Reactor dynamics

These concepts were implemented according to the following scheme the liquid element surrounding the bubble and the bulk are considered as two separate dynamic reactors that operate independent of each other and interact at discrete time intervals. In the beginning of the contact time, the interface is being detached from the bulk. When overcome by the bubble, it returns to the bulk and is mixed with it. Hostomsky and Jones (1995) first used such a framework for crystal precipitation in a flat interface stirred cell. To formulate it for a... 

The transformation of CF3CH2CI was studied at 320 C in a pulse flow reactor. Indeed, in a dynamic reactor, the agnificant alkene formation leads to a rapid deactivation of the catalyst. The reaction is carried out in absence of HF in order to favour the dehydrofluorination reaction. Products distribution is shown in Fig. 1. 

Consequently the catalytic activity for the CF3CH2CI fluorination reaction was measured in the presence of an excess of HF in a fixed bed dynamic reactor (fig. 2). 

In a dynamic reactor for propane metathesis, (=SiO)2Ta-H remains active during several days. The results are comparable to those obtained in batch mode, in terms of turnover number (TON) and selectivity (Figure 3.10). 

Most of the dynamic reactor relief simulation codes, described in A4.2 above, incorporate two-phase flow models. The models vary in their ease-of-use for stand-alone calculation. The use of complex two-phase flow models within a dynamic simulation can lead to very long run-times. 

The main physicochemical processes in thin-film deposition are chemical reactions in the gas phase and on the film surface and heat-mass transfer processes in the reactor chamber. Laboratory deposition reactors have usually a simple geometry to reduce heat-mass transfer limitations and, hence, to simplify the study of film deposition kinetics and optimize process parameters. In this case, one can use simplified gas-dynamics reactor such as well stirred reactor (WSR), calorimetric bomb reactor (CBR, batch reactor), and plug flow reactor (PFR) models to simulate deposition kinetics and compare theoretical data with experimental results. 

Fluid Dynamics Fluid Mixing Liquids, Structure and Dynamics Reactors in Process Engineering Rheology of Polymeric Liquids... 

For proper control of industrial fixed bed reactors it is necessary to know their dynamic behaviour. This behaviour may be investigated by a series of experiments where a single process variable is changed at a time (1-6). In general such experiments allow for the development of a reactor model which describes the dynamic reactor behaviour. However, very often a large number of experiments is required. 

Dynamic reactor studies are not new, but they have not been widely used in spite of the fact that they can provide a wealth of information regarding reaction mechanisms. In this research, oxidation of carbon monoxide over supported cobalt oxide (C03O4) was studied by both dynamic and conventional steady state methods. Among metal oxides, cobalt oxide is known to be one of the most active catalysts for CO and hydrocarbon oxidation, its activity being comparable to that of noble metals such as palladium or platinum. 

If the reactants are in the gas phase, the reactor may be either static or dynamic. Small static reactors are convenient for basic research where either the reactants are expensive (e.g. isotopically labelled molecules) or the reaction slow. Dynamic reactors, where reactants flow through the catalyst bed, provide a better simulation of practical use in a fixed bed reactor the catalyst remains in place, and it is in the form of large particles or pellets. 

In a static reactor the rate changes with time as the reactants are consumed, and the initial rate is often used. In a dynamic reactor under steady state conditions the rate is independent of time, and with a known flow of reactant into the reactor the observed fractional conversion is readily changed into a rate. What is of great interest in understanding a catalysed reaction is the response of the rate to variations in operating conditions, especially the concentrations or pressures of the reactants, and temperature. It is frequently observed that, at least over some limited range of temperature, the Arrhenius equation in the form... 

Equations (4.13) to (4.15) represent a nonlinear, dynamic reactor model suitable for simulation on a digital computer. From this model we can derive other models that are useful for control explorations of... 

Heterogeneously catalyzed reactions are usually studied under steady-state conditions. There are some disadvantages to this method. Kinetic equations found in steady-state experiments may be inappropriate for a quantitative description of the dynamic reactor behavior with a characteristic time of the order of or lower than the chemical response time (l/kA for a first-order reaction). For rapid transient processes the relationship between the concentrations in the fluid and solid phases is different from those in the steady-state, due to the finite rate of the adsorption-desorption processes. A second disadvantage is that these experiments do not provide information on adsorption-desorption processes and on the formation of intermediates on the surface, which is needed for the validation of kinetic models. For complex reaction systems, where a large number of rival reaction models and potential model candidates exist, this give rise to difficulties in model discrimination. 

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. 

Dynamic regime (T When the period of the oscillation is of the order of the system s characteristic response lime, the system is in intermediate or dynamic periodic operation. The transient behavior of the system has to be determined to predict the effects of periodic operation. Dynamic reactor operation may result in considerably higher performance if resonance phenomena are involved, and therefore this range of operation is of particular interest for optimization of the reactor. 

Introduction of CO + (760 Torr) in a molar ratio 2 1 in the glass equipment was followed by a stepwise increase of temperature from 25 up to 200°C. Analysis of the gas phase gave the results represented on Figure la. At 176°C the conversion of CO to hydrocarbons is close to 1 % with mainly propylene (32%), methane (26,1 %) ethylene (9,2 %), 1-butene (7,3 %), cis-2-butene (3,6 %), trans-2-butene (5,5 %), isobutene (1 %) and C, hydrocarbons (7 %). All the paraffins except methane are present in much smaller amount than olefins. Figure (lb) represents typical results obtained in Fischer-Tropsch synthesis in a dynamic reactor using a catalyst derived from Fe CO) jj/A Oj (3e). 

Surface properties of unmodified carbon-silica adsorbents (carbosils X, H, B, Y) and the same adsorbents modified with the products of pyrolysis of n-heptanol (H) and benzyl alcohol (B) in an autoclave (A) and dynamic reactor (R). The carbosils were prepared by the pyrolysis of methylene chloride adsorbents X and Y), n-heptyl alcohol (H) and benzyl alcohol (B) on the silica surface... 

The initial conditions used for dynamics reactor simulations depend upon the start-up procedure adopted in industry for each particular chemical process. A possible set of initial conditions corresponds to uniform variable fields given by the inlet values. 

This section aims to give an overview of adsorption processes of metal ions by activated carbon. Three cases are detailed (1) the adsorption of metal ions onto virgin activated carbon adsorption capacities are given in static and dynamic reactors, and the influence of various operating conditions is shown (2) the adsorption of metal ions onto activated carbon preloaded with organic matter (3) the saturation of activated carbon by organic matter and metal hydroxides after its use in wastewater treatment. The influence of metal hydroxides on activated carbon regeneration is demonstrated. 

The two key steps of the preparation were the use of an in situ dynamic reactor and the anchoring of teta-n-butylgermanium under inert atmosphere on the rhodium surface covered with preadsorbed hydrogen. The initial amount of tetra-n-bulylgermanium introduced varied in the range from about 280 to 11 200 wt.-ppm Ge corresponding nominally to 1/20 a Ge-monolayer (Ge 1/20) or two Ge-monolayers (Ge 2) (see Table 1). The final Ge loading of catalysts was determined by the Service Central d Analyse du CNRS (France). 

The same experiments performed in the batch reactor gave additional parameters pressure increase (Table 1 Figure 3), decomposition rate (AP.Af ) and ignition delay. The pressure increase is due to the formation of various gaseous products (equation 1-4) which can be evaluated using a dynamic reactor. 

Problems may be encountered in photochemical synthesis when high concentrations of reactants are used. So it is interesting that the yield of reactions at low concentrations of reactants has been increased, without the usual disadvantages, using a poor solvent for the reactants and a conventional dynamic reactor. ... 

The safety assessment of a process performed in a CSTR must not be restricted to the steady state operating conditions but has to include the dynamic reactor behaviour. 

Provided that the necessary amount of physicochemical substance data as well as kinetic and thermodynamic reaction data has thoroughly been obtained experimentally, one can choose today whether to base the vent design for a monoproduction process on either a steady model or on a simulation of the dynamic reactor behaviour with the help of specifically developed computer codes, such as e.g. SAFIRE and RELIEF . 

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