Dispersion fractionation

A more direct source of energy for animals is provided by the starches found m many plants Starch is a mixture containing about 20% of a water dispersible fraction called amylose and 80% of a second component amylopectm... 

Supported noble metal catalysts (Pt, Pd, Ag, Rh, Ni, etc.) are an important class of catalysts. Depositing noble metals on high-area oxide supports (alumina, silica, zeolites) disperses the metal over the surface so that nearly every metal atom is on the surface. A critical property of supported catalysts is that they have high dispersion (fraction of atoms on the surface), and this is a strong function of support, method of preparation, and treatment conditions. Since noble metals are very expensive, this reduces the cost of catalyst. It is fairly common to have situations where the noble metals in a catalyst cost more than 100,000 in a typical reactor. Fortunately, these metals can usually be recovered and recycled when the catalyst has become deactivated and needs to be replaced. 

Fig. 26. Results obtained by Miller et al. in a 0.30-gal. vessel, propellor in draft tube, (a) Effect of power input and dispersed fraction, (b) Effect of system on interaction rate at 4> = 0.20.

Organic particles are also observed in the rough-disperse fraction of... 

Dispersion fraction of metallic atoms on the surface contributing to adsorption. 

Deflocculation, including its secondary effects, is a result of ion exchange on the surface of clay particles. The efficacy of this colloid-chemical adjustment is illustrated by the example reported by Norton (1952) addition of NaOH solution to mono-disperse fraction of H -kaolinite prepared by dialysis gives rise to an (approximately) 200-fold decrease in apparent viscosity, affected instantaneously in the region of pH 5-6, where complete exchange of ions for Na " has taken place. 

Metals Dispersion (Fraction of Metal Exposed) in the Catalysts... 

A completely different behavior is reported for blends in which the crystallizable phase is dispersed. Fractionated crystallization of the dispersed droplets, associated with different degrees of undercooling and types of nuclei is the rule. The most important reason is a lack of primary heterogeneous nuclei within each crystallizable droplet. An important consequence of fractionated crystallization may be a drastic reduction in the degree of crystallinity. 

PP-g-MA/PA-6 77/23 50/50 composition PP matrix PA-6 dispersed fractionated crystallization => coincident cryst. with PP Compatibilization => interfacial tension -1 => droplet size -1 => lack of heterogeneity of type 1 crystallization by nuclei of type 2 which in his turn induces PP-MA crystallization [Tang and Huang, 1994a]... 

Mel nikov, I.A., 1976. Finely dispersed fraction of suspended organic matter in eastern Pacific ocean waters. Oceanol. Acad. Sci. U.S.S.R., 15 (2) 182—186. 

Mono-disperse fractions of molar masses 200000 and 400000 g mol are added to the polymer of example 3.1 so that the ratios of the numbers of chains, in order of increasing M, become 1 1 2 1 Calculate the number-average and weight-average molar masses of the resulting polymer and hence show that the polydispersity index has increased. 

Carboxylic, hydroxyl, adipoyl chloride, and sodium adipate end-groups of the high molar mass poly(butylene adipate) (PBA), S5mthesized by polycondensation of an equimolar mixture of adipoyl chloride and 1,4-butanediol, were characterized by MALDI-TOF. Narrow dispersed fractions with low molar masses (<6000 Da) were collected by SEC fractionation, prior to MALDI analysis. ° ... 

Fig. 7.5 Graph of the migratory front velocity in terms of the disperser fraction n for a Dirac delta PDFAA. Symbols are the calc ated velocities from the RD, DG, and RT models for the values of fi in Table 7.1. The shaded area corresponds to the observational range. Reprinted from [292]. Copyright 2006, with permission from Elsevier...

Stoupin et al. assume a core stracture surrounded by a more amorphous shell rich in Ru, and therefore determine a parameter Sru = (n - (1-D)/xru)/D, where D is the dispersion (fraction of atoms at the surface) determined assuming spherical particles and based on the estimated particle size from the EXAFS (or XRD) results, and n is the nominal molar ratio (R Ru, perhaps determined from XRF). Here Sr represents the relative composition of the snrface (i.e., it is the fraction of Ru atoms relative to the total on the surface), and xr is an estimate of the relative composition of the core using in situ EXAFS results. Their final results suggest that the surface of a PtRu ETEK cluster is rich in Ru, and is heavily oxidized, similar to Hwang s and our conclusions. 

Singer and coworkers also found that the dispersed fraction was more toxic than the oil or dispersant alone [74-76]. This group tested the toxicity of Prudhoe Bay oil and Corexit 9527 to red abalone (Halliotis rufescens), a kelp forest mysid Holesimysis costata) and the topsmelt Atherinops affinis). The dispersed oil showed much higher toxicological responses in fact, no responses were noted with the WAF (water-accommodated fraction) itself. The toxicity of the dispersant and dis-... 

Due to the resolution limit of LM, only agglomerates in the range of some micrometers and larger can be detected. The fraction of CNTs which cannot be detected is considered the dispersed fraction. In the case of even sections or thin sections with thicknesses of a few microns, the area fraction of all detectable agglomerates (also sometimes called the area ratio) can be used as a relative measure for dispersion. This means only samples with the same total amount of CNTs can be compared. A lower amount of dispersed CNTs is indicated by comparatively higher values of A. ... 

The following H2 chemisorption results are reported for a 1.5% Rh/Al203 catalyst. What is the amount of hydrogen chemisorbed on Rh What is the dispersion (fraction exposed) of the Rh ... 

In the example given in Figure 13.11, polyamide membranes with different mean pore sizes were used (0.2 pm, 0.45 pm, 0.8 pm). A small disperse fraction of 5%, and a high emulsifier concentration (2% of emulsifier Tween 80) was chosen in order to avoid coalescence. Figure 13.11 gives Sauter diameters of the emulsions produced with membranes of different mean pore sizes after the first, second and third pass at 12 bar through the membrane. The Sauter diameter of the emulsion premix was 12 pm. 

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