RAPID MICROWAVE PYROLYSIS OF COAL - METHODOLOGY AND EXAMINATION OF THE RESIDUAL AND VOLATILE PHASES

Substances such as CuO, Fe3O4 and even metallurgical coke (termed 'receptors') heat rapidly in a microwave oven at 2.45 GHz. The receptor, when mixed with Creswell coal and subjected to microwave radiation, induces rapid pyrolysis of the coal. Condensable tar yields of 20 wt% are obtained with coke, 27 wt% with Fe3O4 and as high as 49 wt% in some experiments with CuO. Despite the high final temperature (1200-1300 degrees C after 3 min), analyses suggest that the volatiles are released in the lower part of the temperature regime but that some secondary cracking does occur. The tars are similar in composition, although with coke the proportion of aromatic hydrogen is greater than with CuO and Fe3O4. X-ray photoelectron spectroscopy shows that both pyridinic and pyrrolic nitrogen are present in the tars and chars, and that the dominant form of tar sulfur is thiophenic. There is evidence that mineral sulfur is immobilized when CuO in particular is the receptor. The chars formed show a degree of graphitization and are themselves excellent microwave receptors. In the presence of oxide receptors, char-oxide redox reactions occur, with loss of char, reduction of oxide and enhanced yields of CO and CO2. Of the lighter hydrocarbons identified in the gas phase, methane predominates. The data obtained are compared with those for other pyrolysis methods.