Formation of Hydrogen Chloride during Temperature-Programmed Pyrolysis of Coals with Different Ranks

The evolution of HCl during pyrolysis of 16 coals with different ranks at a heating rate of 10 °C/min has been studied with an online monitoring method. Approximately 50%−95% of total chlorine is converted to HCl up to 800 °C, and the remainder is mostly retained in the char, which leads to a strong reverse correlation between the two. As the sum of Na and Ca naturally present in coal increases, the amount of HCl tends to decrease. The temperature dependence of the rate of HCl evolved differs with each coal and shows at least four peaks at 280, 360, 480, and 580 °C. The former two peaks are present for two coals alone, whereas the higher temperature HCl formation at ≥450 °C is common for almost all of the coals. The HCl peaks at 280 and 360 °C are considerably small by water washing. When model chlorine compounds added to activated carbon, such as hydrated NaCl, hydrated CaCl2, and organic hydrochlorides, are pyrolyzed in the same manner as above, HCl formation occurs dominantly between 250 and 450 °C in ...