Transport Tubular membrane

In subsequent studies attempting to find a correlation of physicochemical properties and antimicrobial activity, other parameters have been employed, such as Hammett O values, electronic distribution calculated by molecular orbital methods, spectral characteristics, and hydrophobicity constants. No new insight on the role of physiochemical properties of the sulfonamides has resulted. Acid dissociation appears to play a predominant role, since it affects aqueous solubiUty, partition coefficient and transport across membranes, protein binding, tubular secretion, and reabsorption in the kidneys. An exhaustive discussion of these studies has been provided (10). 

Porous Membrane DS Devices. The applicability of a simple tubular DS based on a porous hydrophobic PTFE membrane tube was demonstrated for the collection of S02 (dilute H202 was used as the scrubber liquid, and conductometric detection was used) (46). The parameters of available tubular membranes that are important in determining the overall behavior of such a device include the following First, the fractional surface porosity, which is typically between 0.4 and 0.7 and represents the probability of an analyte gas molecule entering a pore in the event of a collision with the wall. Second, wall thickness, which is typically between 25 and 1000 xm and determines, together with the pore tortuosity (a measure of how convoluted the path is from one side of the membrane to the other), the overall diffusion distance from one side of the wall to the other. If uptake probability at the air-liquid interface in the pore is not the controlling factor, then items 1 and 2 together determine the collection efficiency. The transport of the analyte gas molecule takes place within the pores, in the gas phase. This process is far faster than the situation with a hydrophilic membrane the relaxation time is well below 100 ms, and the overall response time may in fact be determined by liquid-phase diffusion in the boundary layer within the lumen of the membrane tube, by liquid-phase dispersion within the... 

R.E. Buxbaum and A.B. Kinney, Hydrogen Transport Through Tubular Membranes of Palladium-coated Tantalum and Niobium, Ind. Eng. Chem. Res. 35, 530 (1996). 

Buxbaum R.E., Kinney A.V. Hydrogen transport through tubular membranes of palladium-coated tantalum and niobium. Ind.Eng.Chem.Res. 1996 35 530-537. 

Furthermore, in the apical tubular membrane, the transport proteins Oatpl, Oatkl, and Oatk2, the Na +/phosphate cotransporter NPTl, and the primary active export proteins P-glycoprotein, Mrp2, Mrp4, and Berp have been identified [12, 95, 97-100]. Substrate requirements of the ABC transporters have already been discussed in the context of hepatic transport systems. Renal ABC transporters are well... 

In response to other needs in the energy and transportation sector, membranes are evolving that transport molecular species, ions, electrons, and combinations of these species. For example, mixed oxide ion-electronic conductors that become the wall of tubular reactors will soon move out of the laboratory and be used to oxidize methane by transport of oxygen from the air side to the fuel side, where the methane is converted to carbon monoxide and hydrogen. This technology eliminates the need for huge and expensive air separation plants to supply oxygen. 

Air separation membranes are typically dense ceramic (typically perovskite) membranes, which selectively permeate oxygen in ionic form. Over the past two decades. Air Products (ITMs) and Praxair (oxygen transport membranes [OTMs]) have worked towards the commercial scale-up of these membranes for applications in power generation, gasification, and gas to liquid conversion [94]. Air Products has focused on a planar configuration, whereas Praxair on tubular membranes. 

The effect of slip coefficient on concentration polarisation (CP) was mathematically modeled for flat membrane and tubular membrane systems [12,13,15,16]. Lowering of CP due to slip coefficient as a function of product water recovery ( ) for different normalised diffusion coefficients (a) is shown in Figure 6.8. The data show that CP decreases both with and a. Since a is a measure of particle diffusion from the membrane surface to the bulk solution, slip-flow possibly augments diffusive back-transport of particles from the membrane surface to the bulk solution. Thus, the slip-flow velocity model possibly accounts for higher or actual UF/MF flux, which is under-predicted by the gel polarisation model discussed in Chapter 1. 

The term membrane means a permeable phase acting as a selective barrier and controlled by mass transport. A membrane can be porous or dense material, and separation takes place due to a difference in chemical potential gradients (Dittmeyer et al, 2001). There are two materials involved in an MR a membrane and a catalyst. A membrane can have catalytic and separation functions by itself, or each material can function independently depending upon how the catalyst and membrane are incorporated in an MR. In a tubular MR, the catalyst bed is packed in the annulus or inside the tube, in which case the MR is termed a packed bed membrane reactor. 

When flow in a tubular membrane device is laminar, with material diffusing from the flowing fluid into and across the membrane, the transport equations become distributed in both radial and axial directions and in consequence lead to PDEs. One of the boundary conditions for this PDE is given by the relation... 

Plate-and-frame as well as spiral-wound modules house flat membranes. Capillary and hollow fibers are packed in larger bundles in a pressure vessel. Commercially relevant are flat membranes and hollow fibers. However, new developments in perovskite membranes for oxygen transport are based on tubular membranes as well. ... 

An essential requirement for diffusion of Na+ ions is the creation of a concentration gradient for sodium between the filtrate and intracellular fluid of the epithelial cells. This is accomplished by the active transport ofNa+ ions through the basolateral membrane of the epithelial cells (see Figure 19.4). Sodium is moved across this basolateral membrane and into the interstitial fluid surrounding the tubule by the Na+, K+-ATPase pump. As a result, the concentration of Na+ ions within the epithelial cells is reduced, facilitating the diffusion of Na+ ions into the cells across the luminal membrane. Potassium ions transported into the epithelial cells as a result of this pump diffuse back into the interstitial fluid (proximal tubule and Loop of Henle) or into the tubular lumen for excretion in the urine (distal tubule and collecting duct). 

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