Pyrolysis of five coals has been carried out at 1000−1350 °C and different heating rates with fixed-bed and free-fall reactors to examine carbon structures in devolatilized chars. The X-ray diffraction measurements show the formation of crystallized carbon with turbostratic structures, depending strongly on coal type and severity of pyrolysis. The proportion of the carbon with low rank coals decreases by demineralization with acid washing but contrarily increases by subsequent addition of Ca2+ ions, irrespective of heating rate, and a small amount of 0.5−1 wt % Ca works efficiently. It is thus likely that Ca2+ ions naturally present as ion-exchanged forms in low rank coals determine dominantly the extent of carbon crystallization at higher temperatures. The Ca added is transformed to fine particles of CaO upon pyrolysis, and a larger amount of CO is formed in the presence of the Ca. A mechanism for the Ca-enhanced carbon crystallization is discussed in terms of solid−solid interactions between CaO particles and amorphous carbon.

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Catalytic NH 3 decomposition with limonite rich in a-FeOOH has been studied as a hot gas cleanup method to remove a low concentration of NH 3 from fuel gas produced in coal gasification. Fine particles of metallic Fe formed from a-FeOOH achieve the almost complete decomposition of 2000 ppm NH 3 to N 2 at 500°C under a high space velocity of 45,000 h )1 and show the stable catalytic performance for 50 h. The predominant catalytic mechanism involving the formation and subsequent decomposition of Fe nitrides may be proposed on the basis of the XRD and TPD results.

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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 g450°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 CaCl 2 , and organic hydrochlorides, are pyrolyzed in the same manner as above, HCl formation occurs dominantly between 250 and 450°C in every case. The pretreatment of a brown coal char with HCl at 500°C and subsequent temperatureprogrammed desorption (TPD) measurement up to 950°C suggest that HCl reacts with the nascent char upon pretreatment to form several types of Cl functional forms, from which the HCl desorption takes place at 450-750°C upon TPD. The HCl evolved at <450°C during pyrolysis may arise from water-soluble Cl functional groups in coal, whereas the HCl formation at g450°C observed for almost all of the coals may proceed through a mechanism involving secondary reactions of HCl evolved at a lower temperature.