Laboratory reactors model

Atwood et al, (1989) developed a reactor model that included axial and radial mass and heat dispersions to compare the performance of laboratory... 

The micro-mixed reactor with dead-polymer model simulated the product of the laboratory reactor well within experimental accuracy. 

In spite of visual indications of at least partial segregation, the concept of micro-mixing proved to be most useful in modeling the laboratory reactor. 

Two reactors were built and put into operation. The design of the first reactor was based on minimal intermediate reactor modeling and subsequently operated for less than 4 h in the laboratory. From the pictures of the reactor after operation, shown in Figure 11.9, and operational pressure-drop data, shown in Figure 11.10, it was readily concluded that carbon deposition was a problem. A second reactor was designed with the full use of an intermediate model to overcome initially unrecognized limitations in the first reactor. 

The complete unsteady-state model for adsorption-desorption and surface reactions of the plug flow laboratory reactor was based on the following equations NH3 mass balance on the catalyst suiface ... 

Once the above-discussed components of the model have been determined, they are added to the final model of a monolith (or even filter) reactor. The monolith reactor model has already been described in Section III. The next stage is to validate the model by comparing the predictions of the model based on laboratory data, with the real-world data measured on an engine bench or chassis dynamometer. At this stage the reason(s) for any discrepancies between the prediction and experiment need to be determined and, if required, further work on the kinetics done to improve the prediction. This process can take a number of iterations. Model validation is described in more detail in Section IV. D. Once all this has been done the model can be used predictively with confidence. 

Chemical Kinetics Reactor models include chemical kinetics in the mass and energy conservation equations. The two basic laws of kinetics are the law of mass action for the rate of a reaction and the Arrhenius equation for its dependence on temperature. Both of these strictly apply to elementary reactions. More often, laboratory data are... 

As discussed in Sec. 7, the intrinsic reaction rate and the reaction rate per unit volume of reactor are obtained based on laboratory experiments. The kinetics are incorporated into the corresponding reactor model to estimate the required volume to achieve the desired conversion for the required throughput. The acceptable pressure drop across the reactor often can determine the reactor aspect ratio. The pressure drop may be estimated by using the Ergun equation... 

The C,-fraction of naphtha crackers is used as a feedstock in the Mitsubishi fluid bed process for the production of maleic anhydride. This process was commercialized in 1970. Many data related to this process including the catalyst screening, laboratory experiments, pilot plant design, reactor behaviour and the development of higher selectivity catalysts may be found in the patent literature (12-17).The patents thus give a nearly complete picture of the scale-up process. The data have been used in the present investigation to test the fluid bed reactor model. 

In Figure 5 results of the model calculations for the laboratory reactor with 4 cm diameter are shown. The corresponding measurements were carried out with a feed of 4 mole % 1-butene mixed with air (12). The fluidized bed was kept at a temperature of 410 °C. With the exception of k numerical values of the rate constants were calculated according to Varma and Saraf. For... 

The state of mixing in a given reactor can be evaluated by RTD experiments by means of inert tracers, by temperature measurements, by flow visualization and, finally, by studying in the reactor under consideration the kinetics of an otherwise well-known reaction (because its mechanism has been carefully elucidated from experiments carried out in an ideal reactor, the batch reactor being generally chosen as a reference for this purpose). From these experimental results, a reactor model may be deduced. Very often, in the laboratory but also even in industrial practice, the real reactor is not far from ideal or can be modelled successfully by simple combinations of ideal reactors this last approach is of frequent use in chemical reaction engineering. But... 

In this chapter the emphasis is on the methods to obtain data relevant for kinetic modeling and comparison of catalyst activities for the ultimate purpose of engineering applications. Some laboratory reactor types will be discussed, the procedure for kinetic modeling outlined together with the related parameter estimation and the determination of the rate constants in the rate expression. It should serve as a comprehensive reference to this type of activity in catalysis. Most of it comes from authoritive reviews [2-14],... 

The present chapter is not meant to be exhaustive. Rather, an attempt has been made to introduce the reader to the major concepts and tools used by catalytic reaction engineers. Section 2 gives a review of the most important reactor types. This is deliberately not done in a narrative way, i.e. by describing the physical appearance of chemical reactors. Emphasis is placed on the way mathematical model equations are constructed for each category of reactor. Basically, this boils down to the application of the conservation laws of mass, energy and possibly momentum. Section 7.3 presents an analysis of the effect of the finite rate at which reaction components and/or heat are supplied to or removed from the locus of reaction, i.e. the catalytic site. Finally, the material developed in Sections 7.2 and 7.3 is applied to the design of laboratory reactors and to the analysis of rate data in Section 7.4. 

The present investigation has the overall objective of testing the predictive ability for a trickle-bed reactor model in which the gaseous reactant is limiting. First, a model is presented which contains particle-scale incomplete contacting as one of the key parameters. Second, model predictions for various limiting cases are compared to experimental results obtained in a laboratory scale trickle-bed reactor using independently measured model parameters and available literature mass transfer correlations. 

The choice of experimental reactor is important to the success of the kinetic modeling effort. The short bench-scale reaction tubes sometimes used for studies of this sort give little or no insight into best mathematical form of the kinetic model, conduct the reaction over varying temperatures and partial pressures along the tube, and inevitably operate at velocities that are a small fraction of those to be encountered in the plant-scale reactor. Rate models from laboratory reactors of this sort rarely scale-up well. The laboratory differential reactor suffers from velocity problems but does at least conduct the reaction at known and relatively constant temperature and partial pressures. However, one usually runs into accuracy problems because calculated reaction rates are based upon the small observed differences in concentration between the reactor inlet and outlet. 

From the above it follows that in most practical situations a model, that takes into account only an intraparticle mass and an interparticle heat transfer resistance will give good results. However, in experimental laboratory reactors, which usually operate at low gas flow rates, this may not be true. In the above criteria the heat and mass transfer coefficients for interparticle transport also have to be known. These were amply discussed in Section 4.2. 

In the right-hand side of Equation (41), we must insert the results of the kinetic model, that is. Equations (38) and (39) with the kinetic parameters obtained in the laboratory reactor. The solution of the partial differential equation provides formic acid and hydrogen peroxide exit concentrations as a function of the radial position. 

The radiation flux af fhe wall of radiation entrance (Figure 22) was determined by actinometric measurements (Zalazar et al., 2005). Additionally, the boundary condition for fhis irradiafed wall (x = 0) was obtained using a lamp model with superficial, diffuse emission (Cassano et al., 1995) considering (i) direct radiation from fhe two lamps and (ii) specularly reflected radiation from fhe reflectors (Brandi et al., 1996). Note that the boundary conditions at the irradiated and opposite walls consider the effect of reflection and refraction at the air-glass and glass-liquid interfaces, as well as the radiation absorption by the glass window at low wavelengths (the details were shown for fhe laboratory reactor). The radiation model also assumes that no radiation arrives from fhe top and bottom reactor walls (x-y plane at z = 0 and z = Zr). 

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