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Mixed metal oxide containing iron with the high-sulfur capacity and reactivity is considered as one of the most favorable sorbents for desulfurization in hot gas. The stability and life of iron-based sorbents are the main challenges for the hot gas cleanup techniques. Not only the effect of gas atmosphere but also the effect of ZnO and MgO on the stability of iron-based sorbent was studied in this work. The mechanism and factors influencing sorbent stability are discussed. The results showed that the coexistence of CO and H 2 result in the instability of the zinc-iron-based sorbents. The reaction of carbon deposit is the crucial step affecting the stability of sorbent for hot gas desulfurization. ZnO in the sorbent is adverse to the physical stability of the iron-based sorbents. MgO in the sorbent hardly affects the physical stability of the iron-based sorbents but improves the capacity of removing the hydrogen sulfide from hot coal gas at 773 K.

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The sulfidation behaviors of iron-based sorbent with MgO and MgO-TiO2 are studied under different isothermal conditions from 623 to 873 K in a fixed bed reactor. The results of sorbents sulfidation experiments indicate that the sorbents with MgO and TiO2 additives are more attractive than those without additives for desulfurization of hot coal gas. The sulfur capacity (16.17, 18.45, and 19.68 g S/100 g sorbent) of M1F, M3F, and M5F sorbent containing 1, 3, and 5% MgO, respectively, is obviously bigger than that (15.02 g S/100 g sorbent) of M0F without additive. The feasible sulfidation temperature range for M3F sorbent is 773−873 K. The M3F sorbent is optimally regenerated at the temperature of 873 K, under the gas containing 2% oxygen, 15% steam and N2, in the space velocity of 2500 h−1. The sorbent regenerated is also well performed in the second sulfidation (the effective sulfur capacities of 17.98 g S/100 g sorbents and the efficiency of removal sulfur of 99%). The capacity to remove sulfur decreases with steam content increasing in feeding gas from 0 to 10%, but it can restrain the formation of carbon and iron carbide. The addition of TiO2 in sorbent can shift the optimal sulfidation temperature lower. The iron-based sorbent with 3% MgO and 10% TiO2 (MFT) is active to the deep removal of H2S and COS, especially in the temperature range of 673−723 K. The sulfur removal capacity of MFT sorbent is 21.60 g S/100 g sorbent.

Effect of lignite as support precursor on desulfurization performance of semicoke supported zinc oxide sorbent.

A series of iron-manganese-based sorbents were prepared by co-precipitation and physical mixing method, and used for H 2 S removal from hot coal gas. The sulfidation tests were carried out in a fixed-bed reactor with space velocity of 2000 h -1 (STP). The results show that the suitable addition of manganese oxide in iron-based sorbent can decrease H 2 S and COS concentration in exit before breakthrough due to its simultaneous reaction capability with H 2 S and COS. Fe 3 O 4 and MnO are the initial active components in iron-manganese-based sorbent, and FeO and Fe are active components formed by reduction during sulfidation. The crystal phases of iron affect obviously their desulfurization capacity. The reducibility of sorbent changes with the content of MnO in sorbent. S7F3M and S3F7M have bigger sulfur capacities (32.68 and 32.30 gS/ 100 g total active component), while S5F5M has smaller sulfur capacity (21.92 gS/100 g total active component). S7F3M sorbent has stable sulfidation performance in three sulfidation-regeneration cycles and no apparent structure degradation. The sulfidation performance of ironmanganese-based sorbent is also related with its specific surface area and pore volume.

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