Ideally mixed reactors

A disadvantage of the differential reactor is the inaccuracy in the determination of conversion and selectivity due to the small concentration changes. The second difficulty in the treatment of experimental data is caused by possible flow nonuniformities. Since the average residence time is short and the fluid elements moving with different axial velocities do not mix, the simplified Equation 5.30 may not be valid. This is because the reactor operates as a segregated flow reactor rather than a plug flow or ideal mixed reactor, on which Equation 5.30 is based. 

One of the most important characteristics of continuous flow reactors is the flow pattern [26]. In the ideal mixed reactor it is assumed that the concentrations and the temperature are uniform in the entire reactor... 

It should be noted that any deviation from ideal plug flow reactor behaviour is called back mixing. The opposite unit of the plug flow reactor is a continuous perfect or ideal mixing reactor. 

Irrespective of the catalytic system activity, the conventional flow sheet of liquid oiigopiperyiene rubber production [25, 26] includes an ideal mixing reactor (12 m ) or a cascade of ideal mixing reactors (each reactor 1.5 m ) as the main device, equipped with mechanical mixing devices as well as outside and inside condensers (coolant - recirculated water) (Figure 5.13a). 

Intensification of the technological flow motion, during various production processes, leads to increasing the process rates. This is especially true for the chemical interaction occurring in ideal mixing reactors. If it is impossible to replace them with small-sized devices and maintain the intensive mixing of the reaction mixture, an external circuit system may be used to pump the reaction mass (Figure 5.14). Multiplicity of the reaction mixture is defined by specific chemical reaction conditions and the required parameters of the end products. 

Effective reactant mixing, nsing novel technology withont ideal mixing reactors, increases the end-prodnct yield, process productivity, product quality (decreases the amount of by-products which are insoluble in water), and decreases the equipment cost significantly. 

Let us consider the radical homopolymerization with an initiator / and one monomer X in a solvent S. After prepolymerization in an ideally mixed reactor, where the polymer-radical Y and the macromolecule Z arise, quantities of I and S are added. 

Other recent contributions to this aspect of the subject include those of Thompson et concerning a numerical technique for analysing particle-size distribution data for latices produced by continuous emulsion polymerization reactors, of Azizyan et alJ on the calculation of the number of steps in the continuous emulsion polymerization of vinyl acetate and chloroprene, of Lukhovitskii and Listratov on continuous emulsion polymerization in an ideal mixing-reactor, and of Brooks et al. on the emulsion polymerization of styrene in a continuous stirred reactor. The results presented in this last paper are particularly interesting in that the polymerization rates were Initially very high, but declined subsequently and did not always attain a steady value, but sometimes oscillated with time. 

The ideally stirred tank reactor is perfectly uniform with regard to concentration and temperature. The general mass balance for such an ideally mixed reactor (either operated batchwise or in continuous mode) reads as ... 

Another important virtue of this scheme is that part of the alkaline polymerizate of the PO produced in reactor-polymerizer 2 (Fig. 1), of intermediate molecular weight, may be used further in batch operation setups, for the production of other grades of oligoethers. Reactors 2 and 5 are divided into sections by means of perforated partitions, so that each of them functions as an ideal mixing reactor while the number of sections is sufficient to ensure conditions in the liquid phase that yield the same molecular characteristics as those of the corresponding product from a batch operation reactor. 

Figure 97. Product distribution in methane chlorination, ideal mixing reactor a) Methane b) Monochioromethane c) Dichloromethane d) Trichloromethane e) Felrachioromethane... 

These are processes or sections of processes, which can be assumed to be ideally mixed and consequently all state variables are only dependent on time and are independent of a certain location. Examples of these processes are ideally mixed reactors, evaporators and one-stage separators. These processes can be described by a combination of elementary balances ... 

The previous chapter dealt with ideally mixed reactors. Tubular reactors, as shown in Fig. 13.1, oflen give a higher conversion than ideally mixed reactors for the same reaction conditions because on average the reactant concentration is higher. They are therefore, theoretically, preferred over stirred tank reactors. 

The conversion for the plug flow reactor and ideally mixed reactor are graphically shown in Fig. 13.4 for different values of. ... 

It can be seen that for small values of the Peclet number, which corresponds to large values of the diffusion, the behavior approximates the response of an ideally mixed reactor. For large Peclet numbers, i.e. small values of the diffiision, the behavior the behavior approximates the behavior of a pure dead-time process. 

In region HI, bounded by the lines corresponding to Kax = 1 at the bottom and Dax = 1 at the top, the reaction zone thickness grows and the flame cannot be described by the flamelet approach based on the laminar curved flame model. As a limiting case the ideal mixing reactor model (the chemical reaction speed is neglected in comparison with the turbulent mixing time) is considered. 

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