ISO 625:1996

INTERNATIONAL
STANDARD
Second edition
1996-02-I 5
Solid mineral fuels - Determination of
carbon and hydrogen - Liebig method
Combustibles minkraux solides - Dosage du car-bone et de
I ’h ydrogene - M&hode de Liebig
Reference number
IS0 625:1996(E)
IS0 625:1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work
of preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrdtechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 625 was prepared by Technical Committee
lSO/TC 27, Solid mineral fuels, Subcommittee SC 5, Methods of
analysis.
This second edition cancels and replaces the first edition (IS0 625:1975),
which has been technically revised.
Annex A of this International Standard is for information only.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
0 IS0
IS0 625: 1996(E)
Introduction
An alternative method to that specified in this International Standard is
given in IS0 609:1996, Solid mineral fuels - Determination of carbon and
hydrogen - High temperature combustion method.
. . .
III
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IS0 625: 1996(E)
INTERNATIONAL STANDARD 0 IS0
Solid mineral fuels - Determination of carbon and
hydrogen - Liebig method
IS0 1015:1992, Brown coals and /ignites - Determi-
1 Scope
nation of moisture content - Direct volumetric
method.
This International Standard specifies a method of de-
termining the total carbon and the total hydrogen in
IS0 I 170:1977, Coal and coke - Calculation of
hard coal, brown coal and lignite, and coke, by the
analyses to different bases.
Liebig method.
IS0 1988:1975, Hard coal - Sampling.
The results include the carbon in the carbonates and
the hydrogen combined in the moisture and in the
IS0 2309:1980, Coke - Sampling.
water of constitution of silicates. A determination of
moisture is carried out at the same time, and an ap-
IS0 5068: 1983, Brown coals and /ignites - Determi-
propriate correction is applied to the hydrogen value
nation of moisture content - Indirect gravimetric
obtained by combustion. A determination of carbon
method.
dioxide may also be made and the total carbon value
corrected for the presence of mineral carbonates.
IS0 5069-2:1983, Brown coals and /ignites - Prin-
ciples of sampling - Part 2: Sample preparation for
determination of moisture content and for general
analysis.
2 Normative references
3 Principle
The following standards contain provisions which,
A known mass of coal or coke is burnt in a current of
through reference in this text, constitute provisions
oxygen in a tube impervious to gases, the products
of this International Standard. At the time of publi-
of the incomplete combustion being further burnt
cation, the editions indicated were valid. All standards
over copper oxide; all the hydrogen is converted to
are subject to revision, and parties to agreements
water and all the carbon to carbon dioxide. These
based on this International Standard are encouraged
products are absorbed by suitable reagents and de-
to investigate the possibility of applying the most re-
termined gravimetrically. Oxides of sulfur are retained
cent editions of the standards indicated below.
by lead chromate, chlorine by a silver gauze roll and
Members of IEC and IS0 maintain registers of cur-
oxides of nitrogen by granular manganese dioxide.
rently valid International Standards.
4 Reagents and materials
IS0 331:1983, Coal - Determination of moisture in
the analysis sample - Direct gravimetric method.
WARNING - Care should be exercised when
handling reagents, many of which are toxic.
IS0 687:1974, Coke - Determination of moisture in
the analysis sample.
During the analysis, unless otherwise stated, use only
IS0 925: 1980, Solid mineral fuels - Determination reagents of recognized analytical grade and only dis-
of carbon dioxide content - Gravimetric method. tilled water or water of equivalent purity.

IS0 625:1996(E)
4.1 Magnesium perchlorate, anhydrous, less than
5 Apparatus
I,2 mm in size and preferably within the size range
I,2 mm to 0,7 mm.
weighing to the
5.1 Analytical balance, capable of
nearest 0,l mg.
WARNING - Due regard must be taken of local
regulations when disposing of exhausted mag-
5.2 Purification train, for absorbing water vapour
nesium perchlorate. Regeneration of magnesium
and carbon dioxide from the oxygen used for the
perchlorate must not be attempted, owing to the
combustion. Assemble the train using a series of U-
risk of explosion.
tubes containing the following reagents in the order
stated, in the direction of flow:
4.2 Sodium hydroxide on an inert base, preferably
of a coarse grading, for example 3,0 mm to I,5 mm,
magnesium perchlorate (4.1) for absorbing water;
a)
but not finer than the grading I,2 mm to 0,7 mm, and
preferably of the self-indicating type.
b) sodium hydroxide on an inert base (4.2) for ab-
sorbing carbon dioxide;
4.3 Manganese dioxide, granular, I,2 mm to
magnesium perchlorate for absorbing the water
0,7 mm. d
evolved in the reaction between carbon dioxide
Manganese dioxide in the granular form and the size
and sodium hydroxide.
required can be prepared as follows.
The purification train shall be large enough to render
Dissolve manganese sulfate in water and boil the
frequent recharging unnecessary, even with continu-
solution. Make the solution alkaline with ammonium
ous use.
hydroxide and add solid ammonium persulfate, in
small portions, to the boiling solution until precipi-
5.3 Combustion assembly
tation is complete. Filter through a hardened fast-filter
paper, wash with water by decantation, then with di-
5.3.1 Furnaces. The combustion tube is heated by
lute sulfuric acid and finally with water until acid-free.
three furnaces. For the I,25 mm combustion tube
Transfer the moist precipitate to a mortar and place in
described in clause 6, the following approximate
an oven until most of the water has evaporated, but
lengths are appropriate:
the powder is still damp. Press the mass into a cake
with a pestle, using firm pressure. Complete the dry-
a) furnace No. 1 (to heat the boat and its contents
ing, break up the cake cautiously and sieve to separ-
to 925 “C) - 250 mm;
ate the I,2 mm to 0,7 mm size.
b) furnace No. 2 (to keep the entire copper oxide
4.4 Copper gauze of mesh app roximately 1 mm
I
section of the tube heated to 800 “C) -
and 1 0 mm wide.
500 mm;
c) furnace No. 3 (to cover the lead chromate and the
4.5 Copper oxide, wire form, chopped to particles
roll of pure silver gauze and to heat the former to
approximately 3 mm long with a diameter of approxi-
about 500 “C) - 200 mm.
mately 0,2 mm.
5.3.2 Combustion tube, of fused silica or suitable
4.6 Lead chromate, fused, size range 2,4 mm to
hard glass. The diameter of the tube shall be 12 mm
I,2 mm.
to 15 mm. A suitable length is I,25 m.
4.7 Pure silver gauze, of mesh approximately
5.3.3 Combustion boat, of platinum, porcelain or
1 mm, made of wi re approximately 0, 3 mm in diam-
fused silica, approximately 70 mm long.
eter.
5.4 Absorption train, for absorbing the water and
4.8 Oxygen, hydrogen-free, preferably prepared
carbon dioxide evolved by the combustion of the
from liquid air and not by electrolysis. Electrolytically
sample. Assemble the train using the following re-
prepared oxygen shall be passed over red-hot copper
agents in the order stated, in the direction of flow.
oxide before use to remove any trace of hydrogen.
magnesium perchlorate (4.1) for absorbing the
a)
water evolved during the combustion;
4.9 Glass wool.
0 IS0 IS0 625:1996(E)
manganese dioxide, which is contained in a guard
b) granular manganese dioxide (4.3) for absorbing
tube (figure2), providing a long contact time with
oxides of nitrogen;
minrmum mass.
c) magnesium perchlorate for absorbing the water
evolved from the manganese dioxide; A typical absorption train, with details of the packing,
is shown in figure3. A is the absorber for water, B is
sodium hydroxide on an inert base (4.2) for ab-
a guard-tube absorber for oxides of nitrogen, and C
sorbing carbon dioxide;
absorbs any water evolved from the manganese di-
oxide. Carbon dioxide is absorbed in D, the mag-
magnesium perchlorate for absorbing the water
nesium perchlorate in the upper portion absorbing any
produced in the reaction between carbon dioxide
water produced in the reaction between carbon diox-
and sodium hydroxide.
ide and sodium hydroxide. A second carbon dioxide
absorber, E, should be added as a precautionary
Midvale tubes (figure I), which provide a large area
measure.
of reaction, are used for all the reagents except
Dimensions in millimetres
Indicator spot ---,
@ ext. 33 to 34
Wall thickness I to I,25
@ ext. 55
to 6
r
Figure 1 - Midvale tube
0 IS0
IS0 625: 1996(E)
Dimensions in millimetres
A----- 14/Z con ical ground joint
/- 30 )
Manganese dioxide
Glass wool /
Figure 2 - Guard tube
IS0 625: 1996(E)
-
1 Magnesium perchlorate, I,2 mm to 0,7 mm size
4 Manganese dioxide
2 Sodium hydroxide (see 4.2), I,2 mm to 0,7 mm size 5 Inlet
3 Glass wool
NOTE - In this illustration the optional second carbon dioxide absorber, E, is shown.
Figure 3 - Absorption train
nitrogen dioxide which is absorbed by the manganese di-
Stoppered U-tubes may be used, if preferred, in place
oxide.
of the Midvale tubes.
5.5 Oxygen flow-rate controller, a reducing valve
Place glass wool (4.9), previously dried at 105 “C for
on the oxygen cylinder together with a small needle
1 h, above and below the absorbents to prevent the
valve and flowmeter, capable of measuring a flow of
carry-over of dust by the flow of oxygen, and to pre-
up to 100 ml/min, immediately before the purification
vent the cracking of the Midvale tube by the heat of
train, is generally adequate. It may be useful to attach
reaction.
a bubbler device at the exit end of the assembled
apparatus to give a visual indication of the rate of
If water is condensed in the first absorber, some ni-
flow.
trogen dioxide may dissolve in it and be considered
as water. Because of the conversion factor from
5.6 Heat-resistant
stopper (acrylonitrile or
water to hydrogen, the error in the hydrogen deter-
chloroprene) for connecting the absorption train to the
mination thus caused is small, in the order of 0,05 %
combustion tube.
of hydrogen. This can only be avoided by heating the
absorption tube to a temperature that is sufficiently
high to prevent condensation of water.
5.7 Copper gauze roll, for constraining the reagents
in the appropriate sections of the combustion tube
(5.3.2). Roll the copper gauze into rolls IO mm long
NOTE 1 Oxides of nitrogen formed in the combustion
and of sufficient diameter to ensure a close fit in the
would, in the absence of precautions, be absorbed by the
combustion tube.
sodium hydroxide and measured as carbon dioxide. The er-
ror in the carbon determination thus caused, in the order of
5.8 Copper gauze spiral, through which passes a
0,2 % of carbon, is substantially avoided by the use of a
stout copper wire provided with a loop to facilitate
guard tube (see figure2) in which the gases pass through
an annular space to allow oxidation of nitrogen monoxide to removal from the combustion tube (5.3.2).
0 IS0
IS0 625:1996(E)
- IO mm space for a heat-resistant stopper (5.6).
5.9 Silver gauze roll, for absorbing chlorine. Roll
the pure silver gauze (4.7) to form a plug, 100 mm
The arrangement is shown in figure4.
long and of sufficient diameter to ensure a close
sliding fit in the combustion tube (5.3.2). A stout, pure
NOTE 2 The copper gauze spiral and rolls are oxidized
silver wire is passed through the centre of the roll to
during the preliminary heating in a current of oxygen.
facilitate its removal from the tube.
5.10 Heat-resistant wire, approximately 2,5 mm
6.2 Conditioning the combustion tube
thick and 500 mm long, with a bent end to place the
Before starting a determination with a newly-packed
boat in the correct position in the combustion tube
combustion tube, heat the tube throughout its length,
and to transfer the used boat from the combustion
tube onto a rigid refractory sheet. while passing a current of purified oxygen at a rate
of 12 ml/min. Heating shall be continued for 3 h, with
furnace No. I at a temperature of 925 “C, furnace
6 Preparation of the apparatus
No. 2 at a temperature of 800 “C and furnace No. 3,
containing that portion of the tube packed with lead
6.1 Preparation of the combustion tube
chromate and pure silver gauze, at a temperature of
about 500 “C. The empty space adjacent to the exit
For a combustion tube I,25 mm long and 12 mm to
end of the tube shall be heated in such a manner that,
15 mm in diameter, the following arrangement of the
without charring the rubber stopper, condensation of
spacing is suitable:
steam is avoided.
- IO mm space for a rubber stopper;
6.3 Conditioning the absorption train
- 300 mm space to allow the furnace to be removed
behind and away from the boat;
Connect the absorption train to the apparatus and
purge with purified oxygen for 20 min, with the fur-
- 80 mm occupied by a copper gauze spiral (5.8)
naces at their working temperatures. Disconnect ab-
(see note 2);
sorbers A and D (and E, if used) (see figure3) from the
absorptio
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