Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Modeling multiple reaction

In the simplest case of a PFR model, several key assumptions must be made in order to simplify the problem, some of which are outlined below. Note that not all of these assumptions are necessary, however the removal of these assumptions does increase the complexity of the problem. The PFR model can be used to model multiple reactions as well as reactions involving changing temperatures, pressures and densities of the flow. Although these complications are ignored in what follows, they are often relevant to industrial processes. [Pg.79]

Another multiple-reaction irreversible surface reaction process is the dimer-monomer-monomer (DMM) model as proposed in Ref. 99. This model is suitable for investigating, on the one hand, the influence caused by dimer traces in the MM model, and on the other hand the effect of monomer traces in the ZGB model. In fact, the DMM model assumes the following reaction steps ... [Pg.425]

Airlift loop reactor (ALR), basically a specially structured bubble column, has been widely used in chemical industry, biotechnology and environmental protection, due to its high efficiency in mixing, mass transfer, heat transfer etc [1]. In these processes, multiple reactions are commonly involved, in addition to their complicated aspects of mixing, mass transfer, and heat transfer. The interaction of all these obviously affects selectivity of the desired products [2]. It is, therefore, essential to develop efficient computational flow models to reveal more about such a complicated process and to facilitate design and scale up tasks of the reactor. However, in the past decades, most involved studies were usually carried out in air-water system and the assumed reactor constructions were oversimplified which kept itself far away from the real industrial conditions [3] [4]. [Pg.525]

The various energy transfer constraints enter into the analysis primarily as boundary conditions on the difference equations, and we now turn to the generation of the differential equations on which the difference equations are based. Since the equations for the one-dimensional model are readily obtained by omitting or modifying terms in the expressions for the two-dimensional model, we begin by deriving the material balance equations for the latter. For purposes of simplification, it is assumed that only one independent reaction occurs within the system of interest. In cases where multiple reactions are present, one merely adds an appropriate term for each additional independent reaction. [Pg.502]

As compared with the other closures discussed in this chapter, computation studies based on the presumed conditional PDF are relatively rare in the literature. This is most likely because of the difficulties of deriving and solving conditional moment equations such as (5.399). Nevertheless, for chemical systems that can exhibit multiple reaction branches for the same value of the mixture fraction,162 these methods may offer an attractive alternative to more complex models (such as transported PDF methods). Further research to extend multi-environment conditional PDF models to inhomogeneous flows should thus be pursued. [Pg.255]

The chemical engineer almost never encounters a single reaction in an ideal single-phase isothermal reactor. Real reactors are extremely complex with multiple reactions, multiple phases, and intricate flow patterns within the reactor and in inlet and outlet streams. An engineer needs enough information from this course to understand the basic concepts of reactions, flow, and heat management and how these interact so that she or he can begin to assemble simple analytical or intuitive models of the process. [Pg.6]

A vertically oriented sand filter has multiple reactions occurring in the media, which cannot be modeled analytically. The flow in the filter is close to a plug flow. Determine... [Pg.184]

We have chosen to concentrate on a specific system throughout the chapter, the methanation reaction system. Thus, although our development is intended to be generally applicable to packed bed reactor modeling, all numerical results will be obtained for the methanation system. As a result, some approximations that we will find to apply in the methanation system may not in other reaction systems, and, where possible, we will point this out. The methanation system was chosen in part due to its industrial importance, to the existence of multiple reactions, and to its high exothermicity. [Pg.114]

When the rate equation is complex, the values predicted by the two models are not necessarily limiting. Complexities can arise from multiple reactions, variation of density or pressure or temperature, incomplete mixing of feed streams, minimax rate behavior as in autocatalytic processes, and possibly other behaviors. Sensitivity of the reaction to the mixing pattern can be established in such cases, but the nature of the conversion limits will not be ascertained. Some other, possibly more realistic models will have to be devised to represent the reaction behavior. The literature has many examples of models but not really any correlations (Naumann and Buffham, 1983 Wen and Fan Westerterp et al., 1984). [Pg.560]

Sundmacher K, Uhde G, Hoffmann U. Multiple reactions in catalytic distillation processes for the production of fuel oxygenates MTBE and TAME analysis by rigorous model and experimental validation. Chem Eng Sci 1999 54 2839-2847. [Pg.367]

Kinetic mechanisms involving multiple reactions are by far more frequently encountered than single reactions. In the simplest cases, this leads to reaction schemes in series (at least one component acts as a reactant in one reaction and as a product in another, as in (2.7)-(2.8)), or in parallel (at least one component acts as a reactant or as a product in more than one reaction), or to a combination series-parallel. More complex systems can have up to hundreds or even thousands of intermediates and possible reactions, as in the case of biological processes [12], or of free-radical reactions (combustion [16], polymerization [4]), and simple reaction pathways cannot always be recognized. In these cases, the true reaction mechanism mostly remains an ideal matter of principle that can be only approximated by reduced kinetic models. Moreover, the values of the relevant kinetic parameters are mostly unknown or, at best, very uncertain. [Pg.15]

The modeling of electrochemical processes has evolved over the past 50 years to the point where complex problems involving multiple reactions, temperature variations, and physical property variations can be treated. Essentially all contemporary models require iterative computer techniques to simulate system behavior. [Pg.247]

Especially in the past, the kinetics of pyrolyses have often been reported as being proportional to the concentration of the feed hydrocarbon raised to some power. In such cases, the reaction order tends to shift to higher values with increased conversions and temperatures. These oversimplified models fail to account for the multiple reactions and products, but are reasonably successful for predicting the reactions, especially those at low conversions. [Pg.537]

Another approach has been to model sequential reactions by using multiple advection-dispersion equations [207]. The use of multiple ADEs provides a more realistic model where each reactant can degrade, sorb, and disperse. Simulations using this type of model reveal that breakthrough of degradation products could occur despite complete removal of the parent compound, TCE [207]. Additional simulations were used to explore the effect of slow sorption (i.e., nonequilibrium sorption), and the results suggest that it is reasonable to assume that an FePRB will reach steady-state conditions under typical field conditions. [Pg.403]

In the light of the previous discussion it is quite apparent that a detailed mathematical simulation of the combined chemical reaction and transport processes, which occur in microporous catalysts, would be highly desirable to support the exploration of the crucial parameters determining conversion and selectivity. Moreover, from the treatment of the basic types of catalyst selectivity in multiple reactions given in Section 6.2.6, it is clear that an analytical solution to this problem, if at all possible, will presumably not favor a convenient and efficient treatment of real world problems. This is because of the various assumptions and restrictions which usually have to be introduced in order to achive a complete or even an approximate solution. Hence, numerical methods are required. Concerning these, one basically has to distinguish between three fundamentally different types, namely molecular-dynamic models, stochastic models, and continuous models. [Pg.360]

The mathematical model for the plug flow reactor with multiple reactions... [Pg.319]

This review shows that due to the constraints of the analytical three-dimensional models in dealing with realistic boundary, flow, and transport conditions, and the computational complexity involved in numerical schemes, previous multiple-reaction models simplified or avoided three-dimensional models. Additionally, they do not fully utilize the current power of remote computing services provided through the Internet. Due to the lack of web-based remote computing capability, users usually need to install the computational software on their local computers before running them. [Pg.65]

Progress was also reported in modeling the reaction and transportation processes on fuel cell catalysts and through membranes, using multiple paradigms as well as starting from first principle quantum mechanics to train a reactive force field that can be applied for large scale molecular dynamics simulations. It is expected that the model would enable the conception, synthesis, fabrication, characterization, and development of advanced materials and structures for fuel cells . [Pg.332]


See other pages where Modeling multiple reaction is mentioned: [Pg.214]    [Pg.214]    [Pg.31]    [Pg.513]    [Pg.931]    [Pg.423]    [Pg.378]    [Pg.191]    [Pg.38]    [Pg.210]    [Pg.217]    [Pg.403]    [Pg.235]    [Pg.226]    [Pg.401]    [Pg.112]    [Pg.56]    [Pg.208]    [Pg.428]    [Pg.7]    [Pg.931]    [Pg.290]    [Pg.294]    [Pg.604]    [Pg.211]    [Pg.260]    [Pg.2]    [Pg.191]    [Pg.178]    [Pg.187]   
See also in sourсe #XX -- [ Pg.298 ]




SEARCH



Model multiple

Multiple reactions

Plug-flow model multiple reactions

Reaction multiple reactions

Segregation model multiple reactions

© 2024 chempedia.info