Solid-liquid filtration equipment considerations

Laboratory experiments may also be necessary to aid in the selection and preliminary design of separation operations. The separation of gas mixtures requires consideration of absorption, adsorption, and gas permeation, all of which may require the search for an adequate absorbent, adsorbent, and membrane material, respectively. When nonideal liquid mixtures are to be separated, laboratory distillation experiments should be conducted early because the possibility of azeotrope formation can greatly complicate the selection of adequate separation equipment, which may involve the testing of one or more solvents or entrainers. When solids are involved, early laboratory tests of such operations as crystallization, filtration, and drying are essential. 

A better understanding of the basic principles of ultrafiltration has permitted the development of much more efficient equipment and corresponding commerical applications. A detailed consideration of the theory of ultrafiltration was published by Porter (134), who dealt specifically with the problem Of concentration polarization. As shown in Figure 4.4, the movement of particles toward the membrane results in the formation of a concentrated sol layer of high viscosity. This can reduce the flux or rate of filtration to a small fraction of that of the liquid medium in the absence of colloid. The resistance to flow is not due to plugging of pores, or even to an actual solid layer (gel) of close-packed colloidal particles. In has been observed... 

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