Pulps — Kraft liquor — Determination of residual alkali using potentiometric titration

This document describes a procedure for determining the content of residual alkali in Kraft black liquors having a dry matter content up to 40 %. The method is based on a potentiometric titration with hydrochloric acid and is intended for black liquor samples with an initial pH ≥ 11,0. The lower limit of determination is 0,1 g/l of eq. NaOH.

Pâtes — Liqueur Kraft — Détermination de l’alcali résiduel par titrage potentiométrique

General Information

Status

Published

Publication Date

09-Mar-2023

ICS

85.040 - Pulps

Technical Committee

ISO/TC 6 - Paper, board and pulps

Drafting Committee

ISO/TC 6 - Paper, board and pulps

Current Stage

6060 - International Standard published

Start Date

10-Mar-2023

Due Date

18-Dec-2023

Completion Date

10-Mar-2023

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Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23772
First edition
2023-03
Pulps — Kraft liquor — Determination
of residual alkali using potentiometric
titration
Pâtes — Liqueur Kraft — Détermination de l’alcali résiduel par
titrage potentiométrique
Reference number
ISO 23772:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 23772:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023

be reproduced or utilized 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 ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 23772:2023(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 1

5 Reagents ........................................................................................................................................................................................................................ 2

6 Apparatus .................................................................................................................................................................................................................... 2

7 Sampling and sample pretreatment................................................................................................................................................3

8 Calibration and check of pH meter ................................................................................................................................................... 3

9 Procedure ....................................................................................................................................................................................................................3

10 Calculation .................................................................................................................................................................................................................. 4

11 Report .............................................................................................................................................................................................................................. 5

Annex A (informative) Precision data ................................................................................................................................................................ 6

Bibliography ................................................................................................................................................................................................................................ 7

iii
© ISO 2023 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 23772:2023(E)
Foreword

ISO (the International Organization for Standardization) 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 represented 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 develop 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/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 the 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 of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 6, Paper, board and pulps.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2023 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 23772:2023(E)
Pulps — Kraft liquor — Determination of residual alkali
using potentiometric titration
1 Scope

This document describes a procedure for determining the content of residual alkali in Kraft black

liquors having a dry matter content up to 40 %.

The method is based on a potentiometric titration with hydrochloric acid and is intended for black

liquor samples with an initial pH ≥ 11,0.
The lower limit of determination is 0,1 g/l of eq. NaOH.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
residual alkali
residual effective alkali
content of hydroxide ions remaining in the black liquor

Note 1 to entry: The hydroxide ions can result when sodium (or potassium) sulphide is dissolved in water and

sulphide ions are hydrolysed.

Note 2 to entry: The result is expressed in moles of hydroxide ions per litre of sample or in grams of sodium

hydroxide per litre of sample.
4 Principle

The alkaline species contained in the black liquor sample are titrated potentiometrically with

hydrochloric acid to the first inflection point, which occurs at pH between 11,0 and 11,5. Before the

titration, sodium carbonate is added to the sample to give a better inflection point and to buffer the

titration solution. If the initial pH of the black liquor sample is between 11,0 and 12,5, a known volume

of sodium hydroxide shall be added to the sample before the titration. The content of residual alkali is

calculated from the consumption of the acid at the first inflection point. The result is corrected by a

correction factor to obtain only the hydroxide ions concentration and remove the contribution of other

alkaline species.
Precision data are available in Annex A.
© ISO 2023 – All rights reserved
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ISO 23772:2023(E)
5 Reagents

All chemicals shall be of analytical grade. The water used in the titration and in the preparation of

reagents shall be distilled or deionized.

WARNING — The use of this document can involve hazardous materials, operations and

equipment. It does not purport to address all of the safety or environmental problems associated

with its use.

5.1 Sodium carbonate solution 1 M, dissolve 106,0 g of sodium carbonate, Na CO in water and

2 3
dilute to 1 litre with water.

5.2 Hydrochloric acid 1 M, The actual concentration of hydrochloric acid, HCl, shall be known to the

nearest 0,001 M.
NOTE Commercially available standard solutions can be used.

5.3 Sodium hydroxide solution 1 M, Dissolve 40,0 g of sodium hydroxide, NaOH, in water in a 1 litre

volumetric flask and dilute to the mark with water. Check the concentration by titration with a standard

acid. The actual concentration shall be known to the nearest 0,005 M.
NOTE Commercially available standard solutions can be used.
5.4 Ethanol, for washing the electrodes.

5.5 Buffer solutions, having pH values such as 7,0 and 11,0. Suitable buffer solutions are commercially

available or can be prepared as follows:

— pH 7,00, 25 °C: Dissolve 6,80 g of potassium dihydrogen phosphate, KH PO , previously dried for

2 4

2 h at 105 °C, and 1,16 g of sodium hydroxide, NaOH, in water in a 1 l volumetric flask and dilute to

the mark.

— pH 11,00, 25 °C: Dissolve 3,55 g of disodium hydrogen phosphate, Na HPO , previously dried for 2 h

2 4

at 105 °C, and 0,16 g of sodium hydroxide, NaOH, in water in a 1 l volumetric flask and dilute to the

mark.
6 Apparatus
The usual laboratory apparatus and, in particular, the following shall be used.

6.1 Automatic titrator or pH-meter, an automatic device for potentiometric titration including a

motorized burette (10 ml or 20 ml) and a recorder shall be used.
NOTE If necessary, a manual titrator and a separate pH meter can be used.

6.2 Electrodes, suitable glass and reference electrodes. A combined pH glass electrode may be used.

A high sodium pH-electrode is recommended.
NOTE Clean the electrodes with ethanol (5.4) if the response time deteriorates.
6.3 Fume hood, to ventilate any gases.
© ISO 2023 – All rights reserved
---------------------- P
...

DRAFT INTERNATIONAL STANDARD
ISO/DIS 23772
ISO/TC 6 Secretariat: SCC
Voting begins on: Voting terminates on:
2022-05-04 2022-07-27
Pulps — Kraft liquor — Residual alkali (Hydroxide ion
content)
ICS: 85.040
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
This document is circulated as received from the committee secretariat.
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 23772:2022(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/DIS 23772:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

be reproduced or utilized 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 ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/DIS 23772:2022(E)
Contents Page

5.1 General ........................................................................................................................................................................................................... 2

5.2 Sodium carbonate solution 1 M ............................................................................................................................................... 2

5.3 Hydrochloric acid 1 M ...................................................................................................................................................................... 2

5.4 Sodium hydroxide solution 1 M ............................................................................................................................................... 2

5.5 Ethanol ........................................................................................................................................................................................................... 2

5.6 Buffer solutions ...................................................................................................................................................................................... 2

6.1 General ........................................................................................................................................................................................................... 2

6.2 Automatic titrator or pH-meter ............................................................................................................................................... 3

6.3 Electrodes ................................................................................................................................................................................................... 3

6.4 Fume hood .................................................................................................................................................................................................. 3