Functional Forms of Nitrogen and Sulfur in Coals and Fate of Heteroatoms during Coal Carbonization

Tsubouchi Naoto, Mochizuki Yuuki, Ono Yohei, Uebo Kazuya

doi:10.2355/tetsutohagane.98.161

The functionalities of the nitrogen (coal-N) and sulfur (coal-S) present in three caking coals with carbon contents of 76-81 wt%-dry and the fate of these heteroatoms during coal carbonization have mainly been studied by the X-ray photoelectron spectroscopy (XPS) and with a fixed bed quartz reactor, respectively. The XPS measurements exhibit that about 80-90 % of the coal-N exists as pyrrolic-N and pyridinic-N, and the rest can be assigned to quaternary-N (pyridinic-N associated with the hydroxyl groups from phenols or carboxylic acids), whereas the coal-S consists of thiophenic-S, alkyl-S and FeS₂, and the proportion of the former is as high as 60-70 %. When the coal sample is carbonized in He at a heating rate of 3°C/min, yield of N-containing species observed at 1000°C increases in the order of HCN ≤ tar-N < NH₃ < N₂ < oil-N < coke-N, regardless of the type of coal, and the latter two are present predominantly as NH₄⁺ and in polynuclear aromatic structures, respectively. On the other hand, yield of S-containing species at 1000°C increases in the order of COS < CS₂ < tar-S < oil-S < H₂S < coke-S with all coals, and more than 95 % of the coke-S can be regarded as thiophenic-S. These tendencies are also observed with physical mixtures of each coal investigated. Possible mechanisms for the formation of gaseous N- or S-containing compounds in the carbonization process are discussed on the basis of the results of some thermodynamic calculations.

Functional Forms of Nitrogen and Sulfur in Coals and Fate of Heteroatoms during Coal Carbonization

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