1 Scope
This standard specifies the principles, reagents and materials, apparatus, test steps, result calculation and accuracy of semi-micro Kjeldahl method and semi-micro gasification method for determining nitrogen in coal, coke and coal water mixture.
Kjeldahl method is applicable to lignite, bituminous coal, anthracite and coal water mixture; gasification method is applicable to bituminous coal, anthracite and coke.
Note: For anthracite with high metamorphic grade, the sample digestion time by Kjeldahl method is too long, which may lead to low determination result, and the gasification method can be used in this case.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this standard. For dated references, subsequent amendments (excluding corrections) to, or revisions, of any of these publications do not apply to this standard. However, parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition applies.
GB/T 212 Proximate analysis of coal (GB/T 212-2008, ISO 11722: 1999; ISO 1171: 1997; ISO 562: 1998, NEQ)
GB 474 Preparation of coal sample (GB 474-1996, eqv ISO 1988: 1975)
GB/T 483 General rules for analytical and testing methods of coal
3 Semi-micro Kjeldahl method
3.1 Principle
Weigh a certain amount of air-dried coal sample or dry sample of coal water mixture, add mixed catalyst and sulfuric acid, decompose by heating, and convert nitrogen into ammonium bisulfate. Add excessive sodium hydroxide solution, evaporate ammonia and absorb it in boric acid solution. Titrate with sulfuric acid standard solution, and calculate the nitrogen content in the sample according to the amount of sulfuric acid.
3.2 Reagents
3.2.1 Mixed catalyst: mix anhydrous sodium sulfate, mercury sulfate and chemically pure selenium powder according to the mass ratio of 64:10:1 (e.g., 32g+5g+0.5g), grind and evenly mix for later use.
3.2.2 Sulfuric acid.
3.2.3 Potassium permanganate or chromic anhydride.
3.2.4 Sucrose.
3.2.5 Anhydrous sodium carbonate: guaranteed reagent, standard reagent or sodium carbonate purity standard substance.
3.2.6 Mixed alkali solution: dissolve 370g sodium hydroxide and 30g sodium sulfide in water to prepare 1,000mL solution.
3.2.7 Boric acid solution: 30g/L.
Dissolve 30g boric acid in 1L hot water, heat to dissolve and filter out insoluble substances during preparation.
Foreword i
1 Scope
2 Normative references
3 Semi-micro Kjeldahl method
4 Semi-micro gasification method
5 Method precision
6 Test report
Annex A (Informative) Comparison between clause numbers in this standard and those in ISO 333: 1996
Annex B (Informative) Comparison between clause numbers in this standard and those in ISO/TS 11725: 2002
Annex C (Informative) Technical differences between this standard and ISO 333: 1996 and the relevant reasons
Annex D (Informative) Technical differences between this standard and ISO/TS 11725: 2002 and the relevant reasons
