Changes in coal composition during air oxidation at 200–250°C

Abstract

Air oxidation of two bituminous coals and a lignite was carried out in a fluidized bed reactor at 200–250 °C. The gaseous products were analysed by gas chromatography and solid samples were titrated to determine carboxylic and total acidity and were subjected to ^(13)C n.m.r. spectrometry to determine the fraction of aromatic carbon. Elemental composition, heating value and ash content were also determined. During the first few hours oxidation-induced devolatilization proceeded simultaneously with oxidation. Oxidation of the high volatile bituminous coal for 12 h at 200 °C raised the carboxylic groups from 0.37 to 2.1 meq g^(−1) and the total acidity from 1.5 to 5.3 meq g^(−1). The acidic groups seem to be largely distinct from oxygenated groups that are precursors to CO and CO_2 products. Oxidation of the same coal at 200 °C consumed aromatic as well as aliphatic carbon at relative amounts 1:3 to 1:4.

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