DEPOLYMERIZATION OF COALS PROMOTED BY ZINC HALIDES NEAR 100-DEGREES-C

Thermogravimetry (TG) and in situ electron spin resonance (ESR) spectroscopy of four coals mixed with up to equal amounts of ZnCl2, ZnBr2, and ZnI2 are reported for temperatures from 25 to 500-degrees-C. TG measurements show that, between 50 and 175-degrees-C, zinc halides promote nearly 30% mass loss due to release of volatiles and, in ESR spectroscopy, a corresponding increase in the free-radical density is observed in flowing N2 gas. For one case, viz., ZnCl2, the effect of different loadings has been measured and the nature of volatiles has been investigated by gas chromatography/mass spectrometry (GC/MS). These observations demonstrate that significant depolymerization of coals promoted by zinc halides occurs at temperatures between 100 and 150-degrees-C and, at 200-degrees-C, the presence of benzene derivatives signifies cracking. These results are important because the earlier studies of coal liquefaction with zinc halides were limited to temperatures less-than-or-equal-to 300-degrees-C.