Sorbents molecular sieves

Nanoscale sihcon oxide is widely used in microelectronics, optoelectronics and electronics are parts of the means of fire protection, coatings, high temperature adhesives, paints, various mortars. Medical and biotechnology applications comprising silica nanoparticles and sorbent molecular sieves of DNA delivery vehicles, proteins, anticancer agents [17]. 

R. M. Barrer, Zeolites and Clay Minerals as Sorbents and Molecular Sieves , p. 174, Academic Press, London and New York (1978). 

Sohd sorbent materials have the abiUty to adsorb water vapor until an equiUbrium condition is attained. The total weight of water that can be adsorbed in a particular material is a function of the temperature of the material and of the relative humidity of the air (see Adsorption). To regenerate the sorbent, its temperature must be raised or the relative humidity lowered. The sohd sorbents most commonly used are siUca (qv), alumina (see Aluminum compounds), and molecular sieves (qv). 

Fig. 2. Molecular sieve process where Kl is a molecular sieve sorbent bed ( ), the adsorption system and (-), the regeneration system.

Certain chemicals (sorbents) have the ability to absorb moisture from a gas they may be either solid or liquid. Performance of a chemical dehumidifi cation device depends on the sorbent used. The sorbent must t>e able to attract and remove the sorbate, such as water, from the gas stream, Stirbems absorb water on the surface of the material by adsorption or by chemically combining with water (absorption). If the unit is regenerative, the process is reversible, allowing water to be removed. This is achieved by a sorbent such as silica gel, alumina gel, activated alumina, lithium chloride salt, lithium chloride solution, glycol solution, or molecular sieves. In the case of nonregenerative equipment, hygroscopic salts such as calcium chloride, urea, or sodium chloride are used. 

R. M. Barrer, in Zeolites and Clay Minerals as Sorbents and Molecular Sieves, Academic Press, London, 1978 F. Asinger, Die Petrolchemische Industrie, Akademie-Verlag, Berlin, 1971, pp. 73-95 K. Lindner, Seife-Ole-Fette-Wachse 94 81, 110 (1968) E. Guccione, Chem. Eng. 72(9) 104 (1965). 

Characteristics of attrition and adsorption were investigated to remove CO2 in fluidized hed using activated carhon, activated alumina, molecular sieve 5 A and molecular sieve 13X. For every dry sorbent, attrition mainly still occurs in the early stage of fluidization and attrition indexs(AI) of molecular sieve 5A and molecular sieve 13X were higher than those of activated carbon and activated alumina. Percentage loss of adsorption capacity of molecular sieve 5A and molecular 13X were 14.5% and 13.5%, but that of activated carbon and activated alumina were 8.3% and 8.1%, respectively. Overall attrition rate constant (Ka) of activated alumina and activated carbon were lower than other sorbents. 

Therefore, in this study, activated carbon, activated alumina, molecular sieve 5A, and molecular sieve 13X were used as dry sorbents to control carbon dioxide in a fluidized bed. In addition, the attrition and percentage loss of adsorption capacity of the dry sorbents were investigated. 

Fig. 1 shows that minimum fluidization velocities of activated carbon, activated alumina, molecular sieve 5A and molecular sieve 13X are 8.0 cm/s, 8.5 cm/s, 6.2 cm/s and 6.5 cm/s, respectively. Also, theoretical calculation values of minimum fluidization velocity and terminal velocity of each dry sorbent were summarized in Table 1. 

Barrer RM (1978) Zeolites and clay minerals as sorbents and molecular sieves. Academic Press, London... 

The Brunauer type I is the characteristic shape that arises from uniform micro-porous sorbents such as zeolite molecular sieves. It must be admitted though that there are indeed some deviations from pure Brunauer type I behavior in zeoHtes. From this we derive the concept of the favorable versus an unfavorable isotherm for adsorption. The computation of mass transfer coefficients can be accompHshed through the construction of a multiple mass transfer resistance model. Resistance modehng utilizes the analogy between electrical current flow and transport of molecular species. In electrical current flow voltage difference represents the driving force and current flow represents the transport In mass transport the driving force is typically concentration difference and the flux of the species into the sorbent is resisted by various mechanisms. 

Barter, P. M. Zeolites and Clay Minerals as Sorbents and Molecular Sieves. 

The prerequisites of the evaluation of data characteristic of intracrystalline processes in the case of zeolite sorbents are discussed, along with the conditions under which diffusion can be compared to self-diffusion. Selected results of investigations carried out in the author s laboratory are given in order to demonstrate the consistency of sorption kinetic data with intracrystalline mobility data of single components on molecular sieves (HS). Various types of surface barrier which may influence the uptake rate are also described. 

Pore Size and Distribution. The pore diameter must be sufficient to allow the substances of interest to migrate into the pores to the adsorbing surface. Sorbents with very small pores, such as the carbon molecular sieves, are used to collect small molecules like permanent gases (e.g., methyl formate on Carbosieve B). 

Table I shows some of the characteristics of the commonly used sorbents. The charcoals are by far the most frequently used solid sorbent for organic vapors. Over 130 methods have been validated in our five-year study using coconut, petroleum, and synthetic charcoal. The other sorbents include silica gel, used primarily for amines, and porous polymers, used for substances not amenable to collection on charcoal or silica gel. Other researchers have used other sorbents, including Florisil, alumina, and molecular sieves.

Although a number of books now contain chapters or sections dealing with zeolites, this subject has been the primary focus in very few volumes. The most noteworthy of these is the treatise by D. W. Breck, Zeolite Molecular Sieves, published by Wiley in 1974. The earliest modem ones are the Russian texts on Molecular Sieves and Their Use, published by V. A. Sokolov, N. S. Torocheshnikov, and N. V. Kel tsev in 1964, and S. P. Zhdanov s Chemistry of Zeolites in 1968. Other significant works include the 1976 ACS Monograph on Zeolite Chemistry and Catalysis edited by J. A. Rabo, and the volume on Zeolites and Clay Minerals as Sorbents and Molecular Sieves by R. M. Barrer, published in England in 1978. 

Three general types of solid sorbents are mainly used for trapping VOCs in air inorganic sorbents like silica gels or molecular sieves, carbon-based porous materials and porous organic polymers. 

The main types of inorganic sorbents are silica gels, molecular sieves/zeolites, aluminum oxides and magnesium silicates. Carbon-based sorbents include activated charcoals, carbon blacks, graphihzed carbon blacks and graphitized molecular sieves. Styrene-divinylbenzene copolymers, ethylvinylbenzene/divinylbenzene... 

Carbon based sorbents and charcoal Molecular sieves... 

Therefore, the solid sorbent should ideally have a low affinity to water, a characteristic easily met by the porous organic polymers. In contrast, the carbon-based sorbents and molecular sieves as well as some inorganic sorbents show a comparatively high uptake of water. If such sorbents are used in high-humidity environments special measures have to be employed to remove water during or after sampling. Possible methods are ... 

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