1、Designation: D 3246 05An American National StandardStandard Test Method forSulfur in Petroleum Gas by Oxidative Microcoulometry1This standard is issued under the fixed designation D 3246; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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.1. Scope*1.1 This test method covers determination of sulfur in therange from 1.5 to 100 mg/kg (ppm by mass) by
3、weight inhydrocarbon products that are gaseous at normal room tem-perature and pressure.NOTE 1The test method has been tested cooperatively only onhigh-purity ethylene gas. Precision data have not been developed for otherproducts.1.2 The values stated in SI units are to be regarded as thestandard. T
4、he values given in parentheses are for informationonly.1.3 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 and health practices and determine the applica-bility
5、 of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 1265 Practice for Sampling Liquefied Petroleum (LP)Gases (Manual Method)D 1193 Specification for Reagent WaterD 3120 Test Method for Trace Quantities of Sulfur in LightLiquid Petroleum Hydrocarbons by Oxidative Micr
6、ocou-lometryD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformanceF 307 Practice for Sampling Pressurized Gas for GasAnaly-sis2.2 Other Standards:Compressed Gas Association Booklets G-4 and G-4-1 onthe Use of Oxygen33. Summary of Tes
7、t Method3.1 A sample is injected into a combustion tube maintainedat about 800C having a flowing stream of gas containingabout 80 % oxygen and 20 % inert gas (for example, nitrogen,argon, etc.). Oxidative pyrolysis converts the sulfur to sulfurdioxide which then flows into a titration cell where it
8、reactswith triiodide ion present in the electrolyte. The triiodide thusconsumed, is coulometrically replaced and the total currentrequired to replace it is a measure of the sulfur present in thesample injected.3.2 The reaction occurring in the titration cell as sulfurdioxide enters is:I321 SO21 H2OS
9、O31 3I21 2H1(1)The triiodide ion consumed in the above reaction is gener-ated coulometrically thus:3I2I321 2e2(2)3.3 These microequivalents of triiodide (iodine) are equal tothe number of microequivalents of titratable sample ion enter-ing the titration cell.3.4 A liquid blend containing a known amo
10、unt of sulfur isused for calibration.4. Significance and Use4.1 Trace quantities of sulfur compounds in hydrocarbonproducts can be harmful to many catalytic chemical processesin which these products are used. Maximum permissible levelsof total sulfur are normally included in specifications for suchh
11、ydrocarbons. It is recommended that this test method be usedto provide a basis for agreement between two laboratorieswhen the determination of sulfur in hydrocarbon gases isimportant.4.2 On liquefied petroleum gas, total volatile sulfur ismeasured on an injected gas sample. For such material a liqui
12、dsample must be used to measure total sulfur.5. Interferences5.1 This test method is applicable in the presence of totalhalide concentrations of up to 10 times the sulfur level and totalnitrogen content of up to 1.0 %. Free nitrogen does notinterfere.1This test method is under the jurisdiction of AS
13、TM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1973. Last previous edition approved in 1996 as D 324696.2For referenced ASTM standards, v
14、isit 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.3Available from Compressed Gas Association, 1235 Jefferson Davis Hwy.,Arlington, VA 22202.1*A
15、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.5.2 This test method is not applicable in the presence oftotal heavy metal concentrations (for example, Ni, V, Pb, etc.)in
16、excess of 500 mg/kg.NOTE 2To attain the quantitative detectability that the method iscapable of, stringent techniques should be employed and all possiblesources of sulfur contamination must be eliminated.6. Apparatus4,56.1 Pyrolysis FurnaceThe sample should be pyrolyzed inan electric furnace having
17、at least two separate and indepen-dently controlled temperature zones, the first being an inletsection that can maintain a temperature sufficient to volatilizeall the organic sample. The second zone shall be a pyrolysissection that can maintain a temperature sufficient to pyrolyzethe organic matrix
18、and oxidize all the organically bound sulfur.A third outlet temperature zone is optional.6.1.1 Pyrolysis furnace temperature zones for light liquidpetroleum hydrocarbons should be variable as follows:Inlet zone up to at least 700CCenter pyrolysis zone up to at least 1000COutlet zone (optional) up to
19、 at least 800C6.2 Pyrolysis Tube, fabricated from quartz and constructedin such a way that a sample, which is vaporized completely inthe inlet section, is swept into the pyrolysis zone by an inert gaswhere it mixes with oxygen and is burned. The inlet end of thetube shall hold a septum for syringe e
20、ntry of the sample andside arms for the introduction of oxygen and inert gases. Thecenter or pyrolysis section should be of sufficient volume toassure complete pyrolysis of the sample.6.3 Titration Cell, containing a sensor-reference pair ofelectrodes to detect changes in triiodide ion concentration
21、 anda generator anode-cathode pair of electrodes to maintainconstant triiodide ion concentration and an inlet for a gaseoussample from the pyrolysis tube. The sensor electrode shall beplatinum foil and the reference electrode platinum wire insaturated triiodide half-cell. The generator anode and cat
22、hodehalf-cell shall also be platinum. The titration cell shall requiremixing, which can be accomplished through the use of amagnetic stirring bar, stream of inert gas, or other suitablemeans. (WarningExcessive speed will decouple the stirringbar, causing it to rise in the cell and damage the electro
23、des. Thecreation of a slight vortex is adequate.)6.4 Microcoulometer, having variable attenuation gain con-trol, and capable of measuring the potential of the sensing-reference electrode pair, and comparing this potential with abias potential, amplifying the potential difference, and applyingthe amp
24、lified difference to the working-auxiliary electrode pairso as to generate a titrant. Also the microcoulometer outputvoltage signal shall be proportional to the generating current.6.5 Recorder, having a sensitivity of at least 0.1 mV/25 mmwith chart speeds of 12 to 25 mm/min. Use of a suitableelectr
25、onic or mechanical integrator is recommended but op-tional.6.6 Sampling Syringe for LiquidA microlitre syringe of10-L capacity capable of accurately delivering 1 to 10 L ofliquid blend into the pyrolysis tube 75 mm by 24-gage needlesare recommended to reach the inlet zone of the pyrolysisfurnace.NOT
26、E 3Since care should be taken not to overload the pyrolyzingcapacity of the tube by too fast a sample injection rate, means should beprovided for controlling the sample addition rate (0.1 to 0.2 L/s).6.7 Sampling Syringe for GasA gas syringe capable ofdelivering up to 5 cm3of gas sample into the pyr
27、olysis furnace.A 25-mm by 28-gage needle should be attached to the syringe.6.8 Exit Tube Insert, with quartz wool.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifi
28、cations of the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.6Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2
29、 Purity of WaterThe water used in preparing the cellelectrolyte should be demineralized or distilled or both. Waterof high purity is essential. See Specification D 1193 for reagentwater.NOTE 4Distilled water obtained from an all borosilicate glass still, fedfrom a demineralizer, has proven very sati
30、sfactory.7.3 Acetic Acid (rel dens 1.05)Concentrated acetic acid(CH3COOH). (WarningMay cause burns. See A1.1.)7.4 Argon, Helium, or Nitrogen, high-purity grade (HP)used as the carrier gas. High-purity grade gas has a minimumpurity of 99.995 %. (WarningHazardous pressure. SeeA1.2.)7.5 Cell Electrolyt
31、e SolutionDissolve 0.5 g of potassiumiodide (KI) and 0.6 g of sodium azide (NaN3) in approximately500 mL of high-purity water, add 5 mL of acetic acid (CH3COOH) and dilute to 1000 mL.NOTE 5Bulk quantities of the electrolyte should be stored in a darkbottle or in a dark place and be prepared fresh at
32、 least every 3 months.7.6 Gas RegulatorsTwo-stage gas regulators must beused on the reactant and carrier gas.7.7 Iodine(I2), 20 mesh or less, for saturated referenceelectrode. (WarningToxic fumes. See A1.3.)7.8 Isooctane (2,2,4-trimethyl pentane)A high purityisooctane of pesticide quality has been f
33、ound satisfactory.(WarningCombustible, very harmful. See A1.4.)4The apparatus described in 6.1 to 6.5 inclusive, is similar in specifications toequipment available from Tekmar-Dohrmann, 7143 E. Kemper Rd., Cincinnati, OH524549. For further detailed discussions, in equipment, see: PreprintsDivision o
34、fPetroleum Chemistry, American Chemical Society, Vol 1, No. 3, Sept. 712, 1969,p. B232 “Determination of Sulfur, Nitrogen, and Chlorine in Petroleum byMicrocoulometry,” by Harry V. Drushel.5Tekmar-Dohrmann is the sole source of supply of the apparatus known to thecommittee at this time. If you are a
35、ware of alternative suppliers, please provide thisinformation to ASTM Headquarters. Your comments will receive careful consider-ation at a meeting of the responsible technical committee,1which you may attend.6Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Wash
36、ington, 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.D3246052N
37、OTE 6The most reliable solvent is a sulfur-free form of the sampletype to be analyzed. Alternatively, use a high-purity form of cyclohexaneboiling point 80C (176F), isooctane (2,2,4-trimethyl pentane) boilingpoint, 99.3C (211F), or hexadecane boiling point, 287.5C (549.5F).7.9 n-Butyl Sulfide (CH3CH
38、2CH2CH2)2S.7.10 Oxygen, high-purity grade (HP),6used as the reactantgas. (WarningOxygen accelerates combustion. See A1.5.)7.11 Potassium Iodide (KI), fine granular.7.12 Sodium Azide (NaN3), fine granular. (WarningHighly toxic. Can react violently with shock, friction or heat.)7.13 Sulfur, Standard S
39、olution (approximately 30 mg/kg)Pipet 10 mL of sulfur stock solution (reagent 7.14) into a100-mL volumetric flask and dilute to volume with isooctane.NOTE 7The analyst may choose other sulfur compounds for standardsappropriate to sample boiling range and sulfur type which cover theconcentration rang
40、e of sulfur expected.7.14 Sulfur, Standard Stock Solution (approximately 300ppm (g/g)Weigh accurately 0.5000 g of n-butyl sulfide intoa tared 500-mL volumetric flask. Dilute to the mark withisooctane and reweigh.S, mg/kg 5gof n2butyl sulfide 3 0.2187 3 106gofn2butyl sulfide 1 solvent!(3)7.15 Calibra
41、tion Check Sample(s)portions of one or moreliquid petroleum or product standards of known sulfur contentand not used in the generation of the calibration curve. Acalibration check sample or samples shall be used to verify thevalidity of the calibration curve as described in Section 10.7.16 Quality C
42、ontrol (QC) Sample(s)preferably portionsof one or more gaseous petroleum materials that are stable andrepresentative of the samples of interest. These QC samplescan be used to verify that the testing process is in statisticalcontrol as described in Section 12.8. Sampling8.1 Supply samples to the lab
43、oratory in high-pressuresample cylinders, obtained using the procedures described inPractice D 1265 and Practice F 307.8.2 Because of the reactivity of most sulfur compounds, ithas been found desirable to use TFE-fluorocarbon-coatedcylinders or other specially treated sample containers. Testsamples
44、as soon as possible after receipt.9. Preparation of Apparatus9.1 Carefully insert the quartz pyrolysis tube in the pyroly-sis furnace and connect the reactant and carrier gas lines.9.2 Add the electrolyte solution to the titration cell and flushseveral times. Maintain an electrolyte level of18 to14
45、in. (3.2to 6.4 mm) above the platinum electrodes.9.3 Place the heating tape on the inlet of the titration cell.9.4 Place an exit tube insert packed loosely with about 1 in.(25 mm) of quartz wool into the exit end of the pyrolysis tube.The quartz wool end of the exit tube should be in the hot zoneof
46、the pyrolysis tube.9.5 Depending upon the instrumentation used, set up thetitration cell to allow for adequate mixing of its contents andconnect the cell inlet to the outlet end of the pyrolysis tube.Position the platinum foil electrodes (mounted on the movablecell head) so that the gas inlet flow i
47、s parallel to the electrodeswith the generator anode adjacent to the generator cathode.Assemble and connect the coulometer and recorder (integratoroptional) as designed or in accordance with the manufacturersinstructions. Fig. X1.2 illustrates the typical assembly and gasflow through a coulometric a
48、pparatus.9.5.1 Turn the heating tape on.9.6 Adjust the flow of the gases, the pyrolysis furnacetemperature, titration cell, and the coulometer to the desiredoperating conditions. Typical operational conditions are givenin Table 1.10. Calibration and Standardization10.1 Prepare a series of calibratio
49、n standards covering therange of sulfur concentration expected. Follow instructions in7.13, 7.14, or dilute to appropriate level with isooctane.10.2 Adjust the operational parameters (9.5).NOTE 8A ratio of 80 % oxygen to 20 % inert gas gives an acceptablerecovery, and permits the use of a larger sample and a more rapid-chargingrate.10.3 The sample size can be determined either volumetri-cally or by mass. The sample size should be 80 % or less of thesyringe capacity.10.3.1 Volumetric measurement can be obtained by fillingthe syri
