1、Designation: D 3227 04aDesignation: 342/00An American National StandardStandard Test Method for(Thiol Mercaptan) Sulfur in Gasoline, Kerosine, AviationTurbine, and Distillate Fuels (Potentiometric Method)1This standard is issued under the fixed designation D 3227; the number immediately following th
2、e 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 reapproval.This standard has been approved for
3、 use by agencies of the Department of Defense.1. Scope*1.1 This test method covers the determination of mercaptansulfur in gasolines, kerosines, aviation turbine fuels, anddistillate fuels containing from 0.0003 to 0.01 mass % ofmercaptan sulfur. Organic sulfur compounds such as sulfides,disulfides,
4、 and thiophene, do not interfere. Elemental sulfur inamounts less than 0.0005 mass % does not interfere. Hydrogensulfide will interfere if not removed, as described in 9.2.1.2 The values in acceptable SI units are to be regarded asthe standard. The values in parentheses are for informationonly.1.3 T
5、his 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 and health practices and determine the applica-bility of regulatory limitations prior to use. For specificwarning
6、 statements, see Sections 6, 8, 9, and Appendix X1.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 1250 Guide for Use of the Petroleum MeasurementTablesD 1298 Test Method for Density, Relative Density (SpecificGravity), or API Gravity of Crude Petroleum and LiquidP
7、etroleum Products by Hydrometer MethodD 4052 Test Method for Density and Relative Density ofLiquids by Digital Density MeterD 4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD 6299 Practice for Applying Stat
8、istical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformance3. Summary of Test Method3.1 The hydrogen sulfide-free sample is dissolved in analcoholic sodium acetate titration solvent and titrated potentio-metrically with silver nitrate solution, using as an indicator thep
9、otential between a glass reference electrode and a silver/silver-sulfide indicating electrode. Under these conditions, themercaptan sulfur is precipitated as silver mercaptide and theend point of the titration is shown by a large change in cellpotential.4. Significance and Use4.1 Mercaptan sulfur ha
10、s an objectionable odor, an adverseeffect on fuel system elastomers, and is corrosive to fuelsystem components.5. Apparatus5.1 As described in 5.2-5.5; alternatively, any automatictitration system may be used that, using the same electrode pairdescribed in 5.3, is capable of performing the titration
11、 asdescribed in Section 9 and selecting the endpoint specified in11.1 with a precision that meets or is better than that given inSection 14.5.2 MeterAn electronic voltmeter, operating on an inputof less than 9 3 1012A and having a sensitivity of 62mVover a range of at least 61 V. The meter shall be
12、electrostati-cally shielded, and the shield shall be connected to the ground.35.3 Cell System, consisting of a reference and indicatingelectrode. The reference electrode should be a sturdy, pencil-type glass electrode, having a shielded lead connected toground. The indicating electrode shall be made
13、 from a silver1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Nov. 1, 2004. Published November 2004. Originallyapproved in 1973. Last previous e
14、dition approved in 2004 as D 322704.2For 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 page onthe ASTM website.3Any apparatus that will
15、give equal or better precision is acceptable.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.wire, 2 mm (0.08 in.) in diameter or larger, mounted in aninsulated suppor
16、t. Silver billet electrodes can also be used.5.4 Buret, 10-mL capacity, graduated in 0.05-mL intervals,with a tip that extends approximately 120 mm (5 in.) below thestopcock.5.5 Titration Stand, preferably built as an integral part of themeter housing and provided with supports for the electrodesand
17、 electrical stirrer, all connected to ground. No permanentchange in meter reading should be noticeable upon connectingor disconnecting the stirring motor.6. Reagents and Materials6.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thata
18、ll 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 without lessen
19、ing theaccuracy of the determination.6.1.1 Commercially available solutions may be used inplace of prepared laboratory solutions, when they are certifiedto meet the required concentrations.6.1.2 Alternate volumes of solutions and solvents may beprepared, when an equivalent concentration is maintaine
20、d.6.2 WaterReagent grade, Type I, Specification D 1193.6.3 Cadmium Sulfate, Acid Solution (150 g/L)Dissolve150 g of cadmium sulfate (3CdSO48H2O) in water.(WarningPoison. May be fatal if swallowed or inhaled. Aknown carcinogen (animal positive).) Add 10 mL of diluteH2SO4(WarningPoison. Causes severe
21、burns. Harmful orfatal if swallowed or inhaled) and dilute to 1 L with water.6.4 Potassium Iodide, Standard Solution (approximately 0.1mol/L)Dissolve 17 g of KI (weigh to 0.01 g) in 100 mL ofwater in a 1-L volumetric flask and dilute to 1 L. Calculate theexact molarity.6.5 Propan-2-ol(WarningFlammab
22、le. WarningUnless inhibited against it, peroxides can form in propan-2-olwhen stored in the same container that is exposed to air. Whenthis happens and the propan-2-ol evaporates to dryness, anexplosion can occur. When peroxides are suspected, they maybe removed by percolation through an activated a
23、luminacolumn.)6.6 Silver Nitrate, Standard Alcoholic Solution (0.1 mol/L)Dissolve 17 g of AgNO3in 100 mL of water in a 1-Lvolumetric flask and dilute to 1 L with propan-2-ol (99 %) (seeNote 1). Store in a dark bottle and standardize at intervalsfrequent enough to detect a change of 0.0005 or greater
24、 inmolarity.NOTE 1It is important to pass the propan-2-ol through a column ofactivated alumina to remove peroxides that may have formed on storage;failure to remove peroxides will lead to low results. It is not necessary toperform this step if the alcohol is tested and found free of peroxides.6.6.1
25、StandardizationAdd six drops of concentratedHNO3(relative density 1.42) (WarningPoison. Causes se-vere burns. Harmful or fatal if swallowed or inhaled) to 100mL of water in an appropriately sized beaker (for example, a200-, 250-, or 300-mL size beaker is typically large enough).Remove oxides of nitr
26、ogen by boiling for 5 min. Cool toambient temperature. Pipet 5 mL of 0.1 mol/L KI solution intothe beaker and titrate with the AgNO3solution choosing theend point at the inflection of the titration curve.6.7 Silver Nitrate, Standard Alcoholic Solution (0.010 mol/L)Prepare daily when the test is bein
27、g performed by dilutionof the 0.1 N standard. Pipet 100 mL of the 0.1 mol/L standardinto a 1-L volumetric flask and dilute to volume with propan-2-ol. Calculate the exact molarity.6.8 Sodium Sulfide Solution (10 g/L)Dissolve 10 g ofNa2S in water and dilute to 1 L with water. Prepare fresh asneeded.6
28、9 Sulfuric Acid, dilute. Cautiously dilute five volumes ofwater with one volume of sulfuric acid (relative density 1.84).(WarningAdding the acid will generate heat: mix well. Ifwater begins to boil, cool before adding more acid.) Note thatonly limited volumes are required because only 10 mL areneed
29、ed for each litre of cadmium sulfate solution.6.10 Titration SolventLow molecular weight mercaptans,as usually found in gasoline, are readily lost from the titrationsolution if an acidic titration solvent is used. For the determi-nation of the higher molecular weight mercaptan as normallyencountered
30、 in kerosines, aviation turbine fuels, and distillatefuels, the acidic titration solvent is used to achieve more rapidequilibrium between successive additions of the titrant.6.10.1 Alkaline Titration SolventDissolve 2.7 g of sodiumacetate trihydrate (NaC2H3O23H2O) or 1.6 g of anhydroussodium acetate
31、 (NaC2H3O2) in 25 mL of water free ofdissolved oxygen and pour into 975 mL of propan-2-ol (99 %)(Note 1). When necessary, remove dissolved oxygen by purg-ing the solution with a rapid stream of nitrogen for 10 min eachday prior to use; keep protected from the atmosphere. Tominimize oxygen from disso
32、lving in the solution duringstorage, an option exists to nitrogen blanket the solution priorto sealing the solvent container.6.10.2 Acidic Titration SolventDissolve 2.7 g ofNaC2H3O23H2Oor1.6gofNaC2H3O2in 20 mL of water freeof dissolved oxygen and pour into 975 mL of propan-2-ol(99 %) (Note 1) and ad
33、d 4.6 mL of glacial acetic acid. Whennecessary, remove dissolved oxygen by purging the solutionwith a rapid stream of nitrogen for 10 min each day prior touse; keep protected from the atmosphere. To minimize oxygenfrom dissolving in the solution during storage, an option existsto nitrogen blanket th
34、e solution prior to sealing the solventcontainer.6.11 Polishing Paper or Cloth, 620 m average particlesize abrasive.7. Sampling7.1 Take the sample in accordance with Practice D 4057 orPractice D 4177.4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington,
35、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., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D 3227 04a27.2 Me
36、thanethiol (methyl mercaptan) has a boiling point of6.2C and may be expected to be present in light untreatedgasolines. Therefore, when the presence of this low boilingthiol (mercaptan) is known or expected, specimen to be testedshall be kept below 4C to prevent the loss of mercaptan fromsuch sample
37、s.8. Preparation of Apparatus8.1 Glass ElectrodeAfter each manual titration, or batchof titrations, in the case of automatic titration systems, wipe theelectrode with a soft, clean tissue and rinse with water. Cleanthe electrode at frequent intervals (at least once a week) bystirring in cold chromic
38、 acid solution (WarningCausessevere burns. A recognized carcinogen. Strong oxidizercontact with other material may cause fire. Hygroscopic. Anequivalent, chromium-free cleaning solution may be used) fora few seconds (10 s maximum). When not in use, keep lowerhalf of the electrode immersed in water.8
39、2 Silver/Silver-Sulfide ElectrodeEach day prior to use,or as triggered by the analysis of a quality control (QC) sample(see Section 12), prepare a fresh silver sulfide coating on theelectrode by the following method:8.2.1 Burnish electrode with polishing paper or cloth until aclean, polished silver
40、 surface shows.8.2.2 Place electrode in operating position and immerse it in100 mL of titration solvent containing 8 mL of Na2S solution.8.2.3 Add slowly from a buret, with stirring, 10 mL of 0.1mol/L AgNO3solution over a period from 10 to 15 min.8.2.4 Remove electrode from solution, wash with water
41、 andwipe with a soft, clean tissue.8.2.5 Between manual titrations, or batches of titrations inthe case of automatic titration systems, store the electrode aminimum of 5 min in 100 mL of titration solvent containing 0.5mL of the 0.1 mol/L AgNO3solution.9. Procedure9.1 Determination of DensityIf the
42、 sample is to be mea-sured volumetrically, determine the density by Test MethodD 1298 or Test Method D 4052 at the temperature at which thetest portion will be taken, either directly or from the densitydetermined at a reference temperature and converted to thetransfer temperature by use of the Petro
43、leum MeasurementTables (Guide D 1250).9.2 Removal of Hydrogen SulfideTest the sample qualita-tively for hydrogen sulfide (H2S) by mixing 5 mL of the samplewith 5 mL of the acid CdSO4solution. If no precipitateappears, proceed with the analysis of the sample as describedin 9.3. If a yellow precipitat
44、e appears, remove the H2Sinthefollowing manner: Place a quantity of the sample, three to fourtimes that required for the analysis, in a separatory funnelcontaining a volume of the acid CdSO4solution equal to onehalf that of the sample and shake vigorously. Draw off anddiscard the aqueous phase conta
45、ining the yellow precipitate.Repeat the extraction with another portion of the CdSO4solution. Again draw off the aqueous phase, and wash thesample with three 25 to 30-mL portions of water, withdrawingthe water after each washing. Filter the hydrocarbon through arapid paper. Test a small portion of t
46、he washed sample, such asin a test tube or vial, with a few millilitres of the CdSO4solution as described previously. If no further precipitate isformed, proceed as directed in 9.3. If a precipitate appears,repeat the extraction with the CdSO4solution until all of theH2S has been removed. (WarningCe
47、rtain straight run gaso-lines can contain significant amounts of both low molecularweight mercaptans and dissolved elemental sulfur, which,when heated under total reflux conditions, may produce H2Sbythe inter-reaction of both. This phenomenon is particularlynoticed in straight run gasolines produced
48、 from some naturalgas condensates. Therefore, it is advisable that during theremoval of H2S (and after all H2S has been extracted), that noheat should be applied to the sample.)9.2.1 When the test results obtained are not for refereepurposes and Quality Assurance/Quality Control (QA/QC)protocol perm
49、its, an alternative test for, and a procedure for theremoval of, hydrogen sulfide can be used. This process useslead acetate paper and sodium hydrogen carbonate and isdescribed in Appendix X1.9.2.2 There are available automated instruments that elimi-nate the necessity to remove H2S when present, prior toperforming the analysis, since the H2S titration curve does notinterfere with the titration curve of the thiol or mercaptandetermination. Such equipment may be used when the test isnot for referee purposes. The precision statement does notinclude dat
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