Adsorptive drying

The refrigeration method of drying air is the most energy efficient, down to a lower limit of about 0.005 kg/ kg moisture content at atmospheric pressure. Equipment to work at frosting conditions can be duplicated, one evaporator defrosting while the other is operating. Below this limit, chemical or adsorption drying must be used [61]. 

The transfer of mass from one phase to another is involved in the operations of distillation, absorption, extraction, humidification, adsorption, drying, and crystallization. The principal function of the equipment used for these operations is to permit efficient contact between the phases. Many special types of equipment have been developed that are particularly applicable for use with a given operation, but finite-stage contactors and continuous contactors are the types most commonly encountered. A major part of this chapter, therefore, is devoted to the design aspects and costs of stagewise plate contactors and continuous packed contactors. 

The unit operation of adsorption drying which is particularly suited for removing or eliminating small concentrations of substances, such as in the drying of air and gas and the removal of trace contaminants in gas streams has received considerable attention (B5)-(C2). This topic involves a different set of fundamental principles and has not been treated in this article. 

Polyvinylidene-difluoride Low non-specific adsorption Dry autoclavable Good solvent compatibility Moderate flow rate and total throughput Hydrophobic base, made hydrophilic by chemical surface treatment may lose hydrophilic modification due to chemical attack High-cost filter material... 

Basmadjian, D. Adsorption Drying of Gases and Liquids, Advances in Drying Hemisphere Publishing Co.. 1984 Vol. 3 305-357. 

A limitation in the use of DRIFT for adsorption studies is that the spectrum is obtained from a relatively dry sample. Use of high water contents is not possible due to the strong aqueous adsorption. Drying of an oxide suspension may or may not favor the conversion of a monodentate to a bidentate complex, depending on the reaction. For example both reactions... 

In addition to heterogeneous azeotropic distillation, several alternative methods are available for ethanol dehydration such as extractive distillation, adsorption, and pervapo-ration. A comprehensive review of the subject, including 302 references, has been presented by Vane. A recent paper by Kiss and Paul claims that the heterogeneous azeotropic distillation process is more economical than adsorptive drying because of the large amount of energy required to regenerate the adsorbent. 

Alikhani Z, Raghavan GSV, Mujumdar AS. Adsorption drying of com in zeolite granules using a rotary drum. Drying Technology 10(3) 783-797, 1992. 

The incipient wetness and adsorption drying allow to narrow the particle size distribution (see Fig. 1). Most probably, this results from a very fast water removal from the porous space. 

Sorbents are solid materials which trap water through absorption or adsorption. Drying of water from solvents by absorption means that the water is incorporated throughout the sorbent. Drying of water from solvents by adsorption means that the water doesn t penetrate the sorbent material but remains on the surface of the sorbent. Absorption is a volume-controlled process adsorption is an area-controlled process. 

Fixed beds, also called packed beds, play a vital role in chemical processes. Their simplicity induced applications in many unit operations such as adsorption, drying, filtration, dust collection, and other catalytic and noncatalytic reactors. The primary operating cost for a fixed bed is the pressure drop through the packed bed of solids. Thus to understand the design and operation of a packed bed requires study of packing characteristics of particles and their effect on pressure drop through the bed. 

Direct and indirect operations The operations depending upon contact of two immiscible phases particularly,can be further subclassified into two types. The direct operations produce the two phases from a single-phase solution by addition or reWval of heat. Fractional distillation, fractional crystallization, and one form of fractional extraction are of this type. The indirect operations involve addition of a foreign substance and include gas absorption and stripping, adsorption, drying, leaching, liquid extraction, and certain types of fractional crystallization. 

Figure 7.1.12. Continuous adsorption drying system using pressure-swing adsorption. (After Skarstrom (1960 1975).)...

Mass transfer basically means the net movement of mass of a species from one phase to another. It occurs in many processes such as evaporation, adsorption, drying, precipitation, and distillation. Consider the reaction of a gas with a liquid in the presence of a solid insoluble heterogeneous catalyst. In such a catalytic system, mass transfer would refer to the dissolution of the gas in the liquid and transfer of the dissolved gas and the liquid to the active sites of the catalyst particles. 

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