Facilitated transport membranes types

Another type of gas exchange process, developed to the pilot plant stage, is separation of gaseous olefin/paraffin mixtures by absorption of the olefin into silver nitrate solution. This process is related to the separation of olefin/paraffin mixtures by facilitated transport membranes described in Chapter 11. A membrane contactor provides a gas-liquid interface for gas absorption to take place a flow schematic of the process is shown in Figure 13.11 [28,29], The olefin/paraffin gas mixture is circulated on the outside of a hollow fiber membrane contactor, while a 1-5 M silver nitrate solution is circulated countercurrently down the fiber bores. Hydrophilic hollow fiber membranes, which are wetted by the aqueous silver nitrate solution, are used. 

Teramoto M, Kitada S, Ohnishi N, Matsuyama H, and Yonehara N. Separation and concentration of CO2 by capillary-type facilitated transport membrane module with permeation of carrier solution. J Mem Sci, 2004 234(1-2) 83-94. 

Facilitated transport membrane offers an attractive alternative to achieve high selectivity and high flux simultaneously.10,11 This type of membrane is based on the reversible reaction of the targeted gas with the reactive carrier contained in the membrane. There are two main types of reactive carriers the mobile carrier, which can move freely across the membrane, and the fixed carrier, which is covalently bonded on the polymer backbone and only has limited mobility. In mobile-carrier membranes, the carrier reacts with a targeted component on the feed side of a membrane, and the reaction product moves across the membrane and releases this component on the sweep side. As a result, the component being facilitated permeates through the membrane preferably, and the other components, which are not affected by facilitated transport, are retained on the retentate side. In fixed-carrier... 

Another type of membrane with high CO2 separation performances is the facilitated transport membrane. Membranes of this type are those in which an amine-based liquid supported by a solid membrane promotes a selective CO2 permeation. They exhibit generally a remarkably high selectivity and also high permeability at low CO2 pressure in the feed gas. Unfortunately, they suffer from very poor stability. For the separation of CO2, fixed carrier membranes were found to have high permselectivity without the drawback of poor stability, but with much lower permeability [13-15]. However, all membranes with amine-based carriers suffer from a strong reduction in performance with the reduction in the relative humidity in the gas mixtures, because the presence of water in the... 

To overcome the problem of low selectivity, use of facilitated transport membranes has been proposed (2,5) and many works on the CO2 facilitated transport were well summarized in review articles (4,5). As the amine type carriers of CO2, monoethanolamine (MEA) (6-8), diethanolamine (DEA) (7,9,10) and triethanolamine (7) have been investigated. Most of the data were obtained by the "tracer transport experiments" where the tracer flux of 02 through the membrane of aqueous amine solution which had been equilibrated with a known partial pressure of CO2 was measured (6,7). However, very few quantitative studies have been performed for the "net transport experiments" where the partial pressure of CO2 in the downstream side was kept lower than that in the upstream side (9,10). 

Facilitated transport membranes have been attracting attention since they have veiy high selectivity, compared with conventional polymer membranes (7). This high selectivity is attributable to carriers which can react reversibly with permeant specif There are two types of facilitated (carrier) transport membranes. One is the mobile carrier membrane in which the carrier can diffuse in the membrane, and the other is the fixed carrier membrane in ich the carrier cannot move. 

Facilitated transport membranes for gas separation were prepared conventionally by impregnating the pores of microporous supports with the carrier solutions. This type of membrane is a typical mobile carrier membrane and is known as a supported liquid membrane (SLM) or immobilized liquid membrane (ILM). 

This type of facilitated transport membrane is favorable at a relatively low feed pressure in the presence of water because reactive carriers increase the CO2 permeability drastically and CO2 permeance significantly at low CO2 partial pressures. Therefore, these liquid membranes have been studied by a number of researchers over the years. 

This chapter reviews the recent developments of two types of facilitated transport membranes (1) supported liquid membranes (SLMs) with strip dispersion and (2) carbon-dioxide-selective polymeric membranes, for environmental, energy, and biochemical applications. 

Fig. 15.2 Basic mechanisms of liquid membrane extraction (a) type I facilitated transport (A + B AB) (b) type II facilitated transport (A + B B + C).

The emulsion liquid membrane for cephalosporins relies essentially on facilitated transport. There are basically, however, two types of facilitated transport in emulsion liquid membrane system, i. e.. Type I and Type II facilitation. In the first type, the concentration gradient of the membrane soluble solute/permeate... 

Emulsion liquid membrane extraction of cephalosporins conform to the type II facilitated transport. Here the solute transport is either associated with a cotransport or counter-transport of an anionic species depending on whether ion-pair or ion-exchange extraction is exploited in the ELM system. 

In SLM extraction, the transport mechanism is influenced primarily by the chemical characteristics of the analytes to be extracted and the organic liquid in the membrane into which the analytes will interact and diffuse. Analyte solubility in the membrane and its partition coefficient will have the main impact on separation and enrichment. Analyte transport in SLM extraction can be substantially categorized into two major types one is diffusive transport (or simple permeation) and the other covers facilitated transport (or carrier-mediated transport).73... 

The other type of transport, facilitated transport, involves an analyte-specific carrier mixed in the organic membrane phase at a certain concentration. The solubility of the carrier in the surrounding aqueous phases has to be very low to prevent leakage, which would prevent specific analyte transport across the membrane. 

These membranes are similar to the simple sorption-diffusion membranes, but involve some additional phenomena as well as simple penetrant dissolution and diffusion. Two types can be identified (i) facilitated transport for various gas types, and (ii) palladium and related alloys for hydrogen. 

Be familiar with the composition and structure of biologic membranes. Be able to place the various phospholipids in the membrane bilayer. Know the function and position of membrane proteins and their possible movements. Know how membrane fluidity is controlled. Know the nature of various mechanisms to transport substances across membranes, receptor-mediated endocytosis, active and facilitated transport, ionophores, and the various types of channels. Be able to solve simple mathematical problems by creating solute gradients across membranes. Know the names of substances that inhibit the various modes of transport across membranes. 

In contrast to active transport, passive transport as a whole does not involve energy consumption and, therefore, only can work down a concentration gradient (or other types of gradients, such as electrochemical potential, thermal, or pressure gradients). In other words, passive transport of molecules equalizes their chemical potential on both sides of the membrane. The process of passive transport can be subdivided into two different mechanisms passive diffusion and facilitated transport. Passive diffusion is a physico-chemical process, whereas in facilitated transport, molecules pass through the membrane via special channels or are translocated via carrier proteins. Both passive diffusion and facilitated transport, in contrast to active transport, follow a gradient, where facilitation merely lowers the activation energy for the transport process. 

The mode of transport through a membrane may be passive, active, or facilitated type. In passive transport, the membrane acts as a barrier and permeation of the components is determined by their diffusivity and concentration in the membrane or just by their size. In facilitated transport along with the chemical potential gradient, the mass transport is coupled to specific carrier components in the membrane. In active transport driving force for transport is achieved by a chemical reaction in the membrane phase. 

Teramoto M, Matsuyama H, Nakai K, Uesaka T, and Ohnishi N. Eacilitated uphill transport of eicosapentaenoic acid ethyl ester through bulk and supported liquid membranes containing silver nitrate as carrier A new type of uphill transport. J Mem Sci, 1994 91(1-2) 209-213. Teramoto M, Matsuyama H, and Ohnishi N. Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier. J Mem Sci, 1990 50 269-278. 

Type 2 facilitation is also known as carrier facilitated transport, since a carrier compound, that is, an extractant or complexing agent, solubilized in the organic phase is used to assist transfer across the membrane. In this simation, the solute of interest reacts with the carrier to form a complex that is only soluble in the membrane phase. The solute is de-complexed by a stripping solution contained in the internal phase. An example of such a process is the removal of a metal ion such as copper or zinc from wastewater by the extractant DEHPA (di-2-ethyUiexyl phosphoric acid, represented as HE) as shown in Figure 25.2. In this case, the carrier also enhances the selectivity as most extractants are specifically designed to extract particular metal ions... 

Yan N. A mass transfer model for type-II-facilitated transport in liquid membranes. Chem Eng Sci 1993 48 3835-3843. 

Shukla, J.P., Kumar, A., and Singh, R.K., Effect of solvent type on neutral macrocycle facilitated transport of uranyl ions across supported liquid membranes using dicyclohexano 18-crown-6 as carrier. Radiochim. Acta, 1992, 57 185-194. 

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