Paper Example on Zeolites for Gas Adsorption

Zeolites are Nanoporous, crystalline materials used for many decades in applications ranging from catalysis over gas separation to ion-exchange. They are silicates of calcium, sodium or potassium together with aluminum in the anion structure. Are found as minerals, and can be synthesized in the laboratory. The unfamiliar feature of this class of inorganic materials is that their crystal structure consists of interconnected TO4 tetrahedra, where T usually stands for Si and Al.

Chemically more diverse elements, in which aluminum and silicon are, for example, substituted with Be P, and Fe. However, high-silica materials are most relevant from in the industrial sector. They typically possess high thermal and hydrothermal stability under process conditions. During the 1940s a series of zeolites with low Si/Al ratios were hydrothermally synthesized through mimicking of the geothermic development of natural zeolites. The successful synthesis of zeolites laid the foundation for a rapid growth of zeolite industry in the 20th and 21st centuries.

The term zeolite originates from the Greek words zero (to boil) and lithos. The first mineral to be discovered was named stability (Cronstedt, 1765) was described as boiling stone. In 1862, St. Claire Deville tried to manufacture zeolites in the laboratory. However, the most prominent early synthesis turning point from a technical viewpoint were made in the 1950s by Zeolites for Gas Adsorption

Zeolites are crystalline, nanoporous elements used over time in processes such as catalysis in gas separation to ion-exchange. They are silicates of calcium, sodium or potassium together with aluminum in the anion structure. Are found in nature as minerals, and manufactured in the laboratory. The unfamiliar feature of this type of inorganic materials is that their crystal structure consists of interconnected TO4 tetrahedra, where T usually stands for Si and Al.

Chemically more diverse elements exist, in which silicon and aluminum are, for example, substituted with Be P, and Fe. However, materials with high-silica materials content are most important from an industrial point of view because they possess exceptionally high thermal and hydrothermal stability under process conditions. During the 1940s a series of zeolites with low Si/Al ratios were hydrothermally synthesized through mimicking of geothermic formation of natural zeolites. The successful manufacture of zeolites laid the foundation for a rapid growth of zeolite industry in the 20th and 21st centuries.

The word zeolite emerged from the Greek words zero (to boil) and lithos. The first mineral to be discovered was named stability (Cronstedt, 1765) was described as boiling stone. In 1862, St. Claire Deville tried to manufacture zeolites in the laboratory. However, the most prominent early synthesis turning point from a technical viewpoint was in the 1950s made by Breck and Milton at Union Carbide. They developed the reactive gel crystallization, which is today perceived as the standard synthesis method for zeolites.

Adsorption is the deposition of molecules onto the surface. The molecules that get adsorbed on the surface is known as the adsorbent and the surface on which adsorption occurs referred to as the adsorbate. It occurs whenever there is exposure of a solid to air or liquid. It involves enrichment of material or increase in density.Wood, sand, and clay possess adsorbent properties and used by ancient Greeks, Romans, and Egyptians (Robens, 1994). Some of the applications of adsorption included clarification of fat and oil, water desalination and treatment of several diseases. The earliest research paper was done independently by Priestly 19775 and Abbe Fontana in 1977(Dietz 1944; Forester & Giles, 1971).

Decolorizing characteristic noted by Russian Chemist Lowitz in 1785. The exothermal feature of gas adsorption first recorded by De Saussure in 1814. The wetting of solids by gases discovered by Favre in 1854 who also published the first measurements of heat of adsorption of various gases on charcoal. The first attempt to relate the amount of gas adsorbed to pressure made by Chappius and Keysar in 1881. During the same year, Keysar introduced the term adsorption, and over the years the terms isotherms and isothermal curve were applied to the results of adsorption measurements done at a constant temperature (Forester & Giles, 1971)

In 1802, a discovery of when a liquid is added to a powder, there was heat production by Leslie. The heat that arose after sand immersion in water was referred to as Poulet effect in France in 1822. (Gore,1894) Discovered that the amount of heat was related to the surface area of the powder. Gurvich (1915) suggested that the amount of heat was also dependent on the polarity of the liquid and the nature of the powder.

In 1881, Van Bemmlen was the first to record isotherms of adsorption from solution (Forester & Giles,1972). He investigated the absorptive power of soils, and he noted the importance of colloidal structure and drew the importance of the equilibrium concentration in contact with the ground.

Adsorption is of great value in technology. It is applied in catalysts or catalyst support, in large scale as desiccants, in the purification of liquids, separation of gases, pollution control or respiratory protection.It plays a vital role in many solid reactions and biological mechanisms. Adsorption is of crucial importance also in the application of surface properties such as the texture of fine powders such as cement and fillers. Adsorption also used in laboratories on porous materials such as clay, ceramics, and membranes. Gas adsorption has become the most used procedure in determining the pore size distribution and surface area of a diverse range of powder and porous material. In 1916, Langmuir stated that with highly porous adsorbents such as charcoal is impossible to know the exact area which adsorption takes place. This observation criticized by many investigators who have applied Langmuir monolayer equation to adsorption data obtained with zeolites and activated carbons. His work on gas adsorption on both liquid and solid surfaces involved the formation of the monomolecular layer.It surfaced way for more procession in the interpretation of adsorption from solution data.

Recently, Hydrogen is a crucial energetic trajectory. The most used industrial method to produce ultrapure hydrogen is by absorption of steam methane. Hydrogen first formed as a mixture mainly composed of hydrogen, carbon monoxide, methane, and carbon dioxide. A purification step by pressure swing adsorption is carried out by using activated carbon and 5A zeolite as adsorbents.

The design of this process requires basic data about the adsorption and diffusion of the components, which only found in a limited number of adsorbents. Henrys law constants and reciprocal diffusion time constants have measured for hydrogen, carbon monoxide, methane, and carbon dioxide. (Deitz, 1944; Forrester and Giles, 1971). Adsorptive separation procedure such as pressure swing adsorption can be employed on a large scale to separate and purify hydrogen. (Forrester and Giles, 1972)

In conclusion, in more than two decades, zeolites have been used in gas hydrogen and carbon dioxide absorption. The capacity of hydrogen and carbon dioxide or other zeolites depends on mixture on activated carbon. Dye absorption is of significant technological advancement. it is evident that previous findings of zeolites have been of crucial importance in the industrial sector.

References

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