Sorbents aluminas

Alumina, which is discussed in greater detail in Chapter 5, and cellulose are the two most often used nonsilica-based sorbents. Alumina has been used to separate compounds such as fat-soluble vitamins, alkaloids, and antibiotics. Cellulose-based ion-exchange layers have wide application for sulfonamides, nucleic acids, and steroid sulfates. 

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). 

Hydrated alumina is one of the most widespread hydrophilic polar sorbents for concentration and separation of different substances. In water Al Oj shows cation or anion exchange properties and its protolytic and adsorption characteristics depend on a way of obtaining. 

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. 

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. 

Table 2 summaries overall attrition rate constants (Ka) and physical properties for each dry sorbent. As shown in Table 2, Ka of activated alumina was the lower than any other sorbent, but was similar to activated carbon. However, we used activated carbon as dry sorbent to control CO2 because it is the most cost-effective among others.

Plates with 0.5- to 2-mm layer thickness are normally nsed for increased loading capacity. Layers can be self-made in the laboratory, or commercially precoated preparative plates are available with silica gel, alumina, cellulose, C-2 or C-18 bonded siliea gel, and other sorbents. Resolution is lower than on thinner analytical layers having a smaller average partiele size and particle size range. Precoated plates with a preadsorbent or eoneentrating zone faeilitate application of sample bands. 

A special feature of aluminum oxides is the fact that these sorbents are adjusted to different pH values for thin-layer chromatographic purposes. The acidic aluminas are in the pH range of 4.0 to 4.5, whereas neutral signifies a pH range between 7.0 and 8.0, and basic aluminas have a pH value of approximately 9.0 to 10.0. 

For preparative purposes, it is recommended to prewash the plates. Silica gel or alumina layers are mostly employed, and such active sorbents adsorb not only water... 

There are several types of sorbent materials in the market today, other than commonly used silica and alumina. Some of these sorbents are chemically modihed to a certain extent to improve the properties of the thin layer for a wide variety of compounds, as well as for better resolution. 

Although the improved extraction kinetics also increase the concentration of coextractives in the final extract, some degree of selectivity can be achieved by careful selection of the solvent or solvents used. Matrix co-extractives may be removed, or at least partially removed, by placing a suitable sorbent, such as alumina, at the exit of the extraction cell to remove lipid co-extractives. Excellent recoveries of both polar and nonpolar pesticides from a wide range of foodstuffs have been reported. Specific applications include organophosphorus and A-methylcarbamate pesticides. 

Prior to the development of modern SPE formats, liquid-solid partitioning with charcoal, silica, Florisil, and/or alumina was common to aid in the removal of lipids in the determination of nonpolar pesticides, but these sorbents are less useful in the cleanup of semi-polar and polar pesticides owing to the large elution volumes needed. Applications of modern SPE are discussed in Section 3.2. 

This technique is based on the same separation mechanisms as found in liquid chromatography (LC). In LC, the solubility and the functional group interaction of sample, sorbent, and solvent are optimized to effect separation. In SPE, these interactions are optimized to effect retention or elution. Polar stationary phases, such as silica gel, Florisil and alumina, retain compounds with polar functional group (e.g., phenols, humic acids, and amines). A nonpolar organic solvent (e.g. hexane, dichloromethane) is used to remove nonpolar inferences where the target analyte is a polar compound. Conversely, the same nonpolar solvent may be used to elute a nonpolar analyte, leaving polar inferences adsorbed on the column. 

The principal adsorbents used in GSC are silica, alumina, graphltlzed carbon blacks, porous polymer beads, zeolites and cyclodextrlns [8,430,431,445]. The bonded phase sorbents discussed in section 2.2.3 could also be considered as modified adsorbents in many respects. 

AUTO-PUREX G A process for removing carbon dioxide from air by PSA, using alumina as the sorbent. Developed by Marutani Chemical Plant Engineering Company, Japan. 

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