1、Designation: D6423 08D6423 14Standard Test Method forDetermination of pHe of Ethanol, Denatured FuelEthanol,Ethanol and Fuel Ethanol (Ed75-Ed85)Fuel Blends1This standard is issued under the fixed designation D6423; the number immediately following the designation indicates the year oforiginal adopti
2、on 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.1. Scope*1.1 This test method covers a procedure to determine a measure of the acid st
3、rength of high ethanol content fuels. These includeethanol, denatured fuel ethanol,ethanol and fuel ethanol (Ed75-Ed85). fuel blends. The test method is applicable to fuels containingnominally 70 volume % ethanol, or higher, as described in Specifications denatured fuel ethanol and ethanol fuel blen
4、ds containingethanol at 51 % by volume, or more.D4806 and D5798.1.2 Acid strength as measured in this test method is defined as pHe. A pHe value for alcohol solutions is not comparable to pHvalues of water solutions. For example, a 1.510 -5 M (18 ppm) solution of H2SO4 gives a pH of about 5.5 in wat
5、er solution, but,depending on buffering strength, a pHe as low as 1 to 2 in unadditized alcohol fuel.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 value of pHe measured will depend somewhat on the fuel blen
6、d, 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.1.3.1 Hydrogen ion activity in water is expressed as pH and hydrogen ion activity in ethanol is expressed as pH
7、e.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 safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced D
8、ocuments2.1 ASTM Standards:2D1193 Specification for Reagent WaterD4175 Terminology Relating to Petroleum, Petroleum Products, and LubricantsD4806 Specification for Denatured Fuel Ethanol for Blending with Gasolines for Use asAutomotive Spark-Ignition Engine FuelD5798 Specification for Ethanol Fuel B
9、lends for Flexible-Fuel Automotive Spark-Ignition Engines3. Terminology3.1 For general terminology, refer to Terminology D4175.3.2 Definitions:3.2.1 denaturants, nnatural gasoline, gasoline components, unleaded gasoline, or toxic or noxious materials added to fuelethanol to make it unsuitable for be
10、verage use but not unsuitable for automotive fuel use.under a formula approved by a regulatoryagency to prevent the imposition of beverage alcohol tax. D48063.2.1.1 Discussion1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is
11、the direct responsibility of SubcommitteeD02.A0.02 on Oxygenated Fuels and Components.Current edition approved Dec. 15, 2008Dec. 15, 2014. Published February 2009February 2015. Originally approved in 1999. Last previous edition approved in 20042008as D642399(2004).D6423 08. DOI: 10.1520/D6423-08.10.
12、1520/D6423-14.2 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 standards Document Summary page on the ASTM website.This document is not an ASTM standard and is in
13、tended 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 accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the cur
14、rent 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 Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Denaturants are only those mat
15、erials added by the denaturer to comply with the approved 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.denaturants underformula(s) approved by the applicable regulatory agency to preven
16、t the imposition of beverage alcohol tax. D48063.2.3 ethanol, nethyl alcohol, the chemical compound, C2H5OH.3.2.4 fuel ethanol (Ed75-Ed85), fuel blend, na blend of ethanol and hydrocarbons for use in flexible-fuel automotivespark-ignition engines of which the ethanol portion is nominally 75 to 85 vo
17、lume % denatured ethanol.51 % to 83 % by volume.D57983.2.5 flexible-fuel vehicle, na vehicle designed to operate on either unleaded gasoline or ethanol fuel blends or mixtures ofboth. D57983.2.6 fuel ethanol, na grade of undenatured ethanol with other components common to its production (including w
18、ater) thatdo not affect the use of the product as a component for automotive spark-ignition engine fuels. D48063.2.7 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 alcohol fuelseth
19、anol-hydrocarbon blends defined by this apparatus andprocedure.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. (ohms). Meters designed for use with ion-specific electrodes normally meet this c
20、riteria.4.2 Readings are taken at exactly 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 shoul
21、d be minimized.4.3 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 a
22、lternately soaking several times in 11 mol M L NaOHsolution and 11 mol M L H2SO4 (or 11 mol M L HCl) for about 30 s each. New electrodes are treated by this procedure beforefirst use.5. Significance and Use5.1 The acid strength, as measured by pHe, is a good predictor of the corrosion potential of e
23、thanol fuels. It is preferable to totalacidity because total acidity does not measure acid strength; overestimates the contribution of weak acids, such as carbonic acid;and maycan underestimate the corrosion potential of low concentrations of strong acids, such as sulfuric acid.6. Apparatus6.1 pH me
24、terAs recommended for use with ion-specific electrodes, commercially available pH meters with an input of 1012ohms 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-Tr
25、ode4 with a glass body shall be used.(See Note 1.) Because the measurement is (of necessity) not made at equilibrium, it is essential that this exact electrode pair beused to ensure the reproducibility of results. Critical features of this electrode include a high leak-rate sleeve-junction reference
26、electrode and a large membrane glass measuring 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
27、perform better and have longer life in alcohol 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 t
28、ype of salt bridge junction, or other smalldifferences, which may affect their nonequilibrium response.NOTE 1This equipment, as listed in RR:D02-XXXX, was used to develop the precision statement and no statistically significant differences werefound between these pieces of equipment: ORION Ross Sure
29、-Flow combination electrode3 and Metrohm ETOH-Trode.4 This listing is not anendorsement or certification by ASTM International.3 The specified electrode (ORION Cat. No. 8172BN)8172BNWP) is available from many laboratory supply companies, or from the manufacturer: Orion ResearchIncorporated, Laborato
30、ry Products Group, The Schrafft Center, 529 Main Street, Boston, MA02129.Thermo Fisher Scientific, 22Alpha Road, Chelmsford, MA, 01824, USA,1-978-232-6000, I. For Europe: https:/ For Asia Pacific: http:/ For Latin America: www.fish-.4 The specified electrode (Metrohm Part # 60269100) is available fr
31、om the manufacturer: Metrohm AG, Ionenstrasse 9101 Herisau Switzerland. Metrohm USA, 6555Pelican Creek Circle, Riverview, FL, 33578. Metrohm Pensalab InstrumentaoAnaltica LTDA, Rua Minerva, 167-Perdizes, So Paulo, SP, Brazil CEP05007-030. MetrohmSingapore Pte, Ltd., 31 Toh Guan Road East, #06-08 LW
32、Techno Centre, Singapore, 608608.D6423 1426.3 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 buffer calibration solutions. The effectof alcoh
33、olic 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 glass electrode response (withchange in tem
34、perature) 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 2222 C 6 2C.2 C.6.5 Beakers, borosilicate glass, 100 mL.mL, graduations are useful to deter
35、mine 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 canmay be used, along with a TFE-fluorocarbon-coated stirring barapproximately
36、19 19 mm to 25-mm25 mm long.6.7 Timer, capable of measuring seconds.7. Reagents and Materials7.1 Purity of ReagentsReagent grade Reagent-grade chemicals shall be used in all tests. Unless otherwise indicated, it isintended that all reagents conform to the specifications of the Committee onAnalytical
37、 Reagents of theAmerican Chemical Societywhere such specifications are available.5 Other grades may be used, provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy of the determination. Commercially prepared solutions are acce
38、ptablefor use.7.2 Buffer SolutionsCommercially available, waterbased buffer solutions (pH=4.00 and pH=7.00) are acceptable for thestandardization.7.3 11 mol M L Hydrochloric Acid (HCl)Mix one volume of concentrated (12(12 mol M) L) HCl with eleven volumes ofdistilled water.7.4 3 Mmol/L Potassium Chl
39、oride (KCl)The electrode is shipped with this filling solution already prepared.7.5 1 Mmol/L Sodium Hydroxide (NaOH)Dissolve 4 g of NaOH pellets in 100 mL of distilled water.7.6 1 Mmol/L Sulfuric Acid (H2SO4)Mix one volume of concentrated (18 M)mol/L) H2SO4 with 17 volumes of distilled water.7.7 Pur
40、ity of WaterUnless 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 chang
41、e the pHe of the 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.Gl
42、ass bottles without 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 fuel ethanol-hydrocarbon blend to be sampled before taking the sample.9. Standardization of Assembly9.1 Turn on the pH meter and allo
43、w it to warm up thoroughly 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 buffer
44、s, solutions, and the electrode to equilibratethermally.9.2 Clean/rehydrate the electrode after every ten samples and new electrodes before first use by alternately soaking severalfourtimes in 11 mol M L NaOH solution and 11 mol M L H2SO4 (or 11 mol M L HCl) for about 30 s each. Remove the electrode
45、and rinse it well with distilled water into a waste container.9.3 Calibrate the pH meter to pH=7.00 with a water-based pH=7.00 buffer solution. Remove 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 solutio
46、n, using the slope adjustment. The slopemustshall be in the 9595 % to 100 % range, or the electrode will have to be cleaned or replaced. Remove the electrode and rinse5 Reagent Chemicals, American Chemical Society Specifications, , American Chemical Society, Washington, D.C. For suggestions on the t
47、esting of reagents not listed bythe 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 143it with distilled water into a was
48、te container. Return the electrode to the pH=7.00 buffer.buffer, and if the measured pH is notbetween 6.90 and 7.10 then return 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 3M3 molL aqueous KCl solution, supplied with the electrode.10.3
49、 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 ethanol-hydrocarbon blend sample for each measurement. Since manyfuel alcohols ethanol-hydrocarbon blend samples are poorly buffered and have low ionic strength, it is important to use a newaliquot for each measurement for best accuracy.10.5 Place about 5060 mL of sample in a 100-mL100 mL beaker containi
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