Sorbent materials

Some industrial processes produce predorninately latent air conditioning loads. Others dictate very low humidities and when the dew point falls below 0°C, free2ing becomes a major concern. Dehydration equipment, using soHd sorbents such as siUca gel and activated alurnina, or Hquid sorbents such as lithium chloride brine and triethylene glycol, may be used. The process is exothermic and may require cooling the exiting air stream to meet space requirements. Heat is also required for reactivation of the sorbent material. 

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). 

Adsorption Processes. The processes based on adsorption of hydrogen sulfide onto a fixed bed of soHd material are among the oldest types of gas treating appHcations (4). Two common sorbent materials for low concentration gas streams are iron oxide and zinc oxide. 

The sulfur removed via these fixed-bed metal oxide processes is generally not recovered. Rather the sulfur and sorbent material both undergo disposal. Because the sorbent bed has a limited capacity and the sulfur is not recovered, the appHcation of these processes is limited to gas streams of limited volumetric rate having low concentrations of hydrogen sulfide. 

H. E. Hauck and W. lost, Sorbent materials and precoated layers in thin-layer cltromatography , Chromatogr. Sci. 47 251-330 (1990). 

Chapter 3 through Chapter 8 deal with the basic aspects of the practical uses of PLC. Chapter 3 describes sorbent materials and precoated layers for normal or straight phase (adsorption) chromatography (silica gel and aluminum oxide 60) and partition chromatography (silica gel, aluminum oxide 150, and cellulose), and precoated layers for reversed-phase chromatography (RP-18 or C-18). Properties of the bulk sorbents and precoated layers, a survey of commercial products, and examples of substance classes that can be separated are given. 

Sorbent Materials and Precoated Layers for Straight Phase... 

SORBENT MATERIALS AND PRECOATED LAYERS FOR STRAIGHT PHASE CHROMATOGRAPHY... 

Both inorganic and organic sorbent materials are suitable for apphcation in partition PLC. The relevant material in this connection is cellulose. Celluloses are natural products with the universal chemical formula (CgHioOj),. These native celluloses have a fibrous structure and they need to be groimd and purified before use in PLC. Besides native cellulose, microcrystalline cellulose can also be used in partition PLC. In this case the cellulose has been recrystaUized and is rod-shaped. The specific surface area of celluloses is in the range of about 2 m /g. 

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. 

Cost of the sorbent material it is an important factor in the selection of the sorbent material. Materials that exhibit excellent adsorption attributes, and are readily available at low cost, are considered the main targets for researchers working in the field of C02 capture. Besides, the environmental impact of synthesizing these materials is considered one of the greatest challenges to overcome. 

The surfaces of sorbent materials, e.g., oxide particles in soil, are often less complex than the exterior of protein molecules. However, if such particles are (partly) covered with organic materials, e.g., humic acids and/or fulvic acids, their surface chemistry may be very complex as well. Also, surfaces of biological structures, such as those of plant roots, may be heterogeneous. 

The sorbent materials are supplied as finely dispersed colloidal particles, whose surfaces are smooth. Some of their properties are presented in Table 3. The sorbents cover different combinations of hydrophobicity and sign of the surface charge. Thus, the model systems presented allow systematic investigation of the influences of hydrophobicity, electric charge, and protein structural stability on protein adsorption. 

The solid sorbent material must also be heated and cooled for regeneration and absorption cycles. Because the solid C02 sorbents operate at higher temperatures than the liquid absorption systems, they provide opportunities for simultaneous WGS reaction with C02 removal improving the CO conversion in sorbent-enhanced reaction process (SERP). A number of studies have been reported on the SERP concept and are currently underway as discussed in later sections. 

Developments of sorbent materials for high-temperature C02 removal from synthesis gas and their utilization as SERPs appears attractive, however, the development scale may be considered as laboratory/bench scale. 

Magnetite deserves further investigation as robust inorganic sorbent material. 

Wissiack R., Rosenberg E., and Grasserbauer M., 2000. Comparison of different sorbent materials for online solid-phase extraction with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry of phenols. J Chromatogr B 896 159. 

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