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Oxidation of Hydrogen Sulfide in Coal Gases Producing Liquid Element Sulfur

Kyung C. Kwon1, Laneddye Carter1, Claudell Burnell1, Tikia Allen1, Tara Johnson1, and Robie Lewis2. (1) Chemical Engineering, Tuskegee University, 514 Engineering Building, University Ave, Tuskegee, AL 36088, (2) Gasification & Combustion Projects Division, National Energy Technology Laboratory

Removal of hydrogen sulfide (H2S) from coal gases and sulfur recovery as elemental sulfur are key steps in the development of advanced power plants that employ coal and natural gas, and produce electric power and clean transportation fuels.  The conventional method of sulfur removal and recovery employing amine scrubbing, Claus, and tail-gas treatment involves a number of steps and is energy intensive.  A novel process called Single-Step Sulfur Recovery Process (SSRP) is under development at various research groups. In this process, the H2S in the coal gas is selectively oxidized in a single step to elemental sulfur using sulfur dioxide (SO2) or oxygen (O2) in the presence of alumina-or-carbon-based catalyst pellets in a packed/fluidized bed.  

A monolithic catalyst reactor (MCR) for the development of a single-step sulfur recovery process is used to remove H2S from a simulated coal gas in this study. Sulfur dioxide is used as an oxidizer to convert H2S into liquid element sulfur at 125 to 155oC.  The monolith catalyst is wash-coated with gamma alumina oxide. A performance of the monolithic catalyst is presented in terms of H2S removal capacity, deactivation, and selectivity of COS with various catalyst promoters at various reactor operation conditions.

The objectives of this research are to formulate monolithic catalysts for removal of H2S from coal gases and minimum formation of COS with monolithic catalyst supports, gamma-alumina wash, and catalytic metals, to develop a catalytic regeneration method for a deactivated monolithic catalyst, to measure kinetics of both direct oxidation of H2S to elemental sulfur with SO2 as an oxidizer and selective formation of COS in the presence of a simulated coal gas mixture containing H2, CO, CO2, and moisture, using a monolithic catalyst reactor. This heterogeneous catalytic reaction has gaseous reactants such as H2S and SO2. However, this heterogeneous catalytic reaction has heterogeneous products such as liquid elemental sulfur and steam. The molar ratio of H2S to SO2 in the monolithic catalyst reactor is maintained at 2 for all the reaction experiment runs.

Experiments on conversion of hydrogen sulfide into elemental sulfur and selective formation of COS are carried out for the space time range of 90 560 seconds at 125 - 155oC and 40 200 psia to evaluate effects of reaction temperature, moisture concentration, space time, pressure, and catalyst age on conversion of hydrogen sulfide into elemental sulfur and selective formation of COS.