1、Designation: D7795 12D7795 15Standard Test Method forAcidity in Ethanol and Ethanol Blends by Titration1This standard is issued under the fixed designation D7795; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last rev
2、ision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope Scope*1.1 This test method covers the determination of acidity as acetic acid (see Specification D4806) in commonly available gra
3、desof denatured ethanol, and ethanol blends with gasoline ranging from E95 to E30. This test method is used for determining lowlevels of acidity, below 200200 mg mg/kg kg (ppm mass), with the exclusion of carbon dioxide.1.1.1 Test Method Procedure ADeveloped specifically for measurement of acidity b
4、y potentiometric titration. This is thereferee method.1.1.2 Test Method Procedure BDeveloped specifically for measurement of acidity by color end point titration.1.2 The ethanol and ethanol blends may be analyzed directly by this test method without any sample preparation.1.3 Review the current and
5、appropriate Material Safety Data Sheets (MSDS) for detailed information concerning toxicity, firstaid procedures, and safety precautions and proper personal protective equipments.1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this stan
6、dard.1.5 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. Some specif
7、ic hazards statements are given in Section 7 on Hazards.2. Referenced Documents2.1 ASTM Standards:2D770 Specification for Isopropyl AlcoholD1193 Specification for Reagent WaterD4175 Terminology Relating to Petroleum, Petroleum Products, and LubricantsD4806 Specification for Denatured Fuel Ethanol fo
8、r Blending with Gasolines for Use asAutomotive Spark-Ignition Engine FuelD6300D6708 Practice for Determination of Precision and Bias Data for Use in Test Methods for Petroleum Products andLubricantsStatistical Assessment and Improvement of Expected Agreement Between Two Test Methods that Purport toM
9、easure the Same Property of a MaterialE200 Practice for Preparation, Standardization, and Storage of Standard and Reagent Solutions for Chemical Analysis3. Terminology3.1 Definitions:3.1.1 acidity, nthe quality, state, or degree of being acid. D41753.1.1.1 DiscussionThe amount of acid titrated with
10、a base (NaOH or KOH) in a sample of ethanol or ethanol blend with gasoline, calculated as aceticacid in mg/kg (ppm mass).3.2 Abbreviations:3.2.1 KHC8H4O4KHP-Potassium Acid Phthalate1 This test method is under the jurisdiction ofASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants a
11、nd is the direct responsibility of SubcommitteeD02.06 on Analysis of Liquid Fuels and Lubricants.Current edition approved Dec. 1, 2012Dec. 15, 2015. Published February 2013February 2016. Originally approved in 2012. Last previous edition approved in 2012 asD7795 12. DOI: 10.1520/D7795-12.10.1520/D77
12、95-15.2 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 intended o
13、nly 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 current ver
14、sionof 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 States14. Summary of Test Method4.1 Samples a
15、re purged with nitrogen prior to and during titration for the elimination of carbon dioxide and then a knownamount of ethanol or ethanol blend sample is analyzed potentiometrically either using a monotonic or dynamic end point titrantaddition, as specified in Test Method Procedure A, or by color end
16、 point titration, as specified in Test Method Procedure B, usinga base (NaOH) solution. Acid content is calculated as milligrams of acetic acid per kilogram of sample.5. Significance and Use5.1 This test method measures acidity in ethanol or ethanol blends quantitatively. Denatured fuel ethanol may
17、contain additivessuch as corrosion inhibitors and detergents as well as contaminants from manufacturing that can affect the acidity of finishedethanol fuel. Very dilute aqueous solutions of low molecular mass organic acids, such as acetic acid, are highly corrosive to manymetals. It is important to
18、keep such acids at a very low level.5.2 Acceptable levels of acidity in Ethanolethanol or Ethanolethanol blends can vary with different specifications but in generalit is below 200 mg/kg (ppm). Knowledge of the acidity can be required to establish whether the product quality meets specification.6. I
19、nterferences6.1 Basic solutions will absorb carbon dioxide from the air to produce carbonate ions in the titrant and change the concentrationof the titrant. Care should be taken to minimize exposure of basic titrants to the air as much as possible. Verify the concentrationof the titrant (standardize
20、 the titrant) frequently enough to detect concentration changes of 0.00050.0005 mol ML (M) andespecially if prolonged exposure to the air occurs.6.2 Minimize exposure of the ethanol or ethanol blend samples to the air to avoid contamination by carbon dioxide.7. Hazards7.1 Each analyst shall be acqua
21、inted with the potential hazards of the equipment, reagents, products, solvents and proceduresbefore beginning laboratory work. Sources of information include: instrument manuals, MSDS, various literature, and other relatedsources. Safety information should be requested from the supplier. Disposal o
22、f waste materials, reagents, reactants, and solventsshall comply with all the laws and regulations from all applicable governmental agencies.7.2 Ethanol or ethanol blend products are intended for industrial use only.7.3 The following hazards are associated with the application of this test method an
23、d the use of an automatic titrator.7.3.1 Chemical Hazard:7.3.1.1 A solution of potassium hydroxide or sodium hydroxide is corrosive and shall be handled with the appropriate personalprotective equipment such as gloves, chemical goggles, and lab coat or chemical-resistant apron. Always add the base t
24、o waterwhen diluting 50 % NaOH.7.3.1.2 Ethanol is a flammable and toxic solvent that is used to prepare the lithium chloride electrolyte solution for the referenceelectrode. When handling a flammable solvent, work in a well-ventilated area away from all sources of ignition.TEST METHOD PROCEDURE APOT
25、ENTIOMETRIC TITRATION8. Apparatus8.1 Potentiometric TitratorAutomatic titration systems capable of adding fixed increments of titrant at fixed time intervals(monotonic) or variable titrant increments with electrode stability between increment additions (dynamic) with endpoint seekingcapabilities as
26、prescribed in the method. At the very least, the automatic titration system shall meet the performance andspecification requirements as warranted by the manufacturer.8.2 A monotonic or dynamic mode of titrant addition shall be used. During the titration, the speed and volume of the additionmay vary
27、depending on the rate of change of the system. The recommended minimum volume increment is 0.05 mL 0.05 mL forlow acidity samples such as E30, and the recommended maximum volume increment is 0.1 mL. A signal drift of 10 mV/min andendpoint recognition set to last is recommended to ensure endpoint det
28、ection. When using a monotonic titrant addition the waitingtime between increment additions shall be sufficient to allow for mixing and a stable electrode response. Wait at least 10 s betweenadditions.8.3 Buret, 5 mLcapacity, capable of delivering titrant in 0.02 mLor larger increments. The buret ti
29、p shall deliver titrant directlyinto the titration vessel without exposure to the surrounding air.The buret used for base solutions shall have a guard tube containingcarbon dioxide absorbent.8.4 Titration Stand, suitable for supporting the electrode, stirrer and buret tip.8.5 Sensing Electrode, stan
30、dard pH, suitable for non-aqueous titrations.8.6 Reference ElectrodeSilver/Silver Chloride (Ag/AgCl) Reference Electrode, filled with 1M-3M LiCl in ethanol.D7795 1528.7 Combination pH ElectrodesSensing electrodes may have the Ag/AgCl reference electrode built into the same electrodebody, which offer
31、s the convenience of working with and maintaining only one electrode.Acombination pH electrode designed fornonaqueous titrations of organic solvents is needed for titration of ethanol and ethanol blends. The combination pH electrode shallhave a sleeve junction on the reference compartment and shall
32、use an inert ethanol electrolyte, 1 mol/L to 3 mol/L (M) LiCl inethanol. Combination pH electrodes shall have the same or better response than a dual electrode system.They shall have a movablesleeve for easy rinsing and addition of electrolyte.8.8 Titration Beaker, borosilicate glass or plastic beak
33、er of suitable size for the titration.8.9 Sparging System, a gas delivery system suitable to deliver directly into the liquid sample, with an external pressure of 10psi (69 kPa).69 kPa (10 psi).8.10 Variable-Speed Mechanical Stirrer, a suitable type, equipped with a propellertype stirring paddle. Th
34、e rate of stirring shallbe sufficient to produce vigorous agitation without spattering and without stirring air into the solution. A propeller with blades 6mm in radius and set at a pitch of 30 to 45 is satisfactory. A magnetic stirrer and stirring bars is also satisfactory.8.10.1 If an electrical s
35、tirring apparatus is used, it shall be electrically correct and grounded so that connecting or disconnectingthe power to the motor will not produce a permanent change in the instrument reading during the course of the titration.9. Reagents and Materials9.1 Purity of ReagentsReagent grade chemicals s
36、hall be used in all tests. Unless otherwise indicated, it is intended that allreagents shall conform to the specifications of the committee on Analytical Reagents of the American Chemical Society, wheresuch specifications are available.3 Other grades may be used, provided it is pure enough to be use
37、d without lessening the accuracyof the determination.9.1.1 Commercially-available solutions may be used in place of laboratory preparations provided the solutions have beencertified as being equivalent.9.1.2 Alternate volumes of the solutions may be prepared, provided the final solution concentratio
38、n is equivalent.9.2 Purity of WaterUnless otherwise indicated, reference to water shall be understood to mean reagent water that meets therequirements of either Type II or III of Specification D1193.9.2.1 Prepare CO2 free water by sparging 1 L of water (9.2) with nitrogen (9.8) for no less than 3 mi
39、n.9.3 Potassium Acid Phthalate (KHC8H4O4), primary standard, driedPlace 4-5 g 4 g to 5 g of primary standard potassium acidphthalate KHC8H4O4 of 100-mesh 100 mesh fineness, in a weighing bottle at 120C120 C for 2 h. Stopper the container and coolit in a desiccator.9.4 Potassium hydrogen phthalateHyd
40、rogen Phthalate (KHP) SolutionAccurately weigh approximately 1.0 g of dried KHPand record the mass to the nearest 60.0001 g and transfer it to a 500 mL Class A volumetric flask swept free of carbon dioxide.Add 200 mL 200 mL of Type II DI water that is free of carbon dioxide, stopper and swirl gently
41、 until it is dissolved. Dilute to 500mL and mix thoroughly. Express the concentration of KHP in solution as Molarity in moles of KHP per litre of solution. The useof a volumetric flask can be avoided by weighing 1.0 g of dried KHP to the nearest 0.0001 g into a beaker and adding 500 g ofType II carb
42、on dioxide free DI water. Record the total mass of water and KHPto the nearest60.01 g and express the concentrationof KHP in the solution as mg KHP per gram of solution. Mix thoroughly to dissolve the KHP and store it in a closed container.9.5 Sodium Hydroxide, Standard Solution (0.01 N)Prepare and
43、standardize a 0.01N0.01 N sodium hydroxide (NaOH) solutionin accordance with the Preparation and Standardization of Solutions, Precision and Bias, Preparation of 50 % of NaOH Solutionsand standardizations section of Practice E200.9.5.1 Alternatively, KOH (0.01 N)N) in isopropyl alcohol solution may
44、be used instead of 0.01 N)N) NaOH.9.6 Alcohols, refined, ethyl or isopropyl.NOTE 1Isopropyl alcohol (99 % grade) conforming to Specification D770, or 190 proof ethyl alcohol conforming to formula No. 3A of the U.S,Bureau ofAlcohol, Tobacco, and Firearms as defined in Title 27, Code of Federal Regula
45、tions (or equivalent regulations in other jurisdictions) is suitablefor use as the solvent. The use of methyl alcohol is not recommended.9.7 Lithium Chloride ElectrolytePrepare a 1-31 mol/L to 3 molL (M) solution of lithium chloride (LiCl) in ethanol per theelectrode manufacturers recommendation.9.8
46、 Nitrogen, 99.9 % pure.9.9 Commercial Aqueous pH 4 and pH 7 Buffer SolutionsThese solutions shall be replaced at regular intervals consistent withtheir stability or when contamination is suspected. Information relating to their stability is provided by the manufacturer.3 Reagent Chemicals, American
47、Chemical Society Specifications, American Chemical Society, Washington, DC. For suggestions on the testing 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
48、.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.D7795 15310. Preparation of Apparatus10.1 Prepare the titrator in accordance with the manufacturers instructions. Any visible air bubbles in the buret tip shall beeliminated prior to titration since this can lead to errors.10.2 Preparation of
49、ElectrodesWhen the combination pH electrode contains Ag/AgCl reference with an electrolyte which isnot 1 mol/L to 3 mol/L (M) LiCl in ethanol, the electrolyte shall be replaced. Drain the electrolyte from the electrode (vacuumsuction), wash away all the salt (if present) with water and then rinse with ethanol. Rinse several times with LiCl electrolytesolution. Finally, replace the sleeve and fill the electrode with the LiCl electrolyte to the filling hole. When refitting the sleeve,ensure that there will be a free flow of electrolyte into the system.10.
