Reaction rates initial

Tubular Reactors. The tubular reactor is exceUent for obtaining data for fast thermal or catalytic reactions, especiaHy for gaseous feeds. With sufficient volume or catalyst, high conversions, as would take place in a large-scale unit, are obtained conversion represents the integral value of reaction over the length of the tube. Short tubes or pancake-shaped beds are used as differential reactors to obtain instantaneous reaction rates, which can be computed directly because composition changes can be treated as differential amounts. Initial reaction rates are obtained with a fresh feed. Reaction rates at... 

The reactions in the regulated-set cements containing Cjj A3CF2 (note mixed notation) as a principal phase resemble those in ordinary Portiand cements. Initial reaction rates are controlled by ettringite formation. Setting occurs with formation of the monosulfate, along with some transitory lower-limed calcium aluminate hydrates that convert to the monosulfate within a few hours. 

The well-known difficulty with batch reactors is the uncertainty of the initial reaction conditions. The problem is to bring together reactants, catalyst and operating conditions of temperature and pressure so that at zero time everything is as desired. The initial reaction rate is usually the fastest and most error-laden. To overcome this, the traditional method was to calculate the rate for decreasingly smaller conversions and extrapolate it back to zero conversion. The significance of estimating initial rate was that without any products present, rate could be expressed as the function of reactants and temperature only. This then simplified the mathematical analysis of the rate fianction. 

The initial reaction rate (v0) obtained from each substrate concentration was fitted to Michaelis-Menten kinetics using enzyme kinetics. Pro (EKP) Software (ChemSW product,... 

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

The inhibition analyses were examined differently for free lipase in a batch and immobilised lipase in membrane reactor system. Figure 5.14 shows the kinetics plot for substrate inhibition of the free lipase in the batch system, where [5] is the concentration of (S)-ibuprofen ester in isooctane, and v0 is the initial reaction rate for (S)-ester conversion. The data for immobilised lipase are shown in Figure 5.15 that is, the kinetics plot for substrate inhibition for immobilised lipase in the EMR system. The Hanes-Woolf plots in both systems show similar trends for substrate inhibition. The graphical presentation of rate curves for immobilised lipase shows higher values compared with free enzymes. The value for the... 

In our study we first investigated separately the kinetics of the hydrogenation of phenol and of the hydrogenation of cyclohexanone (7), and from twenty-six different equations, using statistical treatment of the data, we found the best equations for the initial reaction rates to be... 

Using similar arguments as with the demethylation of xylenes (p. 31) we can assume from the form of the integral dependences shown in Fig. 7 that here also neither adsorption nor desorption is a rate-determining step. This is, after all, in agreement with the form of the best equations (19a) and (19b) found for the initial reaction rates of single reactions. 

The study of the initial reaction rates of isolated (97) and of competitive reactions (98) led to the best equations of the same type single reactions... 

From the simplified method using relative reactivities and initial reaction rates 0.87 0.74 3.4 0.28... 

Fig. 8. Relationship between relative reactivities S and the ratios of the initial reaction rates rj°/VA° of alkylphenols to phenol in the hydrogenation on Ni-catalyst containing 8.4% (wt.) AUOa at 160°C and initial molar ratio of hydrogen to organic substances G = 19. Alkyl substituents in phenols Me—methyl, Et—ethyl, Pr—n-propyl, i-Pr— isopropyl, s-Bu—sec-butyl, t-Bu—terc-butyl.

Fig. 9. Decrease of the catalytic activity of palladium on pumice with time. A— catalytic activity of Pd in initial measurements at 30°C B—catalytic activity of Pd at 30°C after mercury vapor is frozen out C—catalytic activity of Pd at 118°C after removing mercury vapor. (r0)i and (r0) are the initial reaction rates for the first and nth reactions (mm Hg/min). After Mann and Lien (41)-...

The attention of the authors was particularly directed toward the increased activity of the nickel catalyst film when copper was added. This increase is revealed in a change of the initial reaction rate of copper itself and of all the alloys (except those containing 25-35% nickel) they are more active than nickel itself. A respectively similar difference was observed for the activation energy and the preexponential factor. 

Decomposition of Ag20. Dubinin et al. [642] have shown that the induction period to Ag20 decomposition at 603 K is reduced and the initial reaction rate is increased by the deposition of a thin film of Ag (or of Ni) on the reactant surface. Close contact between reactant and additive must be established for the effective promotion of salt breakdown since no activating influence was detected during reactions of mechanical mixtures of Ag20 and Ag. 

Most research workers have employed an aqueous sulphuric acid solution of the aromatic, but a few have used other solvent systems and sulphonating agents. Principal among these are Hinshelwood et a/.139, who measured the rates of sulphonation of aromatics by sulphur trioxide in nitrobenzene at temperatures between 0 and 100 °C, a minimum of about 40 °C being employed for each compound. The initial reaction rate was given by... 

A plot of the initial reaction rate versus concentration, on logarithmic scales. The reaction is the polymerization of methyl methacrylate, and the concentration is that of the initiator, azobisisobutyronitrile. The slope is 0.496, showing that the reaction is half-order with respect to the initiator concentration. 

When 0.52 g of H2 and 0.19 g of 12 are confined to a 750.-mL reaction vessel and heated to 700. K, they react by a second-order process (first order in each reactant), with k = 0.063 L-mol -s 1 in the rate law (for the rate of formation of HI), (a) What is the initial reaction rate (b) By what factor does the reaction rate increase if the concentration of H2 present in the mixture is doubled ... 

Plot the concentrations of the A and C cells vs. iterations n over this time frame. Determine the initial reaction rate from the first linear portion of the [C] vs. n plot also determine k from this plot. Next plot 1/[A] vs. n and determine k from this plot. Compare this value of k with that from the initial reaction rate. Does the y-intercept agree with the expectation from Eq. (8.5) ... 

Lipase BC induced the enantioselective polymerization of 3-methyl-4-oxa-6-hexanolide (MOHEL). The initial reaction rate of the 5 -isomer was seven times... 

Pectolytic activity was also studied in batch reactors, following the reaction progress in thermostated quartz cuvettes. The reaction medium (3 cm ) was prepared with 1.5 g/L pectin in the standard buffer and 0.063 mg of enzyme. The absorbance of the reaction mixture against the substrate blank was continuously recorded at the spectrophotometer (Perkin Elmer Lambda 2, USA). Typical reaction time was 15 minutes, but initial reaction rates were estimated considering only the absorbances recorded during the first 200 seconds, range of totally linear response. 

Ce compounds (benzene + cyclohexane) are formed (Fig. 8b). Increasing the temperature increases the initial reaction rate, but also strongly enhances the amount of AsPhs having reacted (Fig. 8a) and the quantity of Ce evolved (Fig. 8b). 

The initial reaction rate of a non-porous single-channel micro reactor, filled with porous catalyst particles, was 2.0 10 mol min [12]. The same value of the porous 10-channel micro reactor was about three times larger. When normalized for the metal content of the device, the reaction rates of the porous reactor and the particle-containing reactor become similar, 6.5 10 and 4.5 10 mol min m , respectively. 

GL 17] ]R 12] ]P 16] The initial reaction rates were close to 0.01 mol min per reaction channel without prior activation of the catalyst [36]. This is in agreement with literature data on intrinsic kinetics. 

The catalyst reuse is carried out without treating Pd/ ACF between the runs. Negligible leaching (<10% within the experimental error) was observed after catalyst reuse. Figure 8 shows the initial reaction rate and the selectivity for several runs. After activity drops in the first run, it stabilizes at 0.085 0.008 kmolHj/kgp /s, while selectivity to 1-hexene is 94+1%. Kinetic curves are identical from the second to the sixth runs. 

In order to achieve a true comparison between both catalytic systems, colloidal and molecular, which display very different reaction rates, a series of experiments were carried out with the homogeneous molecular system, decreasing the catalyst concentration in the studied allylic alkylation reaction. The reaction evolution is monitored taking samples at different reaction times and analysing each of them by NMR spectroscopy (to determine the conversion) and HPLC chromatography with chiral column (to determine the enantioselectivity of I and II). For molecular catalyst systems, the Pd/substrate ratio was varied between 1/100 and 1/10,000. For the latter ratio, the initial reaction rate was found comparable to that of the colloidal system (Figure 2a), but interestingly the conversion of the substrate is quasi complete after ca. 100 h in... 

During caustic waterflooding the alkali can be consumed by the dissolution of clays and is lost in this way. The amount lost depends on the kinetics of the particular reaction. Several studies have been performed with kaolinite, using quartz as a yardstick, because the kinetic data are documented in the literature. The initial reaction rate has been found pH independent in the pH range of 11 to 13 [517]. The kinetics of silica dissolution could be quantitatively described in terms of pH, salinity, ion-exchange properties, temperature, and contact time [1549]. 

It should be noted that the reaetion using Et-DuPhos-Rh catalyst is not limited by hydrogen mass transfer sinee the hydrogen mass transfer rate is at least 5 times as fast as the initial reaction rate. Furthermore, the overall reaction time, 700 minutes, remained the same regardless of the size of the reactor. 

Data for the initial reaction rate for the catalytic dehydrogenation of sec-butyl alcohol to methyl ethyl ketone are given in Table 16.13 (Thaller and Thodos, 1960 Shah, 1965). The following two models were considered for the initial rate ... 

Table 17.11 Inhibition Kinetics Initial Reaction Rates in the Presence of Inhibitors A or B at Different Substrate Concentrations...

The four constants in Equation 17.14 may be estimated by fitting the equation to the measured initial reaction rate data presented in Figure 17.3. Because equimolar concentrations of the two substrates, PCP and H202, were used in the experiments, Equation 17.14 may be simplified as follows ... 

Calculation of kinetic parameters - In the experiments carried out in the single autoclave the H2 pressure was not maintained and the consumption of H2 controlled the conversion of AcOBu, which could be described by pseudo-first order rate constant. In the activity tests performed in SPR16 the conversion of AcOBu increased linearly up to ca. 50 % with reaction time. Initial reaction rates were calculated from AcOBu conversion vs. reaction time dependence, the initial concentration of substrate and the amount of catalyst or the amount of promoters in 1 g of catalyst. 

Abbreviations k = pseudo-first order rate constant R2 = correlation coefficient r° = initial reaction rate in mmole/gcataiystxh r0Pi and r°Re = reaction rate related to the amount of Pt and Re, respectively C = conversion of AcOBu at t=24 h selectivity to BuOH was above 90 % a2 g catalyst was used. 

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