Facilitated oxygen transport

The simultaneous movement of ionic and electronic charge carriers under the driving force of a gradient in the electrochemical potential of oxygen facilitates transport of oxygen in the oxide bulk. The flux density of oxide anions is given (Figure 8.12) [77-79,109] by the ambipolar diffusion equation (see Section 5.7.6) [110,111]... 

Small-molecule transport other than olefin and molecular oxygen facilitated transport through a metal-polymer complex containing carriers (silver ions and metalloporphyrins, respectively) has also received attention, such as nitrogen transport by a cyclopentadienylmanganese and benzenechromium complex attached to a polymer [50,51], and CO2 and H2S transport based on ion-... 

The mechanism of facilitated transport involves using the metal ion only in its reduced state in the oxidized state the oxygen-carrying capacity is virtually nil. It is thus natural that electrochemical processes should be attempted to improve both the flux and selectivity obtained with the membranes described above by exploiting this 02 capacity difference. For example, the best of the ultra-thin membranes developed by Johnson et al. [24] delivered oxygen at a rate equivalent to a current density of only 3 mA/cm2, at least an order lower than that achievable electrochemically. Further, the purity was but 85% and the lifetime of the carrier less than a year. 

Fig. 9. Facilitated transport of oxygen by a carrier in a liquid membrane.

Lachowicz, E., Rozanska, B., Teixidor, F., Meliani, H., Barboiu, M. and Hovnanian, N. (2002) Comparison of sulphur and sulphur-oxygen ligands as ionophores for liquid-liquid extraction and facilitated transport. Journal of Membrane Science, 210, 279—290. 

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...

Carrier Facilitated Transport Oxygen/Nitrogen Separations... 

The first demonstration of facilitated transport of oxygen was performed by Scholander [22] using thin films of cellulose acetate impregnated with aqueous hemoglobin solutions. Later Bassett and Schultz [65] demonstrated the process with cobalt dihistidine, a synthetic carrier. The enhancements obtained in these... 

Figure 11.27 Examples of cobalt-based facilitated transport oxygen carriers [66]...

Figure 11.28 The oxygen/nitrogen selectivity plotted against oxygen permeability for polymeric membranes [68] and Co(3-MeOsaltmen)-based facilitated transport membranes [66]...

One promising approach to facilitated transport pioneered by Nishide and coworkers at Wasada University is to chemically bind the oxygen carrier to the polymer backbone, which is then used to form a dense polymer film containing no solvent [28], In some examples, the carrier species is covalently bonded to the polymer matrix as shown in Figure 11.29(a). In other cases, the polymer matrix contains base liquids which complex with the carrier molecule through the base group as shown in Figure 11.29(b). Because these films contain no liquid solvent, they are inherently more stable than liquid membranes and also could be formed into thin films of the selective material in composite membrane form. So far the selectivities and fluxes of these membranes have been moderate. 

W.J. Ward III and W.L. Robb, Carbon Dioxide-Oxygen Separation Facilitated Transport of Carbon Dioxide Across a Liquid Film, Science 156, 1481 (1967). 

H. Nishide, H. Kawakami, S.Y. Sasame, K. Ishiwata and E. Tsuchida, Facilitated Transport of Molecular Oxygen in Cobaltporphyrin/Poly(l-trimethylsilyl-l-propyne) Membrane, J. Polym. Sci., Part A Polym. Chem. 30, 77 (1992). 

Ward, W.J.I. and Robb, W.L. (1967) Carbon dioxide-oxygen separation Facilitated transport of carbon dioxide across a liquid film. Science, 156, 1481. 

The largest temperature difference occurs at the center of the tissue (z = 1), and for typical tissue fiber conditions, the maximum temperature difference is w/2 = 1.7 X 10 5oC at the tissue core. A similar increase with the effect of the chemical-binding reaction between myoglobin and oxygen is approximately 1.1 X 10-5oC. Equation (2) shows that the temperature difference increases with the square of the fiber thickness. Since the radii of skeletal muscle fibers are approximately 20 p.m. the temperature difference is not considerable. However, some experiments suggest that there is a temperature effect on the rate of facilitated transport (Dowd et al., 1991). 

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.

H. K. Lonsdale, Liquid membranes for the production of oxygen-enriched air II. Facilitated transport membranes, J. Membr. Sci. 31 (1987) 31-67. 

W. J. Ward, L. Robb, Carbon dioxide-oxygen separation Facilitation transport of carbon dioxide across hquid film, Science 156 (1967) 1481-1483. 

E. Tsushida, H. Nishide, M. Ohyanagi, H. Kawakami, Facilitate transport of molecule oxygen in the membranes of polymer — coordinated cobalt Schiff-base complexes, Macromolecules 20 (1987) 1907-1912. 

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