Reaction Rate Effects

Since industrial nitration occurs, in most cases, in two-phase systems a number of workers have investigated the kinetics in both organic and acid phases (Refs 18b, 46 81). The consensus is that nitration occurs mainly in the acid phase. In what follows we will examine reaction rate effects in industrial-type nitrations for producing TNT, NG and EGDN... 

TNT Reaction rate effects in the production of MNT and DNT were already examined in Section VI. Here we will examine reaction rate effects for the trinitration stage, ie, DNT - TNT... 

Wilkinson s method for, 32-33 with respect to a species, 6 with respect to concentration, 16 with respect to time. 16 Reaction profile diagram. 84—85 Reaction rates, effect on of concentrations, 9 of ionic strength, 206-214 of light, 9... 

Proceeding on the same line, Hagerdal et al. reported that perfluorinated resin supported sulfonic sites (NATION 501) can hydrolyze disaccharides [25]. In particular, these authors studied the effect of the addition of sodium chloride in the hydrolysis of cellobiose, a subunit of cellulose much more resistant to hydrolysis than sucrose. They observed that the presence of sodium chloride in water dramatically increased the conversion of cellobiose. Indeed, in the presence of 10 wt% of sodium chloride, 80% of cellobiose was converted at 95°C after 6 h. For comparison, when 1% of sodium chloride was added, only 50% of cellobiose was hydrolyzed. It should be noted that without addition of sodium chloride only 15% conversion was achieved, thus pushing forward the key role of sodium chloride on the reaction rate. Effect of salt on the reaction rate was attributed to a change of the pH caused by the release of proton in the reaction medium (due to an exchange of the supported proton by sodium). 

Apparently, the discrepancies detected for the substitution data are largely the consequence of a multiplicity of minor influences operative in the transition state. The deviations are sufficiently diverse in character to require the significance of additional influences on the stability of the transition state. Four other important factors are complexing of the substituent with the electrophilic reagent or catalyst, the involvement of 7r-complex character in the transition state for the reaction, rate effects originating in the rupture of carbon-hydrogen bonds, and differential solvation of the electron-deficient transition states. 

To keep the temperature low the heat of reaction must be removed in an appropriate way, and to achieve a sufficient reaction rate effective catalysts have to be applied. The process is therefore performed in steps, with intermediate heat removal between the individual catalyst beds, in which the reaction runs adiabatically. Recently, quasi-isothermal reactors have been developed in which cooling tubes run though the catalyst layers. 

The results presented in the previous sections show that the anodic reactions on a silicon electrode may proceed via different paths depending on the conditions and that those in HF solutions and those in KOH solutions are rather different. They also show that the mechanistic models proposed for the reactions in HF and KOH solutions from the many studies in the literature are largely separated. However, in both HF and KOH solutions, the silicon/electrolyte interface is fundamentally similar differing only in the concentrations of hydroxyl and fluoride ions. Thus, a reaction scheme must be coherent with respect to the experimental observations in both FIF and KOH solutions. For comparison. Table 5.8 summarizes the characteristic features of the reactions occurring on silicon in FIF and KOH, in terms of nature of the reaction, rate, effective dissolution valence, photoeffect, and uniformity of the surface. 

Since the time enzyme was pretreated with ultrasonic irradiation could influence the reaction rate, effect of pretreatment time on the reaction was therefore investigated. As shown in Table II, the reaction rate increased with increasing pretreatment time up to 30 min. Further increase in the pretreatment time beyond 30 min, however, resulted in little change in reaction rate. So, the optimum pretreatment time was thought to be 30 min. 

Figure 9.22 A schematic diagram showing the concentration profile of permeant in a liquid membrane when the Process is (A) diffusion-controlled, (B) boundary-layer-controlled, and (C) reaction-rate controlled. The concentration profile in the membrane in absence of boundary-layer and reaction-rate effects is shown for comparison.17...

In order to analyze experimental results on chemical reactions, a clear separation of equilibrium and reaction-rate effects must be made. Sometimes equilibrium determines the product observed, and sometimes rate of reaction does. In the consideration of both equilibrium and reaction rates, reference to the bond energies of the chem cal bonds involved is frequently helpful some pertinent boiid energies arb pven in Table 6-1. 

Investigation of R OOR deeomposition in the presenee of Et4lsrBr" in pseudofirst order conditions on peroxides has shown the dependence of reaction rate effective constants from the ammonium salt concentration had nonlinear character (Fig. 2). 

LEARNING OBJECTIVES 20-2 20-3 Measuring Reaction Rates Effect of Concentration on Reaction 20-8 Theoretical Models for Chemical Kinetics... 

Most of the terms are like those in Eq. 4.3-1, and they have the same physical significance. The underlined terms are new. The last one deals with changes in reaction rate effected by the fluctuations. The other three describe the mixing caused by turbulent flow, that is, by the dispersion. They are the focus of this section. 

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