ISO 20336:2017

INTERNATIONAL ISO
STANDARD 20336
First edition
2017-10
Solid mineral fuels — Determination
of total sulfur by Coulomb titration
method
Combustibles minéraux solides — Détermination de la teneur totale
en soufre par la méthode de titrage de Coulomb
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagent and materials . 1
6 Apparatus . 2
7 Preparation of test sample . 3
8 Procedure. 4
8.1 Preparation of test . 4
8.2 Calibration . 4
8.3 Calibration procedure . 4
8.4 Procedure . 5
8.5 Calibration check . 5
9 Expression of result . 6
10 Precision . 6
10.1 Repeatability limit . 6
10.2 Reproducibility limit . 6
11 Test report . 6
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 on 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 the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee
SC 5, Methods of analysis.
iv © ISO 2017 – All rights reserved

Introduction
The objective of this document is to provide an alternative method for determining the total sulfur
content in solid mineral fuels with high-temperature combustion — Coulomb titration using automated
instruments.
INTERNATIONAL STANDARD ISO 20336:2017(E)
Solid mineral fuels — Determination of total sulfur by
Coulomb titration method
1 Scope
This document specifies an alternative method of determining the total sulfur content of coal and coke
by high-temperature combustion — Coulomb titration.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 687, Solid mineral fuels — Coke — Determination of moisture in the general analysis test sample
ISO 5068-2, Brown coals and lignites — Determination of moisture content — Part 2: Indirect gravimetric
method for moisture in the analysis sample
ISO 11722, Solid mineral fuels — Hard coal — Determination of moisture in the general analysis test
sample by drying in nitrogen
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
4 Principle
In the presence of the catalyst, a weighed sample is combusted at 1 150 °C in a stream of purified air.
The sulfur oxides are formed and dissolved in the electrolytic solution. The sulfur dioxides are titrated
by the iodine and bromine librated from the electrolysis of the potassium iodide and potassium
bromide solution. The quantity of the electricity consumed by electrolysis is integrated and used to
calculate the content of sulfur dioxides. The instrument is calibrated with certified reference materials.
The percentage of total sulfur in the sample is calculated according to the sulfur dioxides content and
the prior calibration.
5 Reagent and materials
During the analysis, unless otherwise stated, use only reagents of recognized analytical grade and only
distilled water or water of equivalent purity.
5.1 Potassium iodide.
5.2 Potassium bromide.
5.3 Glacial acetic acid.
5.4 Self-indicating silica gel, industrial grade.
5.5 Sodium hydroxide, chemical grade.
5.6 Electrolytic solution.
5 g of potassium iodide (5.1) and 5 g of potassium bromide (5.2) are dissolved in (250 to 300) ml of
water, then add 10 ml of glacial acetic acid.
5.7 Glass wool.
5.8 Aluminosilicate wool.
5.9 Catalyst, tungsten trioxide.
5.10 Certified reference materials (CRMs), coal or coke.
6 Apparatus
6.1 Instrument.
For determining sulfur by Coulomb titration, commercially available, consisting of the following
(
...