1、Designation: D6423 14D6423 18Standard Test Method forDetermination of pHe of Denatured Fuel Ethanol andEthanol Fuel Blends1This standard is issued under the fixed designation D6423; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, t
2、he 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. Scope*1.1 This test method covers a procedure to determine a measure of the acid strength of high ethanol content fu
3、els. These includedenatured fuel ethanol and ethanol fuel blends. The test method is applicable to denatured fuel ethanol and ethanol fuel blendscontaining ethanol at 51 % by volume, or more.1.2 Acid strength as measured in this test method is defined as pHe. A pHe value for alcohol solutions is not
4、 comparable to pHvalues of water solutions.1.2.1 The value of pHe measured will depend somewhat on the fuel blend, the stirring rate, and the time the electrode is in thefuel.1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard
5、.1.3.1 Hydrogen ion activity in water is expressed as pH and hydrogen ion activity in ethanol is expressed as pHe.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate s
6、afety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.5 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Dev
7、elopment of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubric
8、antsD4806 Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use asAutomotive Spark-Ignition Engine FuelD5798 Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines3. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Defin
9、itions:3.2.1 denaturants, nmaterials added to ethanol to make it unsuitable for beverage use under a formula approved by aregulatory agency to prevent the imposition of beverage alcohol tax. D48063.2.1.1 DiscussionDenaturants are only those materials added by the denaturer to comply with the approve
10、d formula; any materials absorbed laterare not denaturants.3.2.2 denatured fuel ethanol, nfuel ethanol made unfit for beverage use by the addition of denaturants under formula(s)approved by the applicable regulatory agency to prevent the imposition of beverage alcohol tax. D48061 This test method is
11、 under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of SubcommitteeD02.A0.02 on Oxygenated Fuels and Components.Current edition approved Dec. 15, 2014Dec. 1, 2018. Published February 2015December 2018. Originally approved
12、in 1999. Last previous edition approved in 20082014as D6423 08.D6423 14. DOI: 10.1520/D6423-14.10.1520/D6423-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the s
13、tandards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accur
14、ately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor
15、Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.3 ethanol, nethyl alcohol, the chemical compound, CCH23HCH52OH. D48063.2.4 ethanol fuel blend, na blend of ethanol and hydrocarbons for use in flexible-fuel automotive spark-ignition engines ofwhich the ethanol portion is 51 % t
16、o 83 % by volume. D57983.2.5 flexible-fuel vehicle, na vehicle designed to operate on either unleaded both gasoline or ethanol fuel blends or mixturesand can operate on any mixture of both. D57983.2.5.1 DiscussionIn the United States, these vehicles have U.S. EPA emissions certifications using gasol
17、ine complying with U.S. EPA requirementsand ethanol fuel blends that meet the requirements of Specification D5798.3.2.5.2 DiscussionFlex-fuel vehicle and FFV are commonly used synonyms for flexible-fuel vehicle.3.2.5.3 DiscussionThe fuels may also contain anti-oxidants, corrosion inhibitors, metal d
18、eactivators, and dyes but do not contain lead additives. Ajurisdiction may set limits on lead content from all sources.3.2.6 fuel ethanol, na grade of undenatured ethanol with other components common to its production (including water) thatdo not affect the use of the product as a component for auto
19、motive spark-ignition engine fuels. D48063.2.6.1 DiscussionThe common components do not include denaturant.3.2.7 hydrocarbon, na compound composed solely of hydrogen and carbon. D57983.3 Definitions of Terms Specific to This Standard:3.3.1 pHe, na measure of the acid strength of ethanol-hydrocarbon
20、blends defined by this apparatus and procedure.4. Summary of Test Method4.1 The sample is analyzed at room temperature using a specified electrode system and a pH meter with an input impedance1012 (ohms). Meters designed for use with ion-specific electrodes normally meet this criteria.4.2 Readings a
21、re taken at exactly 30 s 30 s because the meter reading will change throughout the analysis due to glass-electrodevoltage drift caused by dehydration of the glass-electrode membrane. Because alcohol dehydrates the glass-electrode membrane,time spent soaking in alcohol solution should be minimized.4.
22、3 The electrode is soaked in water-based pH 7 buffer between readings to prepare it for the next sample. This rehydrates theglass electrode, a necessary step to preserve the electrodes response characteristics.4.4 The electrodes are cleaned/rehydrated at least every ten samples by alternately soakin
23、g several times in 1 molL NaOHsolution and 1 molL H2SO4 (or 1 molL HCl) for about 30 s 30 s each. New electrodes are treated by this procedure before firstuse.5. Significance and Use5.1 The acid strength, as measured by pHe, is a good predictor of the corrosion potential of ethanol fuels. It is pref
24、erable to totalacidity because total acidity does not measure acid strength; overestimates the contribution of weak acids, such as carbonic acid;and can underestimate the corrosion potential of low concentrations of strong acids, such as sulfuric acid.6. Apparatus6.1 pH meterAs recommended for use w
25、ith ion-specific electrodes, commercially available pH meters with an input of1012 are acceptable for this test method. Temperature compensation and readability to 0.01 pH unit are recommended.6.2 ElectrodeORION Ross Sure-Flow combination electrode3 or Metrohm ETOH-Trode4 with a glass body shall be
26、used.(See Note 1.) Because the measurement is (of necessity) not made at equilibrium, it is essential that this exact electrode pair be3 The specified electrode (ORION Cat. No. 8172BNWP) is available from many laboratory supply companies, or from the manufacturer: Thermo Fisher Scientific, 22Alpha R
27、oad, Chelmsford, MA, 01824, USA, 1-978-232-6000, I. For Europe: https:/ For Asia Pacific: http:/ For Latin America: .D6423 182used to ensure the reproducibility of results. Critical features of this electrode include a high leak-rate sleeve-junction referenceelectrode and a large membrane glass meas
28、uring electrode. High leak-rate reference electrodes minimize salt-bridge junctionpotential drift, especially in extremely low conductivity solutions like fuel alcohols. For similar reasons, large membrane glasselectrodes (measuring electrodes) were found to perform better and have longer life in al
29、cohol fuels. Since this is a method-basedparameter, other electrodes (even those of similar design) will likely give different results under some or all conditions due to theuse of a different size or type of glass membrane for the pH electrode, a different type of salt bridge junction, or other sma
30、lldifferences, which may affect their nonequilibrium response.NOTE 1This equipment, as listed in RR:D02-1796, was used to develop the precision statement and no statistically significant differences were foundbetween these pieces of equipment: ORION Ross Sure-Flow combination electrode3 and Metrohm
31、ETOH-Trode.4 This listing is not an endorsement orcertification by ASTM International.6.3 Reference Electrode Filling SolutionAlthough some references suggest alcoholic filling solutions for measurements inalcohol, this test method was developed using an aqueous KCl filling solution and aqueous buff
32、er calibration solutions. The effectof alcoholic filling solution was not investigated.6.4 Temperature CompensatorThe thermocompensator is a temperature-sensitive resistance element immersed in the samplewith the electrodes. The thermocompensator automatically corrects for the change in slope of the
33、 glass electrode response (withchange in temperature) but does not correct for actual changes in sample pH with temperature. Because temperature compensationcorrects only for changes in pH electrode response with temperature, the fuel sample must be at 22 C 6 2 C.6.5 Beakers, borosilicate glass, 100
34、 mL, graduations are useful to determine sample size. This size beaker ensures a propervortex with the 60 mL sample. The 100 mL beaker gives sufficient depth to submerge the electrode to the correct level.6.6 Magnetic StirrerAny laboratory magnetic stirrer may be used, along with a TFE-fluorocarbon-
35、coated stirring bar 19 mmto 25 mm long.6.7 Timer, capable of measuring seconds.7. Reagents and Materials7.1 Purity of ReagentsReagent-grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allreagents conform to the specifications of the Committee on Analytical R
36、eagents of the American Chemical Society where suchspecifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the accuracy of the determination. Commercially prepared solutions are accep
37、table for use.7.2 Buffer SolutionsCommercially available, waterbased buffer solutions (pH=4.00 and pH=7.00) are acceptable for thestandardization.7.3 1 molL Hydrochloric Acid (HCl)Mix one volume of concentrated (12 molL) HCl with eleven volumes of distilled water.7.4 3 mol/L Potassium Chloride (KCl)
38、The electrode is shipped with this filling solution already prepared.7.5 1 mol/L Sodium Hydroxide (NaOH)Dissolve 4 g of NaOH pellets in 100 mL of distilled water.7.6 1 mol/L Sulfuric Acid (H2SO4)Mix one volume of concentrated (18 mol/L) H2SO4 with 17 volumes of distilled water.7.7 Purity of WaterUnl
39、ess otherwise indicated, reference to water or distilled water shall be understood to mean reagent waterthat meets the requirements of either Type I, II, or III of Specification D1193.8. Sample Containers8.1 Care must be used in sample container selection to avoid reactions that change the pHe of th
40、e sample. Do not use steel,plated steel, or epoxy-coated steel containers or PVC-coated glass bottles for samples.Avoid closures with a paper seal. Fluorinatedhigh-density polyethylene and spun aluminum sample containers with polyethylene or TFE-fluorocarbon closures are acceptable.Glass bottles wit
41、hout an external PVC coating and utilizing TFE-fluorocarbon or polyethylene cap seals are also acceptable.8.2 Rinse the container with a portion of the ethanol-hydrocarbon blend to be sampled before taking the sample.9. Standardization of Assembly9.1 Turn on the pH meter and allow it to warm up thor
42、oughly in accordance with the manufacturers instructions. Note thetemperature of the sample to be tested. If temperature compensation is to be manual, adjust the temperature dial of the meter tocorrespond to the temperature of the sample to be tested and allow time for all buffers, solutions, and th
43、e electrode to equilibratethermally.4 The specified electrode (Metrohm Part # 60269100) is available from the manufacturer: Metrohm AG, Ionenstrasse 9101 Herisau Switzerland. Metrohm USA, 6555Pelican Creek Circle, Riverview, FL, 33578. Metrohm Pensalab InstrumentaoAnaltica LTDA, Rua Minerva, 167-Per
44、dizes, So Paulo, SP, Brazil CEP05007-030. MetrohmSingapore Pte, Ltd., 31 Toh Guan Road East, #06-08 LW Techno Centre, Singapore, 608608.5 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, D.C. For suggestions on the testing of reagents not listed byt
45、he American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and NationalFormulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D6423 1839.2 Clean/rehydrate the electrode after every ten samples and new e
46、lectrodes before first use by alternately soaking four timesin 1 molL NaOH solution and 1 molL H2SO4 (or 1 molL HCl) for about 30 s each. Remove the electrode and rinse it withdistilled water into a waste container.9.3 Calibrate the pH meter to pH=7.00 with a water-based pH=7.00 buffer solution. Rem
47、ove the electrode and rinse it withdistilled water into a waste container.9.4 Calibrate the pH meter to pH=4.00 with a water-based pH=4.00 buffer solution, using the slope adjustment. The slope shallbe in the 95 % to 100 % range, or the electrode will have to be cleaned or replaced. Remove the elect
48、rode and rinse it with distilledwater into a waste container. Return the electrode to the pH=7.00 buffer, and if the measured pH is not between 6.90 and 7.10 thenreturn to subsection 9.2.10. Procedure10.1 Make sure sample is at 22 C 6 2 C.10.2 Fill the electrode as needed with 3 molL aqueous KCl sol
49、ution, supplied with the electrode.10.3 Standardize the assembly with two reference buffer solutions, as described in 9.3 and 9.4.10.4 Start with a new aliquot (fresh portion) of ethanol-hydrocarbon blend sample for each measurement. Since manyethanol-hydrocarbon blend samples are poorly buffered and have low ionic strength, it is important to use a new aliquot for eachmeasurement for best accuracy.10.5 Place about 60 mL of sample in a
