Classification of membranes

Table 16.1. Classification of membrane separation processes for liquid systems...

Industrial membrane processes may be classified according to the size range of materials that they are to separate and the driving force used in separation. There is always a degree of arbitrariness about such classifications, and the distinctions that are typically drawn. Table 16.1 presents classification of membrane separation processes for liquid systems. 

In the field of membrane filtration, a distinction is made based upon the size of the particles, which are retained by the membrane. That is micro-, ultra-, nanofiltration and reverse osmosis. Figure 4.8 shows a schematic picture of the classification of membrane processes. The areas of importance for application with homogeneous catalysts are ultra- and nanofiltration, depicted in gray. 

Klein, P., Kanehisa, M., and DeLisi, G. (1985). The detection and classification of membrane-spanning proteins. Biochim. Biophys. Acta 815, 468—476. 

FIGURE 19.5 Classification of membranes with respect to their state, morphology, and shape. 

Sadee W, Graul RC, Lee AY. Classification of membrane transporters. In Amidon GL, Sadee W, eds. Membrane transporters as drug targets. New York Kluwer Academic/Plenum Publishers 1999. p. 29-58. 

Brockhoff, P.B. (2005) Classification of membrane permeability of drug candidates a methodological investigation. QSAR Comb. Sci., 24, 449-457. 

Table 1.1, Classification of Membrane Reactors (Adapted from Sanchez and Tsotsis, [1.24]).

As previously noted, a broader classification of membrane reactors can be made relevant to the role the membrane plays with respect to the removal/addition of various species [1.25, 1.49, 1.67]. Membrane reactors could be classified as reactive membrane extractors when the membrane s function is to remove one or more products. Such action could result in increasing the equilibrium yield, like in the catalytic dehydrogenation re-... 

FIGURE 2-4 Classification of membrane transport mechanisms. Light blue circles depict the substrate. Size of the... 

A third classification of membrane proteins consists of lipid-anchored proteins bound to the iimer or outer surface of the membrane. The glycophosphatidylinosi-tolglycan (GPI) anchor is a covalently attached lipid that anchors proteins to the... 

Classification of membrane reactors with catalysts is based on the location of the catalyst. The notation introduced by Tsotsis et al. has been widely adopted, and will be used here. Table 1 gives a list of the acronyms used in this paper. 

The following brief classification of membrane electrodes can be used [42] inert membranes (cellulose, some sorts of porous glass) ion exchange membranes. 

FIGURE 23.2 Classification of membrane processes based on particle size (pore mean diameter) or molar mass (MWCO, molar... 

Table 7.3 A general classification of membrane reactor (MR) types...

Table 1 shows the classification of membrane separation techniques according to the properties of the membranes used. 

Figure 13.1 Broad classification of membrane reactors. E = empty, F = fluidized bed, P = packed bed.

It can be seen in this figure that membranes have found a wide range of applications corresponding to quite different membrane processes. It is clear that the membranes developed for such a range of processes must be necessarily very different in their structure, properties, and manufacture. A useful classification of membranes can be made based on different criteria [2]. Among them, a classification based on structural aspects is of key importance as far as it determines the functional properties of the membrane as a barrier. 

On the other hand, membranes can be symmetric or asymmetric. Asymmetric membranes have a porous support and a thin skin layer which gives selectivity. If the two layers are made of different materials, the membrane is called composite. A more or less complete classification of membranes, along with the main features of each kind of membrane, is shown in Fig. 2. 

Advanced treatment processes are required to remove microorganisms, disinfection by-product (DBP) precursors, synthetic organic chemicals (SOCs), susp ded and colloidal particles, natural organic matter, and salts from drinking water supplies. Microfiltration (MF) and ultrafiltiation (UF) are low-pressure membrane processes that can be applied to remove microorganisms and suspended and colloidal particles. Classification of membrane technologies based on their pore size and the size of particles and molecules retained is illustrated in Figure 6.1. 

The selection of a module shape depends on a number of factors, including cost, heat management, manufacturability, maintainability, operability, efficiency and membrane replacement. Membrane modules and thus membrane reactors can be combined into number of stages. The options for membrane system layout are virtually endless, as stages can be combined in various ways incorporating both compressors and recycle streams. Furthermore, membrane reactors inevitably contain catalysts and there are several ways in which the catalyst can be incorporated (Tsotsis et al., 1993). The classification of membrane reactors that incorporate catalysts is mainly based on the location of the catalyst with respect to the membrane as shown in Table 9.2. 

---