Selective layer thickness

Neglecting convection effects, the solution-diffusion model gives the following expressions for water (1) and salt (2) molar fluxes through a membrane with a selective layer thickness of L and a transmembrane pressure drop Ap (Merten, 1966) ... 

Example 30.5. Ultrafiltration tests with a 1.5-cm tubular membrane at — 25,000 gave a permeate flux of 40 L/m -h and 75 percent rejection for a 5 percent polymer solution. The polymer has an average molecular weight of 30,000, and the estimated diffusivity is 5 x 10 cm s. (fl) Neglecting the effect of molecular diffusion in the pores, predict the fraction rejected for a flux of 20 L/m -h, and predict the maximum rejection, (b) Estimate the fraction rejected for the low-molecular-weight fraction of the pol3mier with M 10,000. (c) If the selective layer thickness is 0.2 fan, does molecular diffusion have a significant effect on the rejection for case (a) ... 

Developer Substrate Support Membrane selective layer Selective layer thickness (pm) Membrane surface (m") Manufacturing method Geometry... 

The Energy Research Centre of the Netherlands (ECN) that produces membranes of Pd on alumina support with a surface area equal to 0.4 m and selective layer thickness of 3-9 pm. 

Concerning hydrogen selective membranes, industry is mainly focused on the manufacture of composite membranes made of a thin Pd film on porous substrates. Reducing the selective layer thickness allows membrane cost to be decreased (decreasing the Pd thickness by a factor two reduces the total Pd cost by a factor four) and increasing the hydrogen flux, which is in inverse proportion with the film thickness. On the other side, the porous substrates provides the mechanical... 

Once the structural number of the pavement (SN) is determined, using the equation given in Section 13.4.5, the thickness of each layer (D,) is determined by selecting layer thicknesses so that the right-hand side of the equation is equal to SN. This implies that this method does... 

Another parameter to consider is membrane thickness and the membrane selective layer thickness. This is a key parameter in membrane processes as it influences both membrane selectivity and membrane resistance against flux. 

Sqiaration selectivity obtained at laboratory scale on composite membranes (selective layer thickness 0.3. 5 im) by MTR Inc. with the following operating conditions feed = 60% methane/20%carbon dioxide/20 /o nitrogen feed pressure = 200 psig. 

Three key elements determine the potential and applications of a hollow-fiber membrane (1) pore size and pore size distribution, (2) selective layer thickness, and (3) inherent properties (chemistry and physics) of the membrane material. Pore size and its distribution usually determine membrane applications, separation factor, or selectivity. The selective layer thickness determines the membrane flux or productivity. Material chemistry and physics govern the intrinsic permselectivity for gas separation and pervaporation, fouling characteristics for RO (reverse osmosis), UF (ultrafiltration), and MF (microfiltration) membranes, chemical resistance for membranes used in harsh environments, protein and drug separation, as well as biocompatibUity for biomedical membranes used in dialysis and biomedical and tissue engineering. 

Figure 31.13 Visual estimation of the dense-selective layer thickness of dual-layer hollow-fiber membranes with different heat treatment methods (left) 15°C for 3 h and right) 150°C for 1 h. (Li et al., 2004b).

A stream at 220 atm and 100 °C containing 27.2% NH3, 54.5% H2, and 18.2% NH3 is currently being recycled to an ammonia synthesis reactor. You want to feed it through a hollow-fiber module with a fiber volume fraction of 0.5 to recover 90% of the ammonia. The module s membranes are 240 pm in diameter, have a permeability P of 4.0 10 cm /sec, and a selective layer thickness I equal to 35 pm. How long should gas spend in this module ... 

Since natural Au consists solely of Au, the interface-selective enrichment technique cannot be applied in Au studies. The absorber thickness for Au is required to be large and therefore multilayered samples of Au layers/3r/ metal layers have to be prepared. The spectra for Au/Fe with varying Au-layer thickness are shown in Fig. 7.83 [437]. The results were interpreted as follows large magnetic hyperfine fields at Au sites exist only within two monolayers at the interface region, which are supposed to be induced by direct coupling with anti-ferromagnetically oriented Fe 3d atoms. 

In terms of hydrodynamics, the boundary layer thickness is measured from the solid surface (in the direction perpendicular to a particle s surface, for instance) to an arbitrarily chosen point, e.g., where the velocity is 90-99% of the stream velocity or the bulk flow ((590 or (599, respectively). Thus, the breadth of the boundary layer depends ad definitionem on the selection of the reference point and includes the laminar boundary layer as well as possibly a portion of a turbulent boundary layer. 

The mass of the porous layer can either be determined by weighing the sample before and after anodization and determination of the dissolved mass AmD or by weighing the sample with and without the PS layer and determination of mPS. The latter case needs an etchant with a high selectivity between bulk and PS, which is not required for the former case. The PS volume is given by the layer thickness D and the electrode area A exposed to the electrolyte. 

In this chapter we discuss the measurement and analysis of simple epitaxial stractures. After showing how to select the experimental conditions we show how to derive the basic layer parameters the composition of ternaries, mismatch of quaternaries, misorientation, layer thickness, tilt, relaxation, indications of strain, curvature and stress, and area homogeneity. We then discuss the hmitations of the simple interpretation. 

In the oxide region of gold electrodes, residual lead can be present, resulting from irreversible adsorption, and presence of hydroxide species has been postulated ]265]. Pb UPD on Au(lll) has also been studied in selected organic solvents, mainly propylene carbonate [284]. Results similar to those in aqueous solutions have been obtained. Deposition of Pb on Au electrodes coated by silver has also been studied [285]. Depending on the silver layer thickness, results typical for Pb deposited on Au or Ag have been obtained. 

The surface plasmon resonance minimum reflectivity in Figure 20-23 shifts by —0.15° when 1 mM NAD+ binds to the imprinted polymer. The shift is not as great for the related species NADH, NADP+, and NADPH, confirming that the imprinted polymer selectively binds NAD+. When the observed reflectivity was fitted to the theoretical response, the polymer film was calculated to be 22 3 nm thick and had a binding capacity of 2.26 xg NAD+/cm2. When 1 mM NAD+ binds to the polymer, the refractive index of the polymer layer changes from 1.45 to 1.40 and the layer thickness increases by 3.0 0.2 nm. 

The effect of concentration of the selective solvent for PS on the PEO crystallization was also explored by Gervais and Gallot (1973a). As expected, increasing the solvent concentration reduced the melting temperature of the PEO. It was found that for a given copolymer at a fixed temperature the number of folds increased (thus the PEO layer thickness decreased) as the solvent concentration increased. This is illustrated in Fig. 5.26 which shows regions of stability of structures with different number of PEO folds in the temperature-concentration plane.The PS layer was observed to swell (and the PS interfacial area to increase)... 

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