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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The effect of aging in nitrogen upon the regeneration characteristics of the coke deposits on chromia-alumina catalysts has been investigated. To this end, the coked catalysts have been subjected to various treatments in nitrogen, and the chemical composition and reactivity of the deposits have been investigated. The results show that the process of aging in nitrogen gives rise to significant changes in both the composition and reactivity of the coke deposits, due to the stripping of the coke fractions with a higher volatility. This obviously has important consequences upon the subsequent regeneration, which are also discussed and tested in regeneration experiments using coked catalyst of different ages.

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