High-Temperature Desulfurization of Gasifier Effluents with Rare Earth and Rare Earth/Transition Metal Oxides

Abstract

We have improved the application of mixed rare-earth oxides (REOs) as hot gas desulfurization adsorbents by impregnating them on stable high surface area supports and by the inclusion of certain transition metal oxides. We report comparative desulfurization experiments at high temperature (900 K) using a synthetic biomass gasifier effluent containing 0.1 vol % H 2 S, along with H 2 , CO 2 , and water. More complex REO sorbents outperform the simpler CeO 2 /La 2 O 3 mixtures, in some cases significantly. Supporting REOs on Al 2 O 3 (∼20 wt % REO) or ZrO 2 actually increased the sulfur capacities found after several cycles on a total weight basis. Another major increase in sulfur capacity took place when MnO x or FeO x is incorporated. Apparently most of the Mn or Fe is dispersed on or near the surface of the mixed REOs because the capacities with REOs greatly exceeded those of Al 2 O 3 -supported MnO x or FeO x alone at these conditions. In contrast, incorporating Cu has little effect on sulfur adsorption capacities. Both the REO and transition metal/REO adsorbents could be regenerated completely using air for at least five repetitive cycles.

Fabrication and Fractality of Fe2O3-CeO2/ZSM-5 Composites for High-Temperature Desulfurization

“…Many metal oxides have been applied for high-temperature desulfurization, such as, ZnO [6,7], CuO [8,9], MnO x [10,11], and CeO 2 [12][13][14]. However, iron oxide is the most widely used sorbent for hot coal gas desulfurization in the field of the coal chemical industry owing to its good adsorption capacity, abundant resource, lower cost, and good physical strength [15][16][17][18][19].…”

Alkane reforming on partially sulfided CeO2 (1 1 1) surfaces

“…A single material capable of performing both cleanup steps at gasifier effluent temperatures would aid process integration [1,2]. MO x -CeO 2 materials can be used to adsorb sulfur [3][4][5][6][7][8] as well as reform hydrocarbons [8][9][10][11][12][13]. These two processes have mostly been studied independently from one another on oxides, though reforming in the presence of sulfur species has been examined on metal catalysts [14,15].…”

“…The overall mechanism to reform methane over a ceria surface is established [4,11,19]. The adsorption of sulfur using M-doped ceria has also been examined using both experimental and computational techniques [3][4][5][6][7]. Dooley and coworkers recently examined the impact of partial sulfidation of an oxide on reforming catalytic chemistry on ceria [8].…”

“…In gasifier effluent cleanup, the adsorption step is typically performed at temperatures lower than those coming off the gasifier and subsequent catalytic steps, leading to process energy inefficiencies [1]. M-doped ceria has shown promise as a high temperature sulfur sorbent [3][4][5][6][7] as well as a hydrocarbon reforming catalyst [3,[9][10][11][12][13][16][17][18]. Few studies have examined hydrocarbon reforming on CeO 2 -based oxides in the presence of S-containing molecules.…”

“…Ceria adsorbs sulfur, forming oxy-sulfides, and doping ceria can increase its sulfur capacity [3][4][5][6][7]. CeO 2 -ZrO 2 has a higher sulfur capacity compared to CeO 2 alone, and the additional sulfur capacity is thought to result from increased surface area and reducibility of CeO 2 -ZrO 2 compared to pure ceria [7].…”