BS ISO 17315-2014 Petroleum products and other liquids Ethanol Determination of total acidity by potentiometric titration《石油产品和其它液体 乙醇 使用电位滴定法测定总酸度》.pdf

1、BSI Standards PublicationBS ISO 17315:2014Petroleum products andother liquids Ethanol Determination of total acidityby potentiometric titrationBS ISO 17315:2014 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 17315:2014.The UK participation in its preparation w

2、as entrusted to TechnicalCommittee PTI/13, Petroleum Testing and Terminology.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correcta

3、pplication. The British Standards Institution 2014. Published by BSI StandardsLimited 2014ISBN 978 0 580 80575 2ICS 75.160.20Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Com

4、mittee on 31 October 2014.Amendments issued since publicationDate Text affectedBS ISO 17315:2014 ISO 2014Petroleum products and other liquids Ethanol Determination of total acidity by potentiometric titrationProduits ptroliers et autres liquides thanol Dosage de lacidit totale par titration potentio

5、mtriqueINTERNATIONAL STANDARDISO17315First edition2014-10-01Reference numberISO 17315:2014(E)BS ISO 17315:2014ISO 17315:2014(E)ii ISO 2014 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2014All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilize

6、d otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright o

7、fficeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 17315:2014ISO 17315:2014(E) ISO 2014 All rights reserved iiiContents PageForeword ivIntroduction v1 Scope . 12 Terms and definitions . 13 Reagents and

8、 materials . 14 Apparatus . 35 Apparatus calibration . 36 Procedure. 37 Calculation 48 Expression of results 59 Precision . 59.1 General . 59.2 Repeatability, r .59.3 Reproducibility, R .6Bibliography 7BS ISO 17315:2014ISO 17315:2014(E)ForewordISO (the International Organization for Standardization)

9、 is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be repre

10、sented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.The procedures used to devel

11、op this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/

12、IEC Directives, Part 2 (see www.iso.org/directives).Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during th

13、e development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.For an explanation on the meaning o

14、f ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe committee responsible for this document is ISO/TC 28, Petro

15、leum products and lubricants, Subcommittee SC 7, Liquid biofuels.iv ISO 2014 All rights reservedBS ISO 17315:2014ISO 17315:2014(E)IntroductionDiluted hydrous solutions of organic acids, e.g. acetic acid, can corrode many materials. Thus, it is necessary to determine and keep at low values the acid c

16、ontent in the final product.An ethanol sample can have organic acids from the productive process, from its handling, contained in additives, or due to sample degradation or contamination. The relative content of those components can be determined by titration with a strong alkaline solution.The nume

17、ric result of total acidity is a measure of the amount of acid components in the sample. Total acidity is used as a quality control parameter of final product to prevent long-run corrosion problems.For this reason, final product obtained from a blend of ethanol and other fuels has to have a limited

18、acidity. ISO 2014 All rights reserved vBS ISO 17315:2014BS ISO 17315:2014Petroleum products and other liquids Ethanol Determination of total acidity by potentiometric titrationWARNING The use of this International Standard can involve hazardous materials. This International Standard does not purport

19、 to address all the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.1 ScopeThis International Standard specifies a

20、test method for the determination of total acidity of ethanol by potentiometric titration. The total acidity is reported as acetic acid mass, in milligrams, per ethanol volume, in litres, or as mass percent of acetic acid (% m/m), if the density of ethanol is known.NOTE 1 For the purposes of this In

21、ternational Standard, the terms “% m/m” and “% v/v” are used to represent the mass fraction and the volume fraction of a material, respectively.NOTE 2 This method was evaluated with ethanol samples with different water contents (0,7 % m/m and 7 % m/m) and acidity values (5 mg to 50 mg HAc per litre

22、of sample).2 Terms and definitionsFor the purposes of this document, the following terms and definitions apply.2.1total acidityamount of acids contained in the ethanol sample, calculated as acetic acid, determined by potentiometric titration with a strong alkaline solution, as given in this Internat

23、ional Standard3 Reagents and materials3.1 Deionized water, with a maximum conductivity of 1 S/cm, Grade 2 or equivalent.3.2 Potassium hydrogen phthalate (KHC8H4O4), standard grade.3.3 Solution of lithium chloride (LiCl) in ethanol, 1 mol/l to 3 mol/l.3.4 Buffer solution, with pH 4 and pH 7.NOTE The

24、above values of pH are only indicative. The values shown on the buffer certificates are those which are intended to be used in the analysis.3.5 Hydrochloric acid solution (HCl), 1,0 mol/l, a solution prepared in accordance with the following or a commercially available standardized hydrochloric acid

25、 solution of equivalent concentration. In order to prepare HCl, 1,0 mol/l, transfer (84,0 0,5) ml of concentrated hydrochloric acid (37 % v/v) to a 1 000 ml volumetric flask containing about its half capacity of water (3.1). Complete the volume and homogenize the solution. Stock the solution in an a

26、mber flask at a temperature below 25 C. This solution has a 6 mo shelf life.INTERNATIONAL STANDARD ISO 17315:2014(E) ISO 2014 All rights reserved 1BS ISO 17315:2014ISO 17315:2014(E)3.6 Sodium hydroxide solution (NaOH), 1,0 mol/l, a solution prepared in accordance with the following or a commercially

27、 available standardized sodium hydroxide solution of equivalent concentration. In order to prepare NaOH, 1,0 mol/l, weigh in a beaker (40,0 0,1) g of sodium hydroxide, dissolve with 200 ml of water (3.1) and stir until complete dissolution, and homogenize. Transfer to a volumetric flask of 1 000 ml

28、and complete the volume with water (3.1). Stock the solution in a polyethylene flask and keep at a temperature below 25 C. This solution has a 2 mo shelf life.3.7 Sodium hydroxide solution (NaOH), 0,02 mol/l, a solution prepared in accordance with 3.7.1 or a commercially available standardized sodiu

29、m hydroxide solution of equivalent concentration.3.7.1 In order to prepare NaOH, 0,02 mol/l, transfer to a 500 ml volumetric flask (10,0 0,1) ml of sodium hydroxide solution, 1,0 mol/l, and complete the volume with water (3.1) and homogenize. Stock the solution in a polyethylene flask and keep at a

30、temperature below 25 C. The reagent shall be restandardized frequently enough to detect concentration changes. The solution shall be protected against carbon dioxide absorption. The solution has a 15 d shelf life.3.7.2 Determine the actual molar concentration of sodium hydroxide solution (3.7.1) as

31、follows.a) Dry the potassium hydrogen phthalate (3.2) in a drying oven at (120 5) C for a minimum of 2 h and store in a desiccator.b) In a beaker, weigh approximately 100 mg of potassium hydrogen phthalate (3.7.2 a) and record the mass value.c) Add 100 ml of water (3.1) and stir until complete disso

32、lution.d) Start the procedure as follows if the solution and the apparatus system are at a temperature around 20 C to 25 C.e) Carry out a potentiometric titration with the sodium hydroxide solution 0,02 mol/l (3.7.1) until the equivalency point using the apparatus described in Clause 4, and after ch

33、ecking the apparatus calibration according Clause 5.f) Using 100 ml of water (3.1), carry out a blank potentiometric titration with the sodium hydroxide solution 0,02 mol/l (3.7.1) until the equivalency point using the apparatus described in Clause 4.g) Calculate molar concentration of the solution

34、using Formula (1):CmVV=()o204 23,(1)whereC is the actual molar concentration of solution, in mol/l;m is the mass of potassium hydrogen phthalate, in mg;V is the volume of sodium hydroxide solution 0,02 mol/l used for titration of potassium hydrogen phthalate solution 3.7.2 e), in ml;Vois the volume

35、of sodium hydroxide solution 0,02 mol/l used for blank titration 3.7.2 f ), in ml;204,23 is the molar mass of potassium hydrogen phthalate, in g/mol.2 ISO 2014 All rights reservedBS ISO 17315:2014ISO 17315:2014(E)3.7.3 The NaOH concentration is determined as an average of three analyses. The relativ

36、e standard deviation (RSD) of three determinations shall be lower than 1 %.WARNING HCl and NaOH are corrosive. It can cause severe burns or blindness. Evolution of heat produces a violent reaction or eruption upon too rapid mixture with water.4 Apparatus4.1 Automatic volumetric potentiometric titrat

37、or.4.2 Glass electrode and reference system, of silver/silver chloride (Ag/AgCl) or combined glass electrode with reference system of silver/silver chloride (Ag/AgCl), single liquid junction and LiCl 1,0 mol/l to 3,0 mol/l in ethanol as internal electrolyte.4.3 Magnetic or mechanical stirrer.4.4 Ana

38、lytical balance, with 0,1 mg precision.4.5 Burette, of 10 ml maximum capacity.4.6 Burette, of 20 ml minimum capacity.4.7 Volumetric pipette, of (50 0,05) ml capacity.4.8 Volumetric flasks, of 100 ml, 500 ml, and 1000 ml capacity.4.9 Desiccator.4.10 Oven, with an accuracy of (120 5) C.4.11 Polyethyle

39、ne flask, of 1 000 ml capacity.4.12 Amber flask, of 1 000 ml capacity.5 Apparatus calibration5.1 Calibrate the electrode according to manufacturers instructions using pH 4 and pH 7 buffer solutions.5.2 If the calibration slope is lower than 0,91, carry out the electrode treatment as described in 5.3

40、 and repeat the electrode verification.5.3 Perform the electrode treatment by dipping it alternately in NaOH 1 mol/l solution and HCl 1 mol/l solution at least three times, keeping the electrode for 10 s in each dipping.6 Procedure6.1 Start the procedure described in 6.2 if the ethanol sample and th

41、e apparatus system are at a temperature around 20 C to 25 C. ISO 2014 All rights reserved 3BS ISO 17315:2014ISO 17315:2014(E)6.2 Add to a flask (50 0,05) ml of ethanol sample and insert the electrode and reference system or the combined electrode in such a way that the liquid junction is completely

42、immersed.6.3 Stir the sample gently to avoid development of bubbles.6.4 Titrate the ethanol sample with the NaOH 0,02 mol/l solution using a burette of 10 ml maximum capacity according to the following titration parameters:a) dynamic addition of titrator;b) minimum increment of 0,01 ml and maximum o

43、f 0,05 ml;c) the next increment shall be added if the signal does not change more than 5 mV at each 10 s (30 mV/min);d) the minimum waiting time between increments shall be 5 s and the maximum 20 s;e) minimum addition of 0,3 ml of the titrant after the equivalent point.6.5 The end point of titration

44、 will be determined with the first derivative of inflection point of titration curve.6.6 Repeat the procedure in order to have two results, provided that these results do not present a deviation higher than method repeatability. Calculate the final result as the average of the two values.NOTE 1 Exte

45、rnal CO2sources can change ethanol acidity. In order to avoid possible interferences, the exposure of the ethanol sample to the air has to be minimized.NOTE 2 It has been observed that after a certain number of analyses, the electrode reduces its efficiency due to dehydration. It is recommended that

46、 the electrode is recalibrated after five analyses, according to 5.3.7 Calculation7.1 Calculate the total acidity of ethanol, in mg/l, using Formula (2):ATCVV=60 05 1 00012,(2)whereAT is the total acidity expressed as acetic acid mass, in mg, per ethanol volume, in l;60,05 is the molar mass of aceti

47、c acid, in g/mol;C is the actual molar concentration of sodium hydroxide solution (NaOH), 0,02 mol/l, in mol/l;V1is the volume of ethanol sample used, in ml;V2is the volume of sodium hydroxide solution 0,02 mol/l used to reach the equivalence point of titration, in ml.7.2 Calculate the total acidity

48、 of ethanol in mass percent of acetic acid (% m/m), using Formula (3):4 ISO 2014 All rights reservedBS ISO 17315:2014ISO 17315:2014(E)ATCdVV=60 05 0112,(3)whereAT is the total acidity expressed as mass percent of acetic acid, in % m/m;C is the actual molar concentration of sodium hydroxide solution

49、(NaOH), 0,02 mol/l, in mol/l;60,05 is the molar mass of acetic acid, in g/mol;d is the density of ethanol at the test temperature, in g/ml;V1is the volume of ethanol sample used, in ml;V2is the volume of sodium hydroxide solution 0,02 mol/l used to reach the equivalence point of titration, in ml.8 Expression of resultsReport the total acidity result of the sample, in mg/l, to the nearest 0,1 mg/l, or in % m/m, to the nearest 0,000 1 %.9 Precision9.1 GeneralAn interlaboratory comparison (IC)