1、Designation: D3120 08 (Reapproved 2014)Standard Test Method forTrace Quantities of Sulfur in Light Liquid PetroleumHydrocarbons by Oxidative Microcoulometry1This standard is issued under the fixed designation D3120; the number immediately following the designation indicates the year oforiginal adopt
2、ion 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. Department of Defense
3、.1. Scope1.1 This test method covers the determination of sulfurconcentration in the range from 3.0 to 1000 mgkg 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 to the dete
4、rmination of sulfur in denatured fuel ethanol(Specification D4806), automotive spark ignition engine fuel (Specifica-tion D4814), Ed75Ed85 (Specification D5798) or gasoline-oxygenatefuel blends with greater than 10% ethanol. However, the precision forthese materials has not been determined. Subcommi
5、ttee 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 specified limit. In a
6、ddition, 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 are milligram
7、s 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 limitations prior
8、to use.For specific hazardstatements, see Sections 79.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1298 Test Method for Density, Relative Density, or APIGravity of Crude Petroleum and Liquid Petroleum Prod-ucts by Hydrometer MethodD4052 Test Method for Density, Re
9、lative Density, and APIGravity of Liquids by Digital Density MeterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum ProductsD4806 Specification for Denatured Fuel Ethanol for Blend-ing with Gasolines for Use as Automo
10、tive Spark-IgnitionEngine FuelD4814 Specification for Automotive Spark-Ignition EngineFuelD5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition EnginesD6299 Practice for Applying Statistical Quality Assuranceand Control Charting Techniques to Evaluate AnalyticalMeas
11、urement 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 to 1200C, having aflowing stream of gas containing 50 to 80% oxygen and 20
12、 to50% inert gas (for example, argon, helium, and so forth).Oxidative pyrolysis converts the sulfur to sulfur dioxide, whichthen flows into a titration cell where it reacts with triiodide ionpresent in the electrolyte. The triiodide ion consumed iscoulometrically replaced and the total current (I t)
13、 required toreplace it is a measure of the sulfur present in the sample.3.2 The reaction occurring in the titration cell as sulfurdioxide enters is:I321SO21H2OSO313I212H1(1)1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products, Liquid Fuels, and Lubricants and is the
14、 direct responsibility ofSubcommittee D02.03 on Elemental Analysis.Current edition approved May 1, 2014. Published July 2014. Originally approvedin 1972. Last previous edition approved in 2008 as D3120 08. DOI: 10.1520/D3120-08R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
15、 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 ofDocuments, 732 N. Capitol St., NW, Mail Stop: SDE, Washington, D
16、C 20401.*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 States1The triiodide ion consumed in the above reaction is gener-ated coulometrically thus:3I2I3212e2(2)3.3 These microe
17、quivalents of triiodide ion (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 su
18、ch concentrations of sulfur 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 indu
19、stry.5. Interferences5.1 This 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 contaminatio
20、n eliminated to attain thequantitative 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, andso forth) in excess of 500 mg/kg (ppm).6. Apparatus6.1 The configuration of the pyrolysis tube and
21、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 and oxidative gas flow through acoulometric apparatus for the determination of trace sulfur isshown in Fig. 2.6.3 FurnaceMaintained at a temp
22、erature sufficient tocompletely pyrolyze the organic matrix, 900 to 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 Tube Fabricated from quartz
23、 and con-structed so the sample is vaporized in a heated zone before thefurnace and swept into the oxidation zone by an inert carriergas, where the vaporized sample mixes with oxygen and ispyrolyzed. The inlet shall be constructed large enough toaccommodate a sample boat completely into the oxidatio
24、n zoneof the pyrolysis tube or allow the direct injection of the sampleinto the heated zone before the furnace. The pyrolysis tubeshall have side arms for the introduction of oxygen and inertcarrier gas.6.5 Titration Cell Consisting of a sensor/reference pair ofelectrodes to detect changes in triiod
25、ide ion concentration, agenerator anode-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 refer
26、ence electrode or aplatinum wire in a saturated 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.
27、Other sensor andreference electrodes may 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 Microcoulometer The apparatus microcoulometer,w
28、ith variable attenuation and gain control, 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
29、titrant isgenerated. The microcoulometer 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
30、.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 of samples produces watervapor which, if allowed to condense between the exit of thepyrolysis tube and the titration cell, will abso
31、rb the SO2formedand result in low recovery. 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
32、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 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
33、 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 quantitativeintroduction of sample into the boat and is purged with the inertcarrier gas. The boat driving mechanism then fully inserts the
34、boat 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 controlled and repeatablerate (see Note 3).FIG. 1 Typical Pyrolysis TubeD3120 08 (2014)26.11.1.1 Boat Inlet Cooler (Optional)Sample volati
35、lityand 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 recommended. Switching sample boatsbetween each analysis may prove effective, provided samplesi
36、ze 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.6.11.2 Syringe Inlet SystemThe system shall deliver aquantitative amount of sample from
37、 a microlitre syringe into aheated area before the 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 adj
38、ustable 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 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. Pr
39、ogram 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 at the exit of thepyrolysis tube.6.12 BalanceWith a weighing precision of 60.01 mg.7. Reagents and Materials7.1 Purity of Re
40、agentsReagent 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 Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provide
41、d 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 otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Specification D1193, Type II and III.
42、7.3 Quartz WoolGrade fine.7.4 Acetic Acid (CH3COOH)Glacial acetic acid with spe-cific gravity = 1.05. (WarningPoison. Corrosive. Combus-tible. May be fatal if swallowed. Causes severe burns. Harmfulif inhaled.)7.5 Phosphoric Acid (85 % w/w)Orthophosphoric acid(H3PO4). (WarningPoison. Corrosive. May
43、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 oxygen available for breathing.)7.7 OxygenHigh purity grade (HP),5used as the reactantgas. (WarningOxygen vigorously accelera
44、tes 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) and 0.6 g of sodium azide (NaN3) in approximately500 mL of high-purity water, add 6 mL of glacial acetic acid(CH3COOH), and
45、 dilute to 1000 mL or follow the manufac-turers specifications.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.
46、 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 Nitrate (KNO3), fine granular. Used for the1M Ag/AgCl double junction reference electrode.4Reagent Chemicals, American Chemica
47、l 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 the United States Pharmacopeiaand National Formulary, U.S. Pharm
48、acopeial 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 DeterminationD3120 08 (2014)37.14 Iodine (I), 20 mesh or less, for saturated referenceelectrode.7.15 Toluene, Xylenes, Isoocta
49、neReagent 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. Vapors may causeflash fire.)NOTE 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 Not
