1、Designation: D3227 04a (Reapproved 2010)D3227 13Designation: 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 des
2、ignation 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 b
3、y agencies of the Department of Defense.1. Scope Scope*1.1 This test method covers the determination of mercaptan sulfur in gasolines, kerosines, aviation turbine fuels, and distillatefuels containing from 0.0003 to 0.01 mass % of mercaptan sulfur. Organic sulfur compounds such as sulfides, disulfid
4、es, andthiophene, do not interfere. Elemental sulfur in amounts less than 0.0005 mass % does not interfere. Hydrogen sulfide will interfereif not removed, as described in 9.2.1.2 The values in acceptable SI units are to be regarded as the standard. The values in parentheses are for information only.
5、1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. For specific war
6、ning statements, 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 API Gravity of Crude Petroleum and Liquid Petroleum Produc
7、ts byHydrometer MethodD4052 Test Method for Density, Relative Density, and API Gravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum and Petroleum ProductsD4177 Practice for Automatic Sampling of Petroleum and Petroleum ProductsD6299 Practice for Applying Statist
8、ical Quality Assurance and Control Charting Techniques to Evaluate Analytical Measure-ment System Performance3. Summary of Test Method3.1 The hydrogen sulfide-free sample is dissolved in an alcoholic sodium acetate titration solvent and titrated potentiometricallywith silver nitrate solution, using
9、as an indicator the potential between a glass reference electrode and a silver/silver-sulfideindicating electrode. Under these conditions, the mercaptan sulfur is precipitated as silver mercaptide and the end point of thetitration is shown by a large change in cell potential.4. Significance and Use4
10、.1 Mercaptan sulfur has an objectionable odor, an adverse effect on fuel system elastomers, and is corrosive to fuel systemcomponents.1 This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products and Lubricantsand is the direct responsibility of Subcommittee D02.03 onEleme
11、ntal Analysis.Current edition approved May 1, 2010June 15, 2013. Published May 2010August 2013. Originally approved in 1973. Last previous edition approved in 20042010 asD3227D3227 0404A. A (2010). DOI: 10.1520/D3227-04R10.10.1520/D3227-13.2 For referencedASTM standards, visit theASTM website, www.a
12、stm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what
13、changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the o
14、fficial document.*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 States15. Apparatus5.1 As described in 5.2-5.5; alternatively, any automatic titration system may be used that,
15、 using the same electrode pairdescribed in 5.3, is capable of performing the titration as described in Section 9 and selecting the endpoint specified in 11.1 witha precision that meets or is better than that given in Section 14.5.2 MeterAn electronic voltmeter, operating on an input of less than 9 1
16、0 12 A and having a sensitivity of 62 mV over arange of at least 61 V. The meter shall be electrostatically shielded, and the shield shall be connected to the ground.35.3 Cell System, consisting of a reference and indicating electrode. The reference electrode should be a sturdy, pencil-type glassele
17、ctrode, having a shielded lead connected to ground. The indicating electrode shall be made from a silver wire, 2 mm (0.08 in.)in diameter or larger, mounted in an insulated support. Silver billet electrodes can also be used.5.4 Buret, 10-mL capacity, graduated in 0.05-mL intervals, with a tip that e
18、xtends approximately 120 mm (5 in.) below thestopcock.5.5 Titration Stand, preferably built as an integral part of the meter housing and provided with supports for the electrodes andelectrical stirrer, all connected to ground. No permanent change in meter reading should be noticeable upon connecting
19、 ordisconnecting the stirring motor.6. Reagents and Materials6.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Soci
20、ety, wheresuch specifications are available.4 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently highpurity to permit its use without lessening the accuracy of the determination.6.1.1 Commercially available solutions may be used in place of prepared labora
21、tory solutions, when they are certified to meetthe required concentrations.6.1.2 Alternate volumes of solutions and solvents may be prepared, when an equivalent concentration is maintained.6.2 WaterReagent grade, Type I, Specification D1193.6.3 Cadmium Sulfate, Acid Solution (150 g/L)Dissolve 150 g
22、of cadmium sulfate (3CdSO48H2O) in water. (WarningPoison. May be fatal if swallowed or inhaled. A known carcinogen (animal positive).) Add 10 mL of dilute H2SO4(WarningPoison. Causes severe burns. Harmful or fatal if swallowed or inhaled) and dilute to 1 L with water.6.4 Potassium Iodide, Standard S
23、olution (approximately 0.1 mol/L)Dissolve 17 g of KI (weigh to 0.01 g) in 100 mL of waterin a 1-L volumetric flask and dilute to 1 L. Calculate the exact molarity.6.5 Propan-2-ol( WarningFlammable. WarningUnless inhibited against it, peroxides can form in propan-2-ol whenstored in the same container
24、 that is exposed to air. When this happens and the propan-2-ol evaporates to dryness, an explosion canoccur. When peroxides are suspected, they may be removed by percolation through an activated alumina column.)6.6 Silver Nitrate, Standard Alcoholic Solution (0.1 mol/L)Dissolve 17 g of AgNO3 in 100
25、mL of water in a 1-L volumetricflask and dilute to 1 L with propan-2-ol (99 %) (see Note 1). Store in a dark bottle and standardize at intervals frequent enoughto detect a change of 0.0005 or greater in molarity.NOTE 1It is important to pass the propan-2-ol through a column of activated alumina to r
26、emove peroxides that may have formed on storage; failureto remove peroxides will lead to low results. It is not necessary to perform this step if the alcohol is tested and found free of peroxides.6.6.1 StandardizationAdd six drops of concentrated HNO3 (relative density 1.42) (WarningPoison. Causes s
27、evere burns.Harmful or fatal if swallowed or inhaled) to 100 mL of water in an appropriately sized beaker (for example, a 200-, 250-, or300-mLsize beaker is typically large enough). Remove oxides of nitrogen by boiling for 5 min. Cool to ambient temperature. Pipet5 mL of 0.1 mol/L KI solution into t
28、he beaker and titrate with the AgNO3 solution choosing the end point at the inflection of thetitration curve.6.7 Silver Nitrate, Standard Alcoholic Solution (0.010 mol/L)Prepare daily when the test is being performed by dilution ofthe 0.1 N standard. Pipet 100 mL of the 0.1 mol/L standard into a 1-L
29、 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 of Na2S in water and dilute to 1 L with water. Prepare fresh as needed.NOTE 2Anhydrous sodium sulfide is not widely available, and is expensive. An aqueous solution
30、of hydrated sodium sulfide (Na2S9H2O) at 30.6g/L is satisfactory.3 Any apparatus that will give equal or better precision is acceptable.4 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed byth
31、e American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D3227 1326.9 Sulfuric Acid, dilute. Cautiously dilute five volumes of water w
32、ith one volume of sulfuric acid (relative density 1.84).(WarningAdding the acid will generate heat: mix well. If water begins to boil, cool before adding more acid.) Note that onlylimited volumes are required because only 10 mL are needed for each litre of cadmium sulfate solution.6.10 Titration Sol
33、ventLow molecular weight mercaptans, as usually found in gasoline, are readily lost from the titrationsolution if an acidic titration solvent is used. For the determination of the higher molecular weight mercaptan as normallyencountered in kerosines, aviation turbine fuels, and distillate fuels, the
34、 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 sodium acetate trihydrate (NaC2H3O23H2O) or 1.6 g of anhydrous sodiumacetate (NaC2H3O2) in 25 mL of water free of dissolved oxygen and pou
35、r into 975 mL of propan-2-ol (99 %) (Note 1). Whennecessary, remove dissolved oxygen by purging the solution with a rapid stream of nitrogen for 10 min each day prior to use; keepprotected from the atmosphere. To minimize oxygen from dissolving in the solution during storage, an option exists to nit
36、rogenblanket the solution prior to sealing the solvent container.6.10.2 Acidic Titration SolventDissolve 2.7 g of NaC2H3O23H2O or 1.6 g of NaC2H3O2 in 20 mL of water free of dissolvedoxygen and pour into 975 mL of propan-2-ol (99 %) (Note 1) and add 4.6 mL of glacial acetic acid. When necessary, rem
37、ovedissolved oxygen by purging the solution with a rapid stream of nitrogen for 10 min each day prior to use; keep protected fromthe atmosphere. To minimize oxygen from dissolving in the solution during storage, an option exists to nitrogen blanket thesolution prior to sealing the solvent container.
38、6.11 Polishing Paper or Cloth, 620 m average particle size abrasive.7. Sampling7.1 Take the sample in accordance with Practice D4057 or Practice D4177.7.2 Methanethiol (methyl mercaptan) has a boiling point of 6.2C and may be expected to be present in light untreatedgasolines. Therefore, when the pr
39、esence of this low boiling thiol (mercaptan) is known or expected, specimen to be tested shallbe kept below 4C to prevent the loss of mercaptan from such samples.7.3 Light naphtha fractions of high thiol content (100 mg/kg) boiling below 85C have been shown to be very sensitive to thetitration tempe
40、ratures.NOTE 3Samples with a thiol content above 0.010 mass % may be analyzed by an appropriate reduction in test portion mass, ensuring that theminimum volume of titration solvent plus test portion exceeds 120 mL. If additional titration solvent is used to maintain this requirement, a similar volum
41、eshould be used for the blank titration. No precision has been determined for thiol contents above 0.01 mass %.8. Preparation of Apparatus8.1 Glass ElectrodeAfter each manual titration, or batch of titrations, in the case of automatic titration systems, wipe theelectrode with a soft, clean tissue an
42、d rinse with water. Clean the electrode at frequent intervals (at least once a week) by stirringin cold chromic acid solution ( WarningCauses severe burns. A recognized carcinogen. Strong oxidizercontact with othermaterial may cause fire. Hygroscopic. An equivalent, chromium-free cleaning solution m
43、ay be used) for a few seconds (10 smaximum). When not in use, keep lower half 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 (seeSection 12), prepare a fresh silver sulfide coating on the e
44、lectrode by the following method:8.2.1 Burnish electrode with polishing paper or cloth until a clean, polished silver surface shows.8.2.2 Place electrode in operating position and immerse it in 100 mL of titration solvent containing 8 mL of Na2S solution.8.2.3 Add slowly from a buret, with stirring,
45、 10 mL of 0.1 mol/L AgNO3 solution over a period from 10 to 15 min.8.2.4 Remove electrode from solution, wash with water, and wipe with a soft, clean tissue.8.2.5 Between manual titrations, or batches of titrations in the case of automatic titration systems, store the electrode a minimumof 5 min in
46、100 mL of titration solvent containing 0.5 mL of the 0.1 mol/L AgNO3 solution.9. Procedure9.1 Determination of DensityIf the sample is to be measured volumetrically, determine the density by Test Method D1298 orTest Method D4052 at the temperature at which the test portion will be taken, either dire
47、ctly or from the density determined ata reference temperature and converted to the transfer temperature by use of the Petroleum Measurement Tables (Guide D1250).9.2 Removal of Hydrogen SulfideTest the sample qualitatively for hydrogen sulfide (H2S) by mixing 5 mL of the sample with5 mL of the acid C
48、dSO4 solution. If no precipitate appears, proceed with the analysis of the sample as described in 9.3. If a yellowprecipitate appears, remove the H2S in the following manner: Place a quantity of the sample, three to four times that required forthe analysis, in a separatory funnel containing a volume
49、 of the acid CdSO4 solution equal to one half that of the sample and shakevigorously. Draw off and discard the aqueous phase containing the yellow precipitate. Repeat the extraction with another portionof the CdSO4 solution. Again draw off the aqueous phase, and wash the sample with three 25 to 30-mL portions of water,withdrawing the water after each washing. Filter the hydrocarbon through a rapid paper. Test a small portion of the washed sample,D3227 133such as in a test tube or vial, with a few millilitres of the CdSO4 solution as descr
