Structural rank parameters of Spanish low rank coals and their influence on pyrolysis yields

Abstract

In this paper some structural characteristics of a series of Spanish coals are reported and their influence on the behaviour of coal during slow pyrolysis is studied. Nine Spanish low rank coals ranging from brown coal to sub-bituminous were characterized by proximate and ultimate analyses, maceral composition, Fourier transform infrared spectroscopy (FT-IR) and solid state 13C nuclear magnetic resonance spectroscopy (CP/MAS 13C NMR). Apparent aromaticities, ( f a), varied from 0.43 to 0.61. The aromaticity correlated well with fixed carbon and with the mean reflectance of the samples. All coals exhibited a large content of methylene structures and a high degree of aromatic substitution. From spectroscopic data some structural parameters such as the H ar/H al and the H aru/C ar ratios were estimated. Pyrolysis of samples was carried out at 600°C under slow heating conditions (7°C/min). Attempts were made to establish several relationships between product yields and parameters derived from coal analyses, and spectroscopic data. Tar yields seem to decrease with increasing O/C atomic ratio of coals and increase with the vitrinite content of samples. The negative influence on tar formation of the crosslinking capacity of coals, evaluated from the pyrolysis water and the CO 2 released, was observed. A significant reduction of organic sulphur in char was achieved at 600°C, indicating that in low rank coals this sulphur form is very sensitive to temperature.