Dispersities kinetics

Wauchope and Myers [116] studied the adsorption-dispersion kinetics of Atrazine and Linuron in sediment-aqueous slurries. The resulting adsorption or desorption was very rapid, approaching 75% of equilibrium values within 3-6min. Chlorinated adsorption of the herbicide on the sediment was completely reversible after 2h of adsorption. 

In the context of chemical reactions that are subject to dispersive kinetics as a result of structural disorder, the above model suggests that a widening of the intermediate region between the Arrhenius law and low-temperature plateau should occur. The distribution of barrier heights should also lead to nonexponential kinetic curves (see Section 6.5). 

For colloidal semiconductor systems, Albery et al. observed good agreement between the value of the radial dispersion obtained from dynamic light scattering and the value found from application of the above kinetic analysis to flash photolysis experiments [144], It should be remembered that this disperse kinetics model can only be applied to the decay of heterogeneous species under unimolecular or pseudo-first order conditions and that for colloidal semiconductors it may only be applied to dispersions whose particle radii conform to equation (37), i.e., a log normal distribution. However, other authors [145] have recently refined the model so that assumptions about the particle size distribution may be avoided in the kinetic data analysis. 

The first explanation offered for the phenomenon of dispersive kinetics is that it is caused by a distribution of rates of primary electron transfer, and that the islowi P lifetimes originate from a minority of reaction centres from the islowi tail of this distribution. The energetic basis for this distribution could be an inhomogeneous distribution of a rate-determining parameter such as X, AG or Vda (or any combination of these) (Figure lOA). The principal alternative explanation is that the multiple lifetimes represent a time-dependent energetic relaxation of the P Ha intermediate due... 

FIGURE 10. Possible origin of dispersive kinetics of primary electron transfer. Forward electron transfer is indicated by the solid arrows, thermal repopulation of the P state (a minor process) by the dotted arrows. (A) Static heterogeneityoelectron transfer takes place from the P state to P Ha states with distribution of free energies The reaction therefore occurs with a distribution of driving forces, and hence a distribution of rates. Most thermal repopulation of the P state occurs from the P Ha" states that are highest in energy. A similar model can be constructed based upon a P —> P a" with two or more values for the... 

Indirect evidence in support of both explanations for the dispersive kinetics of P decay comes from analysis of Ha" in reaction centres in the phototrapped state PHa"Qa = involving optical and magnetic resonance measurements at different temperatures and after different illumination times (M,h et al., 1999, 1998 Tiede et al., 1987). These experiments have shown that the Ha BPhe can adopt more than one conformation, and in particular that the 2-acetyl carbonyl substituent group adopts different conformations relative to the plane of the BPhe macrocycle depending on experimental conditions (M,h et al., 1999, 1998). Recent results from FTIR... 

Kolaczkowski, S. V., Hayes, J. M., and Small, G. J., 1994, A theory of dispersive kinetics in the energy transfer of antenna complexes. J. Phys. Chem., 98 13418nl3425. 

Gratzel M. and Frank A. J. (1982), Interfacial electron-transfer reactions in colloidal semiconductor dispersions—kinetic analysis , J. Phys. Chem. 86, 2964-2967. 

The simulation model and the model functions obtained from it can be used in the range 10< Diss < 10 for the calculation of the dispersion kinetics for any condition of vessel geometry, stirrer type and To perform this, it is only necessary to evaluate the assigned Ci value from the mathematical simulation of... 

Fig. 6.5 Comparison of local expansion and dispersity kinetics in foams Surfactant Cio-c sodium alkylsulphates a ) mean initial foam expansion K = 260 ( ), 90 ( ), b) mean equivalent foam eell radius R = 0.48 mm (O), 0.22 mm ( )...

The dispersion time is proportional to the energy consumption of a dispersion machine and should, therefore, not exceed the needed value. If possible, the dispersion kinetics is described in terms of energy, which may allow up-scaling from laboratory to industrial dispersion processes. 

Generally, the state of particle dispersion, which can be observed after a finite mixing time or at the end of an extrusion line, depends on the dispersion kinetics. It basically describes the rate at which the particles are transferred from the undispersed into dispersed state and is strongly related to the ongoing dispersion mechanisms. The occurrence of certain dispersion mechanisms is related to the nature of viscous flow as well as the mechanical stability of the agglomerates. 

Tan BK, Smith D, Spanel P, Davies S J. Dispersal kinetics of deuterated water in the lungs and airways following mouth inhalation real-time breath analysis by flowing afterglow mass spectrometry (EA-MS). J Breath Res. 2010 4 017109. 

Kuhrmi, C. and Berg, M.A., Dispersed kinetics without rate heterogeneity in an ionic liquid measured with multiple population-period transient spectroscopy, J. Phys. Chem. Lett. 1,161-164 (2010). 

All of the experimental dispersion-kinetics runs were not used in the regressions because it was not possible to obtain molecular characterizations in all cases. In some cases, there was some gel or some crystallinity in the polymer which prevented the solubility needed for the GPC characterizations. 

Successful scale-up means that larger scale operations are fiiUy anticipated and understood. Usually, the performance will be poorer than witnessed on a smaller scale. Scale-up must address several interdependent, flow-sensitive physical processes occurring simultaneously. These are dispersion, dispersion kinetics, coalescence, and drop suspension, as mentioned previously. 

Simple theories are described in which breakup results when disruptive forces in the surrounding fluid exceed cohesive forces, due to interfacial tension and drop viscosity. The results for a single drop are then extended to dilute dispersions in order to predict and correlate data for the DSD. The methodology is extended to more concentrated noncoalescing systems of wider practical importance as well as other dispersion devices. The scope includes a broad range of factors. Although most of the section is devoted to the development of the equilibrium mean drop size and DSD, dispersion kinetics and the time evolution of the DSD are included. 

Dispersion kinetics is discussed in Section 12-2.4 for dilute systems and in Section 12-7.4.1 for more concentrated systems. As stated previously, dispersion kinetics in tnrbnlent stirred vessels follows a first-order rate process, and rate constants depend on interfacial tension, drop size, and flow conditions (Hong and Lee 1983, 1985). Figure 12-38 shows a typical drop size versus dispersion time relationship for a batch vessel. Upon introduction of the dispersed phase, the drop size falls off rapidly and approaches the ultimate size within a factor of 2 or so, at times that are often short compared to the process time. However, the decay to equilibrium size is quite slow. This is why equiUbrium drop size correlations perform adequately despite the fact that the process time is often smaller than the time to equilibrium. 

The results presented in Table 5 show the same tendency as presented in Table 4. Both kp and kt are much lower in template polymerization. However, presented calculations are very simplified. It is difficult to accept a stationary state in this process as well as a conventional kinetic equation. Moreover, it was found that the reaction is not a second order, but in order to describe the kinetics a dispersive kinetic equation should be applied. On the basis of these data, we can conclude that in template polymerization, both rate constants, for propagation and termination, are lower than that in a conventional process. 

Schilde C, Kampen I, Kwade A (2010) Dispersion kinetics of nano-sized particles for different dispersing machines. Chem Eng Sci 65 3518-3527... 

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