Simultaneous reaction-separation model

Figure 15 gives a schematic of a simultaneous reaction-separation model. To include separation in a reactor targeting model, we postulate a separation function vector (7) analogous to a residence time distribution function for homogeneous reactors. Here, however, each species has its own residence time distribution function, which is dependent on its separation function 7c-... 

Parallel ketonization of acetic acid and propionic acid was one of the transformations of this type studied in our Laboratory. Ryba6ek and Setinek (94) investigated the kinetics of these reactions in the gaseous phase at 316°C using thorium oxide on activated carbon (p. 27) as the catalyst. This model system allowed the study of each reaction separately as well as of the simultaneous conversion of both acids. 

The presence of water in synthesis gas mixtures along with light components, such as carbon monoxide or hydrogen, has the effect that phase separations may persist even under extreme conditions of temperature and pressure. The need exists to demonstrate that these phase separations, perhaps with simultaneous reaction equilibrium, can be described by models capable of some accuracy. 

The simultaneous reaction and comminution of solid reactants can lead to synergetic effects. A better size reduction by reaction, or a faster reaction due to the simultaneous grinding, are possible. Both processes are quite difficult to describe and must be investigated separately, and also in combination. Until now, very few systems have been modeled and the quality of scale-up calculations is only approximate. 

In this section, we reconsider the van de Vusse process to illustrate our synthesis approach. This example also shows the application of the unified reaction-separation-energy integration model. Comparisons are made between sequential and simultaneous modes of synthesis, and the applicability of the simplified model is verified. 

Supercritical fluids display attractive solvent characteristics which can be manipulated by either the pressure or temperature. Using supercritical fluids as reaction media, simultaneous reaction and separation are also achievable. This methodology has recently been applied to the reactive separation of wood constituents, especially lignin, by supercritical fluids (1-4). Delignification processes using supercritical fluids are of potential Industrial Importance (5,6) and there Is a need for the development of kinetic models which could permit a priori prediction of the rate of lignin removal. The present paper discusses such a model. 

The last mentioned assumption allows the use of separable kinetics. Thus the reaction rate model in a deactivating system may be written as two simultaneous equations ... 

The effects of adorption site blockers on the rates of the surface reactions involving adsorbed hydrogen may be modeled simply by taking into account simultaneously but separately the blocking effect that reduces the number of sites for H adsorption and the effect on the bond in the sites not blocked, without any a priori... 

Chromatographic fixed-bed reactors consists of a single chromatographic column containing a solid phase on which adsorption and reaction take place. Normally a pulse of reactant is injected into the reactor and, while traveling through the reactor, simultaneous conversion and separation take place (Fig. 3). Since an extensive overview of the models and applications of this type of reactor was presented by Sardin et al. [ 132], only a few recent results will be discussed here. Most of the practical applications have been based on gas-liquid systems, which are not applicable for the enzyme reactions, but a few reactions were also reported in the liquid phase. One of these studies, performed by Mazzotti and co-workers [ 141 ], analyzed the esterification of acetic acid into ethyl acetate according to the reaction ... 

The fact that diffusion models describe a number of chemical processes in solid particles is not surprising since in most cases, mass transfer and chemical kinetics phenomena occur simultaneously and it is difficult to separate them [133-135]. Therefore, the overall kinetics of many chemical reactions in soils may often be better described by mass transfer and diffusion-based models than with simple models such as first-order kinetics. This is particularly true for slower chemical reactions in soils where a fast reaction is followed by a much slower reaction (biphasic kinetics), and is often observed in soils for many reactions involving organic and inorganic compounds. 

Many industrial processes involve mass transfer processes between a gas/vapour and a liquid. Usually, these transfer processes are described on the basis of Pick s law, but the Maxwell-Stefan theory finds increasing application. Especially for reactive distillation it can be anticipated that the Maxwell-Stefan theory should be used for describing the mass transfer processes. Moreover, with reactive distillation there is a need to take heat transfer and chemical reaction into account. The model developed in this study will be formulated on a generalized basis and as a consequence it can be used for many other gas-liquid and vapour-liquid transfer processes. However, reactive distillation has recently received considerable attention in literature. With reactive distillation reaction and separation are carried out simultaneously in one apparatus, usually a distillation column. This kind of processing can be advantageous for equilibrium reactions. By removing one of the products from the reactive zone by evaporation, the equilibrium is shifted to the product side and consequently higher conversions can be obtained. Commercial applications of reactive distillation are the production of methyl-... 

It is obvious that the simultaneous inclusion of all possible reactor-reactive separation-separator design options into an automated design framework quickly leads to combinatorial explosion. In combination with the nonlinear models used to describe the reaction, mass, and heat transfer phenomena that occur in the processing units, the resulting synthesis problem is beyond the scope of existing optimization technology, even for relatively small problems. This has led to the... 

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