The solids processes are usually best applied to gases containing low-to-medium concentrations of H2S or mercaptans. The solids processes tend to be highly selective and do not normally remove significant quantities of CO2.

Consequently, the H2S stream from the process is usually high purity. In addition, pressure has relatively little effect on the adsorptive capacity of a sweetening agent.You can get the ifo about iron sponge process via sponge/

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Most of solids processes are of the batch type and tend to have low investment and operating costs.

The iron oxide or dry box process is one of the oldest known methods for removal of sulfur compounds from gas streams. It was introduced to England about the middle of the nineteenth century and is still widely used in many areas of special application.

This process often offers advantage when the sulfur in the gas does not exceed 7–9 ton per day and the concentration does not exceed 2400 g/100 S m3 [1000 grains H2S per 100 S ft3] of gas.

This process consists of wood chips impregnated with varying amounts of hydrate iron oxide (Fe2O3). This reacts with the H2S to form Fe2S3, which may be regenerated with air.