Unsteady state dynamics, main

Outline of the Theoreyical Model. The main assumptions for the unsteady state dynamics are as follows l) Only polymer moleciiles which are raised into excited state by absorbing UV light (photon flux, no wavelength, X) near the absorption band charasteristic of polymers can participate in photochemical reactions (efficiency, n molar concentration, C ). (2) Photochemical reactions are i) depolymerization of activated polymer molecules (first order reaction,... 

In this chapter, modeling of monolith reactors will be considered from a first-principles point of view, preceded by a discussion of the typical phenomena in monoliths that should be taken into account. General model equations will be presented and subsequently simplified, depending on the subprocesses that should be described by a model. A main lead will be the time scales at which these subprocesses occur. If they are all small, the process operates in the steady state, and all time-dependent behavior can be discarded. Unsteady-state behavior is to be considered if the model should include the time scale of reactor startup or if deactivation of the catalyst versus time-on-stream has to be addressed. A description of fully dynamic reactor operation, as met when cycling of the feed is applied, requires that all elementary steps of a kinetic model with their corresponding time scales are incorporated in the reactor model. 

As mentioned in the introduction, the following discussion on modeling results takes as a lead that distinction should be made between steady-state models, unsteady-state models, and dynamic models. The results mentioned focus mainly on automotive exhaust gas treatment, which application has been widely studied, with major emphasis on the oxidation of carbon monoxide. 

For a higher degree of generality than the strictly steady state analysis of this book, the unsteady state models are developed to show very briefly, some of the transient characteristics of the system. The steady state models which are the main concern of this book are obtained by omitting the dynamic terms. The model developed in this section is a distributed model. 

In general, it can be concluded that substantial progresses have been made in the experimental and theoretical analysis of trickle-bed reactors under unsteady-state conditions. But until now these results are not sufficient for a priori design and scale-up of a periodically operated trickle-bed reactor. The mathematical reactor models, which are now available are not detailed enough to simulate all of the main transient behavior observed. For solving this problem specific correlations for specific model parameters (e.g. Hquid holdup, mass transfer gas-solid and liquid-solid, intrinsic chemical kinetic, etc.) determined under dynamic conditions are required. The available correlations for important hydrodynamic, mass-and heat-transfer parameters for periodically operated trickle-bed reactors leave a lot to be desired. Indeed, work for unsteady-state conditions on a larger scale may also be necessary. 

The two main subjects of this book are process dynamics and process control The term process dynamics refers to unsteady-state (or transient) process behavior. By contrast, most of the chemical engineering curricula... 

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