Stirred reactors, multiple

We took the 4- sign on the square root term for second-order kinetics because the other root would give a negative concentration, which is physically unreasonable. This is true for any reaction with nth-order kinetics in an isothermal reactor There is only one real root of the isothermal CSTR mass-balance polynomial in the physically reasonable range of compositions. We will later find solutions of similar equations where multiple roots are found in physically possible compositions. These are true multiple steady states that have important consequences, especially for stirred reactors. However, for the nth-order reaction in an isothermal CSTR there is only one physically significant root (0 < Ca < Cao) to the CSTR equation for a given T. ... 

Y.Q. Cui, R.G.J.M. Van der Lans, HJ. Noorman, and K.C.A.M. Luyben. Compartment mixing model for stirred reactors with multiple impellers. Transactions of IChemE, 74 261-271,... 

FIGURE 10.3 Approaches to modeling flow in stirred reactors, (a) Black box approach, (b) sliding mesh approach, (c) multiple reference frame or inner-outer approach, (d) snapshot approach. 

Magelli, F. Fajner, D. Nonentini, M. Pasquali, G. Solid distribution in vessels stirred with multiple impellers. Chem. Eng. Sci. 1990, 45, 615-625. Fajner, D. Magelli, F. Nocentini, M. Pasquali, G. Solids concentration profiles in a mechanically stirred and staged column slurry reactor. Chem. Eng. Res. Des. 1985, 63, 235-240. 

Vejtasa, S.A. Schmitz, R.A. An experimental study of steady state multiplicity and stability in an adiabatic stirred reactor. AIChE J. 1970,16, 410 19. Schmitz, R.A. Multiplicity, stability, and sensitivity of states in chemically reacting systems - a review. Adv. Chem. Ser. 1975, 148, 156-211. Razon, L.F. Schmitz, R.-A. Multiplicities and instabilities in chemically reacting systems - a review. Chem. Eng. Sci. 1987, 42, 1005-1047. Uppal, A. Ray, W.H. Poore, A.B. On the dynamic behavior of continuous stirred tank reactors. Chem. Eng. Sci. 1974, 29, 967-985. 

A blending time of 10 20 seconds in a large stirred reactor might seem unimportant if the reaction time is many minutes or a few hours, and imperfect mixing does have little effect on the conversion in systems where only one reaction is taking place. However, when there are multiple fast reactions, the amount of byproduct formed may increase if the feed streams are not immediately blended with the bulk liquid, and a mixing delay of only a few seconds can significantly lower the selectivity. 

Topological Methods. The topological properties of the stirred-reactor equations (37) can be used to predict the occurrence of multiple states and to determine their stability. More sophisticated tediniques can be enqiloyed in determining the oscillatory nature and limit-cycle bdiaviour of such systems. The introduction of topological methods in the study of chemical reactors was made by Oavalas in 196S fixed-point methods were introduced in the study of thermodynamically... 

Nocentini, M., Pinelli, D., and MageUi, F. (1998), Analysis of the gas behavior in sparged reactors stirred with multiple Rushton turbines Tentative model validation and scale-up, Industrial Engineering Chemistry Research, 37(4) 1528-1535. 

Type Multiple Impeller The bottom impeller should simultaneously play the role of gas dispersion and solid suspension. Solid suspension in this category has received very limited attention. The only study available is that of Saravanan et al. (1997). These investigators studied solid suspension characteristics of 2-2 type multiple-impeller systems. The top gas-inducing impeller used was 6 FID, while a variety of impellers that generated different flow patterns (Fig. 9.8) were used as the bottom impeller. The difference between multiple-impeller gas-inducing systems and stirred reactors vis-a-vis the location of the gas sparger has already been discussed in Section 9.4.3. Saravanan et al. (1997) found that the value of obeys the... 

Imperfect micro-mixing in viscous reaction media can have a dramatic effect on the selectivity of multiple reaction systems, particularly in stirred reactors with separate feed streams. The reason is that the concentration ratio of the two reactants varies locally between 0 and so that higher order competitive... 

Vejtasa, S.A. and Schmitz, R.A., An experimental study of steady state multiplicity and stability in an adiabatic stirred reactor, AIChE /., 16,410-419,1970. 

Continuous-Flow Stirred-Tank Reactor. In a continuous-flow stirred-tank reactor (CSTR), reactants and products are continuously added and withdrawn. In practice, mechanical or hydrauHc agitation is required to achieve uniform composition and temperature, a choice strongly influenced by process considerations, ie, multiple specialty product requirements and mechanical seal pressure limitations. The CSTR is the idealized opposite of the weU-stirred batch and tubular plug-flow reactors. Analysis of selected combinations of these reactor types can be useful in quantitatively evaluating more complex gas-, Hquid-, and soHd-flow behaviors. 

Multiphase Reactors. The overwhelming majority of industrial reactors are multiphase reactors. Some important reactor configurations are illustrated in Figures 3 and 4. The names presented are often employed, but are not the only ones used. The presence of more than one phase, whether or not it is flowing, confounds analyses of reactors and increases the multiplicity of reactor configurations. Gases, Hquids, and soHds each flow in characteristic fashions, either dispersed in other phases or separately. Flow patterns in these reactors are complex and phases rarely exhibit idealized plug-flow or weU-stirred flow behavior. 

The reactor is loaded with a solution of emulsifier in an organic solvent and the aqueous monomer solution (20-60%) is dispersed in the organic phase by stirring. The obtained emulsion is deoxygenated by purging dry nitrogen or by multiple evacuation and thermostated at 30-60°C. Then, an initiator solution is introduced in the reaction mixture and the process is carried out at 30-60°C for 3-6 h, after which the reaction mixture is aged for 1-5 h. 

In Fig. 28, the abscissa kt is the product of the reaction rate constant and the reactor residence time, which is proportional to the reciprocal of the space velocity. The parameter k co is the product of the CO inhibition parameter and inlet concentration. Since k is approximately 5 at 600°F these three curves represent c = 1, 2, and 4%. The conversion for a first-order kinetics is independent of the inlet concentration, but the conversion for the kinetics of Eq. (48) is highly dependent on inlet concentration. As the space velocity increases, kt decreases in a reciprocal manner and the conversion for a first-order reaction gradually declines. For the kinetics of Eq. (48), the conversion is 100% at low space velocities, and does not vary as the space velocity is increased until a threshold is reached with precipitous conversion decline. The conversion for the same kinetics in a stirred tank reactor is shown in Fig. 29. For the kinetics of Eq. (48), multiple solutions may be encountered when the inlet concentration is sufficiently high. Given two reactors of the same volume, and given the same kinetics and inlet concentrations, the conversions are compared in Fig. 30. The piston flow reactor has an advantage over the stirred tank... 

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