PREPARATION OF FERRITE WITH BIMODAL PORE STRUCTURE

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We have already reported that ZnFe_2O_4 and CaFe_2O_4 prepared with coal exhibited a high reactivity in the desulfurization process at 500-800℃, and could efficiently remove 4000ppm of H_2S to less than a few ppm. ZnFe_2O_4 could be regenerated after the H_2S absorption by air oxidation. When CaFe_2O_4 absorbent was regenerated after the absorption, Fe_2O_3 and CaSO_4 produced (CaS+2FeS+11/2O_2→CaSO_4+Fe_2O_3+2SO_2). Although CaFe_2O_4 could not reproduced after the regeneration, when the regenerated absorbent was used for the H_2S absorption, H_2S concentrations in the effluent gas (4-6ppm) were smaller than that (15-20ppm) of Fe_2O_3, indicating that CaSO_4 in the regenerated absorbent seems to contribute to high absorption rate of H_2S.In order to elucidate a role of CaSO_4,CaSO_4-loaded Fe_2O_3 (Fe_2O_3/CaSO_4) was prepared by impregnation method. The temperature programed reaction (TPR) under argon atmosphere was carried and the decomposition behavior of CaSO_4 was obtained. In Fe_2O_3/CaSO_4, the release of SO_2 was observed from 450 to 500℃. In contrast, for Fe_2O_3,SO_2 was not observed. From these results, in order that metal sulfate have the H_2S absorption capability, it is necessary to be decomposed CaSO_4 into SO_2 and CaO under argon atmosphere until absorption temperature (500℃). CaO and Fe_2O_3 existed in the absorbent contribute in H_2S absorption. When CaO and Fe_2O_3 are simultaneously used, Fe_2O_3 seems to contribute to decrease the high concentration of H_2S to less than 20ppm, and then CaO seems to contribute to decrease 20ppm of H_2S to a few ppm.