Gross-kinetics

Empirical grey models based on non-isothermal experiments and tendency modelling will be discussed in more detail below. Identification of gross kinetics from non-isothermal data started in the 1940-ties and was mainly applied to fast gas-phase catalytic reactions with large heat effects. Reactor models for such reactions are mathematically isomorphical with those for batch reactors commonly used in fine chemicals manufacture. Hopefully, this technique can be successfully applied for fine chemistry processes. Tendency modelling is a modern technique developed at the end of 1980-ties. It has been designed for processing the data from (semi)batch reactors, also those run under non-isothermal conditions. 

In fine chemistry, mathematical models are scarce yet. However, even gross kinetics provides a lot of information on the influence of the mode of operation on seleetivity. In general, semi-quantitative criteria are used in preliminary reactor selection. They are mainly based mainly on operational characteristics, experience, and a rough economic estimation. Factors affecting the choice of the reactor and mode of operation are listed in Table 5.4-42. 

Many fine chemistry proces.ses can be lumped into a system of two parallel or two con.secutive reactions. Selectivity can roughly be assessed using the gross kinetics for such lumped schemes, and this can be used to derive approximate criteria for reactor selection. 

These results underline the fact that gross-activities based on TOFs or half-lives only are not appropriate to compare catalytic systems that are characterized by pre-equilibria. Rather, only an analysis of gross-kinetics on the basis of suitable models can provide detailed information concerning the catalysis. 

Gross-Kinetic Measurements 277 Derivation of Michaelis-Menten Kinetics with Various... 

Catalyst-Substrate Complexes 277 Data from Gross Kinetic Measurements 280 Abbreviations 288 References 288... 

The first results of degradation of polyamides shown above are based on fast melt modification reactions. The determination of the gross kinetical reaction rate was impossible. Only a very vague estimation could be made during reactive extrusion processes. 

The first fundamental examinations with polycondensates like polyanoides and polycarbonates were carried out in an interdisciplinary cooperation between chemists and engineers as published in [33-35] by use of fast in situ chemical reactions at high melt temperature. It is well known that the gross kinetical reaction rate decreases very fast with decreasing temperature. 

The paper summarizes the basic results of our studies related to further development of known concepts of the chemical physics of polymers and creation of new ones in environment protection and life safety. The scientific novelty of our data is in development of the theory of radical-chain processes of polymer formation on the basis of exploring the gross kinetics of radical polymerization of vinyl monomers, estabhshment of the mechanisms of elementary reactions of chain initiation, propagation, and termination. 

The gross kinetics of the hydroperoxide-metal ion-nucleophile reaction can not distinguish between the two pathways. However, comparison of the apparent 3 -order rate constants with the nucleophilicity of N—for a constant RO2H— M system— might be useful. For very good and very poor nucleophiles, the rate will depend on nucleophilicity, with ka and R k, respectively, rate controlling. Mediocre nucleophiles should not show this dependence since k will govern the rate. 

In very complex cases, provides at least a gross kinetics ( pulse of chemical conversion ) ... 

Phillips, A.G. and D.P. Harrison, Gross Error Detection and Data Reconciliation in Experimental Kinetics, Indushial and Engineeiing Chemistiy Reseaieh, 32, 1993,2530-2536. (Measurement test)... 

If the reaction proceeds by more than one pathway, when it attains equilibrium the rates along each pathway (separately) are equal, not merely the total rates. Not only must the gross opposing rates be equal as a condition of thermodynamic equilibrium, but the opposing rates along each pathway must be equal as well. This relation can be applied to the kinetic data for the reaction between thiocyanate and hexaaquairon(3+) ions. The net reaction is... 

Shastri et have examined the kinetics of the reduction of Np(V) by U(rV). The rate of the reaction, zero order in Np(V) and first order in U(IV), shows an inverse dependence on the square of the hydrogen-ion concentration. The gross features of the mechanism are believed to be... 

Although the kinetic studies summarised here are useful guides to the gross features of mechanism it is evident from apparently closely related autoxidations, e.g. those of V(III) and U(IV), that subtle factors operate. Fallab has pointed out that these reductants give similar kinetics and possess similar reduction potentials, yet differ in autoxidation rate by a factor of 3 x 10 , and has discussed differences of this type in terms of the stereochemistry of the electron-transfer process in the coordination sphere. 

What is commonly understood by a fundamental approach is applying theoretically based mathematical models of necessary equipment items. Intrinsic (not falsified by processes other than a chemical transformation) kinetics of all processes are investigated, transport phenomena are studied, flow patterns are identified, and relevant microscopic phenomena are studied. It is intended to separately study as many intrinsic stages as possible and to combine results of these investigations into a mathematical model. Such a model contains only a limited amount of theory (grey models, gross models, or tendency models). Obviously, the extrapolation power of these models strongly depends on the content of theory. The model... 

If a reliable kinetic model and data on cooling capacity are at hand, runaway scenarios can be examined by computer simulations and only final findings have to be tested experimentally. Such an approach has been presented, e.g. by Zaldivar et al. (1992). However, the detailed reaction mechanism and reaction kinetics are rarely known. Therefore, thermokinetic methods with gross (macro-)kinetics dominate among methods for data... 

The complete chemical modelling of a cloud in the ISM looks tractable, if complicated, although there will always be assumptions, some of which will be rather gross, such as surface reaction rates, but they can all be refined in time. Molecular cloud modelling is at the frontier of astrochemistry and it would be hard to consider all of the results. The basic process of generating a kinetic model for a molecular cloud must follow the pathway ... 

Equation (5.19) can also be obtained from the unsteady counterpart of Equation (5.5). If internal conduction is taken as zero in Equation (5.5), this adiabatic equation arises. Equation (5.19) also becomes the basis of an alternative method for determining the bulk kinetic properties. The method is called the adiabatic furnace used by Gross and Robertson [5]. The furnace is controlled to make its temperature equal to the surface temperature of the material, thus producing an adiabatic boundary condition. This method relies on the measurement of the time for ignition by varying either ra or Too, the initial temperature. 

Gross, D. and Robertson, A.F., Self-ignition temperatures of materials from kinetic-reaction data, J. Research National Bureau of Standards, 1958, 61, 413-7. 

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