Overview
ISO 24196:2022 specifies a laboratory method for determining the total lignin content in kraft lignin, soda lignin and hydrolysis lignin. The method combines a two‑step sulfuric acid hydrolysis to dissolve carbohydrates with gravimetric determination of acid‑insoluble lignin (Klason lignin) and spectrophotometric measurement of acid‑soluble lignin (UV absorbance at 205 nm). The standard is intended for lignin isolated from kraft or soda pulping processes or lignin recovered after biomass hydrolysis.
Keywords: ISO 24196:2022, lignin content determination, kraft lignin, soda lignin, hydrolysis lignin, Klason lignin, acid‑soluble lignin, sulfuric acid hydrolysis, lignin purity.
Key topics and technical requirements
- Principle: Two‑step sulfuric acid hydrolysis dissolves carbohydrates; the remaining residue is weighed as acid‑insoluble lignin; soluble fraction is analysed spectrophotometrically and total lignin is the sum of both fractions.
- Sample size & prep: Representative sample of ~2–3 g (air‑dry) for sampling; test specimen ~100 mg oven‑dried equivalent. Resin content should be removed by petroleum ether extraction prior to analysis and reported.
- Equipment & conditions: Requires autoclave (120 ± 3 °C), water bath (30 ± 1 °C), drying oven (105 ± 2 °C, conduction type), Gooch filtering crucible, analytical balance (0.1 mg) and UV‑VIS spectrophotometer with quartz cuvettes.
- Reagents: 72 % sulfuric acid for primary hydrolysis; high‑purity water; petroleum ether for resin extraction.
- Analytical details: Procedure is carried out in duplicate. Acid‑insoluble lignin (Klason) is isolated by filtration, dried and weighed. Acid‑soluble lignin is determined by measuring absorbance of filtrate at 205 nm. For hydrolysis lignin a correction is applied for proteins co‑precipitated with lignin (estimate via nitrogen content × 6.25).
- Quality and reporting: Dry matter determination, extraction details, sample origin, resin percentage, and test conditions must be reported. Precision and test‑report requirements are included in the standard.
Applications and users
ISO 24196:2022 is aimed at:
- Lignin producers and pulp mills performing quality control and material specification.
- Research and development labs characterizing lignin for value‑added uses (carbon fibre, adhesives, resins, composites, bio‑chemicals).
- Analytical laboratories verifying lignin purity for industrial processing or trade.
- Sustainability and process engineers tracking recovery‑boiler relief and feedstock consistency.
The method supports harmonized testing for material specification, supplier qualification, R&D benchmarking, and regulatory or commercial reporting.
Related standards
- ISO 21436 (lignin/pulp methods - related principles)
- ISO 14453 (extraction methods referenced for resin removal)
- ISO 24215 (carbohydrate quantification in filtrates)
Warning: the method uses hazardous chemicals (strong sulfuric acid); appropriate laboratory safety and waste protocols are required.
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