Capture mechanism

Ives, K.J. "Capture Mechanisms in Filtration", The Scientific Basis Of Filtration, Noordhoff Int. Publish. Co., Leyden, pp.55,93, 1975. 

The water solubilities of the functional comonomers are reasonably high since they are usually polar compounds. Therefore, the initiation in the water phase may be too rapid when the initiator or the comonomer concentration is high. In such a case, the particle growth stage cannot be suppressed by the diffusion capture mechanism and the solution or dispersion polymerization of the functional comonomer within water phase may accompany the emulsion copolymerization reaction. This leads to the formation of polymeric products in the form of particle, aggregate, or soluble polymer with different compositions and molecular weights. The yield for the incorporation of functional comonomer into the uniform polymeric particles may be low since some of the functional comonomer may polymerize by an undesired mechanism. 

Figure 4-75. Capture mechanism for cartridge filters. Adapted by permission after Shucosky, A. C., Chemical Engineering, V. 95, No. 1,1988, p. 72.

Brake horsepower, centrifugal pumps, 200 Driver horsepower, 201 Burst pressure, 405, 456 Cartridge filters, 274-278 Capture mechanism, 279 Edge filler, 278 Filter media, table, 278 Micron ratings, 277 Reusable elements, 281 Sintered metal, 280 Types, 276, 277, 279 Wound vs. pleated, 276, 277 Centrifugal pumps, operating characteristics, 177-180 Calculations, see hydraulic performance Capacity, 180... 

Particle boundary location, 18 148 Particle capture mechanisms, in depth filtration theory, 11 339-340 Particle changes, in solid-fluid reactions, 21 344... 

The experimental results are consistent with (he hydrodynamic capture mechanism. The measured rate constants are much larger than predicted for the smallest oil drops for the 0.2- and 0.4-mm bubbles, whereas the rate constants become nearly equal as the oil drop size increases. 

Starting material 11 for the Heck reaction is prochiral The three newly established stereogenic centers in product 13 are unambiguously established relative to one another through the Heck and nucleophilic capture mechanisms. In the absence of further chiral information the absolute configuration of the stereogenic centers would remain undefined, and the two enantiomers 13 and eni-13 would be expected to arise in equal amounts. 

Figure 2.31 Separation of particulates can take place at the membrane surface according to a screen filtration mechanism (a) or in the interior of the membrane by a capture mechanism as in depth filtration (b)...

In inertial capture, relatively large particles in the flowing liquid cannot follow the fluid flow lines through the membrane s tortuous pores. As a result, such particles are captured as they impact the pore wall. This capture mechanism is... 

Figure 2.34 Particle capture mechanism in filtration of liquid solutions by depth microfilters. Four capture mechanisms are shown simple sieving electrostatic adsorption inertial impaction and Brownian diffusion...

Comparison between Experimental Results and Model Predictions. As will be shown later, the important parameter e which represents the mechanism of radical entry into the micelles and particles in the water phase does not affect the steady-state values of monomer conversion and the number of polymer particles when the first reactor is operated at comparatively shorter or longer mean residence times, while the transient kinetic behavior at the start of polymerization or the steady-state values of monomer conversion and particle number at intermediate value of mean residence time depend on the form of e. However, the form of e influences significantly the polydispersity index M /M of the polymers produced at steady state. It is, therefore, preferable to determine the form of e from the examination of the experimental values of Mw/Mn The effect of radical capture mechanism on the value of M /M can be predicted theoretically as shown in Table II, provided that the polymers produced by chain transfer reaction to monomer molecules can be neglected compared to those formed by mutual termination. Degraff and Poehlein(2) reported that experimental values of M /M were between 2 and 3, rather close to 2, as shown in Figure 2. Comparing their experimental values with the theoretical values in Table II, it seems that the radicals in the water phase are not captured in proportion to the surface area of a micelle and a particle but are captured rather in proportion to the first power of the diameters of a micelle and a particle or less than the first power. This indicates that the form of e would be Case A or Case B. In this discussion, therefore, Case A will be used as the form of e for simplicity. 

The present study is to develop the better understeinding of the intricate reaction between activated kaolinite granules and vapors of cadmium, lead and cesium chlorides. The capturing mechanisms were observed from the analysis of pre- and post-sorption sorbent samples. The effects of temperature and metal vapor diffusion on the capturing rate were observed from the analysis of long time experimental sorption data. 

A related matter concerns the physical mechanism by which radicals (primary or oligomeric) are acquired by the reaction loci. One possibility, first proposed by Garden (1968) and subsequently developed by Fitch and Tsai (1971), is that capture occurs by a collision mechanism. In this case, the rate of capture is proportional to, inter alia, the surface area of the particle. Thus, if the size of the reaction locus in a compartmentalized free-radical polymerization varies, then a should be proportional to r, where r is the radius of the locus. A second possibility (Fitch, I973) is that capture occurs by a diffusion mechanism. In this case, the rate of capture is approximatdy proportional to r rather than to r. A fairly extensive literature now exists concerning this matter (see, e.g., Ugelstad and Hansen, 1976, 1978. 1979a, b). The consensus of present opinion seems to favor the diffusion theory rather than the collision theory. The nature of the capture mechanism is not. however, relevant to the theory discussed in this chapter. It is merely necessary to note that both mechanisms predict that the rate of capture will depend on the size of the reaction locus constancy of a therefore implies that the size of the locus does not change much as a consequence of polymerization. 

These capture mechanisms are dependent on the critical re-entrainment velocity, which is the velocity at which droplets first break up from the rock surface and constrictions and are re-entrained into the flow stream. This critical velocity is a function of surface properties of the system and the droplet-size to pore-size ratio. Small double-layer repulsive forces and small droplet-size to pore-size ratios lead to large critical velocities. Soo and Radke (29) found the effect of velocity on emulsion flow in porous media to be dependent on the capillary number ([xv/0a, where x is fluid viscosity, v is velocity, is porosity, and a is surface tension). At low capillary numbers... 

Filtration Model. A model based on deep-bed filtration principles was proposed by Soo and Radke (12), who suggested that the emulsion droplets are not only retarded, but they are also captured in the pore constrictions. These droplets are captured in the porous medium by two types of capture mechanisms straining and interception. These were discussed earlier and are shown schematically in Figure 22. Straining capture occurs when an emulsion droplet gets trapped in a pore constriction of size smaller than its own diameter. Emulsion droplets can also attach themselves onto the rock surface and pore walls due to van der Waals, electrical, gravitational, and hydrodynamic forces. This mode of capture is denoted as interception. Capture of emulsion droplets reduces the effective pore diameter, diverts flow to the larger pores, and thereby effectively reduces permeability. 

Figure 22. The two types of capture mechanisms of emulsion flow in porous media. (Reproduced with permission from reference 12. Copyright 1986 Pergamon Press PLC.)...

By investigating bilayer and blend light-emitting diodes at different temperatures we give conclusive evidence that barrier-free capture is the only capture mechanism occurring at the hetero junction between PFB and F8BT (at moderate voltages). 

As explained in Section 2.2.1, the barrier-free electron-hole capture mechanism (depicted in Fig. 2.1(b)) relies on the fact that charge transport is blocked by the barriers that result from the offsets of the HOMO and LUMO levels of the two polymers. Since the carriers cannot progress across the heterojunction,... 

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