Laboratory reactors description

The two-phase (gas-solid) continuous stirred-tank reactors are represented by laboratory reactors as, for instance, one-pass differential reactors, reactors with forced recirculation, one-pellet reactors, etc. The industrial applications are the fluidized beds.2 Table V presents a list of experimental studies along with a very brief description of each system studied. 

Table 2 Laboratory and pilot scale reactor description and operating conditions... 

Each type of reactor is examined with respect to these criteria and given a rating of good (G), fair (F), or poor (P). What follows is a brief description of each of the laboratory reactors. The reasons for rating each reactor for each of the criteria are given in the CD-ROM. 

Modeling of monolith reactors from first principles presents a valuable tool in the design of such reactors and in the analysis of the underlying phenomena. The results presented show that the reactor behavior can be adequately described and understood by a combination of the reactor s transport characteristics and the intrinsic kinetics obtained with a laboratory reactor of another type. As such we can generalize monolith models to other reaction networks, e.g., extend the given description of the dynamic operation for combined CO oxidation and NO reduction in the automotive exhaust gas converter to include other reactions, like the oxidation of various hydrocarbons and of hydrogen. The availability, however, of a proper kinetic model is a definite prerequisite. 

This appendix gives a brief description of the computer programs used to estimate thermodynamic, kinetic and molecular transport data, computer programs for the generation, analysis and reduction of reaction mechanisms and computer programs for the simulation of laboratory reactors. 

The fixed-bed laboratory reactor is regarded as an ideal isothermal plug flow reactor. The reactor model consists of the continuity equations for (1) N2, CO, NO, O2, CO2, N2O and NO2 in the gas phase, (2) surface species adsorbed on the noble metal surface, (3a) surface species adsorbed on the ceria surface, (3b) species in the ceria sub-layer, (4) CO2 adsorbed on the y-AI2O3 support. A detailed description can be found in [28]. 

While transport effects may be eliminated in laboratory reactors, and experiments have shown that certain reactions oscillate under what may be considered isothermal and gradientless conditions, the Langmuir-Hinshelwood mechanism by itself with conventional mass-action kinetics does not give a satisfactory description of them. A number of "extra" features have been added in modeling studies reported in the literature. Among them are an activation energy which depends on the concentration of adsorbed species in one or more of the reaction steps [37, 52 - 54], transition between active and inactive forms of an adsorbed component [7, 17, 55, 56], and periodic switching of the reaction mechanism [16, 18, 40, 57]. 

H. W. Bertini, Descriptions of S elected Accidents That Have Occurred at Nuclear Reactor Facilities, Report ORNL/NSIC-176, Oak Ridge National Laboratory, Oak Ridge, Term., Apr. 1980. 

Most reactors have evolved from concentrated efforts focused on one type of reactor. Some processes have emerged from parallel developments using markedly different reactor types. In most cases, the reactor selected for laboratory study has become the reactor type used industrially because further development usually favors extending this technology. Descriptions of some industrially important petrochemical processes and their reactors are available (74—76). Following are illustrative examples of reactor usage, classified according to reactor type. 

OS 79] ]R 17] ]no protocol] 4-Methoxybenzaldehyde and methyl diethoxyphos-phonoacetate were reacted by means of the Wittig-Horner-Emmons reaction [85] (see a more detailed description in [42]). A modified micro reaction system consisting of two mixers, for deprotonation of the phosphonates and introduction of the aldehyde, connected to an HPLC capillary of 0.8 m length and 0.25 mm diameter was employed. The micro reactor showed higher yields than laboratory batch synthesis. 

B. Flow Reactors. Laboratory-scale catalytic reactors and reactors for the reaction of solids with gases arc often constructed from metal. One of the principal objectives in the use of laboratory-scale catalytic reactors is the determination of rate data which can be associated with specific physical and chemical processes in a catalytic reaction. Descriptions are available for these kinetic analyses as they relate to reactor designs and reaction conditions. ... 

A universal method of handling the problem is mathematical modelling, i.e., a quantitative description by means of a set of equations of the whole complex of interrelated chemical, physical, fluiddynamic, and thermal processes taking place concurrently or consecutively in a reactor. Constants of these equations are determined in laboratory experiments. If the range of determining factors (reactive mass compositions, temperature, reaction rates, and so on) in an actual process lie within or only slightly outside the limits studied in laboratory experiments, the solution of the determining set of equations provides a reliable idea of the process operation. 

The usual description of these different polymerization processes suggests that all produce stable latexes and various hypotheses have been advanced to explain the stability of these latexes to such factors as added electrolyte, mechanical shear and freezing and thawing. In the literature, there is little mention of the fact that many of these polymerizations produce varying amounts of coagulum, i.e., polymer recovered in a form other than that of a stable latex. This coagulum is produced in all sizes of polymerization reactors, ranging from the smallest laboratory... 

Catalytic reaction engineering is a scientific discipline which bridges the gap between the fundamentals of catalysis and its industrial application. Starting from insight into reaction mechanisms provided by catalytic chemists and surface scientists, the rate equations are developed which allow a quantitative description of the effects of the reaction conditions on reaction rates and on selectivities for desired products. The study of intrinsic reaction kinetics, i.e. those determined solely by chemical events, belongs to the core of catalytic reaction engineering. Very close to it lies the study of the interaction between physical transport and chemical reaction. Such interactions can have pronounced effects on the rates and selectivities obtained in industrial reactors. They have to be accounted for explicitly when scaling up from laboratory to industrial dimensions. 

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