Membrane macroporous polymeric

Ilinitch et al. [13, 14] have studied the catalytic oxidation of sulfides. For this reaction, macroporous polymeric membranes, impregnated with a sodium salt of tetra(sulfophthalocyanine)cobalt(II) (Co-TSPC), were used. The MR utilized included macroporous membranes and operated in a flow-through configuration. 

Alkaline zinc-Mn02 batteries generally employ macroporous non woven separators made from cellulose or synthetic fibers (poly(vinyl alcohol) (PVA), nylon, rayon, and so on). Attempts to improve separators have generally been unsuccessful. For rechargeable Zn-Mn02 batteries, the separators are made from cellophane, grafted membranes, or polymeric films. 

In gas separation applications, polymeric hollow fibers (diameter X 100 fim) are used (e.g. PAN) with a dense skin. In the skin the micropores develop during pyrolyzation. This is also the case in the macroporous material but is not of great importance from gas permeability considerations. Depending on the pyrolysis temperature, the carbon membrane top layer (skin) may or may not be permeable for small molecules. Such a membrane system is activated by oxidation at temperatures of 400-450 C. The process parameters in this step determine the suitability of the asymmetric carbon membrane in a given application (Table 2.8). 

The transport properties across an MIP membrane are controlled by both a sieving effect due to the membrane pore structure and a selective absorption effect due to the imprinted cavities [199, 200]. Therefore, different selective transport mechanisms across MIP membranes could be distinguished according to the porous structure of the polymeric material. Meso- and microporous imprinted membranes facilitate template transport through the membrane, in that preferential absorption of the template promotes its diffusion, whereas macroporous membranes act rather as membrane absorbers, in which selective template binding causes a diffusion delay. As a consequence, the separation performance depends not only on the efficiency of molecular recognition but also on the membrane morphology, especially on the barrier pore size and the thickness of the membrane. 

Figure 2.1 Polymeric membrane shapes and cross-sectional structures. Tubular membranes are similar to flat sheet membranes because they are cast on a macroporous tube as support. Capillary membranes are hollow fibers with larger diameter, that is, >0.5 mm.

By far the majority of polymeric membranes, including UF membranes and porous supports for RO, NF or PV composite membranes, are produced via phase separation. The TIPS process is typically used to prepare membranes with a macroporous barrier, that is, for MF, or as support for liquid membranes and as gas-liquid contactors. In technical manufacturing, the NIPS process is most frequently applied, and membranes with anisotropic cross-section are obtained. Often,... 

While gellike and macroporous resins cover the vast majority of SPS, the use of other supports has also been explored. Cellulose (33, 34) in the form of paper sheets has been employed for multiple simultaneous SPS of peptides with a relatively low loading of 0.5-0.6 j,mol/cm. Cotton (35) has been used for the same application with a loading of around 0.1 mmol/g. Glass (36) was among the first supports used for the synthesis of large numbers of peptides, due to its chemical inertness and solidity. Various polymeric membranes (37, 38) were also used to prepare peptides on SP. Several of these supports will be mentioned also as related to combinatorial hbrary synthesis (see Section 6.4.1 and 6.4.2). 

They consist of a thin layer (<10 fxm) of a nanoporous (3-1OA) carbon film supported on a meso-macroporous inorganic solid (alumina) or on a carbonized polymeric structure [15]. They are produced by pyrolysis of polymeric films. The following two types of membranes are produced ... 

The nanoporous carbon membrane consists of a thin layer (<10pm) of a nanoporous (3-7 A) carbon film supported on a meso-macroporous solid such as alumina or a carbonized polymeric structure. They are produced by judicious pyrolysis of polymeric films. Two types of membranes can be produced. A molecular sieve carbon (MSC) membrane contains pores (3-5 A diameters), which permits the smaller molecules of a gas mixture to enter the pores at the high-pressure side. These molecules adsorb on the pore walls and then they diffuse to the low-pressure side of the membrane where they desorb to the gas phase. Thus, separation is primarily based on differences in the size of the feed gas molecules. Table 7 gives a few examples of separation performance of MSC membranes. ° Component 1 is the smaller component of the feed gas mixture. 

AU the techniques used to increase the stabihty of the SLM, such as the geUed SLM techniques [10, 11] (Fig. 7.5B) and the addition of thin top-layer by interfacial polymerization reaction on the SLM (Fig. 7.5C) [12], are essentiaUy applied in the removal of (metal) ions from solution. The stability of liquid membranes used for the separation of gases is more comphcated. Here, the addition of a top-layer on the macroporous support can negatively influence the permeabihty of gases through the membrane. Therefore, a careful choice of the layer material is important because it has to be impermeable to the solvent and should posses a high permeabihty for the gas molecules considered. In addition, the thickness of the top-layer as weU as that of the whole liquid membrane has to be minimized. 

Despite the physical strength offered by a macroporous support, most immobilized liquid membrane (ILM) systems are not practical for industrial separations because they are not sufficiently stable. The two most important types of instability are solvent evaporation and loss of solvent and/or carrier from the support caused by a pressure differential across the membrane. These Instabilities can be completely eliminated by removing the solvent, l.e., replacing the liquid membrane with a polymeric membrane (PM). 

---