1、Designation: D6721 01 (Reapproved 2015)Standard Test Method forDetermination of Chlorine in Coal by Oxidative HydrolysisMicrocoulometry1This standard is issued under the fixed designation D6721; the number immediately following the designation indicates the year oforiginal adoption or, in the case o
2、f 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.1. Scope1.1 This test method covers the determination of totalchlorine in coal.1.2 The values stated in SI
3、 units are to be regarded asstandard. No other units of measurement are included in thisstandard.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
4、practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D2013 Practice for Preparing Coal Samples for AnalysisD3173 Test Method for Moisture in the Analysis Sample ofCoal and CokeD3180 Practice for Calculating Coal and Coke Analyse
5、sfrom As-Determined to Different BasesD4621 Guide for Quality Management in an OrganizationThat Samples or Tests Coal and Coke (Withdrawn 2010)3D5142 Test Methods for Proximate Analysis of the AnalysisSample of Coal and Coke by Instrumental Procedures(Withdrawn 2010)3E29 Practice for Using Significa
6、nt Digits in Test Data toDetermine Conformance with SpecificationsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other StandardsISO 5725-6:1994 Accuracy of measurement methods andresults-Part 6: Use in practice of accuracy values43. Summary of Tes
7、t Method3.1 A 5.00 to 40.00 mg sample of coal is combusted withtungsten accelerator in a humidified oxygen gas flow, at 900C.Halogens are oxidized and converted to hydrogenated halides,which are flushed into a titration cell where they accumulate.Chlorine is converted to hydrochloric acid. Once the
8、chloride iscaptured in the electrolyte of the titration cell, it can bequantitatively determined by microcoulometery, where chlo-ride ions react with silver ions present in the electrolyte. Thesilver ion thus consumed is coulometrically replaced and thetotal electrical work needed to replace it is p
9、roportional to thechloride in the test sample.4. Significance and Use4.1 This test method permits measurements of the chlorinecontent of coals.5. Interferences5.1 Bromides and iodides, if present are calculated aschloride. However, fluorides are not detected by this testmethod.6. Apparatus6.1 Hydrol
10、ysis Furnace, which can maintain a minimumtemperature of 900C.6.2 Hydrolysis Tube, made of quartz and constructed suchthat when the sample is combusted in the presence of tungstenaccelerator and humidified oxygen, the byproducts of combus-tion are swept into a humidified hydrolysis zone. The inlet e
11、ndshall allow for the introduction and advancement of the sampleboat into the heated zone. The inlet shall have a side arm for theintroduction of the humidified oxygen gas. The hydrolysis tubemust be of ample volume, and have a heated zone with quartzwool so that complete hydrolysis of the halogens
12、is ensured.1This test method is under the jurisdiction of ASTM Committee D05 on Coaland Coke and is the direct responsibility of Subcommittee D05.29 on MajorElements in Ash and Trace Elements of Coal.Current edition approved Jan. 1, 2015. Published January 2015. Originallyapproved in 2001. Last prev
13、ious edition approved in 2006 as D6721 01(2006).DOI: 10.1520/D6721-01R15.2For 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 A
14、STM website.3The last approved version of this historical standard is referenced onwww.astm.org.4Available from International Organization for Standardization 1 Rue deVaremb, Case Postale 56, CH-1211, Geneva 20, SwitzerlandCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Consho
15、hocken, PA 19428-2959. United States16.3 Titration Cell, containing a reference electrode, a work-ing electrode, and a silver sensor electrode, a magnetic stirreras well as an inlet from the hydrolysis tube.6.4 Microcoulometer, capable of measuring the potential ofthe sensing-reference electrode pai
16、r, comparing this potentialwith a bias potential, and amplifying the difference to theworking electrode pair to generate current. The microcoulom-eter output voltage should be proportional to the generatingcurrent.6.5 Controller, with connections for the reference, working,and sensor electrodes, for
17、 setting operating parameters and fordata integration.6.6 Hydration Tube, containing water, positioned before thegas inlet on the side arm of the combustion tube, through whichoxygen gas bubbles to provide a hydrated gas flow.6.7 Dehydration Tube, positioned at the end of the hydro-lysis tube so tha
18、t effluent gases are bubbled through a 95 %sulfuric acid solution. Water vapor is subsequently trappedwhile other gases flow into the titration cell.6.8 Gas-Tight Sampling Syringe, having a 50 L capacity,capable of accurately delivering 10 to 40 L of standardsolution.6.9 Sample Boats, made of quartz
19、, ceramic or platinum.6.10 Balance, analytical, with a sensitivity to 0.00001 g.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 specification of the Committeeon Analytic
20、al Reagents of the American Chemical Society,where such specifications are available. Other grades may beused, provided that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.7.2 Purity of WaterUnless otherwise indicated, referencesto wa
21、ter shall be understood to mean reagent water conformingto Specification D1193, Type II or Type III.7.3 Acetic Acid (sp gr. 1.05), glacial acetic acid(CH3COOH).7.4 Argon or Helium, carrier gas, minimum 99.9 % purity.7.5 Sodium Acetate, anhydrous, (NaCH3CO2), fine granular.7.6 Cell Electrolyte Soluti
22、onDissolve 1.35 g sodium ac-etate (NaCH3CO2) in 100 mL water. Add to 850 mL of aceticacid (CH3COOH) and dilute to 1000 mL with water.7.7 Tungsten Powder, combustion accelerator, (-100 mesh)minimum 99.9 % purity.7.8 Oxygen, combustion gas minimum 99.6 % purity.7.9 Gas RegulatorsUse two-stage gas regu
23、lators for thecarrier and combustion gases.7.10 Potassium Nitrate (KNO3), fine granular.7.11 Potassium Chloride (KCl), fine granular.7.12 Working Electrode Solution (10 % KNO3), Dissolve50 g potassium nitrate (KNO3) in 500 mL of water.7.13 Inner Chamber Reference Electrode Solution (1 MKCl)Dissolve
24、7.46 g potassium chloride (KCl) in 100 mL ofwater.7.14 Outer Chamber Reference Electrode Solution (1 MKNO3)Dissolve 10.1 g potassium nitrate (KNO3) in 100 mLof water.7.15 Sodium Chloride (NaCl), fine granular.7.16 Sulfuric Acid (sp gr. 1.84), (H2SO4), concentrated.7.17 2,4,6-Trichlorophenol (TCP) (C
25、6H3OCl3), fine granu-lar.7.18 Methanol (MeOH) (CH3OH), 99.9 % minimum purity.7.19 Working Chlorine Standard (1g/L)Weigh accu-rately 0.1856 g of 2,4,6-Trichlorophenol to the nearest 0.1 mg.Transfer to a 100 mL volumetric flask. Dilute to the mark withmethanol.WSCI5 gofTCP 30.5386 31000/100! (1)where:
26、TCP = 2,4,6-Trichlorophenol, andWSCI= the working chlorine standard concentration.8. Hazards8.1 Consult the current version of OSHA regulations, sup-pliers Material Safety Data Sheets, and local regulations forall materials used in this test method.9. Sampling9.1 Prepare the analysis sample in accor
27、dance with MethodD2013 to pass a 250-m (60 mesh) sieve.9.2 Analyze a separate portion of the analysis sample formoisture content in accordance with Test Method D3173 orTest Methods D5142.10. Preparation of Apparatus10.1 Fill the hydration tower with water and connect it tothe quartz furnace tube inl
28、et.10.2 Set the furnace temperature to 900C.10.3 Adjust the gas flows according to manufacturersspecification, typically 200 mL/min for oxygen and 100mL/min for the carrier gas.10.4 Prepare the sulfuric acid dehydration scrubber, andconnect it to the outlet of the quartz furnace combustion tube.10.5
29、 Clean and prepare the electrode system for the titrationcell per instrument specifications.10.6 Fill the titration cell with fresh electrolyte solution tojust above the top fill mark.10.7 Place the titration cell on the magnetic stirring deviceand connect the electrode system to the controller. Do
30、notconnect the gas flow from the dehydration scrubber to thetitration cell.D6721 01 (2015)210.8 Initiate a conditioning run of the titration cell toestablish titration gain and endpoint values.10.9 Once the titration cell is properly conditioned, connectthe gas flow from the dehydration scrubber to
31、the titration cell.10.10 Let the titration cell stabilize to a background poten-tial of less then 1.0 mv.10.11 To ensure quality data, care must be taken to avoidcontaminating the sample boats during the course of theanalytical procedure. Do not touch the boats with fingers.Handle and transfer the b
32、oats using tongs and store said boatsin a sealed container such as a glass desiccator, containing nodesiccant. Prepare the combustion boats by heating them in thecombustion tube with oxygen flow for a minimum of five min.11. Recovery Factor11.1 Confirm the instrument carrier gas and time delaysettin
33、gs. Typical delays for solvent injections are 2.0 min forcarrier gas and 2.5 min to titration start.11.2 Inject 10 L of chlorine standard solution through theinjection port into a prepared combustion boat. Advance thecombustion boat slowly into the heated zone of the furnace.Record the recovered g C
34、hlorine as RC.11.3 Repeat this recovery measurement a minimum of threetimes.11.4 Calculate the Recover Factor (RF) for each measure-ment according to Eq 2.RF 5WSCl310!RC(2)where:RF = the recover factor,WSCl= the working chlorine standard concentration, andRC = the recovered chlorine value.11.5 Calcu
35、late the average recovery factor.11.6 If the average recovery factor is from 0.95 to 1.05, therecovery factor shall be assumed to be 1.0 and the instrumentcan be used for sample analysis.11.7 If the average recovery factor is less than 0.95 orgreater than 1.05, then the instrument shall be re-calibr
36、ated byrunning 5 L, 10 L, 20 L, 30 L and 50 L volumes of theChlorine working standard, after confirming that the apparatusis in proper working condition and after setting up theapparatus in accordance with Section 10 Preparation of Appa-ratus (Note 1).NOTE 1A low recovery factor is usually indicativ
37、e of leaks in thecombustion system or improper packing of the combustion tube. Highrecovery factors are generally indicative of contamination.12. Blank Determination12.1 Carry out a conditioning run with 100 mg 6 10 mg oftungsten powder. Note the value of chlorine recovered but donot use this value
38、in any blank calculations.12.2 Weigh 100 mg 6 10 mg of tungsten into the preparedcombustion boat and record the g of chlorine in 100 mgtungsten.12.3 Repeat the blank measurement until three successivemeasurements of less than 0.1 g of chlorine are obtained.12.4 Calculate the average blank value from
39、 the threemeasurements less than 0.1 g chlorine and record as B.13. Procedure13.1 Follow the manufacturers instructions to program thecarrier gas to switch to oxygen immediately after the sampleboat is completely inside the combustion furnace. Delay thestart of the titration for a time sufficient to
40、 collect thebyproducts of the sample combustion in the titration cell,typically 2.0 min.13.2 Weigh approximately 10 mg of sample into a preparedcombustion boat. Record the weight to the nearest 0.01 mg asW. The recommended sample sizes for coals with higher andlower chlorine respectively are outline
41、d in the following table.Chlorine Range, mg/kg Sample Size, mg20.0 to 100 40100 to 300 20300 1013.3 Cover the specimen with approximately 100 mg oftungsten powder accelerator.13.4 Proceed with the combustion titration analysis by firststarting the controller count down and then advancing thesample b
42、oat directly into the combustion furnace hot zone.Record the measured Chlorine value as M.14. Calculation14.1 The as determined chlorine concentration is calculatedas follows:Chlorine, mg/kg 5 1000 3 M 2 B!/W! (3)where:M = measured chloride value, g,B = blank chloride value, g, andW = weight of samp
43、le, mg.15. Report15.1 The results of the chlorine analysis can be reported toother bases, differing from each other in the manner by whichmoisture is treated.15.2 Use the percent moisture, as determined by TestMethod D3173 or Test Method D5142, in the analysis samplepassingaN60(250 m) sieve, to calc
44、ulate the results of theanalysis to a dry basis.15.3 Procedures for converting the values obtained on theanalysis sample to other bases are described in Practice D3180.16. Precision and Bias516.1 The precision of this test method for the determinationof Chlorine in coal, is shown in Table 1. The pre
45、cisioncharacterized by the repeatability (Sr, r) and reproducibility(SR, R) is described in Table A1.1 in Annex A1.5Supporting data have been filed at ASTM International Headquarters and maybe obtained by requesting Research Report RR:D05-1030.D6721 01 (2015)316.1.1 Repeatability Limit (r)The value
46、below which theabsolute difference between two test results of separate andconsecutive test determinations, carried out on the samesample in the same laboratory by the same operator using thesame apparatus on samples taken at random from a singlequantity of homogeneous material, may be expected to o
47、ccurwith a probability of approximately 95 %.16.1.2 Reproducibility Limit (R)The value below whichthe absolute difference between two test results, carried out indifferent laboratories using samples taken at random from asingle quantity of material that is as nearly homogeneous aspossible, may be ex
48、pected to occur with a probability ofapproximately 95 %.16.2 BiasNIST Standard Reference Material NIST 1630awas included in the interlaboratory study to ascertain possiblebias between reference material values and those determinedby this method. A comparison of the NIST values and thoseobtained in t
49、he interlaboratory study are given in Table 2.NOTE 2When possible , the analysis of several reference materials ,spanning the concentration range of interest, is the most meaningful wayto investigate measurement bias. When a matrix match is possible theuncertainty in sample measurements can be equatable to that observed inmeasurement of the Certified Reference Material (CRM). When such amatch is not possible, but a CRM with a related matrix is available, the testsample uncertainty may be related to those observed when measuring theCRM. Differ
