Changes in the chemical structure of low rank coal after low temperature oxidation or demineralization by acid treatment: Analysis by FT-i.r. and u.v. fluorescence

Abstract

The studies have been conducted on low rank coal: Flambant de Provence, France (prv = 0.44). FT-i.r. and u.v. synchronous fluorescence spectroscopy are used to study structural changes in low rank coal after natural oxidation or acid (HCl/HF) demineralization. The observed variations deal mainly with a decrease in the aliphatic structures and an increase in the oxygenated species. A quantitative oxidation study of the effect of temperature, time, mineral matter and oxygen concentrations has been conducted by FT-i.r. An attempt has been made to describe the oxygenated species by FT-i.r. and a comparison of their evolution has been conducted. Various oxidation mechanisms are proposed. The u.v. fluorescence shows that in these conditions a change in the polyaromatic ring absorptions occurs, mainly in the 2, 3 range. This corresponds to an oxidation or even loss of some aliphatic substituents. The results are compared with those obtained by 13C n.m.r. of solid coal, and also with the coking and caking value of the oxidized coals.