The behavior of different mixed oxides, including zinc titanates (ZT) and zinc ferrites modified with CuO (ZFC) or TiO2 (ZFT), as hot gas desulfurizing sorbents was investigated. The sorbents were prepared by calcination at 650 °C of a mixture of bulk oxides in three different stoichiometries in order to form new phases and modify their textural properties. Tests of stability against reduction were obtained by thermoprogrammed reduction, and kinetic studies of the sulfidation reaction were carried out in a thermobalance in the temperature range of 550−650 °C. Kinetic parameters of the intrinsic reaction were obtained assuming a grain model. The sulfidation behavior of the sorbents as extrudates was investigated in a fixed-bed reactor in terms of breakthrough curves. Fresh and sulfided samples were characterized by Hg porosimetry, X-ray diffraction, and SEM-EDX. The study shows that the addition of TiO2 or CuO to zinc ferrite based sorbents calcined at 650 °C has little effect on the stability against reduction but markedly influences their textural properties. The stabilizing effect of Ti is observed in samples calcined at higher temperature or in non-iron-containing sorbents. The calculated kinetic constants indicate that the Zn content and the incorporation of Cu have an enhancing effect on the kinetics of the sulfidation process. Including H2 in the feed gas decreases the reactivity and increases the activation energy. Extrudated sorbents showed a good performance as desulfurizing agents and maintained the H2S concentration in the outlet gas below 20 ppm. ZT sorbent exhibited a poor efficiency, which makes the addition of Ti questionable.

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Mixed oxides, prepared by calcination at 950 °C for 6 h of powder mixtures of manganese and copper oxides, have been studied as regenerable sorbents for hot coal gas desulfurization. For the stabilization of copper in the oxidation states 2+ or 1+ under strong reducing conditions of coal gas, different concentrations of component oxides have been used enhancing the formation of different mixed oxides. Copper was not stabilized by manganese oxides, but its presence in the fresh sorbent was completely necessary because it increases the sorbent reactivity and keeps the H 2 S concentration in the outlet gas from a reactor below 50 ppmv. Thermogravimetric experiments and performance tests in a fixed bed reactor have allowed the optimization of the operating conditions for a sorbent MC (1:0.1) showing a good performance in multicycle tests without apparent decay.