Rate and conversion

Prices of spandex fibers are highly dependent on thread size selling price generally increases as fiber tex decreases. Factors that contribute to the relatively high cost of spandex fibers include (/) the relatively high cost of raw materials, (2) the small size of the spandex market compared to that of hard fibers which limits scale and thus efficiency of production units, and (J) the technical problems associated with stretch fibers that limit productivity rates and conversion efficiencies. 

When free-radical initiation is used, cocatalysts, eg, phosphites (112), and uv photoinitiators such as acetophenone derivatives (113) can be used to increase the rate and conversion of the olefins to the desired mercaptans. 

In thioamidation the nitrile groups of PAN have a much higher reactivity than those of the corresponding model compounds. This fact is explained by the specific character of the polymeric nature of PAN and by the mutual influence of adjacent groups. As it is seen from the data presented in Fig. 4, the highest reaction rate and conversion level, as compared with low-molecular nitriles, is observed in the thioamidation of PAN. 

EfiBdent hydrogen supply iiom decalin was only accomplished by the si terheated liquid-film-type catalysis under reactive distillation conditions at modaate heating tempaatures of 210-240°C. Caibcm-supported nano-size platinum-based catalysts in the si ietheated liquid-film states accelerated product desorption fixjm file catalyst surface due to its temperature gradient under boiling conditions, so that both hi reaction rates and conversions were obtained simultaneously. 

The present paper tests the assumed original and enhancement mechanisms with rates and conversions for a broad range of contaminants measured under a fixed mass concentration (50 mg/m ) feed condition. The plots compared are reaction rates vs. (1) dark adsorption, Ot. (2) second order rate constant for (OH ) (TCE absent) or (Cl ) (TCE present), and (3) the product of these gas phase second order rate constant times the reactant dark coverage. Where a second order gas phase rate constant was not available, we estimated its value from correlations of kci vs. koH for tke same class of compounds. 

OS 14] [R 17] [no protocol[ Further studies related to the desymmetrization of thiorueas showed that for the diphenylthiourea/cydohexylamine system reasonable reaction rates and conversions were achieved [42, 85], It is notable that the temperatures of up to 91°C applied slightly exceed the boiling point of the solvent acetonitrile. 

The conversion reaches a maximum at 30 Hz. At a higher rate of rotation the increased separatory power of the centrifuge leads to a reduction of the volume of the mixed phase in which the reaction takes place. At reduced rotational speeds of the centrifuge the mixing process becomes less efficient, resulting in larger average drop sizes in the dispersed phase and thus to reduced mass transfer rates and conversion levels. 

Chiral Bronsted acid co-catalysts do not promote formation of optically enriched products in analogous couplings to pyruvates, although increased rate and conversion in response to the Bronsted acid co-catalyst is unmistakably apparent. For pyruvates, protonation likely occurs subsequent to the C-C... 

Consider the reaction studied in Illustration 10.1. Autothermal operation is to be achieved using a CSTR with an effective volume of1000 gal followed by a PFR of undetermined volume. Pure species A enters at a rate of 40.0 gal/hr and at a temperature of 20 °C. The overall fraction conversion is to be 0.97. This flow rate and conversion level will suffice to meet the annual production requirement of 2 million lb of B. Both the CSTR and the PFR are to be operated adiabatically. What PFR volume will be required, and what will be the temperature of the effluent stream ... 

In the suspended state, however, no temperature gradient arises at the catalyst surface since the active site temperature is the same as the boiling point of the solution. Only small magnitudes of reaction rates and conversions were obtained in the suspended state because of diminished rate constant k and enlarged retardation constant K (Table 13.2). 

To examine the catalyst deterioration under the present superheated liquid-film conditions, a long-term tetralin dehydrogenation over the carbon-supported platinum catalyst (Pt/C) was carried out under the superheated liquid-film conditions (heating temperature 240°C) at the amount ratio of 1.1 g/0.5 mL/min [13]. Figure 13.21 shows the time courses of reaction rate and conversion in the tetralin dehydrogenation. High conversion (around 50%) was maintained for longer than 5 h. 

As already shown by Wiese et al. [17] mass transport rates in biphasic catalysis can be dramatically influenced by hydrodynamics in a tube reactor with Sulzer packings. Above all, the volume rate of the catalyst phase in which the substrates are transported by diffusion plays a decisive role in accelerating the mass transport rate. This effect was also investigated for citral hydrogenation in the loop reactor. Overall reaction rates and conversions as a function of the catalyst volume rate can be seen in Fig. 15. 

The subsection, results and conclusions, focuses on the results and conclusions with respect to sought quantities, that is, the ignition front rate, conversion rate, and conversion stoichiometry. Each work is rounded off with comments by this author, with respect to the content of the physical model and the mathematical model making up the theory of the measurement method, as well as the application of verification methods. 

The review by Trewhella and Grint points out that a factor import in the ability of organic sulfur to enhance liquefaction is the reductive conversion of sulfur functional groups to H2S (. As the relative concentration of H2S increases, improvements are observed in both liquefaction rates and conversions (25). 

Thus, if the reactors are operating at the same temperature with the same flow rate and conversion... 

As an example consider free-radical polymerization. When an occasional free radical is formed here and there in the reactor it triggers an extremely rapid chain of reactions, often thousands of steps in a fraction of a second. The local reaction rate and conversion can thus be very high. In this situation the immediate surroundings of the reacting and growing molecules—and hence the state of segregation of the fluid—can greatly affect the type of polymer formed. 

What reactor size, feed rate, and conversion should be used for optimum operations What is the unit cost of B for these conditions if unreacted A is discarded ... 

Acetaldehyde is obtained from the reaction of synthesis gas with methanol, methyl ketals or methyl esters. The reactions are carried out with an iodide-promoted Co catalyst at 180-200 °C and 2000-5000 psig. In comparing the various feedstocks, the best overall process to make acetaldehyde involves the reductive carbonylation of methyl esters. In this case, acetaldehyde selec-tivities are > 95% ut acceptable rates and conversion. 

As we see, for a specific reaction, the higher the inlet concentration, the higher the conversion and the exit temperature. This is a result of the positive effect of the temperature rise, due to the exothermic nature of the reaction, on the rate coefficient and thus on the reaction rate and conversion. Note that for higher inlet CO concentration, the conversion for the isothermal operation is the same, while for the adiabatic operation the conversion is higher for higher inlet concentrations. Furthermore, the conversion in the adiabatic fixed bed is always higher in comparison to the isothermal fixed bed. Of course, these results are such because the reaction is of first order in respect to CO. 

The presence of defects caused by incomplete reaction in the particles has been found while comparing intra- and intermolecular reaction rates in polycomplexes obtained by mixing polymer solutions, and by matrix polymerization 461. In the latter case a polycomplex is formed simultaneously with the chain growth which is connected with the complementary macromolecule, the matrix. This process of polycomplex formation is closer to the equilibrium one — in any case there are considerably fewer obstacles here for forming an uninterrupted sequence of intermolecular bonds. That is why the rate and conversion of thermochemical reactions (which are connected with the presence or absence of defects — loops or tension in double-stranded chains of the polycomplex) depend on how the polycomplex have been obtained. After its destruction and reconstruction (e.g., by increasing and then decreasing of pH in the case of p.c. (PMA — PVPD)) the matrix polycomplex does not differ from the one obtained by mixing 46). 

Creating or maintaining uniform distributions of temperature, flow rate, and conversion degree appear to be most important during the flow of chemically reactive liquids, especially since the reaction leads to changes in material viscosity of several orders of magnitude. Even in the... 

Flynn, J.A. and Wall, L.A. (1967) Initial kinetic parameters from thermogravi-metric rate and conversion data. 

Figure 12.3 Heat release rate and conversion under isothermal condition for the Prout-Tompkins model.

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