1、Designation: D3227 16Designation: 342/00Standard Test Method for(Thiol Mercaptan) Sulfur in Gasoline, Kerosine, AviationTurbine, and Distillate Fuels (Potentiometric Method)1This standard is issued under the fixed designation D3227; the number immediately following the designation indicates the year
2、 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 agencies of the U.S. Depa
3、rtment 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 % by mass ofmercaptan sulfur. Organic sulfur compounds such as sulfides,disulfides, and thiophene, do not
4、interfere. Elemental sulfur inamounts less than 0.0005 % by mass does not interfere.Hydrogen sulfide will interfere if not removed, as described in9.2.1.2 The values in acceptable SI units are to be regarded asthe standard.1.2.1 ExceptionThe values in parentheses are for informa-tion only.1.3 This s
5、tandard 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 stat
6、ements, see Sections 6, 8, 9, and Appendix X1.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1250 Guide for Use of the Petroleum Measurement TablesD1298 Test Method for Density, Relative Density, or APIGravity of Crude Petroleum and Liquid Petroleum Prod-ucts by Hyd
7、rometer MethodD4052 Test Method for Density, Relative Density, and APIGravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD6299 Practice for Applying Statistical Qualit
8、y Assuranceand Control Charting Techniques to Evaluate AnalyticalMeasurement System Performance3. 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 indicat
9、or thepotential 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 su
10、lfur has 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 ti
11、tration 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 1012A and having a sensitivity of 62mVover a range of at least 61 V. The meter shal
12、l be 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 to1This test method is under the jurisdicti
13、on of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricantsand is the direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved Oct. 1, 2016. Published November 2016. Originallyapproved in 1973. Last previous edition approved in 2013 as D3227 13. DOI:
14、10.1520/D3227-16.2For 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 give equal or bette
15、r precision is acceptable.*A Summary 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 States1ground. The indicating electrode shall be made from a silverwire, 2 mm (0.08 in.) in diameter o
16、r larger, mounted in aninsulated support. 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 provi
17、ded with supports for the electrodesand 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 ot
18、herwise indicated, it is intended 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
19、purity to permit its use without lessening 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 a
20、n equivalent concentration is maintained.6.2 WaterReagent grade, Type I, Specification D1193.6.3 Cadmium Sulfate, Acid Solution (150 gL)Dissolve150 g of cadmium sulfate (3CdSO48H2O) in water.(WarningPoison. May be fatal if swallowed or inhaled. Aknown carcinogen (animal positive).) Add 10 mL of dilu
21、teH2SO4(WarningPoison. Causes severe burns. Harmful orfatal if swallowed or inhaled) and dilute to 1 L with water.6.4 Potassium Iodide, Standard Solution (approximately0.1 molL)Dissolve 17 g of KI (weigh to 0.01 g) in 100 mLof water in a 1 L volumetric flask and dilute to 1 L. Calculatethe exact mol
22、arity.6.5 Propan-2-ol(WarningFlammable. 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 b
23、y percolation through an activated aluminacolumn.)6.6 Silver Nitrate, Standard Alcoholic Solution(0.1 molL)Dissolve 17 g of AgNO3in 100 mL of water in a1 L volumetric flask and dilute to 1 L with propan-2-ol (99 %)(see Note 1). Store in a dark bottle and standardize at intervalsfrequent enough to de
24、tect a change of 0.0005 or greater 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
25、and found free of peroxides.6.6.1 StandardizationAdd six drops of concentratedHNO3(relative density 1.42) (WarningPoison. Causessevere burns. Harmful or fatal if swallowed or inhaled) to100 mLof water in an appropriately sized beaker (for example,a 200, 250, or 300 mL size beaker is typically large
26、enough).Remove oxides of nitrogen by boiling for 5 min. Cool toambient temperature. Pipet 5 mL of 0.1 molL 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 molL)Prepare d
27、aily when the test is being performedby dilution of the 0.1 N standard. Pipet 100 mL of the0.1 molL standard into a 1 L volumetric flask and dilute tovolume with propan-2-ol. Calculate the exact molarity.6.8 Sodium Sulfide Solution (10 gL)Dissolve 10 g ofNa2S in water and dilute to 1 L with water. P
28、repare fresh asneeded.NOTE 2Anhydrous sodium sulfide is not widely available, and isexpensive. An aqueous solution of hydrated sodium sulfide (Na2S9H2O)at 30.6 g L is satisfactory.6.9 Sulfuric Acid, dilute. Cautiously dilute five volumes ofwater with one volume of sulfuric acid (relative density 1.8
29、4).(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 areneeded for each litre of cadmium sulfate solution.6.10 Titration SolventLow molecular weight mercaptans,as usually found in
30、 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 in kerosines, aviation turbine fuels, and distillatefuels, the acidic titration solvent is used to achieve more rapide
31、quilibrium 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 (NaC2H3O2) in 25 mL of water free of dis-solved oxygen and pour into 975 mL of propan-2-ol (99 %)(Note 1). When necess
32、ary, 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 dissolving in the solution duringstorage, an option exists to nitrogen blanket the solution priorto sealing the solvent co
33、ntainer.6.10.2 Acidic Titration SolventDissolve 2.7 g ofNaC2H3O23H2O or 1.6 g of NaC2H3O2in 20 mLof water freeof dissolved oxygen and pour into 975 mL of propan-2-ol(99 %) (Note 1) and add 4.6 mL of glacial acetic acid. Whennecessary, remove dissolved oxygen by purging the solutionwith a rapid strea
34、m 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 the solution prior to sealing the solventcontainer.4Reagent Chemicals, American Chemical Society Specifications, Am
35、ericanChemical Society, Washington, 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. (U
36、SPC), Rockville,MD.D3227 1626.11 Polishing Paper or Cloth, 6 m to 20 m averageparticle size abrasive.7. Sampling7.1 Take the sample in accordance with Practice D4057 orPractice D4177.7.2 Methanethiol (methyl mercaptan) has a boiling point of6.2 C and may be expected to be present in light untreatedg
37、asolines. Therefore, when the presence of this low boilingthiol (mercaptan) is known or expected, specimen to be testedshall be kept below 4 C to prevent the loss of mercaptan fromsuch samples.7.3 Light naphtha fractions of high thiol content(100 mgkg) boiling below 85 C have been shown to be veryse
38、nsitive to the titration temperatures.NOTE 3Samples with a thiol content above 0.010 % by mass may beanalyzed by an appropriate reduction in test portion mass, ensuring thatthe minimum volume of titration solvent plus test portion exceeds120 mL. If additional titration solvent is used to maintain th
39、is requirement,a similar volume should be used for the blank titration. No precision hasbeen determined for thiol contents above 0.01 % by mass.8. Preparation of Apparatus8.1 Glass ElectrodeAfter each manual titration, or batchof titrations, in the case of automatic titration systems, wipe theelectr
40、ode with a soft, clean tissue and rinse with water. Cleanthe electrode at frequent intervals (at least once a week) bystirring in cold chromic acid solution (WarningCausessevere burns. A recognized carcinogen. Strong oxidizercontact with other material may cause fire. Hygroscopic. Anequivalent, chro
41、mium-free cleaning solution may be used) fora few seconds (10 s maximum). When not in use, keep lowerhalf of the electrode immersed in water.8.2 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 silv
42、er sulfide coating on theelectrode by the following method:8.2.1 Burnish electrode with polishing paper or cloth until aclean, polished silver 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 (for
43、 example, from a buret), with stirring,10 mLof 0.1 molLAgNO3solution over a period from 10 minto 15 min.8.2.4 Remove electrode from solution, wash with water, andwipe with a soft, clean tissue.8.2.5 Between manual titrations, or batches of titrations inthe case of automatic titration systems, store
44、the electrode aminimum of 5 min in 100 mL of titration solvent containing0.5 mL of the 0.1 molL AgNO3solution.9. Procedure9.1 Determination of DensityIf the sample is to be mea-sured volumetrically, determine the density by Test MethodD1298 or Test Method D4052 at the temperature at which thetest po
45、rtion will be taken, either directly or from the densitydetermined at a reference temperature and converted to thetransfer temperature by use of the Petroleum MeasurementTables (Guide D1250).9.2 Removal of Hydrogen SulfideTest the sample qualita-tively for hydrogen sulfide (H2S) by mixing 5 mL of th
46、esample with 5 mL of the acid CdSO4solution. If no precipitateappears, proceed with the analysis of the sample as describedin 9.3. If a yellow precipitate appears, remove the H2Sinthefollowing manner: Place a quantity of the sample, three to fourtimes that required for the analysis, in a separatory
47、funnelcontaining a volume of the acid CdSO4solution equal to onehalf that of the sample and shake vigorously. Draw off anddiscard the aqueous phase containing the yellow precipitate.Repeat the extraction with another portion of the CdSO4solution. Again draw off the aqueous phase, and wash thesample
48、with three 25 mL to 30 mL portions of water, with-drawing the water after each washing. Filter the hydrocarbonthrough a rapid paper. Test a small portion of the washedsample, such as in a test tube or vial, with a few millilitres ofthe CdSO4solution as described previously. If no furtherprecipitate
49、is formed, proceed as directed in 9.3. If a precipitateappears, repeat the extraction with the CdSO4solution until allof the H2S has been removed. (WarningCertain straight rungasolines can contain significant amounts of both low molecu-lar weight 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 from some naturalgas condensates. Therefore, it is advisable that during the
