Removal of Sulfur from Gasified Coal at or Above 800C

Coal contains substantial sulfur which, if not captured when burned, can significantly impact human health. SO2 and SOx emissions are highly regulated. This SBIR project presents a novel, proprietary approach for removing sulfur from gasified coal products at gasification temperatures. The approach is based on the use of sulfide ion-conducting metal sulfides. At high temperatures, and under a sulfur partial pressure gradient, the sulfur contained in the feedstream will be selectively separated out. The use of such a separation membrane will allow for true hot gas cleanup of sulfur from gasified coal. This will allow the concentration and low-cost capture of the sulfur. Although there are several metal oxides that exhibit oxygen ion conductivity, such as yttria-stabilized zirconia or doped ceria, there are very few materials that exhibit sulfide ion conductivity. There is, however, a class of novel mixed metal sulfides, which do exhibit sulfide ion conductivity. Ion conductivity is a thermally activated process, ideally suiting these materials to high-temperature applications. Like stabilized zirconia and doped ceria, this class of metal sulfides are characterized as solid electrolytes, meaning they are pure ion conductors, with little, if any, electronic conductivity. When used as sensors, or as solid oxide fuel cell membranes, for example, the solid electrolyte is in contact with electrodes connecting it to an external circuit for electron transfer. As a separation membrane, however, the process can be simplified if the external circuit is eliminated. This is done by short circuiting the ion-conducting membrane by providing an electronic pathway. The electronic pathway can be built into the membrane by mixing the solid electrolyte with an electronically conducting phase, forming a two-phase composite. Eltron Research, Inc. has used this strategy successfully with oxygen separation, and it is proposed here for sulfur separation. Eltron has extensive experience in the area of ion-selective ceramic membranes. Eltron also has granted license to Air Products for the use of our proprietary materials in their ITM Syngas and ITM Oxygen processes. In addition, Eltron has a state-of-the-art ceramics processing facility. At the conclusion of Phase I, we will have demonstrated the feasibility of using sulfide ion-conducting membranes for hot gas desulfurization. After Phase II, we will be ready to move the technology out of the laboratory and construct a demonstration-scale facility that can be tied to an existing coal gasifier to demonstrate performance in an industrial setting at an appropriate scale.