ISO 23604:2022

Overview

ISO 23604:2022 - Method of determining specific surface area of coal - specifies a gas-adsorption volumetric method to determine the specific surface area of coal and other powder or porous materials (including nano-powders). The method covers a broad determination range (0.001 m2/g to 1 000 m2/g) and defines procedures from sample preparation and degassing through adsorption isotherm measurement and surface-area calculation.

Key topics and technical requirements

• Principle: Specific surface area is derived from equilibrium gas adsorption at controlled temperature using theoretical models (e.g., BET).
• Reagents & equipment: High‑purity gases (nitrogen ≥99.99 %, helium ≥99.99 %, CO2 ≥99.9 %), liquid nitrogen (77 K), and a specific surface area analyser with degasser, manifold, valves, vacuum pump and temperature probes.
• Sample preparation:
  • Fresh coal preferred; remove oxide layer or salts if present.
  • Particle size and mass guidelines: typically 0.28–0.45 mm particle fraction; sample masses vary by lithology (e.g., 1–5 g).
  • Air‑dry below 40 °C; seal and store in a desiccator.
• Degassing and temperature control:
  • Vacuum degassing to <1.33 Pa; sample degassing temperatures typically 100–300 °C.
  • Use thermogravimetric analysis (TG) to choose maximum heating (below initial pyrolysis).
• Free‑space determination: Use helium expansions with the sample immersed in liquid nitrogen to calculate free volume prior to adsorption measurements.
• Adsorption isotherms:
  • Measure N2 adsorption across relative pressure p/p0 from about 0.01 to 0.995 (recommend ≥15 adsorption points).
  • Desorption branch: measure ≥20 points from p/p0 = 0.995 down to ~0.25.
  • For BET surface-area results, use 5–7 adsorption points in p/p0 = 0.05–0.35.
• Data analysis methods:
  • BET equation for monolayer capacity (Vm) and specific surface area.
  • Langmuir option for Vm calculation.
  • Micropore analysis: micropore filling theory and DR-DA equations to determine micropore volume and micropore surface area.

Applications and users

ISO 23604:2022 is intended for:

• Coal laboratories and coalbed methane (CBM) evaluation teams assessing gas storage capacity.
• Petroleum and mining laboratories for reservoir and porosity characterization.
• Materials science and nanomaterials labs measuring specific surface area of powders and porous media.
• Quality control and R&D in catalysis, adsorption materials and engineered porous products.

Practical uses include reservoir evaluation, adsorption capacity estimation, materials qualification, and research into microporosity and gas–solid interactions.

Related standards

• ISO 9277 - Determination of specific surface area of solids by gas adsorption - BET method (normative reference).
• Terminology alignment with ISO 15901 series for adsorption and pore terminology.

Keywords: ISO 23604:2022, specific surface area, coal, gas adsorption, BET method, adsorption isotherm, micropore volume, surface area analyser, degassing, nitrogen adsorption.