1、Designation: D7457 11Standard Test Method forDetermining Chloride in Aromatic Hydrocarbons andRelated Chemicals by Microcoulometry1This standard is issued under the fixed designation D7457; the number immediately following the designation indicates the year oforiginal adoption or, in the case of rev
2、ision, 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 measurement of chloride inaromatic hydrocarbons, their derivatives, and
3、 related chemicalsas defined by the method. Aromatics typically do not have anysource of chlorides other than organic. The presence of metallicor inorganic chlorides is theoretically possible but not likelyand this method does not purport to address recovery of thosecompounds.1.2 This test method is
4、 applicable to samples with chlorideconcentrations from 0.24 to 5.0 mg/kg. The test method limitof detection (LOD) is 0.07 mg/kg.1.3 This test method is preferred over Test Method D5194for products, such as styrene, that are polymerized by thesodium biphenyl reagent.1.4 In determining the conformanc
5、e of the test results usingthis method to applicable specifications, results shall berounded off in accordance with the rounding-off method ofPractice E29.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard doe
6、s 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 to use. For specific hazardstatements, see
7、Section 9.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD1555M Test Method for Calculation of Volume andWeight of Industrial Aromatic Hydrocarbons and Cyclo-hexane MetricD3437 Practice for Sampling and Handling Liquid CyclicProductsD3505 Test Method for Density or R
8、elative Density of PureLiquid ChemicalsD4052 Test Method for Density, Relative Density, and APIGravity of Liquids by Digital Density MeterD5194 Test Method for Trace Chloride in Liquid AromaticHydrocarbonsD6809 Guide for Quality Control and Quality AssuranceProcedures for Aromatic Hydrocarbons and R
9、elated Ma-terialsE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Other Document:OSHA Regulations, 29 CFR paragraphs 1910.1000 and1910.120033. Terminol
10、ogy3.1 Definitions of Terms Specific to This Standard:3.1.1 calibration factor/recovery factor, nan indication ofthe efficiency of the measurement computed by dividing themeasured value of a standard by its theoretical value.3.1.2 dehydrating tube or drying vessel, na chambercontaining concentrated
11、sulfuric acid that scrubs the combus-tion effluent gases to remove water vapor prior to entering thetitration cell.3.1.3 endpoint routine/test titration, nprocesses whichallow the coulometer to set the endpoint and gain values to beused for sample analysis.1This test method is under the jurisdiction
12、 of ASTM Committee D16 onAromatic Hydrocarbons and Related Chemicals and is the direct responsibility ofSubcommittee D16.04 on Instrumental Analysis.Current edition approved Feb. 1, 2011. Published March 2011. DOI: 10.1520/D745711.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
13、 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 of Documents,732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC
14、 20401, http:/www.access.gpo.gov.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.4 oxidative pyrolysis, na process in which a sample isevaporated in an inert gas atmosphere and combusted after-wards completely in an oxygen-rich a
15、tmosphere at high tem-perature to break down the components of the sample intoelemental oxides.3.1.5 reference electrode, nused in conjunction with sen-sor electrode to measure the potential of the titration cell.3.1.6 sensor electrode, ndetects changes in silver ionconcentration.3.1.7 titration cel
16、l, nvessel that contains the sensor-reference electrode pair and generator electrode pair along withthe cell electrolyte.3.1.8 titration parameters, nvarious instrumental condi-tions that can be changed for different types of analysis andanalyzers.3.1.9 working electrode pair (generator electrode),
17、nanelectrode pair consisting of an anode and a cathode.4. Summary of Test Method4.1 An aliquot of sample is introduced into a combustiontube maintained at 900 to 1100C having a flowing stream ofoxygen combustion gas and argon inert gas. Oxidative pyroly-sis converts the organic and inorganic halides
18、 to hydrogenhalides that then flow into a titration cell where it reacts withsilver ions present in the electrolyte. The silver ion thusconsumed is coulometrically replaced and the total electricalwork to replace it is a measure of the amount of organic halidesin the specimen, which was introduced (
19、see Annex A1).5. Significance and Use5.1 This test method is useful for determining organic aswell as inorganic chloride compounds that can prove harmfulto equipment and reactions in processes involving hydrocar-bons. The combination of both the organic and inorganicchloride is commonly termed “tota
20、l chloride” and since theinorganic chlorides are partially recovered, the result for totalchloride will be biased low.5.2 Maximum chloride levels are often specified for processstreams and for hydrocarbon products.5.3 Organic chloride species are potentially damaging torefinery processes. Hydrochlor
21、ic acid can be produced in hydrotreating or reforming reactors and this acid accumulates incondensing regions of the refinery.6. Interferences6.1 Both nitrogen and sulfur interfere at concentrationsgreater than approximately 0.1 %.6.2 Bromides and iodides, if present, will be calculated aschlorides.
22、 However, fluorides are not detected by this testmethod.6.3 Both organic and inorganic chloride in the sample willbe measured due to conversion of both species to HCL duringthe oxidative pyrolysis process which is commonly termed astotal chloride. The results for total chloride will be biased lowsin
23、ce the measurement of total chloride is the sum of bothorganic and inorganic chloride compounds in the sample andinorganic compounds (if present) are only partially converted.The measurement of only the “organic chloride” in the samplecan be measured by water washing the sample prior to analysisto r
24、emove the inorganic chloride in the sample. Partial loss oforganic halogens which are partially soluble into the waterwash, such as chloroacetic acid, may occur. The water washingprocedure can not be applied to water soluble samples.7. Apparatus7.1 Pyrolysis Furnace, which can maintain at 900 to 110
25、0Cand sufficient to pyrolyze the organic matrix and convert allchlorine present in the sample to hydrogen chloride. Furnacesystems with the furnace orientated horizontally or verticallycan be used.7.2 Pyrolysis Tube, made of quartz and constructed in a waythat the sample can be evaporated in an iner
26、t gas stream, and bepyrolyzed afterwards in the presence of oxygen. The inlet endof the tube must have a sample inlet port with a septum throughwhich the sample can be injected by syringe. The inlet endmust also have side arms for the introduction of oxygen andinert carrier gas. The pyrolysis tube m
27、ust be of ample volume,so that complete pyrolysis of the sample is ensured.7.3 Titration Cell, containing sensor electrode, referenceelectrode and working electrode pair. An inlet from thepyrolysis tube and magnetic stirring is also required.(WarningExcessive stirring speed will decouple the stirrin
28、gbar and cause it to bounce in the titration cell, possiblydamaging the electrodes. A slight vortex in the cell is ad-equate.)7.4 Microcoulometer, with connections for the electrodes,capable of measuring the potential of the sensor electrode, andcomparing this potential with a bias potential, and am
29、plifyingthe difference to the working electrode pair to generate acurrent. The microcoulometer output voltage signal should beproportional to the generating current.7.5 Controlling Unit, for programming and setting theoperating parameters of the instrument and integration of data.7.6 Flow ControlThe
30、 apparatus must be quipped withflow controllers capable of maintaining a constant supply andflow of oxygen and argon gas.7.7 Sample Inlet (Boat Inlet or Direct Injection).7.7.1 Boat Inlet Systems (Horizontal Furnace).7.7.1.1 Automated Boat Drive (Required), having variablestops, such that the sample
31、 boat may be driven into the furnaceand stopped at various points as it enters the furnace therebyensuring the controlled combustion of the sample and prevent-ing the formation of soot or coke, both of which indicateincomplete sample combustion. If direct injection is used witha horizontal system, t
32、he automated boat drive is not required.7.7.1.2 Boat Inlet Cooler (Required)Sample volatility andinjection volume require an apparatus capable of cooling thesample boat prior to sample introduction. Thermoelectriccoolers (peltier) or re-circulating refrigerated liquid deviceshave both been found eff
33、ective. Other approaches can be usedas long as the performance criteria of the method are notaffected. If direct injection is used with a horizontal system, theboat inlet cooler is not required.7.7.1.3 Quartz or Ceramic Sample Boats, of sufficient sizeto hold 90 to 250 L or mg of sample.7.7.2 Direct
34、 Injection (Both Horizontal or Vertical Fur-nace).D7457 1127.7.2.1 Direct Injection (Required)A sample introductionsystem capable of directly injecting sample into the furnace(either vertical or horizontal) at a controlled rate therebyensuring the controlled combustion of the sample and prevent-ing
35、the formation of soot or coke, both of which indicateincomplete sample combustion.7.8 Autosampler (Required), capable of accurately deliver-ing 90 to 240 L of sample into the pyrolysis tube or sampleboat if a boat inlet with automated boat drive and inlet systemis used. An autosampler is required to
36、 ensure the accuracy andperformance of the method is maintained.NOTE 1Multiple rinsing with clean solvent and/or sample betweensample injections and/or between sampling from different sample vials isrecommended to minimize carryover contamination. An independentsolvent flush from a separate vial and
37、 different from the solvent washthereby providing a clean, uncontaminated solvent may also be used.These features may be used as long as they do not degrade theperformance and accuracy of the method.7.9 Dehydrating Tube or Drying Vessel, positioned at theoutlet of the pyrolysis tube so that effluent
38、 gases are bubbledthrough concentrated sulfuric acid. The water vapor formed inthe combustion gases are trapped while all other gases includ-ing hydrogen halides are allowed to flow through into thetitration cell.7.10 Gas-Tight Sampling Syringe, having a capacity up to250 L and capable of accurately
39、 delivering 90 to 240 L ofsample. Syringes of differing sizes (100 or 250 L) arepermissible to be used as long as the precision and accuracy ofthe method are not degraded.7.11 Balance, analytical, with sensitivity to 0.0001 g.7.12 Gas RegulatorsTwo-stage gas regulators must beused for the reactant a
40、nd carrier gas.8. Reagents and Materials8.1 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 Analytical Reagents of the American Chemical Society,where such specif
41、ications are available.4Other grades may beused, provided that the reagent is of sufficiently high purity topermit its use without lessening the accuracy of the determi-nation.8.2 Purity of WaterUnless otherwise indicated, referencesto water shall be understood to mean reagent water conformingto Spe
42、cification D1193, Type I. Type II can be used as long asthe precision and accuracy of the method is not degraded.8.3 SolventThe solvent of choice must be capable ofdissolving the chloride sample. The solvent of choice shouldhave a boiling point similar to the sample being analyzed.Suggested possibil
43、ities include, but are not limited to isooc-tane, toluene, p-xylene and methanol.8.4 Purity of SolventThe blank value of the solvent usedmust be smaller than 0.1 g/Kg chlorides. Before using, theblank value of the solvent must be checked by carrying out achlorine determination with the device being
44、used for thisanalysis.8.5 Acetic AcidGlacial acetic acid (CHRR3COOH), con-centration: 97 %.8.6 Cell Electrolyte SolutionSeveral electrolyte solutionsbased on acetic acid solutions. Please follow instrumentmanufacturers recommendation.NOTE 2Bulk quantities of the electrolyte should be stored in a dar
45、kplace and dark bottle and is recommended to be prepared fresh at leastevery two weeks.8.7 Inner Electrolyte SolutionPlease follow the instru-ment manufacturers recommendation.8.8 Outer Electrolyte SolutionsPlease follow the instru-ment manufacturers recommendation.8.9 Gases.8.9.1 Argon, 99.996 % mi
46、nimum purity required as inertand carrier gas.8.9.2 Oxygen, 99.995 % minimum purity is required as theoxidation gas.8.10 Sodium Acetate, anhydrous, (NaCH3CO2), fine granu-lar.8.11 Sodium Sulfate, (Na2SO4), crystalline and anhydrous.8.12 Sulfuric Acid, (95 to 98 %), (H2SO4) concentrated.8.13 2,4,5-Tr
47、ichlorophenol or 2,4,6-Trichlorophenol (TCP),(C6H3OCl3) fine granular.8.14 100 g/mLChloride Standard Stock SolutionWeigh in the range of 0.8500 to 0.9500 g to the nearest 0.1 mg(target weight of 0.9285 g) of 2,4,5-trichlorophenol or 2,4,6-trichlorophenol to the nearest 0.0001 g and record the actual
48、weight. Transfer to a 500-mL volumetric flask and dilute to themark with the selected solvent (see 8.3 and 8.4). Calculate theexact concentration using calculation Eq 1:g Cl / mL 5TCP! 3 % CL! 3 K1 3 CI500 mL(1)where:TCP = 2,4,5, Trichlorophenol, g,%CL = 0.5385 g-Cl/g-TCP (% Chloride in TCP),K1 =106
49、g/g (used to convert g to g), andCI = % Chemical Impurity; the % purity of TCP used toprepare the Chloride Standard Stock Solution. (forexample: If 99 % purity, use a CI factor = 0.99. Ifno correction for CI is used, use a CI factor = 1.0).8.15 10 g/mL-Chloride Standard Working SolutionPipet50 mL of the chloride standard stock solution (see 8.14) into a500-mL volumetric flask, and dilute to the mark with solvent.NOTE 3Other calibration standard sources and diluents may be usedif precision and accuracy are not degraded.NOTE 4A correcti
