Effects of selective chemical modification of coal on tar and gas formation during pyrolysis

Vitrain from Debiensko bituminous coal was modified by selective chemical reaction to reveal particular structural characteristics of organic matter responsible for the improved or worsened conversion during the solubilization of coal by methanol-NaOH treatment. The selective reactions were: alkylating and non-alkylating reduction according to Sternberg, performic acid oxidation, thermal decarboxylation of the oxidized vitrain, LiAlH4 reduction of the oxidized vitrain and O-methylation of residual hydroxyl groups. The original vitrain and the products of the modification reactions were pyrolysed in a stream of helium at atmospheric pressure and the volatile compounds were continuously detected during thermal programming, using flame ionization detection or mass spectrometry. The compounds detected were: tar and light oils, CO2, CO, SO2, H2S, CH4, H2 and N2. The results are in agreement with the expected changes in chemical structure. A number of coal structural features are revealed by detailed examination of the gas profiles. Oil and gas evolution correlate well with infrared spectroscopy and sequential solvent extraction of the modified samples. The higher oil yield and the lower yields of H2 and N2 can be attributed to the suppression of the regressive effect of the oxygen groups and to the addition of hydrogen centres.