

13、d Fuels, and Lubricants and is the direct responsibility ofSubcommittee D02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved July 1, 2017. Published July 2017. Originally approvedin 2016. Last previous edition approved in 2017 as D7923 17. DOI: 10.1520/D7923-17AE01.2For referen

14、ced 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 page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyrigh

15、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International

16、 Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.1 denatured fuel ethanol, nfuel ethanol made unfit forbeverage use by the addition of denaturants under formula(s)approved by the applicable regulatory agency to prevent the

17、imposition of beverage alcohol tax. D48063.2.2 hydrocarbon, na compound composed solely ofhydrogen and carbon. D57983.2.2.1 DiscussionThe hydrocarbon mixtures used inethanol fuel blends will be unleaded gasoline, gasoline blend-stock for oxygenate blending (BOB), natural gasoline, or otherhydrocarbo

18、ns in the gasoline boiling range. The hydrocarbonblend components will also contain trace quantities of otherelements.3.3 Definitions of Terms Specific to This Standard:3.3.1 coulometric titration, nin reference to Karl Fischertitration methods, a process of measuring the water content ofa sample us

19、ing an electrolytic process to generate iodine insitu.3.3.2 pre-titration, nthe process of adding titrant to reactwith any water in the Karl Fischer system so the system istotally dry prior to addition of a test sample.3.3.3 volumetric titration, nin reference to Karl Fischertitration methods, a pro

20、cess of measuring the water content ofa sample by the physical delivery of a titration reagentcontaining iodine.4. Summary of Test Method4.1 This test method is based on the Karl Fischer (KF)reaction for determining water. Iodine is consumed by water ina one to one molar ratio in the presence of sul

21、fur dioxide,organic base, and methanol or other alcohols. The coulometricmethod generates iodine from iodide by anodic oxidation whilethe iodine is already present in the volumetric KF reagents.5. Significance and Use5.1 Blends of fuel ethanol and hydrocarbon have a limitedsolvency for water that is

22、 dependent upon temperature and theratio of ethanol to hydrocarbon. Good handling practices areimportant during the blending, storage, and transportation offuel to avoid water contamination. High concentrations ofwater can cause haze or phase separation in ethanol andhydrocarbon blends and lead to f

23、reezing problems at lowtemperatures. Water has also been associated with corrosionand filter plugging.6. Interferences6.1 A number of functional groups are known to interferewith Karl Fischer titrations. In hydrocarbons, the most com-mon interferences are mercaptans and sulfides. In ethanol,aldehyde

24、s and ketones are known to interfere with the KarlFischer reagent. Some interferences can be mitigated with theuse of applicable reagents. For fuel grade ethanol and gasolinein areas with stringent environmental regulations, the magni-tude of the interference should be negligible under mostcircumsta

25、nces. A list of several additional functional groupsthat can interfere with Karl Fischer titrations is included in theAppendix (X1.1.1).7. Apparatus7.1 Automatic Titrator:7.1.1 Coulometric Automatic Titrator, consisting of a con-trol unit, titration vessel, dual platinum sensing electrode,generator

26、electrode assembly, and magnetic stirrer. The instru-ment is designed to coulometrically generate iodine that reactsstoichiometrically with the water present in the sample solu-tion. The coulombs of electricity required to generate thereagent are converted to micrograms of water, which isobtained as

27、 a direct digital readout.7.1.2 Volumetric Automatic Titrator, consisting of a controlunit, titration vessel, dual platinum sensing electrode, dispens-ing buret, and magnetic stirrer. The instrument is designed toaccurately dose an iodine containing titrant into the titrationvessel that reacts stoic

28、hiometrically with the water present inthe sample solution. The titrant solution is standardized todetermine milligrams of water per milliliter of Karl Fischerreagent it will neutralize in the sample.7.2 Gas-tight Syringe, fitted with a cannula needle ofappropriate length and gauge for introducing s

29、ample into thetitration chamber or removing excess solution from titrationchamber (see Note 1). The syringe shall be made of glass orother suitably inert material. The volume of the syringe willdepend on the sample size. When injecting by volume, thesample should occupy at least 25 % of the syringe

30、volume.7.2.1 Rinse all glass syringes and needles with dry methanolor ethanol after cleaning, then dry in an oven at 100 C for atleast 1 h and store in a desiccator.7.3 Sample Bottle, suitable for collecting sample and main-taining an air-tight enclosure to prevent intrusion of atmo-spheric moisture

31、.7.4 Oven, temperature 100 C 6 5 C.7.5 Desiccator, standard laboratory type with desiccantcontaining color change indicator.7.6 Analytical Balance, capable of weighing to 60.0001 g.8. Safety Precautions8.1 The reagents contain one or more of the following:iodine, organic base, sulfur dioxide, and me

32、thanol or otheralcohol. Wear chemically resistant gloves when mixing thereagents and removing solution from the titration chamber.Exercise care to avoid inhalation of reagent vapors, or directcontact of the reagent with the skin.9. Sampling9.1 Sampling is defined as all of the steps required to obta

33、inan aliquot representative of the contents of any pipe, tank orother system and to place the sample into a container foranalysis by a laboratory or test facility. Sampling practices arecovered in Practices D4057 and D4177.9.2 Due to the low concentration of water to be measured,and the hygroscopic

34、nature of ethanol, exercise care at all timesto avoid contaminating the sample with moisture from thesample container, the atmosphere, or transfer equipment.9.3 Samples shall be at room temperature at time of analy-sis.D7923 17a129.4 Verify that samples are single phase before taking analiquot to te

35、st. Water or water/ethanol blend will separate fromhydrocarbon if the solubility limit is exceeded. The solubilitylimit depends on the gasoline makeup, concentration of ethanolor other emulsifiers, and sample temperature. Water is infi-nitely soluble in ethanol.9.4.1 For a transparent container, thi

36、s observation can bedetermined by visual inspection. If the material has two phases,shake the sample vigorously to combine. If the separate layerre-forms, the sample is not suitable for testing.9.4.2 If the sample is contained in a non-transparentcontainer, mix the sample and immediately pour a port

37、ion ofthe remaining sample into a clear glass container and observefor evidence of phase separation. If the separate layer forms,the sample is not suitable for testing.9.4.3 Because of the volatile and hygroscopic nature of thesamples, mixing with a mechanical or electronic mixer is notrecommended.9

38、.5 Remove the test specimens for analysis from the samplebottle with a dry, inert gas-tight syringe.PROCEDURE A (COULOMETRIC)10. Reagents10.1 Purity of ReagentsUnless otherwise indicated, it isintended that all reagents shall conform to the specifications ofthe Committee onAnalytical Reagents of the

39、American Chemi-cal Society, where such specifications are available.3Othergrades may be used, provided it is first ascertained that thereagent is of sufficiently high purity to permit its use withoutlessening the accuracy of the determination.10.2 Purity of WaterUnless otherwise indicated, reference

40、to water shall be understood to mean Type II or Type IIIreagent water, conforming to Specification D1193, or better.10.3 Karl Fischer ReagentsCommercial coulometric KFreagents and reagent systems of various types are available foruse with autotitrators for water determination. Traditionally,pyridine

41、 was the organic base used in KF reagents. Pyridine-free formulations are available and are preferred by most KFinstrument manufacturers for use with their equipment. Thepyridine-free reagents are less toxic, less odorous, and morestable than those containing pyridine. The use of pyridine-freereagen

42、ts is recommended whenever possible. Coulometrictitrations normally require two reagent solutions: an anolyteand a catholyte or generator solution. However, with the use ofan integrated or diaphragm-less cell, a single solution thatcontains all of the reagents needed for a KF titration may beused.10

43、.3.1 Catholyte solution, contains ammonium salts andmethanol.10.3.2 Anolyte solution, contains iodide, sulfur dioxide andimidazole buffer in a suitable solvent.10.3.3 One component solution, iodide, sulfur dioxide, imi-dazole buffer, and bases in a suitable solvent. This solution maybe used as the o

44、nly solution in a coulometric system with adiaphragm-less generator cell or as the anolyte solution in adiaphragm cell if specified by the manufacturer.10.3.4 Water Standards, 0.1 % by mass and 1 % by mass,commercially prepared in organic solvent recommended forthis method.11. Preparation of Apparat

45、us11.1 Clean, dry, and assemble the titration chamber asdirected in the manufacturers instructions. Care should betaken to ensure the vessel is sealed from atmospheric moisture.Replace the desiccant if saturated. Connect the leads from thesensing and generator electrodes to the titrator.11.2 Add cat

46、holyte solution (10.3.1) to the generator elec-trode assembly and reseal the vessel according to manufacturerinstructions.11.3 Fill the anode reservoir with anolyte solution (10.3.2)as directed by the manufacturer. The level of the catholytesolution in the inner chamber shall be maintained slightlyb

47、elow the level of the anolyte solution to prevent backflowcontamination of the titration (anolyte) solution. As samplesare analyzed, the volume of the anolyte will increase. This mayslow reactivity of the catholyte due to increased pressure acrossthe membrane.Aportion of the anolyte solution may hav

48、e to beremoved periodically to maintain the correct level. (Note 1)NOTE 1A coulometric system with a diaphragm-less generator elec-trode should be filled with the appropriate one component solution.11.4 Agitate the titration solution by gently swirling thetitration chamber to remove any residual moi

49、sture from thewalls. Allow the solution to stir until inner atmosphere mois-ture is removed and the baseline has been established.12. Verification of Calibration and Quality Control12.1 Autotitrators vary in calibration procedures by manu-facturer. Consult the operating manual for the autotitrator inuse. Stable, prepackaged quality control (QC) water standardsare commercially available with 0.1 % by mass and 1 % bymass water content for this purpose. It is desirable to verifycalibration with a standard solution that approximates the samerange of water expected to