Membrane meanings

Membrane Limitations Chemical attack, fouling, and compaction are prominent problems with RO and NF membranes. Compaction is the most straightforward. It is the result of creep, slow cold flow of the polymer resulting in a loss of water permeability. It is measured by the slope of log flux versus log time in seconds. It is independent of the flux units used and is reported as a slope, sometimes with the minus sign omitted. A slope of—0.001, typical for noncelhilosic membranes, means that for every threefold increase in log(time), 10 seconds, a membrane looses 10 percent of its flux. Since membranes are rated assuming that the dramatic early decline in permeability has already occurred, the further decline after the first few weeks is veiy slow. Compaction is specific to pressure, temperature, and envi-... 

Kameyama, Fukuda and Dokiya (1980, 1981) reported separation experiments of H2-H2S mixtures with porous glass (mean pore diameter 4.5 nm) and an alumina membrane (mean pore diameter 100 nm) up to temperatures of 800°C. They used the separation of H2 from the mixture to shift the equilibrium in the decomposition reaction of H2S. H2S, however, diffused partly along the surface, especially at the lower temperature range, thereby decreasing the separation efficiency. No attempt was made to describe the transport. Shindo et al. (1983, 1984) reported data on the separation of He-C02 mixtures by means of a porous glass membrane over the temperature range 296-947 K. A theoretical analysis was made, studying the... 

Porous anodized alumina (plateshaped membranes), mean pore diameter 80-250 nm. Reactants enter the reactor from opposite membrane sides. 

The fact that LTP induction requires both ligand binding to the NMDA receptor, and sufficient depolarisation of the postsynaptic membrane, means that factors affecting either process will have an impact on whether LTP is ob-... 

Differences between host cell membranes and microbial cell membranes mean that the cascade is only activated in the presence of microorganisms, so C3 tickover cannot give rise to full activation of the alternative pathway in the absence of microbial membrane. Stable deposition of a functional C3 convertase only occurs on the microbial cell surface. The differences that exist include, for example ... 

Absolute temperature (K, subscripts f, feed b, bulk s, strip and m, membrane). Mean solution velocity (ms )... 

Because lipophilicity is critical and SARs are not, relatively simple explanations of anesthetic activity are still appealing. Thus considering the known fact that such compounds do enter cellular membranes means that they are very likely to become intimately associated with lipoidal components of the membrane matrix that, in addition to the genuine lipids (e.g., myelin membranes in the brain are ca. 80% lipid), will include the larger alkyl and aryl portions of the amino acids of the protein components of the membranes. This may in turn result in a partial closure of the ion channels, thereby inhibiting polarization-depolarization of the membrane. 

A look at the open area of the two membranes in Figure 2.1 indicates that the "tortuous-pore" membranes are more porous-having a porosity over 75%. The "capillary-pore" membranes generally have porosities less than 5%. However, the fact that the latter are /is the thickness of the "tortuous pore" membranes means that the flow rates are often comparable. 

Permeation velocity of solution through membrane Mean mobility, Eq. (5.1.10c)... 

RH requirement of the membrane means that a low-pressure system is restricted to temperatures below 100°C since the saturation partial pressure of water increases exponentially with temperature. In addition, it would be highly desirable to have a water-neutral situation in order to obtain a compact and simple system where the water produced at the cathode of the fuel cell as well as the permeated water is collected completely (a condenser would be necessary) to humidify the gases. In this respect, it would be an ideal situation to operate the fuel cell at the intersections of solid and dashed lines, which are the water-neutral operating conditions. The only... 

Membranes Mean surface pore diameter (nm) Pore density (pores Surface porosity (%)... 

The authors studied two membranes. Both were manufactured by PCI Membrane Systems (UK). The first, ES 404, was made from poly(ether sulfone) and the other, XP117, was made from a mixture of polymers chosen to achieve low membrane fouling. Both had the nominal MWCO of 4000 Da. The ES 404 membrane had a smaller mean pore size and a narrower pore size distribution (mean pore size 0.65 0.19 nm, maximum pore size 0.95 nm, minimum pore size 0.22 nm) than the XP 117 membrane (mean pore size 1.05 0.30 nm, maximum pore size 1.54 nm, minimum pore size 0.53 nm). Analytical results of the surface morphology of the membranes are given in Table 7.1. 

Membrane Mean Pore Size, Product Mean Droplet Flux ... 

Sulfur dioxide has also been reported to plasticize polymeric membranes, which produces a more rubbery material and increases the diffusivity of penetrant gases [26-28]. Plasticization also reduces the mechanical integrity of the membrane, meaning it is more likely the membrane will rupture. However, plasticization is a strongly pressure dependent phenomenon, for example it has been reported in polyvinylidene membranes to occur at SO2 pressures greater than 10 psi [29]. For many of the processes in carbon capture, such high partial pressures of SO2 are not observed (Table 11.1), and therefore only minor plasticization by SO2 is likely to occur. 

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. 

It is worthwhile to note that the retarded forward diffusion phenomenon would diminish when the reverse draw solute flux is negligible. This hypothesis is verified using glucose and MgS04 as the draw solutes for the FO experiments. Glucose has a low diffusion coefficient (6.9 X 10 ° m s ) and a Stokes radius of 0.32nm which is comparable to the membrane mean effective pore radius. MgS04 has a considerably low diffusion coefficient (3.5 x 10 ° m s )... 

Zero flux of oxygen through the membrane means that 91nc/9x o = 0, while the maximal value of 91n c/dx is achieved at x = 1 (CCL/GDL interface). Thus, Equation 4.156 can be replaced by an approximate equation... 

Influence of Emulsifier Concentration Emulsions of small droplet sizes and narrow droplet size distributions can be obtained at high emulsifier concentration. Figure 13.12 shows the volume density distributions of emulsions of a disperse phase fraction of cp = 72% and two different emulsifier (Tween 80) concentrations, 2.4% and 4.6%. The production parameters were trans-membrane pressure difference of 12 bar, three passes and membrane mean pore size of 0.8 pm. In both cases the emulsifier concentration is above the critical micelle concentration (CMC). 

Figure 13.12 Volume density distributions for emulsions with different emulsifier concentrations. Disperse phase fraction

Figure 13.13 Sauter diameter of emulsions with different disperse phase concentrations as a function of the pressure difference. Membrane mean pore size 0.8 pm, one pass.

In vesicular solution at pH = 7.1 two emission bands are present in the fluorescence spectra undissociated form and naphtholate anion. At the conditions used in our experiments almost all ArOH molecules are localized in the lipid membrane of vesicles. Described earlier microphase model of microheterogeneous systems can also be applied to vesicles. In such case the term "lipid membrane" means not only lipid bilayer itself but also head group region and adjacent water layers. 

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