Mass transfer regime

Enantioselectivity was roughly the same for the three reactors, being 80-90 and 62-65% for the Rh/Josiphos and Rh/Diop catalysts, respectively [266]. Conversion was very different. For fixed reaction time, the batch reactor and the falling-film microreactor had higher conversions than the Caroussel reactor. This was indicative of operation under mass transfer regime in the latter. On the basis of these data, it was concluded that the mass transfer coefficients kya of the helical falling-film microreactor are in between the boundaries given by the known kta values of 1-2 s 1 for small batch reactors and about 0.01 s-1 for the Caroussel reactor. 

It can be used for process studies conducted into the flow and mass-transfer regimes on the commercial scale. One can use it to examine the phenomena occurring at a specific point in the commercial fixed-bed reactor. 

It is important to note that mediated oxidation using the conventional anodic materials is applied in order to improve the low oxidative action of these materials. Consequently, with these materials mediated oxidation is required during the whole electrochemical treatment, while with the BDD anodes this oxidation is only needed in the region IV of the treatment when the mass-transfer regime limits the treatment efficiency. 

The characteristic time of direct electrochemical oxidation (Tdir) is easily estimated during the mass-transfer regime and is derived by (9.9). 

This chapter examines the possibility of using mediated oxidation during the electrochemical treatment of wastewater with BDD anodes, and a comparison is made of the difference in the mediated oxidation contribution using a BDD anode respect to the conventional anodic materials. The contribution of this oxidation in the conventional anodic materials is the improvement of the low oxidative action of these anodes throughout the entire treatment, while in the case of BDD anode, a positive contribution is only found during the mass-transfer regime that occurs at the end of the electrochemical treatment. 

The experimental approaches [11-13] on the growth rate of silicon on silicon substrate confirm the presence of two growth regimes depending on the temperature a regime controlled by chemical kinetics for temperatures below 1,000°C and a regime controlled by mass transfer regime for temperatures above 1,000°C (Fig. 10.3). 

The experimental time ranges discussed here relate to practical values of electrode radius and diffusion coefficient and are all readily accessible with standard commercial electrochemical instrumentation. A distinguishing feature of a UME is the ability to operate in different mass-transfer regimes. Indeed, we used, in essence, the ability to approach or to achieve the steady-state as the basis for our operational definition of a UME in the opening paragraphs of this section. 

The first order in hydrogen is observed at all pressures, while the reaction order in the substrate can vary from first to zero order. Thus the observed kinetic regularities could be the same in the kinetic and mass transfer regimes under certain conditions, demonstrating the necessity to verify experimentally and by calculations if the kinetic regime is achieved. 

For mass transfer diffusion, is so difficult to find for most insulators that 2 could not be computed. An indication is given of whether each system appears to be in the high-temperature or low-temperature mass transfer regime (described further in the Discussion). Coverages are not reported because selfdiffusion is often involved, or because coverages are often so poorly defined. For several systems, the original anthors reported a product of a D° times the thickness 5 of a hypothetical diffusional layer. This layer is typically conceived to have a thickness between 0.3 and 1 nm [76Furl] to convert the reported values into standard nnits of D° for Table 21, 5 = 1.0 nm was nsed by the present authors. 

Besides this bulk phase elfects surfactants will adsorb at the liquid-liquid interface. Their influence on mass transfer may then be on different mechanism. A blocking effect of adsorption layers in a diffusional transport regime is well known and results in a reduction of mass transfer [54-57] and even Marangoni instabilities [58,59] are found. However, in the kinetical mass-transfer regime, both an enhancement and retartion of mass transfer [59] is with Gibbs surfactant layers. With extracting ionic species, ionic surfactants will induce an electrostatic double layer, which can be related to the -potential. As a result, there exists, in addition to the chemical potentials, an... 

Both amines compete for the same dissolved gas. Reaction rates are such that various mass transfer regimes are covered... 

In fact, the weight p defines an evolution mode or mass transfer regime, which in turn corresponds to an energy conservation yield, as shown in Figure 10.12 for various transfer regimes. 

The selection of reactor type is perhaps the most important problem in SSITKA studies. There are two types of reactors, that is, plug-flow and continuous stirred tank (CSTR), which differ in mass transfer regimes. The decisive advantage of CSTR is that the reaction takes place in gradientless conditions, which considerably simplifies the kinetic studies. However, the rather high response time of gas mixing in the reactor volume may distort the true dynamics of label transfer from reactants to reaction products. 

Here, 0/ and a are respectively the steady-state concentrations of surface species and the relative label concentrations (isotope fractions) in them rf is the rate of a chemical reaction step y is the number of label atoms transferring from one substance to another in elementary reaction step (an analog of stoichiometric coefficient), P is a dimensionless coefficient equal to LW/VNa, where V is the gas-phase volume (crn ), L is the number of active sites per gram of catalyst (mol/g), W is the catalyst weight (g), Na is the number of gas molecules per unit volume (mol/cm ), and 0 Cf(x.j) is the operator depending on the mass transfer regime in the reactor ... 

The mass transfer regime which influences maximum current density the rate of production of intermediates and the extent of mixing between the reaction layer at the surface and the bulk solution. The mass transport regime is determined by the electrolyte flow rate, movement of the electrodes or turbulence promoters. 

Mass Transfer Regimes in Blood Flow The Critical Blood Vessel Diameter Shear rates y in physiological blood flow typically lie in the range 100 - 1000 S" Show that for proteins (D = l(h ° xcF/s), mass transfer in the "larger" blood vessels, d> mm, falls entirely in the developing (L veque) region, while for d < 10" mm, the concentration profile is fully developed. (Hint Use the relation y = 8v/d.)... 

Ozaydin-Ince G, Gleason KK. Transition between kinetic and mass transfer regimes in the initiated chemical vapor deposition from ethylene glycol diacrylate. J Vac Sci Technol A 2009 27 1135. 

Mass Transfer Regimes in Mechanically Agitated Solid-Liquid Systems... 

Figure 5.3.1. Different mass-transfer regimes in absorption of gas A in a liquid containing reactant C.

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