With a CSTR

Since LFR s generally run under temperatures, viscosities and other parameters varying as one proceeds downstream, it follows that process and product control can be more complicated than with a CSTR. 

In summary, we have considered three characteristic times associated with a CSTR /mix, ri/2, and t. Treating the CSTR as a perfect mixer is reasonable provided that /mix is substantially shorter than the other characteristic times. 

Piston Flow in Contact with a CSTR. A liquid-phase reaction in a spray tower is conceptually similar to the transpired-wall reactors in Section 3.3. The liquid drops are in piston flow but absorb components from a well-mixed gas phase. The rate of absorption is a function of as it can be in a transpired-wall reactor. The component balance for the piston flow phase is... 

The piston flow case assumes that the particles spend the same time in the reactor, i, even though the fluid phase is well mixed. This case resembles the mass transfer situation of piston flow in contact with a CSTR as considered in Section 11.1.4. The particles leave the reactor with size Ro — kf i. None will survive if f > Ro/k". Note that i is the mean residence time of the solid particles, not that of the fluid phase. 

The reaction was also tested with a CSTR. The KOH solution and the mixture of Boc-AMP and t-Boc were mixed in the CSTR and the residence time was 30 sec. The results... 

For the reaction, A => Products, measurements of the rate as a function of the concentration were made with a CSTR. 

Data on the reaction, 2A B, were taken with a CSTR with the tabulated time-conversion results in the table. Feed concentrations were Ca0 = 1.5 and Cb0 = 0.5 Ibmol/cuft. Find the rate equation. 

Initial trial values may be selected by comparison of conversion with a CSTR if Pe is small, or with a PFR if Pe is large. 

The reactor is believed equivalent to a PFR in series with a CSTR. A second... 

Example 3-5 Compare the reactor volumes necessary to attain the conversions in the previous examples for first and second order irreversible reactions in a CSTR with a CSTR. 

A way of transforming a two-variable system to one of higher order is to make one of the parameters in the system a function of time. Thus with a CSTR we might vary the pumping rate (and hence alter the residence time) in a time-dependent and perhaps oscillatory manner. The interaction of the original chemical non-linearity and the imposed forcing shows similar patterns to that displayed by the map. Finally, chemical systems with three or more independent concentrations may drive themselves, of their own free will so to speak, to the heights of complexity. 

The reactor is believed equivalent to a PFR in series with a CSTR. A second order reaction with kC0 =2.5 is to be processed there. Find (a) the residence time in each element (b) conversion in segregated flow (c) ideal conversion with the PFR first in series (d) ideal conversion with the CSTR first in series. 

Paraffin to olefin molar ratios for the C3 and Cy fractions are reported in Table I for two sets of runs in which the degree of mass transfer was varied by changing RPM. Even with a CSTR, data on the effect of mass transfer must be Interpreted carefully. An Increase in mass transfer resistance, caused by decreased agitation, causes a drop in conversion. Usually the consumption ratio of H2/CO is different than the feed ratio and hence a drop in conversion is accompanied by a change in the H2/CO ratio in... 

There have been many hybrid multiscale simulations published recently in other diverse areas. It appears that the first onion-type hybrid multiscale simulation that dynamically coupled a spatially distributed 2D KMC for a surface reaction with a deterministic, continuum ODE CSTR model for the fluid phase was presented in Vlachos et al. (1990). Extension to 2D KMC coupled with ID PDE flow model was described in Vlachos (1997) and for complex reaction networks studied using 2D KMC coupled with a CSTR ODEs model in Raimondeau and Vlachos (2002a, b, 2003). Other examples from catalytic applications include Tammaro et al. (1995), Kissel-Osterrieder et al. (1998), Qin et al. (1998), and Monine et al. (2004). For reviews, see Raimondeau and Vlachos (2002a) on surface-fluid interactions and chemical reactions, and Li et al. (2004) for chemical reactors. 

The major purpose of this paper is to present experimental results for the emulsion polymerization of vinyl acetate (VA) and methyl methacrylate (MMA) in a single CSTR. Both steady state and transient results will be presented and discussed. Possible causes for prolonged unsteady behavior will be outlined and several techniques for achieving steady operation with a CSTR will be described. 

Finally, we note that the PSD in a CSTR is strongly sensitive to the residence time distribution, which may be varied over a wide range. Consequently, the production of a latex with a desired PSD is usually more readily achieved with a CSTR process than a batch or semicontinuous process, for the latter depend in a complex manner upon many mechanisms. The production of inonodisperse latexes is an exception to ttiis rule these... 

A tubular prereactor, in series with CSTR system, can offer stability advantages, which will he discussed later. A number of other flow alternatives are also possible with a CSTR-series system but these alternates are not widely utilized. An obvious flow alternative for a reactor system consisting of a series of CSTRs would he to introduce some portion of the total recipe at places other than the front end of the reactor train. These intermediate feeds would, in many respects, be analogous to semicootinuous operation of batch reactors. 

The CSTR can either be used by itself or, in the manner shown in Figure 1-11, as part of a series or battery of CSTRs. It is relatively easy to maintain good temperature control with a CSTR, There is, however, the disadvantage that the conversion of reactant per volume of reactor is the smallest of the flow reactors. Cons iueiit y, very large reactors are necessary to obtain high conversions. 

P14-1b Make up and solve an original problem. The guidelines are given in Problem P4-1. However, make up a problem in reverse by first choosing a model system such as a CSTR in parallel with a CSTR and PFR [with the PFR modeled as four small CSTRs in series Figure P14-l(a)] or a CSTR with recycle and bypass [Figure P14-l(b)]. Write tracer mass balances and use an ODE solver to predict the effluent concentrations. In fact, you could build up an arsenal cf tracer curves for different model systems to compare against real reactor RTD data. In this way you could deduce which model best describes the real reactor. 

This approach was applied to the Williams-Otto process (Balakrishna and Biegler, 1993). In previous studies, this process was optimized with a CSTR reactor followed by waste and product separators and a recycle stream. The application of (P12) to this problem led to a significantly improved process, particularly when the separation costs p ) were low enough to allow coupled reaction and separation. Without separation, the optimal network is a single PFR with twice the return on investment of previous studies. Allowing for separation leads to a tubular reactor with sidestream separators to remove product and waste as they are created. The resulting process objective has a further fivefold improvement. 

External recirculation, also represented schematically in Fig. 8.27, is an alternative to achieve perfect mixing, which is convenient when only gas streams are involved. The minimum external recirculation ratio depends on the reaction kinetics, but typically ratios higher than 10 are required to achieve perfect mixing [9]. Experiments performed with a CSTR give direct access to the net production rates of the species involved by solving the corresponding mass balances ... 

Integrate from Vr/2 = 0 to 8.7 with (3 = 0.15, 7= 30. Compare the conversion with that achieved with a CSTR. 

Figure 14-18(a) describes a real PFR or PER with channeling that is modeled as two PFRs/PBRs in parallel. The two parameters are the fraction of flow 10 the reactors [i.e., (3 and (1 - p)] and the fractional volume [i.e.. a and (1 - Qf] of each reactor. Figure 14-18(b) describes a real PFR/PBR that has a backmix region and is modeled as a PFR/PBR in parallel with a CSTR. Figures H-19(a) and (b) show a real CSTR modeled as two CSTRs with interchange. In one case, the fluid exits from the top CSTR (a) and in the other case the fluid exits from the bottom CSTR. The parameter p represents the interchange volumetric flow rate and a the fractional volume of the top reactor, where the fluid exits the reaction system. We note that the reactor in model 14-19(b) was found to describe extremely well a real reactor used in the production of terephthalic acid. A number of other combinations of ideal reactions can be found in Levenspiel. ... 

The methods used for introducing feed streams into continuous reactors can be quite important. All ingredients are charged and mixed before the latex is formed in most batch reactor processes. The major purposes of mixing after the reaction begins are to facilitate heat removal through the cooling surface and to maintain mass transfer from the monomer phase to the polymer particles. With a CSTR reaction system, however, the feed streams are added to partially converted latexes, and other factors need to be considered. 

Piston flow reactors lack any internal mechanisms for memory. There is no axial dispersion of heat or mass. What has happened previously has no effect on what is happening now. Given a set of inlet conditions (flin, 7i , Text), only one output (flout, 7 out)is possible. A PFR cannot exhibit steady-state multiplicity unless there is some form of external feedback. External recycle of mass or heat can provide this feedback and may destabilize the system. Figure 14.7 shows an example of external feedback of heat that can lead to the same multiple steady states possible with a CSTR. Another example is when the vessel walls or packing has significant thermal capacity. In such cases, a second heat balance must be added to supplement Equation 14.16. See Section 10.6 for a comparable result. 

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