Heterogeneous catalytic reactors

After the rates have been determined at a series of reactant concentrations, the differential method of testing rate equations is applied. Smith [3] and Carberry [4] have adequately reviewed the designs of heterogeneous catalytic reactors. The following examples review design problems in a plug flow reactor with a homogeneous phase. 

At this point we wish to turn to a brief discussion of the types of batch and flow reactors used in industrial practice for carrying out homogeneous fluid phase reactions. Treatment of heterogeneous catalytic reactors is deferred to Chapter 12. 

The term space velocity has somewhat different connotations when dealing with heterogeneous catalytic reactors. In this case it denotes the ratio of the mass flow rate of feed to the mass of catalyst used (W). 

COMMERCIALLY SIGNIFICANT TYPES OF HETEROGENEOUS CATALYTIC REACTORS... 

Heterogeneous Catalytic Reactors in which the Motion of the Catalyst Particles Relative to One Another... 

Commercially Significant Types of Heterogeneous Catalytic Reactors... 

In the design of commercial scale heterogeneous catalytic reactors, the activity of the catalyst will almost invariably change with time. We now wish to focus our attention on the implications of poisoning reactions for efficient use of catalyst surface areas. Since reactant molecules must interact with unpoisoned catalyst sites before reaction can occur, the poisoning process may have two effects on the reaction rate one observes. 

The rates at which chemical transformations take place are in some circumstances strongly influenced by mass and heat transfer processes (see Sections 12.3 to 12.5). In the design of heterogeneous catalytic reactors, it is essential to utilize a rate expression that takes into account the influence of physical transport processes on the rate at which reactants are converted to products. Smith (93) has popularized the use of the term global reaction rate to characterize the overall rate of transformation of reactants to... 

Let us now turn our attention to the problem of determining the global reaction rate at some arbitrary point in a heterogeneous catalytic reactor from a knowledge of the following parameters. 

Fixed or packed bed reactors have many advantages relative to other types of heterogeneous catalytic reactors and, consequently, are em-... 

Chemical mapping of chemical conversion in heterogeneous catalytic reactors using MRI... 

Recall that for a heterogeneous catalytic reactor we had to consider the microscopic concentration profiles around and within a catalyst particle and then elirninate them in terms of the macroscopic position variable z in the reactor design ecpaations (mass transfer limits and effectiveness factors). 

Denis, G. H. Kabel, R. L. 1970 The effect of temperature changes on a tubular heterogeneous catalytic reactor. Chem. Engng Sci. 25, 1057-1071. 

To complete the discussion of factors involved in the design of gas-solid heterogeneous catalytic reactors we will examine several aspects of the kinetics of chemical reactions occurring in the presence of a catalyst surface. We consider, for heuristic purposes, the equilibrium reaction ... 

CVD reactors involve transport phenomena that are analogous to those found in other chemically reacting systems, specifically heterogeneous catalytic reactors and combustion systems. 

Techniques of chromatographic analysis continue to develop and for up-to-date methods, the specialist literature should be consulted [62, 63]. In all cases, reaction samples have to be taken at known time intervals and quenched by an appropriate method (sudden cooling, change of pH, dilution, etc.) before chromatographic analysis. It is important to check the stability of the reaction component to the chromatographic and work-up conditions. For example, are the compounds to be analysed thermally stable to the GC conditions (Conditions inside a GC injection port and, indeed, within the column are not unlike those of a heterogeneous catalytic reactor ) Are they stable to the pH of the HPLC eluent An obvious restriction is that chromatographic component analysis does not lend itself to the study of fast reactions. 

S. O., Application of printed circuit heat exchanger technology within heterogeneous catalytic reactors, in Proceedings of the AIChE Annual Meeting, 2001. 

The trickle bed reactor allows for plug flow reactor assumptions even at extremely low liquid-flow rates. The trickle bed is classified as a continuous heterogeneous catalytic reactor. 

In the following we present a detailed model of the commercial, multiple-wafer-in-tube reactor illustrated in Figure 2. We have selected the LPCVD as an example because of its central role in the microelectronics industry and because it nicely demonstrates the analogies to heterogeneous catalytic reactors, in particular the fixed bed reactor. 

Chemical vapor deposition is a key process for thin film formation in the development and manufacture of microelectronic devices. It shares many kinetic and transport phenomena with heterogeneous catalysis, but CVD reactor design has not yet reached the level of sophistication used in analyzing heterogeneous catalytic reactors. With the exception of the tubular LPCVD reactor, conventional CVD reactors may be viewed as variations on the original horizontal reactor. These reactors have complex flow fields and it is consequently difficult to control and predict the effect of operating conditions on the film thickness and composition. 

Agnew and Potter [6] did the same as Barkelew for heterogeneous catalytic reactors and presented design diagrams to prevent runaway, including also the parameter of the ratio of the tube to the catalyst particle diameters dt/dp. Burghardt and Warmuzinski [7] considered multiple reactions and also took the heat effect of the secondary reaction into account however, they did not study the selectivities achieved in the reactor. 

Industrial catalytic reactors exhibit a great variety of shapes, types and sizes. It is not our aim here to discuss all possibilities a survey of the most important reactor types is given by Ullmann [1]. In general, heterogeneous catalytic reactors can be divided in two categories, depending on the size of the catalyst particles, large and small. 

A quantitative description of heterogeneous catalytic reactors for design, scaling-up, control or optimization purposes requires several parameters. Some of them, including the effective diffusivity and some parameters for the transport models and also the intrinsic chemical rate, should be determined in special experiments. 

The title of this review can be shortened to a consideration of the transient method, as in two earlier reviews (i, 2) in 1976 and 1982. In the simplest version of the method, the composition of a stream in steady flow to an open heterogeneous catalytic reactor is perturbed (step function, pulse, sine or square wave, etc.) and the response of the system to the signal is measured, as manifested by the composition of the outlet stream as a function of time. Of particular interest is the measurement by appropriate spectroscopies of the response during the transient period of the intermediates adsorbed on the surface of the catalyst. 

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