ISO 23604:2022

INTERNATIONAL ISO
STANDARD 23604
First edition
2022-11
Method of determining specific
surface area of coal
Méthode de détermination de la surface spécifique du charbon
Reference number
ISO 23604:2022(E)
© ISO 2022

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ISO 23604:2022(E)
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© ISO 2022
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Published in Switzerland
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ISO 23604:2022(E)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principles . 2
5 Reagents and materials . 2
6 Sample preparation .3
7 Experiments and calculations . 4
7.1 Degas the sample tube degassing . 4
7.2 Sample pretreatment . 4
7.2.1 Degassing of samples . . 4
7.2.2 Heating temperature selection . 4
7.3 Determination of free space volume . 5
7.4 Determination of adsorption isotherms . 5
7.5 Monolayer saturated adsorption, V . 6
m
7.5.1 Calculation of V by adsoprtion isotherm . 6
m
7.5.2 Calculation of V by the Langmuir equation . 6
m
7.6 Specific surface area calculation . 7
7.7 Determination of micropores total volume . 8
7.7.1 Micropore filling theory . 8
7.7.2 DR-DA equation . 8
7.7.3 Experiment procedure . 9
7.7.4 Calculation of adsorption capacity . 10
7.7.5 Formula of micropore specific surface area . 10
Bibliography .11
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ISO 23604:2022(E)
Foreword
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INTERNATIONAL STANDARD ISO 23604:2022(E)
Method of determining specific surface area of coal
1 Scope
This document provides a method for determining the specific surface area of solid materials using gas
adsorption.
This document is applicable to the determination of specific surface area of coal, and other powder
and porous materials including nano-powders and nano-grade porous materials with a determination
2 2
range of 0,001 m /g to 1 000 m /g.
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 9277, Determination of the specific surface area of solids by gas adsorption — BET method
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
surface area
extent of accessible surface area as determined by a given method under stated conditions
[SOURCE: ISO 15901-1:2016, 3.30]
3.2
adsorption
enrichment of the adsorptive gas at the external and accessible internal surfaces of a solid material
[SOURCE: ISO 15901-2:2022, 3.2, modified — "material" added to the definition]
3.3
adsorbate
adsorbed gas
[SOURCE: ISO 15901-2:2022, 3.1]
3.4
saturation vapour pressure
vapour pressure of the bulk liquefied adsorptive gas at the temperature of adsorption (3.2)
[SOURCE: ISO 15901-2:2022, 3.20 modified — "gas" added to the definition]
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ISO 23604:2022(E)
3.5
relative pressure
ratio of the equilibrium adsorption pressure, p, to the saturation vapour pressure (3.4), p , at analysis
0
temperature
[SOURCE: ISO 15901-2:2022, 3.19]
3.6
adsorption amount
amount of gas adsorbed by the adsorbent under the equilibrium adsorption pressure at given
temperature
3.7
adsorption isotherm
curve obtained by plotting the amount of gas adsorbed against the equilibrium pressure or relative
pressure at a constant temperature
3.8
specific surface area
surface area of a solid substance per unit mass (or unit volume)
3.9
micropore
pore with width about 2 nm or less
[SOURCE: ISO 15901-2:2022, 3.13]
4 Principles
The principle of determination of specific surface area by gas adsorption is based on the adsorption
properties of gases on solid surfaces. Under a certain pressure and ultra-low temperature, the physical
adsorption of the sample particles (adsorbent) for gas molecules (adsorbate) is reversible, and there
is a determinate equilibrium adsorption corresponding to a certain pressure. Therefore, the specific
surface area of the sample can be equivalently determined by measuring the equilibrium adsorption on
the basis of a theoretical model.
5 Reagents and materials
5.1 Helium, purity no less than 99,99 %.
5.2 Nitrogen, purity no less than 99,99 %.
5.3 Liquid nitrogen, temperature at 77 K.
5.4 Carbon dioxide, purity no less than 99,9 %.
5.5 Standard sieves(number of mesh), 60 and 35.
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ISO 23604:2022(E)
5.6 Specific surface area analyser (see Figure 1).
Key
1 degasser
2 heating mantle
3 and 5 sample tube
4 manifold
6 dewar bottle
7 vacuum pump
8–15 solenoid valves
16 pressure gauge
17 liquid nitrogen probe/water probe
Figure 1 — Specific surface area analyser
6 Sample preparation
6.1 Fresh coal samples shall be selected for the determination, or otherwise the oxide layer of coal
samples shall be removed.
6.2 If salinity of formation water is higher than 5 000 mg/l, the coal sample shall be cleaned to remove
salt.
6.3 The coal sample is broken into certain particle range and then divided into several samples with
equal reliability.
6.4 Smash and screen the sample and take 5 g to 10 g of the sample with particle sizes of 0,28 mm to
0,45 mm. Put it into the sample bag labelled with the information including sampling date, well number,
depth and layer as well as sample number.
6.5 Air-dry the prepared samples at room temperature or in a thermostat. The temperature of the
thermostat shall not exceed 40 °C. The dried samples shall be sealed and put into a desiccator for later
use.
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ISO 23604:2022(E)
7 Experiments and calculations
7.1 Degas the sample tube degassing
7.1.1 Install the sample tube into the degasser (see Figure 1), which is then heated to 100 °C to 150 °C
and vacuum-degassed.
7.1.2 After the vacuum degree of the degasser reaches below 1,33 Pa, continue vacuum degassing for
30 min and turn off the heating mantle (see Figure 1). Cool the system down to room temperature and
backfill the sample tube with nitrogen to the atmospheric pressure.
7.1.3 Take off the sample tube, plug the nozzle and weigh it, and take the mass as m .
1
7.2 Sample pretreatment
7.2.1 Degassing of samples
The amount of prepared samples is determined by lithology: 2 g to 5 g shall be used for coal rock, tight
sandstone, limestone and gypsum rock, and 1 g to 3 g for mudstone and shale. Put the weighed sample
into the sample tube that is then installed onto the degassing device, select the appropriate heating
temperature (100 °C to 300 °C) according to the physical properties of the coal sample, and execute
vacuum degassing. After the vacuum degree of the degassing device system reaches below 1,33 Pa,
continue vacuum degassing for 4 h, and turn off the heating mantle. Cool the system down to room
temperature and backfill the sample tube with nitrogen to atmospheric pressure. Take off the sample
tube, seal it with the original plug. Weigh the plug-on sample tube and take the resultant mass as m .
2
Therefore, the sample mass m = m − m .
2 1
7.2.2 Heating temperature selection
The sample shall be degassed at high temperature and a vacuum degree less than 1,33 Pa to remove
p
...