1、Designation: D 3120 06e1An American National StandardStandard Test Method forTrace Quantities of Sulfur in Light Liquid PetroleumHydrocarbons by Oxidative Microcoulometry1This standard is issued under the fixed designation D 3120; the number immediately following the designation indicates the year o
2、foriginal 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 use by agencies of the Department
3、 of Defense.e1NOTEEq X2.2 was corrected editorially in April 2007.1. Scope*1.1 This test method covers the determination of sulfurconcentration in the range from 3.0 to 1000 mg/kg in lightliquid hydrocarbons boiling in the range from 26 to 274C (80to 525F).1.2 Other materials falling within the dist
4、illation rangespecified in 1.1, but having sulfur concentrations above 1000mg/kg, may be tested using appropriate dilutions to bring themwithin the specified limit. In addition, sample types that may beoutside the specified distillation range, such as diesels andbiodiesels, may be analyzed by this t
5、est method.1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are provided forinformation only. The preferred units are milligrams perkilogram (mg/kg).1.4 This standard does not purport to address all of thesafety concerns, if any, associated with it
6、s 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 specific hazardstatements, see Sections 7-9.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification f
7、or Reagent WaterD 1298 Test Method for Density, Relative Density (SpecificGravity), or API Gravity of Crude Petroleum and LiquidPetroleum Products by Hydrometer MethodD 4052 Test Method for Density and Relative Density ofLiquids by Digital Density MeterD 4057 Practice for Manual Sampling of Petroleu
8、m andPetroleum ProductsD 4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD 6299 Practice for Applying Statistical Quality AssuranceTechniques to Evaluate Analytical Measurement SystemPerformance2.2 OSHA Regulations:OSHA Regulations 29 CFR, paragraphs 1910.1000 and1910.120033.
9、Summary of Test Method3.1 A liquid sample is introduced into a pyrolysis tubemaintained at a temperature between 900-1200C, having aflowing stream of gas containing 50-80% oxygen and 20-50%inert gas (for example, argon, helium, etc.) Oxidative pyrolysisconverts the sulfur to sulfur dioxide, which th
10、en flows into atitration cell where it reacts with triiodide ion present in theelectrolyte. The triiodide ion consumed is coulometricallyreplaced and the total current (I 3 t) required to replace it is ameasure of the sulfur present in the sample.3.2 The reaction occurring in the titration cell as s
11、ulfurdioxide enters is:I321 SO21 H2OSO31 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 ion (iodine) areequal to the number of microequivalents of titratable SO2ionentering the titration cell.4. Sig
12、nificance and Use4.1 This test method is used to determine the concentrationof sulfur in light liquid hydrocarbons, gasoline, and diesels and1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on
13、 Elemental Analysis.Current edition approved Dec. 1, 2006. Published January 2007. Originallyapproved in 1972. Last previous edition approved in 2003 as D 312003a.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book
14、 of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from U.S. Government Printing Office, Superintendent of Docu-ments, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.1*A Summary of Changes section appears at the end of this
15、standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.their additives, where such concentrations of sulfur can bedetrimental to their production, performance, and use. Themeasurement of sulfur in the production and final product of
16、gasoline and diesel is required for both regulatory purposes andto ensure maximum life expectancy of catalytic convertersused in the automotive industry.5. Interferences5.1 This test method is applicable in the presence of totalhalide concentrations of up to 10 times the sulfur level and totalnitrog
17、en concentrations of up to 1000 times the sulfur level.5.1.1 Stringent techniques shall be employed and all pos-sible sources of sulfur contamination eliminated to attain thequantitative detectability capable with this test method.5.2 This test method is not applicable in the presence oftotal heavy
18、metal concentrations (for example, Ni, V, Pb, etc.)in excess of 500 mg/kg (ppm).6. Apparatus6.1 The configuration of the pyrolysis tube and furnace maybe constructed as is desirable as long as the operating param-eters are met. Fig. 1 is typical of apparatus currently in use.6.2 A typical assembly a
19、nd oxidative gas flow through acoulometric apparatus for the determination of trace sulfur isshown in Fig. 2.6.3 FurnaceMaintained at a temperature sufficient tocompletely pyrolyze the organic matrix, 900-1200C, andcompletely oxidize the organically bound sulfur to SO2.Independently controlled inlet
20、 and outlet temperature zones areoptional. An electrical furnace has been found suitable to use.6.4 Pyrolysis TubeFabricated from quartz and constructedso the sample is vaporized in a heated zone before the furnaceand swept into the oxidation zone by an inert carrier gas, wherethe vaporized sample m
21、ixes with oxygen and is pyrolyzed. Theinlet shall be constructed large enough to accommodate asample boat completely into the oxidation zone of the pyrolysistube or allow the direct injection of the sample into the heatedzone before the furnace. The pyrolysis tube shall have sidearms for the introdu
22、ction of oxygen and inert carrier gas.6.5 Titration CellConsisting of a sensor/reference pair ofelectrodes to detect changes in triiodide ion concentration, agenerator anode-cathode pair of electrodes to maintain aconstant triiodide ion concentration, an inlet for gaseoussample from the pyrolysis tu
23、be, and an outlet to vent the exitgases from the titration cell. The reference electrode can beeither an Ag/AgCl double junction reference electrode or aplatinum wire in a saturated triiodide half-cell. The sensorelectrode and both the anode and cathode electrodes of thegenerator are made of platinu
24、m. The titration cell shall requiremixing, which can be accomplished with a magnetic stir bar,stream of gas, or other suitable means. Other sensor andreference electrodes may be used if they meet the performancecriteria of this test method.NOTE 1Take care not to use excessive stirring and possibly d
25、amagethe electrodes with the stir bar. The creation of a slight vortex is adequate.6.6 MicrocoulometerThe apparatus microcoulometer,with variable attenuation and gain control, shall be capable ofmeasuring the potential of the sensing-reference electrode pairand compare this potential to a bias poten
26、tial. By amplifyingthis potential difference and applying the difference to aworking-auxiliary pair of electrodes (the generator), a titrant isgenerated. The microcoulometer integrates the amount ofcurrent used, calculates the equivalent mass of sulfur titratedand calculates the concentration of sul
27、fur in the sample.6.7 Strip Chart Recorder (Optional)To monitor and plotthe mV potential of the titration cell during the analysis.6.8 Flow ControlThe apparatus shall be equipped withflow controllers capable of maintaining a constant supply ofoxygen and inert carrier gas.6.9 Dryer TubeThe oxidation
28、of samples produces watervapor which, if allowed to condense between the exit of thepyrolysis tube and the titration cell, will absorb the SO2formedand result in low recovery. Steps shall be taken to prevent suchan occurrence. This is easily accomplished by placing aphosphoric acid dehydration tube
29、between the titration cell andexit of the pyrolysis tube. Other approaches, such as heatingtape or permeation tubes, can be used if precision and accuracyare not degraded.6.10 Sampling SyringesMicrolitre syringes able to accu-rately deliver 5 to 80 mL of sample are required. The volumeinjected shoul
30、d not exceed 80% of a syringes capacity.6.11 Sample Inlet SystemEither type of sample inletsystem described can be used.6.11.1 Boat Inlet SystemThe inlet of the pyrolysis tube issealed to the boat inlet system. The system provides a cooledarea before the furnace for the sample boat prior to quantita
31、tiveintroduction of sample into the boat and is purged with the inertcarrier gas. The boat driving mechanism then fully inserts theboat into the oxidation zone of the furnace. The drive mecha-nism shall advance and retract the sample boat into and out ofthe oxidation zone of the furnace at a control
32、led and repeatablerate (see Note 2).6.11.1.1 Boat Inlet Cooler (Optional)Sample volatilityand injection volume may require an apparatus capable ofcooling the sample boat prior to sample introduction. Thermo-electric coolers (peltier) or recirculating refrigerated liquiddevices are strongly recommend
33、ed. Switching sample boatsbetween each analysis may prove effective, provided samplesize is not too large.6.11.1.2 Sample BoatsQuartz or other suitable materialwhich will not react with the sample or sulfur compoundsbeing analyzed and able to withstand the temperatures ex-tremes of the test method.6
34、.11.2 Syringe Inlet SystemThe system shall deliver aquantitative amount of sample from a microlitre syringe into aheated area before the oxidation zone of the pyrolysis tube ata controlled and repeatable rate. There the sample is volatilizedFIG. 1 Typical Pyrolysis TubeD312006e12and the inert carrie
35、r gas stream purging the heated areatransports the volatilized sample into the oxidation zone of thepyrolysis furnace. An adjustable drive mechanism capable ofinjecting the sample from a microlitre syringe at a constant ratebetween 0.5 to 1.0 mL/s is required (see Note 2).NOTE 2Take care not to intr
36、oduce the sample too fast into theoxidation zone of the furnace and overload the combustion capacity of thepyrolysis tube. Program the sample inlet system to deliver the sample ata sufficiently controlled and repeatable rate to prevent any incompletecombustion by-products (coke or soot) from forming
37、 at the exit of thepyrolysis tube.6.12 BalanceWith a weighing precision of 60.01 mg.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 specifications of the Commit-tee on A
38、nalytical 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 lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwi
39、se indicated, referencesto water shall be understood to mean reagent water conformingto Specification D 1193, Type II and III.7.3 Quartz WoolGrade fine.7.4 Acetic Acid (CH3COOH)Glacial acetic acid withspecific gravity = 1.05. (WarningPoison. Corrosive. Com-bustible. May be fatal if swallowed. Causes
40、 severe burns.Harmful if inhaled.)7.5 Phosphoric Acid (85 % w/w)Orthophosphoric acid(H3PO4). (WarningPoison. Corrosive. May be fatal if swal-lowed. Causes severe burns.)7.6 Inert GasArgon or helium, high purity grade (HP),5used as carrier gas. (WarningCompressed gas under highpressure. Gas reduces o
41、xygen available for breathing.)7.7 OxygenHigh purity grade (HP),5used as the reactantgas. (WarningOxygen vigorously accelerates combustion.)7.8 Gas RegulatorsTwo-stage gas regulators shall be usedfor the oxygen and inert carrier gas.7.9 Cell Electrolyte SolutionDissolve 0.5 g of potassiumiodide (KI)
42、 and 0.6 g of sodium azide (NaN3) in approximately500 mL of high-purity water, add 6 mL of glacial acetic acid(CH3COOH), and dilute to 1000 mL or follow the manufac-turers specifications.NOTE 3Take care to store bulk quantities of the electrolyte in a darkplace. It is recommended to prepare fresh el
43、ectrolyte at least every threemonths.7.10 Sodium Azide (NaN3), fine granular. (WarningToxic. Causes eye and skin irritation. Explosive.)7.11 Potassium Iodide (KI), fine granular.7.12 Potassium Chloride (KCl), fine granular. Used for the1M Ag/AgCl double junction reference electrode.7.13 Potassium Ni
44、trate (KNO3), fine granular. Used for the1M Ag/AgCl double junction reference electrode.7.14 Iodine (I), 20 mesh or less, for saturated referenceelectrode.7.15 Toluene, Xylenes, IsooctaneReagent grade. (Othersolvents similar to those occurring in the samples beinganalyzed are acceptable.)Asolvent bl
45、ank correction is requireddue to the inherent sulfur present in the solvents used forstandard preparation and sample dilution. (WarningFlammable solvents. Harmful if inhaled. Vapors may causeflash fire.)NOTE 4The use of solvents with non-detectable levels of sulfurrelative to the sulfur content in t
46、he sample can make the solvent blankcorrection unnecessary.7.16 DibenzothiopheneFW 184.26, 17.399 % (mass/mass) S (see Note 4).4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American
47、Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.5High-purity grade gas has a minimum purity of 99.995 %.FIG. 2 Flow Diagram for Typical Co
48、ulometric Apparatus for Trace Sulfur DeterminationD312006e137.17 n-Butyl SulfideFW 146.29, 21.92 % (mass/mass) S(see Note 4).7.18 Thionaphthene (Benzothiophene)FW 134.20,23.90% (mass/mass) S (see Note 4).NOTE 5A correction for chemical impurity can be applied if deemednecessary.7.19 Sulfur, Standard
49、 Solution (approximately 1000 mg-S/mL)Prepare a stock solution by accurately weighing approxi-mately 0.5748 g of dibenzothiophene or 0.4652 g of n-butylsulfide or 0.4184 g of thionaphathene into a tared 100 mL, typeA volumetric flask. Dilute to volume with a selected solvent.This stock can then be further diluted to prepare sulfur workingand calibration standards as outlined in Tables 1-3 (see Notes6-8).g2S/mL 5A 3 B 3 C 3 106100 mL(3)where:A = grams of standard.B = weight of fraction sulfur (S) in standard.C = weight of fraction stand
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