Kinetics experimental data

The kinetics of cement hydration are concerned with the relations between 

Major influences on the kinetic curve of a cement include the phase composition of the clinker, the particle size distribution of the cement and the RH and temperature regimes during curing. Other influences include the w/c ratio, the content and distribution of admixtures, including gypsum, the reactivities of individual clinker phases and probably others, such as the microstructures of the clinker and of the cement particles. 

By definition, the kinetic curve of a cement is the weighted sum of the curves for its constituent phases as they occur in that cement. The reactivities of individual clinker phases were considered in Section 4.5 and some effects of particle size distribution, which is a particularly important variable, in Section 4.1.4. Although many data relating particle size distribution directly to strength exist, much less is known about its relation to degrees of reaction. Parrott and Killoh (P30) presented data indicating that the rate of hydration, as represented by that of heat evolution, was proportional to the specific surface area during the period of hydration in which the rate was controlled by diffusion. 

The rates of reaction of the clinker phases are greatly influenced by the RH of the atmosphere in which curing occurs. For a typical Portland cement paste of w/c ratio 0.59 cured at 20°C and 100% RH, Patel el al. (P28) found the fractions of the alite, belite, aluminate and ferrite phases hydrated after 90 days to be respectively 0.94, 0.85, 1.00 and 0.51. If the RH was lowered to 80%, the corresponding values were 0.77, 0.19, 0.83 and 0.32. The hydration rate of the belite thus appears to be especially sensitive to RH. On the basis of earlier data from the literature, Parrott and Killoh (P30) concluded that the effect of RH on the hydration rate (da/d/) of each of the phases could be represented by a factor (RH — 0.55)/0.45.  

In contrast to these results, Locher (L39), working with pure CjS, found that hydration was more rapid at a low w/c ratio. 

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Table 17.3 Enzyme Kinetics Experimental Data for the hydrolysis of benzoyl-L-tyrosine ethyl ester (BTEE) by trypsin at 30 °C and pH 7.5...

To interpret the kinetics experimental data of an organic pollutant(s) or leachate from complex organic mixtures, it is necessary to determine the adsorption/ desorption process steps in a given experimental system which govern the overall adsorption/desorption rate. For instance, the adsorption process of an organic compound by a porous adsorbent can be categorized as three consecutive steps ... 

As shown in Table 1, the trend in CYP homology model building is clearly toward a multi-integrated approach using multiple sequence alignments (multiple), structural alignments in combination with mutational, spectroscopic and enzyme kinetic experimental data and new or available pharmacophore models,... 

The activation energy can be estimated from kinetic experimental data at different temperatures. The Arrhenius equation can also be written as... 

A characterization results was showed for a wastewater and sur ce-water in removing DOC using three PACs as shown in Figs. 2, 3, 4 and S. Characterization results parameters of wastewater and surface-water on PAC showed in Table 1 and 2. A characterization procedure in this study is quite suitable for the wastewater to get information depending on the initial distribution of DOC fraction. From the results obtained in this work, kinetic experimental data were predicted on the assumption that the diffusion coefficients were unchanged during the experiments (=1.0 2.0x lO" ). 

Fig. 5.6. Schematic representation of a reaction profile summarizing structural, spectroscopic, thermodynamic and kinetic experimental data...

The relation (8.10) can be used also to analyse kinetic experimental data in the case of complex reactions. Usually the number of species is much larger than the number of independent reactions. Therefore, it is sufficient to choose a number of R key species among the components that can be measured with good accuracy. Let s denote by 91 the known measured reaction rates. Then the system can be solved to find the rates of the individual reactions r. as ... 

The approach adopted is to emphasize exact, or at least nonempirical methods in the description of ufp kinetics. Experimental data and empirical formulas are employed only to substantiate or to illustrate particular theoretical approaches. 

Apparent activation energies derived from the kinetic experimental data. 

The equations look familiar to the overall heat transfer coefficient, Ug, employed in heat exchanger studies. " Assuming this model is correct, one can obtain a numerical value for froni kinetic experimental data and ka can be estimated using mass transfer theory. ... 

Opperhuizen A (1991) Bioaccumulation kinetics experimental data and modelling. In Angeletti G, Bjorseth A (eds) Organic Micropollutants in the Aquatic Environment, Proceedings of the Sixth European Symposium, Lisbon, Portugal. Kluwer Academic Publishers, Amsterdam, pp 61-70. 

Kinetic experimental data obtained were fit to the following equation ... 

Kinetic study has been one of the best mechanistic (reaction) tools to establish the most refined reaction mechanisms. In an attempt to establish such a reaction mechanism, kinetic experimental data on the reaction rate are obtained under a set of reaction conditions that could be explained by a kinetic equation derived on the basis of a proposed reaction mechanism. The study is repeated to obtain kinetic data under slightly or totally dilferent reaction conditions, and if these kinetic data fail to fit the kinetic equation derived on the basis of the earlier reaction mechanism, a further refinement in the mechanism is suggested so that the present and earlier kinetic data could be explained mechanistically. A similar approach has been used to provide quantitative or semiquantitative explanations for the micellar effects on reaction rates. Let us now examine the micellar kinetic models developed so far for apparent quantitative explanations of the effects of micelles on reaction rates. 

Recently a number of experiments have been carried out to clear up the physical nature of the phenomenon [8-11]. A lot of experimental data describing the kinetics of cone s filling with various liquids have been obtained. One of the principal features of the phenomenon is that it takes place only if a gas inside a channel is bounded by liquid surfaces of different curvatures. 

The description of chemical reactions as trajectories in phase space requires that the concentrations of all chemical species be measured as a function of time, something that is rarely done in reaction kinetics studies. In addition, the underlying set of reaction intennediates is often unknown and the number of these may be very large. Usually, experimental data on the time variation of the concentration of a single chemical species or a small number of species are collected. (Some experiments focus on the simultaneous measurement of the concentrations of many chemical species and correlations in such data can be used to deduce the chemical mechanism [7].)... 

Kinetic en aluation Clearly, the most in-depth evaluation would be based on the kinetic modeling of a reaction pathway. Unfortunately, in many cases insufficient experimental data arc available to develop a full kinetic model of a reaction pathway. Nevertheless, it has been shown with various examples that the development of a kinetic model is possible. This has been performed for the acid-... 

The reaction of MeO /MeOH with 2-Cl-5(4)-X-thiazoles (122) follows a second-order kinetic law, first order with respect to each reactant (Scheme 62) (297, 301). A remark can be made about the reactivity of the dichloro derivatives it has been pointed out that for reactions with sodium methoxide, the sequence 5>2>4 was observed for monochlorothiazole compounds (302), For 2.5-dichlorothiazole, on the contrary, the experimental data show that the 2-methoxy dehalogenation is always favored. This fact has been related to the different activation due to a substituent effect, less important from position 2 to 5 than from... 

Fig. 11. "Universal curve" of inelastic mean free path, X, as a function of electron kinetic energy. Solid line is universal curve, points are experimental data...

Eigure 20 compares the predictions of the k-Q, RSM, and ASM models and experimental data for the growth of the layer width 5 and the variation of the maximum turbulent kinetic energy k and turbulent shear stress normalized with respect to the friction velocity jp for a curved mixing layer... 

An analytical model of the process has been developed to expedite process improvements and to aid in scaling the reactor to larger capacities. The theoretical results compare favorably with the experimental data, thereby lending vahdity to the appHcation of the model to predicting directions for process improvement. The model can predict temperature and compositional changes within the reactor as functions of time, power, coal feed, gas flows, and reaction kinetics. It therefore can be used to project optimum residence time, reactor si2e, power level, gas and soHd flow rates, and the nature, composition, and position of the reactor quench stream. 

Mechanisms. Mechanism is a technical term, referring to a detailed, microscopic description of a chemical transformation. Although it falls far short of a complete dynamical description of a reaction at the atomic level, a mechanism has been the most information available. In particular, a mechanism for a reaction is sufficient to predict the macroscopic rate law of the reaction. This deductive process is vaUd only in one direction, ie, an unlimited number of mechanisms are consistent with any measured rate law. A successful kinetic study, therefore, postulates a mechanism, derives the rate law, and demonstrates that the rate law is sufficient to explain experimental data over some range of conditions. New data may be discovered later that prove inconsistent with the assumed rate law and require that a new mechanism be postulated. Mechanisms state, in particular, what molecules actually react in an elementary step and what products these produce. An overall chemical equation may involve a variety of intermediates, and the mechanism specifies those intermediates. For the overall equation... 

An excellent review covers the charge and discharge processes in detail (30) and ongoing research on lead—acid batteries may be found in two symposia proceedings (32,33). Detailed studies of the kinetics and mechanisms of lead —acid battery reactions are pubUshed continually (34). Although many questions concerning the exact nature of the reactions remain unanswered, the experimental data on the lead—acid cell are more complete than for most other electrochemical systems. 

The constant may depend on process variables such as temperature, rate of agitation or circulation, presence of impurities, and other variables. If sufficient data are available, such quantities may be separated from the constant by adding more terms ia a power-law correlation. The term is specific to the Operating equipment and generally is not transferrable from one equipment scale to another. The system-specific constants i and j are obtainable from experimental data and may be used ia scaleup, although j may vary considerably with mixing conditions. Illustration of the use of data from a commercial crystallizer to obtain the kinetic parameters i, andy is available (61). 

When experimental data are not available, methods of estimation based on statistical mechanics are employed (7,19). Classical kinetic theory suggests a contribution to CP of S R for each translational degree of freedom in the molecule, a contribution of S R for each axis of rotation, and of R for each vibrational degree of freedom. A cmde estimate of CP for small molecules can be obtained which neglects vibrational degrees of freedom ... 

Recognizing that there is presentiy a need for property values for tens of thousands of substances, but experimental data for only a small percentage of these substances, group contribution methods are viewed as the only choices for many problems such as newly or yet-to-be-synthesized compounds, situations where available data are well outside the conditions of interest, and reaction kinetics studies involving unknown intermediates. 

Experimental data that are most easily obtained are of (C, t), (p, t), (/ t), or (C, T, t). Values of the rate are obtainable directly from measurements on a continuous stirred tank reactor (CSTR), or they may be obtained from (C, t) data by numerical means, usually by first curve fitting and then differentiating. When other properties are measured to follow the course of reaction—say, conductivity—those measurements are best converted to concentrations before kinetic analysis is started. 

The verification of theoretical data obtained by simulation of peroxide oxidation kinetics of macromolecules with experimental data, obtained from chemiluminescent analysis of blood using automated complex ChLC-1. This automated complex was developed by the authors and laboratory colleagues. 

The methods I- 4 of sample preparation are classics. As a mle they give a high value of blank and some of them take a lot of time. Microwave sample preparation is perspective, more convenient and much more faster procedure than classical mineralization. There are some problems with the combination Cendall-Kolthoff s kinetic method and microwave sample preparation which discussed. The experimental data of different complex organic matrix are demonstrated (food products on fat, peptides, hydrocarbone matrix, urine etc). 

With the chosen coefficient the general character of the simulation agreed with the experimental data. For better agreement, a more detailed kinetic model would be needed. 

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