Solid Bed Absorption

The iron sponge process uses the ehemical reaction of ferric oxide with Hi.S to sweeten gas streams. This process is applied to gases with low H S concentrations (300 ppm) operating at low to moderate pressures (. vO-SOO psig). Carbon dioxide is not removed by this process. 

The reaction of H2S and ferric oxide produces water and ferric sulfide as follows  

The reaction requires the presence of slightly alkaline water and a temperature below 11 O F. If the gas does not contain sufficient water vapor, water may need to be injected into the inlet gas stream. Additionally, bed alkalinity should be checked daily. A pH level of 8-10 should be maintained through the injection of caustic soda with the water. 

The ferric sulfide can be oxidized with air to produce sulfur and regenerate the ferric oxide. The reaction for ferric oxide regeneration is as follows  

The regeneration step must be performed with great care as the reaction with oxygen is exothermic (that is, gives off heat). Air must be introduced slowly so the heat of reaction can be dissipated. If air is introduced quickly the heat of reaction may ignite the bed. 

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Solid bed adsorption processes suffer from that fact that they are generally restricted to low concentrations of hydrogen sulfide in the entering sour gas stream. The development of a short-cycle adsorption nnit for hydrogen sulfide removal might help remove part of this low-concentration restriction for the solid bed absorption processes. 

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