Adsorption and adsorbent materials for H2S

There are several techniques, including hydrodesulfurization, oxidative desulfurization, biodesulfurization, adsorption, absorption, and membrane separation, among others, for removing H2S from natural gas streams or fossil fuel. I'll be discussing adsorption as a way to get rid of hydrogen sulfide from a gas stream in this article and porous materials as adsorbents in desulfurization processes.

Adsorption is the capacity of solids to draw molecules of gases or liquids that come into contact with them to their surfaces. For some systems, the adsorption process is followed by the absorption process, which is the diffusion of the fluid into the solid phase, and the desorption process, which is the opposite of both phenomena and involves the release of molecules from the solid's surface and entry into the gaseous medium.

The attraction forces between the solid and the gas molecules are what produce adsorption. These forces, which can be categorized as either physical (physisorption) or chemical (chemisorption), are in charge of the two different types of adsorption.

A chemical process called chemisorption takes place on the surface of a solid body (at the interface), where an electronic transfer between the adsorbent and the adsorbate results in the formation of a chemical bond. The molecules lose their identity throughout this process since these chemical bonds are what cause chemical compounds to develop; they cannot be restored with desorption. Physical adsorption is caused by Van der Waals-type forces (dipole-dipole interaction, London dispersion, etc.), and during the process, the molecule maintains its identity before returning to its original phase in the desorption process.

Due to their great efficiency and low energy consumption during the process, porous materials have received a lot of attention in research about their usage as adsorbents in desulfurization processes.

Some of these materials include:

Metal oxides

For desulfurization operations, especially at high temperatures, many metal oxides have been investigated. It is important to keep in mind that a variety of variables, including temperature, pressure, flow rate, feed compositions, breakthrough concentration definition, etc., affect how well the materials function when adsorbing H2S. The promising transition-metal oxides for desulfurization at room temperature are ZnO, NiO, CuO, Fe2O3, and Co3O4, according to the sulfidation Gibbs free energy at 298 K.

Carbon activated

Activated carbon is frequently utilized in adsorption and catalytic processes because of its inexpensive cost and large surface area. Specific surface area, pore size, volume, surface chemistry, and other variables can affect how well H2S can be absorbed. Activated carbon materials often require modifications through either chemical impregnation or doping with heteroatoms in order to acquire significant adsorption capabilities for H2S.

Zeolites

Zeolites are frequently employed in a variety of industries, including as catalysts in the oil and gas industry and as adsorbents for the purification of water. In general, unaltered zeolites perform poorly when removing H2S at low temperatures. Changing the synthesis procedure, replacing the cations with different elements, and impregnating the zeolites with other chemicals (such as metal oxides) are common ways to enhance their performance.

Mesoporous silica

Mesoporous silica materials are used in a variety of applications, including catalysis, separation, and the creation of new functional materials, because of their wide and consistent pore sizes, high surface area, and changeable architectures. The H2S adsorption capacity of silica materials is inferior to that of other material types due to their neutral frameworks. Silica compounds' structural qualities make them great support for other functional groups (such as amines, metal oxides, and MOFs), hence these materials frequently are modified with these functional groups to enhance their ability to remove H2S from a variety of gases.

These and other materials that are still being researched are the options suggested as potential candidates for use in technologies that aim to reduce the emissions of this hazardous gas, ensuring a decrease in environmental emissions brought on by acid rain along with CO2, as well as safer working conditions.

Source:

Donglai Mao, John M Griffin, Richard Dawson, Alasdair Fairhurst, Gaurav Gupta, Nuno Bimbo. Porous materials for low-temperature H2S-removal in fuel cell applications. Separation and Purification Technology. Volume 277, 2021, 119426. https://doi.org/10.1016/j.seppur.2021.119426

ROUQUEROL, Jean et al. Adsorption by Powders and Porous Solids: Principles, Methodology and Applications. Second Edition. Editorial Academic Press. (2014)

SOUSTELLE, Michel. Physical Adsorption of Gases by Solids Chapter 6. Thermodynamics of Surfaces and Capillary Systems, First Edition. Editorial ISTE Ltd and John Wiley & Sons, Inc. (2016), p. 163-208

Rondón, et al. Synthesis and characterization of amorphous mesoporous materials impregnated with Hematite (Fe2O3) for use in the H2S removal. Acta Microscópica Vol. 30, No. 1, 2021, pp. 40- 52.

https://acta-microscopica.org/acta/article/view/550