Kinetic modeling aromatics

Wang, H. and Frenklach, M., A detailed kinetic modeling study of aromatics formation in laminar premixed acetylene and ethylene flames. Combust. Flame, 110,173, 1997. 

The cyclotrimerization of alkynes to aromatic compounds, observed to occur efficiently on reduced Ti02 (001) surfaces during TPD experiments, can also be carried out as a genuinely catals tic reaction at low pressures. A kinetic model of the cyclotrimerization reaction describing the pressure and temperature dependence of the behavior observed was constructed (Scheme 1). 

Scheme 1. Proposed kinetic model for the cyclotrimerization of alkynes to aromatic compoimds on reduced Ti02 (001) surfaces. Acetylene is used as the representative alkyne for clarity.

Monomers employed in a polycondensation process in respect to its kinetics can be subdivided into two types. To the first of them belong monomers in which the reactivity of any functional group does not depend on whether or not the remaining groups of the monomer have reacted. Most aliphatic monomers meet this condition with the accuracy needed for practical purposes. On the other hand, aromatic monomers more often have dependent functional groups and, thus, pertain to the second type. Obviously, when selecting a kinetic model for the description of polycondensation of such monomers, the necessity arises to take account of the substitution effects whereas the polycondensation of the majority of monomers of the first type can be fairly described by the ideal kinetic model. The latter, due to its simplicity and experimental verification for many systems, is currently the most commonly accepted in macromolecular chemistry of polycondensation processes. 

De Visscher, A., Van Eenoo, P., Drijvers, D., and Van Langenhove, H. Kinetic model for the sonochemical degradation of monocyclic aromatic hydrocarbons in aqneons solntion, J. Phys. Chem., 100(28) 11636-11642, 1996. 

Lewandowski and Ollis have proposed a simple kinetic model describing the transient photocatalytic oxidation of aromatic contaminants [50]. The model considered three chemical species an aromatic contaminant, preadsorbed onto the catalyst in the dark and refreshed continuously from the gas phase a strongly bound, recalcitrant reaction intermediate and final reaction products (CO or CO2), assumed for simplicity to be strictly gas-phase species. The model also assumed that two types of catalyst site were present on the photocatalyst surface, with the first suitable for the adsorption of aromatic contaminants, as well as reaction intermediates, and the second type considered to be more polar in nature, suitable only for adsorption of partially oxidized reaction intermediates. 

With respect to the kinetics of aromatic oxidations, (extended) redox models are suitable, and often provide an adequate fit of the data. Not all authors agree on this point, and Langmuir—Hinshelwood models are proposed as well, particularly to describe inhibition effects. It may be noted once more that extended redox models also account for certain inhibition effects, for mixtures of components that are oxidized with different velocities. The steady state degree of reduction (surface coverage with oxygen) is mainly determined by the component that reacts the fastest. This component therefore inhibits the reaction of a slower one, which, on its own, would be in contact with surface richer in oxygen (see also the introduction to Sect. 2). 

TJ. Mitchell, S.W. Benson, and S.B. Karra. Kinetic Model for Formation of Aromatics in the High Temperature Chlorination of Methane. Combust. Sci. Techn., 107 223-260,1995. 

H. Wang and M. Frenklach. A Detailed Kinetic Modeling Study of Aromatics Formation in Laminar Premixed Acetylene and Ethylene Flames. Combust. Flame, 110 173-221,1997. 

As discussed earlier, the effects of the meta, para, and ortho positions of chlorine on the dechlorination kinetics of monochlorophenols, dichlorophenols, and trichlorophenols during Fenton oxidation were evaluated by comparing the rate constants of the kinetic model (Tang and Huang, 1995). This study proposed a pseudo first-order steady state with respect to organic concentration. The proposed reaction pathways considered that the hydroxyl radicals would attack unoccupied sites of the aromatic ring. 

Beltran FJ, Rivas FJ, Alvarez P, Alonso MA, Acedo B. A kinetic model for advanced oxidation processes of aromatic hydrocarbons in water application to phenanthrene and nitrobenzene. Ind Eng Chem Res 1999 38 4189-4-199. 

Table IV. Summary of the effect of the number and configurational arrangement of aromatic rings on the hydrogenation kinetics of aromatic model compounds (54)...

A graphical representation of the proposed kinetic model is given in Fig. 1.6. In order to verify the validity of this model, the anodic oxidation of various aromatic compounds in acidic solution has been performed varying organics concentration and current density. 

Regarding fhe kinefic modeling, few contributions propose kinetic models for fhe PC oxidation of phenol and other aromatics (Chen and Ray, 1998, 1999 Li et al., 1999b Wei and Wan 1992 ), with kinetic models being based mainly on the initial rates of reacfion only. Such models fail to account for fhe formafion of fhe differenf reaction intermediates, which may play an important role in the overall mineralization rate. More recently, Salaices et al. (2004) developed a series-parallel kinetic model based on observable aromatic intermediates. This model was applied to a wide range of pH, phenol concenfrafion, and cafalysf t)q)e. In this model, however, some steps... 

Kinetic model i (KM i) aromatics only The first proposed model considers that those aromatic intermediates produced in small amoimts can be neglected and that all remaining aromatics are converted directly into CO2 and water (e.g., formation of carboxylic acids is neglected). A schematic representation of this reaction network is given in Figure 12. 

Kinetic Model 2 (KM 2) lumped acids and CO2 production The kinetic model 1 considers only the oxidation of the major aromatic intermediates. As shown in the previous section, when most of the major intermediates have been depleted, there is still a substantial concentration of other remaining organic intermediates, as the TOC profile indicates. Therefore, it is of particular interest to calculate and predict the total mineralization times. Also, with TOC measurements, it is possible to approximate the amount of CO2 produced in the course of the reaction. In this new series-parallel model, the formation and disappearance of carboxylic acids as well as the production of CO2 has been incorporated. 

The present widespread interest in photoaddition reactions of aromatic compounds originates from observations made over 25 years ago that irradiation of maleic anhydride solutions in benzene produced the 2 1 adduct (33). Numerous accounts concerning the mechanism and scope of the reaction have since appeared and a kinetic model for the process has been proposed. "" The rate of reaction was found to be dependent on the concentrations of benzene, sensitizer, and oxygen but was essentially independent of temperature change in this last parameter does, however, have a pronounced effect on the distribution of 2 1 photoadduct isomers produced from maleic anhydride and methylbenzenes. Subsequent to the early findings on the maleic anhydride system several maleimides were also shown to form 2 1 adducts analogous to (33) with benzene. It is therefore most interesting that the 2 1 adduct (34) of... 

By 1967 the kinetic model for nondissociative thermal electron attachment and revised values for the electron affinities of 16 aromatic hydrocarbons and 7 aromatic carbonyl compounds were reported [24-26]. The ECD Ea values were correlated to theoretical calculations, electronegativities, spectroscopic data, and reduction potentials. The majority of these remain the most precise electron affinities for such compounds. Some values are assigned to excited states based on the multistate model of the ECD postulated in the 1990s [27, 28]. The electron affinities of atoms, molecules, and radicals were reviewed in 1966 [24]. The relative Ea of nitrobenzene, CS2, and SO2 were measured by the thermal charge transfer techniques and the Ea of O2 by photodetachment [30-32]. 

Although the emission from polymers with pendant aromatic groups is complex and there remains controversy concerning the specific kinetic models required to describe their fluorescence decay behaviour, the results presented above illustrate the usefulness of time-resolved fluorescence surfaces for obtaining an overview of the energy relaxation process in polymeric systems. 

Amine-anhydride reactions, equilibrium, 115 Anhydride-amine reaction, equilibrium, 115 Anhydride hydrolysis, polyimides, 58,60r,61/62 Aqueous ion extraction, kinetic model, 438-440 Aromatic polyimides applications, 67 properties, 26 structures, 27,28/ use as dielectric materials, 26... 

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