1、Designation: D 3120 08An 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 ofo
2、riginal 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 Department of
3、 Defense.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 and fuels with oxygenates boiling in therange from 26 to 274C (80 to 525F).NOTE 1Preliminary data has shown that this test method is alsoapplicable t
4、o the determination of sulfur in denatured fuel ethanol(Specification D 4806), automotive spark ignition engine fuel (Specifica-tion D 4814), Ed75Ed85 (Specification D 5798) or gasoline-oxygenatefuel blends with greater than 10% ethanol. However, the precision forthese materials has not been determi
5、ned. Subcommittee D02.03 isundertaking activities to obtain precision statements for these materials.1.2 Other materials falling within the distillation rangespecified in 1.1, but having sulfur concentrations above 1000mg/kg, may be tested using appropriate dilutions to bring themwithin the specifie
6、d limit. In addition, sample types that may beoutside the specified distillation range, such as diesels andbiodiesels, may be analyzed by this test method.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard. The preferred units
7、are milligrams per kilogram(mg/kg).1.4 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 of regulatory limit
8、ations prior to use.For specific hazardstatements, see Sections 7-9.2. Referenced Documents2.1 ASTM Standards:2D 1193 Specification for Reagent WaterD 1298 Test Method for Density, Relative Density (SpecificGravity), or API Gravity of Crude Petroleum and LiquidPetroleum Products by Hydrometer Method
9、D 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 4806 Specification for Denatured Fuel Ethanol for Blend-ing with Gaso
10、lines for Use as Automotive Spark-IgnitionEngine FuelD 4814 Specification forAutomotive Spark-Ignition EngineFuelD 5798 Specification for Fuel Ethanol (Ed75-Ed85) forAutomotive Spark-Ignition EnginesD 6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate
11、 AnalyticalMeasurement System Performance2.2 OSHA Regulations:OSHA Regulations 29 CFR, paragraphs 1910.1000 and1910.120033. 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% oxyg
12、en and 20-50%inert gas (for example, argon, helium, etc.) Oxidative pyrolysisconverts the sulfur to sulfur dioxide, which then 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)
13、required to replace it is ameasure of the sulfur present in the sample.3.2 The reaction occurring in the titration cell as sulfurdioxide enters is:I321 SO21 H2OSO31 3I21 2H1(1)The triiodide ion consumed in the above reaction is gener-ated coulometrically thus:3I2I321 2e2(2)1This test method is under
14、 the jurisdiction of ASTM Committee D02 onPetroleum Products and Lubricants and is the direct responsibility of SubcommitteeD02.03 on Elemental Analysis.Current edition approved Dec. 15, 2008. Published February 2009. Originallyapproved in 1972. Last previous edition approved in 2006 as D 3120061.2F
15、or 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.3Available from U.S. Government Printing Office, Superintendent
16、 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 standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3 These microequivalents of triiodide io
17、n (iodine) areequal to the number of microequivalents of titratable SO2ionentering the titration cell.4. Significance and Use4.1 This test method is used to determine the concentrationof sulfur in light liquid hydrocarbons, gasoline, and diesels andtheir additives, where such concentrations of sulfu
18、r can bedetrimental to their production, performance, and use. Themeasurement of sulfur in the production and final product ofgasoline and diesel is required for both regulatory purposes andto ensure maximum life expectancy of catalytic convertersused in the automotive industry.5. Interferences5.1 T
19、his test method is applicable in the presence of totalhalide concentrations of up to 10 times the sulfur level and totalnitrogen 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 the
20、quantitative detectability capable with this test method.5.2 This test method is not applicable in the presence oftotal heavy 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 de
21、sirable as long as the operating param-eters are met. Fig. 1 is typical of apparatus currently in use.6.2 A typical assembly and oxidative gas flow through acoulometric apparatus for the determination of trace sulfur isshown in Fig. 2.6.3 FurnaceMaintained at a temperature sufficient tocompletely py
22、rolyze the organic matrix, 900-1200C, andcompletely oxidize the organically bound sulfur to SO2.Independently controlled inlet 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 vapor
23、ized in a heated zone before the furnaceand swept into the oxidation zone by an inert carrier gas, wherethe vaporized sample mixes 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
24、 direct injection of the sample into the heatedzone before the furnace. The pyrolysis tube shall have sidearms for the introduction 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-
25、cathode pair of electrodes to maintain aconstant triiodide ion concentration, an inlet for gaseoussample from the pyrolysis tube, 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 sa
26、turated triiodide half-cell. The sensorelectrode and both the anode and cathode electrodes of thegenerator are made of platinum. 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
27、 be used if they meet the performancecriteria of this test method.NOTE 2Take care not to use excessive stirring and possibly damagethe electrodes with the stir bar. The creation of a slight vortex is adequate.6.6 MicrocoulometerThe apparatus microcoulometer,with variable attenuation and gain control
28、, shall be capable ofmeasuring the potential of the sensing-reference electrode pairand compare this potential to a bias potential. By amplifyingthis potential difference and applying the difference to aworking-auxiliary pair of electrodes (the generator), a titrant isgenerated. The microcoulometer
29、integrates the amount ofcurrent used, calculates the equivalent mass of sulfur titratedand calculates the concentration of sulfur 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 equi
30、pped withflow controllers capable of maintaining a constant supply ofoxygen and inert carrier gas.6.9 Dryer TubeThe oxidation 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
31、. Steps shall be taken to prevent suchan occurrence. This is easily accomplished by placing aphosphoric acid dehydration tube 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.6.1
32、0 Sampling SyringesMicrolitre syringes able to accu-rately deliver 5 to 80 mL of sample are required. The volumeinjected should 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 tub
33、e issealed to the boat inlet system. The system provides a cooledarea before the furnace for the sample boat prior to quantitativeintroduction 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
34、. The drive mecha-nism shall advance and retract the sample boat into and out ofthe oxidation zone of the furnace at a controlled and repeatablerate (see Note 3).6.11.1.1 Boat Inlet Cooler (Optional)Sample volatilityand injection volume may require an apparatus capable ofcooling the sample boat prio
35、r to sample introduction. Thermo-electric coolers (peltier) or recirculating refrigerated liquiddevices are strongly recommended. Switching sample boatsbetween each analysis may prove effective, provided samplesize is not too large.FIG. 1 Typical Pyrolysis TubeD31200826.11.1.2 Sample BoatsQuartz or
36、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.6.11.2 Syringe Inlet SystemThe system shall deliver aquantitative amount of sample from a microlitre syringe into aheated area before the
37、oxidation zone of the pyrolysis tube ata controlled and repeatable rate. There the sample is volatilizedand the inert carrier gas stream purging the heated areatransports the volatilized sample into the oxidation zone of thepyrolysis furnace. An adjustable drive mechanism capable ofinjecting the sam
38、ple from a microlitre syringe at a constant ratebetween 0.5 to 1.0 mL/s is required (see Note 3).NOTE 3Take care not to introduce 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
39、 ata sufficiently controlled and repeatable rate to prevent any incompletecombustion by-products (coke or soot) from forming 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 t
40、ests. Unless otherwise 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 ofsuf
41、ficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity of WaterUnless otherwise 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
42、)Glacial acetic acid withspecific gravity = 1.05. (WarningPoison. Corrosive. Com-bustible. May be fatal if swallowed. Causes 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 Ine
43、rt GasArgon or helium, high purity grade (HP),5used as carrier gas. (WarningCompressed gas under highpressure. Gas reduces oxygen available for breathing.)7.7 OxygenHigh purity grade (HP),5used as the reactantgas. (WarningOxygen vigorously accelerates combustion.)7.8 Gas RegulatorsTwo-stage gas regu
44、lators shall be usedfor the oxygen and inert carrier gas.7.9 Cell Electrolyte SolutionDissolve 0.5 g of potassiumiodide (KI) 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 spec
45、ifications.NOTE 4Take care to store bulk quantities of the electrolyte in a darkplace. It is recommended to prepare fresh electrolyte at least every threemonths.7.10 Sodium Azide (NaN3), fine granular. (WarningToxic. Causes eye and skin irritation. Explosive.)7.11 Potassium Iodide (KI), fine granula
46、r.7.12 Potassium Chloride (KCl), fine granular. Used for the1M Ag/AgCl double junction reference electrode.7.13 Potassium Nitrate (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
47、, IsooctaneReagent grade. (Othersolvents similar to those occurring in the samples beinganalyzed are acceptable.)Asolvent blank correction is requireddue to the inherent sulfur present in the solvents used forstandard preparation and sample dilution. (WarningFlammable solvents. Harmful if inhaled. V
48、apors may causeflash fire.)4Reagent Chemicals, American Chemical Society Specifications, AmericanChemical 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 t
49、he 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 Coulometric Apparatus for Trace Sulfur DeterminationD3120083NOTE 5The use of solvents with non-detectable levels of sulfurrelative to the sulfur content in the sample can make the solvent blankcorrection unnecessary.7.16 DibenzothiopheneFW 184.26, 17.399 % (mass/mass) S (see Note 5).7.17 n-Butyl SulfideFW 146.29, 21.92 % (mass/mass) S(see Not
