ISO/PRF 6791

• Abstract:

  Specifies a conventional gravimetric method for the determination. A test portion ist reated with quinoline in a beaker at 70 to 80 °C for 15 to 20 min. Then the dissolved test portion and the residue are brought to a Hartley funnel fitted with a filter pad, and are filtered. The washed and dried residue on the filter pad is weighed.

• Status: Not Published
• ICS: 71.100.10 - Materials for aluminium production
• Technical Committee: ISO/TC 226 - Materials for the production of primary aluminium
• Drafting Committee: ISO/TC 226/WG 1 - Carbonaceous binders, including pitch
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 15-Sep-2026
• Completion Date: 19-Sep-2026

• Revises: ISO 6791:1981 - Carbonaceous materials for the production of aluminium — Pitch for electrodes — Determination of contents of quinoline-insoluble material
• Effective Date: 04-Nov-2023

Overview

ISO/PRF 6791:2026 specifies a gravimetric method for determining the quinoline-insoluble (QI) content in pitch used for electrodes in aluminium production. By standardizing this procedure, the document supports quality control and process optimization in the aluminium industry, ensuring that pitch used for electrode production meets performance and consistency requirements.

The method involves treating a sample portion with quinoline at a controlled temperature, filtering the dissolved mixture through a Hartley funnel equipped with a specified filter pad, and weighing the remaining residue after washing and drying. This gravimetric approach ensures a reliable and repeatable quantification of quinoline-insoluble material content.

Key Topics

• Purpose: To quantify quinoline-insoluble material in carbonaceous electrode pitch, critical for electrode quality in aluminium smelting.
• Sample Preparation: Involves grinding or melting the sample, depending on its hardness, to ensure representative analysis.
• Reagents: Utilizes freshly distilled quinoline and toluene, emphasizing the use of analytical-grade chemicals and adherence to safety measures due to toxicity and flammability.
• Apparatus: Requires laboratory equipment including water bath (70-80°C), Hartley funnel with specified filter pads, and electric oven (105–110°C).
• Gravimetric Procedure: Extraction, filtration, washing, drying, and precise weighing underpin the method’s accuracy and reproducibility.
• Calculation and Reporting: Results are calculated by mass difference and expressed as percentage by mass, with clear guidance on reporting and handling deviations or unusual observations.

Applications

ISO/PRF 6791 is crucial for:

• Aluminium Production Plants: Ensuring pitch quality for the manufacture of carbon electrodes, which affects anode performance, lifespan, and overall process efficiency.
• Quality Control Laboratories: Providing a repeatable and trusted method to monitor and control QI content in pitch batches, supporting consistent production outputs.
• Research and Development: Assisting in optimizing pitch formulations and electrode fabrication processes within the aluminium industry.
• Supplier and Customer Assurance: Facilitating standardized assessment for pitch suppliers and end users, promoting transparency and conformity to international expectations.

By applying this standard, organizations minimize variations in electrode performance, reduce production costs, and uphold product quality throughout the supply chain.

Related Standards

For effective implementation and a comprehensive approach to carbonaceous materials analysis in aluminium production, consider the following related ISO standards:

• ISO 6257 - Carbonaceous materials used in the production of aluminium - Pitch for electrodes - Sampling: Defines sampling methods for pitch to ensure representative testing for analytical purposes.
• Other ISO Standards on Electrode Materials - Covering properties, testing, and handling of carbon materials for the aluminium sector.
• ISO Terminology Resources:
  • ISO Online Browsing Platform: For up-to-date definitions relevant to materials and testing.
  • IEC Electropedia: For related electrotechnical terminology.

Practical Value

Implementing ISO/PRF 6791 enhances operational efficiency and product excellence by:

• Reducing inconsistency in electrode quality through reliable QI content determination
• Enabling data-driven improvements in pitch selection and handling
• Supporting compliance with global aluminium industry requirements

By following this standard, aluminium producers and suppliers demonstrate commitment to best practices in material analysis and foster trust in quality assurance programs.

International
Standard
ISO 6791
Second edition
Carbonaceous materials for the
production of aluminium — Pitch
for electrodes — Determination
of contents of quinoline-insoluble
material
Produits carbonés utilisés pour la production de l'aluminium —
Brais pour électrodes — Détermination du taux de matières
insolubles dans la quinoléine
PROOF/ÉPREUVE
Reference number
ISO 6791:2026(en) © ISO 2026
ISO 6791:2026(en)
© ISO 2026
All rights reserved. Unless otherwise specified, or required in the context of its implementation, 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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 6791:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sample preparation . 3
8 Procedure . 4
8.1 Test portion .4
8.2 Filter preparation . .4
8.3 Determination .4
9 Expression of results . 5
9.1 Method of calculation .5
9.2 Precision . . .5
10 Test report . 5
PROOF/ÉPREUVE
iii
ISO 6791:2026(en)
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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 226, Materials for the primary production of
aluminium.
This second edition cancels and replaces the first edition (ISO 6791:1981), which has been technically
revised.
The main changes are as follows:
— added analysis procedure details to help run the analysis;
— corrected text to formal SI formatting;
— updated test report description.
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.
PROOF/ÉPREUVE
iv
ISO 6791:2026(en)
Introduction
In a carbon paste plant, the pitch content needs to be optimized amongst other factors according to the
quinoline insoluble content of the pitch. Two types of quinoline insoluble (QI) exist: primary and secondary.
Primary QI are formed in the coke oven and are beneficial to the carbon anode quality. Secondary QI (or
mesophase) are formed by additional heat treatment of the pitch and are either neutral or harmful to the
anode quality. Primary QI material is very dense and leads to high coking values of the pitch. Therefore,
a high primary QI pitch has a high binding power. The principle of the method is the extraction of a test
portion
...

ISO/TC 226
Secretariat: SN SNV
Date: 2026-07-21
Carbonaceous materials for the production of aluminium — Pitch
for electrodes — Determination of contentcontents of quinoline-
insoluble material
Copyright notice
ThisProduits carbonés utilisés pour la production de l'aluminium — Brais pour électrodes — Détermination du
taux de matières insolubles dans la quinoléine
PROOF
© ISO document is a working draft2026
All rights reserved. Unless otherwise specified, or committee draft and is copyright-protected by ISO. While required in
the reproductioncontext of working drafts or committee drafts in any form for use by participants in the ISO standards
development process is permitted without prior permission from ISO, neither its implementation, no part of this
document nor any extract from itpublication may be reproduced, stored or utilized otherwise in any form or transmitted
in any form for any other purposeby any means, electronic or mechanical, including photocopying, or posting on the
internet or an intranet, without prior written permission from ISO. Permission can be requested from either ISO at the
address below or ISO’s member body in the country of the requester.
Requests for permission to reproduce this document for the purpose of selling it should be addressed as shown below or
to ISO's member body in the country of the requester:
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Reproduction for sales purposes may be subject to royalty payments or a licensing agreement.
Violators may be prosecuted.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO 2026 – All rights reserved
iii
Contents Page
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sample preparation . 3
8 Procedure . 4
8.1 Test portion . 4
8.2 Filter preparation . 4
8.3 Determination . 4
9 Expression of results . 5
9.1 Method of calculation . 5
9.2 Precision . 5
10 Test report . 5

Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 1
5 Reagents and materials . 1
6 Apparatus . 2
7 Sample preparation . 4
8 Procedure . 4
8.1 Test portion . 4
8.2 Filter preparation . 4
8.3 Determination . 4
9 Expression of results . 5
9.1 Method of calculation . 5
9.2 Precision . 5
10 Test report . 5

iv
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
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.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 226, Materials for the primary production of
aluminium.
This second edition cancel
...