Reactor selectivity

In this case, because there are no raw materials losses in the separation and recycle system, the only yield loss is in the reactor, and the process yield equals the reactor selectivity. 

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. 

One goal of catalyst designers is to constmct bench-scale reactors that allow determination of performance data truly indicative of performance in a full-scale commercial reactor. This has been accompHshed in a number of areas, but in general, larger pilot-scale reactors are preferred because they can be more fully instmmented and can provide better engineering data for ultimate scale-up. In reactor selection thought must be given to parameters such as space velocity, linear velocity, and the number of catalyst bodies per reactor diameter in order to properly model heat- and mass-transfer effects. 

Packed-bed selectivity. Membrane reactor selectivity. Packed bed yield. 

R. Krishna, A Systems Approach to Multiphase Reactor Selection... 

Gezdhmte Chemie im Mikroreaktor, VDI Nachrichten, June 2000 Micro-reactor enterprises shape and material variety of micro reactors selectivity gains and new project regimes direct fluorination faster process development BASF investigations safety increase speed-up of catalyst development production for fine chemistry and pharmacy numbering-up first industrial examples for micro-reactor production [215]. 

All three comparisons reveal that the micro reactor catalysts have higher conversion and yield, owing to enhanced mass transfer (20 vol.-% ethylene, 80 vol.-% oxygen 0.3 MPa 3.17 1 h 230/250 °C) [44]. The selectivity is slightly better in the fixed beds, but, only by about 1-5%. The best fixed-bed and micro reactor selectivity is 65 and 63%, respectively. The best fixed-bed and micro reactor conversion is 37 and 66%, respectively. 

In fine chemistry, mathematical models are scarce yet. However, even gross kinetics provides a lot of information on the influence of the mode of operation on seleetivity. In general, semi-quantitative criteria are used in preliminary reactor selection. They are mainly based mainly on operational characteristics, experience, and a rough economic estimation. Factors affecting the choice of the reactor and mode of operation are listed in Table 5.4-42. 

Many fine chemistry proces.ses can be lumped into a system of two parallel or two con.secutive reactions. Selectivity can roughly be assessed using the gross kinetics for such lumped schemes, and this can be used to derive approximate criteria for reactor selection. 

Microlevel. The starting point in multiphase reactor selection is the determination of the best particle size (catalyst particles, bubbles, and droplets). The size of catalyst particles should be such that utilization of the catalyst is as high as possible. A measure of catalyst utilization is the effectiveness factor q (see Sections 3.4.1 and 5.4.3) that is inversely related to the Thiele modulus (Eqn. 5.4-78). Generally, the effectiveness factor for Thiele moduli less than 0.5 are sufficiently high, exceeding 0.9. For the reaction under consideration, the particles size should be so small that these limits are met. 

Reactor Selectivity (%) Yield (%) Flowrate of chlorine (kmols-1) Volume (m3)... 

S Entropy (kJ-K-1, kJkg-1-K-1, kJkmol-1-K-1), or number of streams in a heat exchanger network (-), or reactor selectivity (-), or reboil ratio for distillation (-), or selectivity of a reaction (-), or slack variable in optimization (units depend on application), or solvent flowrate (kg s-1, kmol-s-1), or stripping factor in absorption (-)... 

In the sonochemical reactors, selection of suitable operating parameters such as the intensity and the frequency of ultrasound and the vapor pressure of the cavitating media is an essential factor as the bubble behavior and hence the yields of sonochemical transformation are significantly altered due to these parameters. It is necessary that both the frequency and intensity of irradiation should not be increased beyond an optimum value, which is also a function of the type of the application and the equipment under consideration. The liquid phase physicochemical properties should be adjusted in such a way that generation of cavitation events is eased and also large number of smaller size cavities are formed in the system. 

Probability in Receptor Binding and Signaling Rakesh K. Jain, Transport Phenomena in Tumors R. Krishna, A Systems Approach to Multiphase Reactor Selection... 

Because of the ubiquitous nature of polymers and plastics (synthetic rubbers, nylon, polyesters, polyethylene, etc.) in everyday life, we should consider the kinetics of their formation (the focus here is on kinetics the significance of some features of kinetics in relation to polymer characteristics for reactor selection is treated in Chapter 18). 

Autocatalysis is a special type of molecular catalysis in which one of the products of reaction acts as a catalyst for the reaction. As a consequence, the concentration of this product appears in the observed rate law with a positive exponent if a catalyst in the usual sense, or with a negative exponent if an inhibitor. A characteristic of an autocat-alytic reaction is that the rate increases initially as the concentration of catalytic product increases, but eventually goes through a maximum and decreases as reactant is used up. The initial behavior may be described as abnormal kinetics, and has important consequences for reactor selection for such reactions. 

Fox, JM., Degen, B.D., Slurry Reactor Design Studies, Topical Report, Reactor Selection Criteria, US Department of Commerce, National Technical Information Service, USA (1990)... 

As well as the operating conditions inside the reactor, the design features have a powerful influence on reactor performance. The type of reactor selected has an influence on efficiencies, on corrosion endurance, solids-operation feasibility, or even reactor reliability. The most important SCWO reactor configurations are listed in the following. 

There are two criteria which can be used to compare the performances of different types of reactor. The first, which is a measure of reactor productivity, is the output of product in relation to reactor size. The second, which relates to reactor selectivity, is the extent to which formation of unwanted byproducts can be suppressed. When comparing reactions on the basis of output as in the present section, only one reaction need be considered, but when in the next section the question of byproduct formation is taken up, more complex schemes of two or more reactions must necessarily be introduced. 

Krishna R, Sie ST. Strategies for multiphase reactor selection. Chem. Eng. Sci. 1994 ... 

J. J. Linderman, P. A. Mahama, K. E. Forsten, and D. A. Lauffenburger, Diffusion and Probability in Receptor Binding and Signaling Rakesh K. Jain, Transport Phenomena in Tumors R. Krishna, A Systems Approach to Multiphase Reactor Selection... 

Reactor Selection Ideal CSTR and PFR models are extreme cases of complete axial dispersion (De = oo) and no axial dispersion (De = 0), respectively. As discussed earlier, staged ideal CSTRs may be used to represent intermediate axial dispersion. Alternatively, within the context of a PFR, the dispersion (or a PFR with recycle) model may be used to represent increased dispersion. Real reactors inevitably have a level of dispersion in between that for a PFR or an ideal CSTR. The level of dispersion may depend on fluid properties (e.g., is the fluid newtonian),... 

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