Oxidation products heterogeneous—homogeneous process

In general, the ethylene to ethane selectivity is governed by the relative rates of the processes shown in Scheme 3.1. Here, combination of methyl radicals (step 2) is a homogeneous process, but all other steps can be both homogeneous and heterogeneous.294 It was also found that further oxidation of the C2 products (steps 4 and 6) becomes important only with increasing C2 concentration in the system.327... 

A heterogeneous catalyzed process for the production of campholenic aldehyde from alpha-pinene oxide has been found, which is competitive with the homogeneous ZnBr2 system due to yields up to 85%. 

This homogeneously catalyzed process technology is not applicable for the production of unsaturated acids, such as acrylic or methacrylic acid. These acids are more typically produced via gas-phase oxidations utilizing heterogeneous catalyst systems such as Mo-V-Al-Cu oxides at much higher temperatures, 250-300 °C [3]. Very few homogeneous catalysts, such as Tl(OAc)3, have been described for the oxidation of olefmic aldehydes with oxygen [4]. 

Novel and innovative approaches for the selective catalytic homogeneous oxidation of alkanes and alkenes to produce industrially important alcohols, aldehydes, ketones, and epoxides aie still urgently needed. Homogeneous catalytic oxidation is a process that is more selective to products and, as well, the reactions aie carried out at lower temperatures in comparison to heterogeneous catalytic oxidation reactions. However, the separation of the homogeneous catalyst from the oxidation products is energy intensive for example, distillation, as well as possible thermal decomposition of the catalyst during distillation. We will discuss... 

The interpretation of these results is based on the facts that, in the presence of oxygen, chain reactions of decomposition and of oxidation are competitive and that it appears new homogeneous processes of free-radical production (which result in an accelerating effect of O2) and new termination processes at least are partly heterogeneous Cwhich result in an inhibiting effect),... 

The set of reactions shown in Table 5.1 accounts for the formation of the main oxidation products methanol, formaldehyde, and water, but does not provide for their further transformation, since only the initial stage of the process is considered. Nevertheless, its analysis can explain the main qualitative features of the DMTM process, although its quantitative modeling requires much more complex, open-type models that would take into account the totality of homogeneous and heterogeneous elementary steps important in this range of conditions. This means that the model includes all the relevant elementary steps and, if required, it can be readily extended and that all the kinetic parameters are taken from independent databases. Thus, these parameters can and should be modified based only on the subsequent recommendations of these databases. 

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