PREPARATION OF FERRITE WITH BIMODAL PORE STRUCTURE

用煤制备的ZnFe_2O_4和CaFe_2O_4在500-800℃的脱硫过程中表现出很高的反应活性，能有效地将4000 ppm的H_2S脱除到几ppm以下。ZnFe_2O_4经空气氧化吸收H_2S后可再生。CaFe_2O_4吸收剂吸收后再生，生成Fe_2O_3和CaSO_4（CaS+2FeS+11/2O_2→CaSO_4+Fe_2O_3+2SO_2）。再生后的CaFe_2O_4虽然不能再生，但再生后的吸收剂用于吸收H_2S时，排出气体中的H_2S浓度（4-6ppm）比再生后的吸收剂低（15- 20 ppm）的Fe_2O_3，表明再生吸收剂中的CaSO_4对H_2S的高吸收率有贡献。采用浸渍法制备了CaSO_4负载Fe_2O_3（Fe_2O_3/CaSO_4）。在氩气保护下进行了程序升温反应（TPR），得到了CaSO_4的分解行为。Fe_2O_3/CaSO_4在450 ~ 500℃范围内均有SO_2的释放。而Fe_2O_3则没有观测到SO_2的存在。实验结果表明，金属硫酸盐要具有吸收H_2S的能力，必须在氩气保护下将CaSO_4分解为SO_2和CaO，直到吸收温度达到500℃。吸收剂中CaO和Fe_2O_3的存在对H_2S的吸收有一定的促进作用。当CaO和Fe_2O_3同时使用时，Fe_2O_3似乎有助于将高浓度的H_2S降低到20 ppm以下，然后CaO似乎有助于将20 ppm的H_2S降低到几ppm。

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.