Mixing CSTR

This program helps calculate the rate of methanol formation in mol/m s at any specified temperature, and at different hydrogen, carbon monoxide and methanol concentrations. This simulates the working of a perfectly mixed CSTR specified at discharge condition, which is the same as these conditions are inside the reactor at steady-state operation. Corresponding feed compositions and volumetric rates can be calculated from simple material balances. 

For the perfeetly mixed CSTR, the internal age distribution funetion is... 

For a perfeetiy mixed CSTR, it is assumed that the vessel eontents are perfeetiy homogeneous and have the same eomposition as the exit stream. Considering a step input into the CSTR, a maeroseopie material balanee gives... 

In using the normalized distribution function, it is possible to directly compare the flow performance inside different reactors. If the normalized function E(6) is used, all perfectly mixed CSTRs have numerically the same RTD. If E(t) is used, its numerical values can change for different CSTRs. 

Control Policy. The control variables which, if perturbed, are most likely to influence the MWD of the product of a free radically initiated solution polymerization carried out in a well mixed CSTR are ... 

Perfectly mixed stirred tank reactors have no spatial variations in composition or physical properties within the reactor or in the exit from it. Everything inside the system is uniform except at the very entrance. Molecules experience a step change in environment immediately upon entering. A perfectly mixed CSTR has only two environments one at the inlet and one inside the reactor and at the outlet. These environments are specifled by a set of compositions and operating conditions that have only two values either bi ,..., Ti or Uout, bout, , Pout, Tout- When the reactor is at a steady state, the inlet and outlet properties are related by algebraic equations. The piston flow reactors and real flow reactors show a more gradual change from inlet to outlet, and the inlet and outlet properties are related by differential equations. 

A real continuous-flow stirred tank will approximate a perfectly mixed CSTR provided that tmix h/i and tmix i. Mixing time correlations are developed using batch vessels, but they can be applied to flow vessels provided the ratio of throughput to circulatory flow is small. This idea is explored in Section 4.5.3 where a recycle loop reactor is used as a model of an internally agitated vessel. 

We have considered two types of ideal flow reactor the piston flow reactor and the perfectly mixed CSTR. These two ideal types can be connected together in a variety of series and parallel arrangements to give composite reactors that are... 

The ideal flow reactors are the CSTR and the PFR. (This chapter later introduces a third kind of ideal reactor, the segregated CSTR, but it has the same distribution of residence times as the regular, perfectly mixed CSTR.) Real reactors sometimes resemble these ideal types or they can be assembled from combinations of the ideal types. 

Part (c) in Example 15.15 illustrates an interesting point. It may not be possible to achieve maximum mixedness in a particular physical system. Two tanks in series—even though they are perfectly mixed individually—cannot achieve the maximum mixedness limit that is possible with the residence time distribution of two tanks in series. There exists a reactor (albeit semi-hypothetical) that has the same residence time distribution but that gives lower conversion for a second-order reaction than two perfectly mixed CSTRs in series. The next section describes such a reactor. When the physical configuration is known, as in part (c) above, it may provide a closer bound on conversion than provided by the maximum mixed reactor described in the next section. 

Batch [well-mixed (CSTR), closed system] Ordinary differential equations (unsteady state) Algebraic equation (steady state)... 

In the reactors studied so far, we have shown the effects of variable holdups, variable densities, and higher-order kinetics on the total and component continuity equations. Energy equations were not needed because we assumed isothermal operations. Let us now consider a system in which temperature can change with time. An irreversible, exothermic reaction is carried out in a single perfectly mixed CSTR as shown in Fig. 3.3. 

It is well known that PFR represents reactors without back-mixing, CSTR represents reactors with the maximum back-mixing, we can therefore study effect of back-mixing on process environmental aspect by studying these two kinds of reactor. 

In the next two chapters of this book we turn to the chemical reactor that is probably the most challenging the tubular or plug flow reactor. The inherent distributed nature of the unit (variables change with axial and radial position) gives rise to complex behavior, which is often counterintuitive and difficult to explain. The increase in the number of independent variables makes the development and solution of mathematical models more complex compared to the perfectly mixed CSTR and batch reactor. 

The second difference is the dynamic response to disturbances or changes in manipulated variables. In a perfectly mixed CSTR, a change in an input variable has an immediate effect on variables in the reactor. In a tubular reactor it takes time for the disturbance to work its way through the reactor to the exit. Therefore there are very significant dynamic lags and deadtimes between changes made at the inlet of the reactor and... 

Example 1.7 Suppose a pilot-scale reactor behaves as a perfectly mixed CSTR so that Equation (1.49) governs the conversion. Will the assumption of perfect mixing remain valid upon scaleup ... 

The reactive tracers were p-nitrophenyl acetate and sodium hydroxide which undergo a second-order reaction to produce p-nitrophen-ylate, an optically detectable product. In a poorly mixed CSTR, segregation was found to increase with viscosity but the interpretation of the experiments is difficult owing to an ill-defined RTD. 

These results are obtained by averaging the concentrations and reaction rate values over all the elements of the corresponding reactors. For zero order kinetics, such an analysis leads to Figure 4 wherein results are presented for a PFR and a completely segregated CSTR.. The case of completely mixed CSTR is trivial (a horizontal line at the maximum rate up to Cay >0). 

Now imagine a perfectly mixed CSTR operating with a tracer material with inlet concentration Cj and effluent concentration Com- The mass balance for this system is... 

The most significant differences between perfectly mixed and segregated flow in a CSTR occur in copoly merizalions. In a batch reaction, the copolymer composition varies with conversion, depending on the reactivity ratios and initial monomer feed composition. In a perfectly mixed CSTR, there will be no composition drifts but the distribution of product compositions will broaden as mixing in the reactor approaches segregated flow. 

The decomposition of N2O over Ni0/Si02 has been studied experimentally (24) in an internally mixed CSTR, and it was proposed that the reaction... 

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