Facilitated transport membranes schematic

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. 

A liquid-free, solid-state membrane containing fixed carriers can also provide high permeability as well as high selectivity. Figure 9-1 lb schematically represents facilitated transport membranes with fixed carriers. The fixed carriers at the upstream interface bind with a specific small molecule to form an adduct. The small molecule bound to the carrier is then released in... 

The typical concentration profile of solute in an SLM system with quaternary ammonium salt as carrier is schematically shown in Fig. 6. To model the facilitated transport within a supported liquid membrane [58,59], the following assumptions are usually made ... 

Schematic representation of the facilitated transport of glucose through a cell membrane.

Figure 1.6 Schematic examples of carrier facilitated transport of gas and ions. The gas transport example shows the transport of oxygen across a membrane using hemoglobin as the carrier agent. The ion transport example shows the transport of copper ions across a membrane using a liquid ion-exchange reagent as the carrier agent...

As with coupled transport, two assumptions are made to simplify the treatment first, that the rate of chemical reaction is fast compared to the rate of diffusion across the membrane, and second, that the amount of material transported by carrier facilitated transport is much larger than that transported by normal passive diffusion, which is ignored. The facilitated transport process can then be represented schematically as shown in Figure 11.17. 

Since biological membranes act as barriers for hydrophilic and large molecules, a mobile carrier molecule, due to increased mobility of the substrate-carrier complex, may increase the transport of a substrate. Facilitated transport may be described by the jumping mechanism for a fast reaction between the carrier and substrate. Consider a schematic of facilitated transport shown in Figure 9.8. If the transport of substance-carrier across the membrane is not fast enough, then the conventional diffusion-reaction system of Eq. (9.180) is described by... 

FIGURE 13.14 Schematic diagrams of facilitated transport of gas using capillary membrane module for removal and enrichment of carbon dioxide, (a) Experimental capillary membrane apparatus and (b) capillary membrane modules with permeation of carrier solution. (From Teramoto, M., Ohnishi, N., Takeuchi, N., et al., Sep. Purif TechnoL, 30, 215, 2003. With permission.)... 

Figure 7. Schematic representation of the complete tyrosinase / ascorbate system in a Liquid Membrane showing diffusion of oxygen, carrier-facilitated transport of substrate and product through the LM, and the reactions occurring in the internal aqueous phase.

Figure 7.11 Schematic of how OTM based catalytic membrane reactors (CMRs) and hydrogen transport membranes (Hj MBN) might facilitate an environmentally benign electric utility.

Reversible complexatlon reactions have long been used to improve the speed and selectivity of separation processes, especially those Involving the separation or purification of dilute solutes (j ). Such reactions are the basis of a multitude of separation unit operations Including gas absorption, solvent extraction, and extractive distillation. When a reversible complexatlon reaction (carrier) Is Incorporated into a membrane, the performance of the membrane can be improved through a process known as facilitated transport. In this process, shown schematically In Figure 1, there are two pathways available for the transport of the solute through the membrane. The solute can permeate through the membrane by a solution-diffusion mechanism and by the diffusion of the solute-carrier complex. Other solutes are not bound by the carrier due to the specificity of the complexatlon reaction this Increases the selectivity of the process. 

Far higher selectivities can be obtained by adding a carrier molecule to the liquid (membrane) which has a high affinity for one of the solutes in phase 1. The carrier accelerates the transport of this specific component. This type of transport is called carrier mediated transport or facilitated transport. The mechanism of facilitated transport can be demonstrated by the simple experiment dqpicted schematically in figure VI > 32. 

The difference between. ordinary diffusive transport and facilitated transport is shown schematically in figure VI - 34. With canier-mediated transport, the transport of component A is enhanced by the presence of a carrier molecule C. Component A and carrier C form the complex AC, which also diffuses through the membrane. In this case two processes occur simultaneously part of component Ais transported by diffusion ( free diffusion ) whilst another part is transported by solute-carrier complex diffusion ( canier-diffusion ). Hence an increased transport of component Acan be observed. 

This reaction is currently unavoidable and appears to be favored at hot and dry operating conditions of the fuel cell. The peroxide decomposition forms reactive radials such as hydroxyl, OH, and peroxyl, OOH, that cause oxidative degradation of both the fuel cell membrane and catalyst support [67]. Both electrodes currently use Pt or Pt alloys to catalyze both the HOR and ORR reactions. The catalyst particles are typically supported on a high surface area, heat-treated carbon to both increase the effectiveness of the catalyst and to provide a path for the electrons to pass through to the external circuit via the gas diffusion media (which is typically also made of carbon) and the current collecting bipolar plates. In addition, the catalyst particles are coated in ionomer to facilitate proton transport however, the electrode structure must also be porous to facilitate reactant gas transport. A schematic of a typical PEM MEA is shown in Fig. 17.1. A boundary condition exists at the catalyst particle where protons from the ionomer, electrons from the electrically conducting Pt and carbon, and reactant gases meet. This is usually referred to as the three-phase boundary. The transport of reactants, electrons, and protons must be carefully balanced in terms of the properties, volume, and distribution of each media in order to optimize operation of the fuel cell. 

Figure 2. Schematic Diagram of the Facilitated Transport Mechanism for a Neutral Species Through a Liquid Membrane. (A is the solute, C is the complexing agent (carrier), and AC is the solute-carrier complex.)...

Figures 12 and 13 show the effects of CO2 feed partial pressures, pc02 on Rc02 and a for dry and water-containing membranes, respectively. In both cases, as the CO2 feed pressure increased, Rco2 decreased while Rn2 was nearly constant. The decrease in Rc02 observed for both dry and water-containing membranes suggests that CO2 permeates by the carrier transport mechanism in both conditions. However, the mechanism may be different for the two cases. In the dry membranes, the facilitated transport of CO2 is expected to be attributable to the weak acid-base interaction between CO2 and amine moiety, as suggested by Yoshikawa et al. (27). Therefore, the dry membrane is a fixed carrier membrane. On the other hand, tertiaiy amine groups in the wet membrane are considered to act as catalyst for the hydration of CO2 as in the case of triethanolamine in a supported liquid membrane (28). The mechanism is schematically represented as follows ...

Figure 6. Schematic representation of glucose in the pore of the facilitative glucose transporter. The amphipathic a-helices of the membrane spanning domains are thought to form a hydrophilic pore through which glucose moves via hydrogen bonding to amino acids. The importance of the hydrogen bonds at positions 1,3, and 6 of the glucose molecule for efficient transport (see text) is shown.

Scheme 8-6 Schematic diagram of enantioselective transport of (S)-i buprofen through a lipase-facilitated support liquid membrane.

A schematic drawing of these three types of transport is given in figure II - 36. The simplest type of earner-mediated transport is diffusion or facilitated diffusion, because the protein carrier allows the solute to diffuse through the membrane. 

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