Hydrogen Sulfide Removal by Activated Carbon
Hydrogen sulfide is a malodorous gas with the smell of rotten eggs at low concentration levels. It is toxic, flammable, explosive, and very easy to corrode metals. A small amount of hydrogen sulfide in the exhaust gas discharged from factories will cause great pollution to the environment. Thus, the elimination of hydrogen sulfide, especially the elimination of low-concentration hydrogen sulfide, is a problem that needs to be solved urgently.
Hydrogen sulfide adsorption process with activated carbon
Activated carbon adsorption and biological treatment are often used for hydrogen sulfide removal because of their good adsorption performance and no secondary contamination. Activated carbon has a large specific surface area and active groups, and can be used alone as an adsorbent or a modified carrier to adsorb low-concentration hydrogen sulfide. The reaction of hydrogen sulfide and oxygen with activated carbon as a catalyst is as follows:
2H2S + O2 → 2S + 2H2O
This reaction is divided into the following processes: (1) The water in the gas is absorbed by the activated carbon and forms a water film on its surface; (2) Hydrogen sulfide and oxygen diffuse into the pores of the activated carbon. Hydrogen sulfide decomposes in the water film and oxygen molecules are also adsorbed and activated by the carbon surface, and react with HS−; (3) The reactive oxygen atoms generated by the cleavage of the O-O bond also react with HS− quickly, and S is gradually deposited on the activated carbon.
Modified activated carbon
However, regular unmodified activated carbon used alone as an adsorbent is hard to meet high purification requirements because its adsorption of hydrogen sulfide is mainly physical adsorption. As the reaction progresses, more and more sulfur particles are formed and block the pores of the activated carbon, whose adsorption performance will be severely reduced.
So activated carbon with significantly improved performance through modification is more favored to use. Many cases use activated carbon impregnated alkaline agents and metal ions. For example, activated carbon impregnated with NaOH has an alkaline surface which is good for the removal of acidic hydrogen sulfide gas. And there are also some that use various fillers as microbial biofilm carriers.
Summary
The use of activated carbon as a catalyst is an economical and effective hydrogen sulfide removal method, especially suitable for gases with a relatively low concentration of hydrogen sulfide such as natural gas. Its operation is easy, and the conversion of hydrogen sulfide to elemental sulfur has little impact on the environment. Modified activated carbon can greatly increase the sulfur removal capacity and improve the desulfurization rate. In addition, due to the wide variety of activated carbon, factors such as its pore structure and chemical properties of the surface should be taken into consideration when selecting suitable activated carbon.