Reactor volume CSTRs

As another example of the first interac tion, a potential parameter in the analysis of the CSTR is estimating the actual reactor volume. CSTR shown in Fig. 30-7. The steady-state material balance for this CSTR having a sin e reaction can be represented as ... 

Peclet number independent of Reynolds number also means that turbulent diffusion or dispersion is directly proportional to the fluid velocity. In general, reactors that are simple in construction, (tubular reactors and adiabatic reactors) approach their ideal condition much better in commercial size then on laboratory scale. On small scale and corresponding low flows, they are handicapped by significant temperature and concentration gradients that are not even well defined. In contrast, recycle reactors and CSTRs come much closer to their ideal state in laboratory sizes than in large equipment. The energy requirement for recycle reaci ors grows with the square of the volume. This limits increases in size or applicable recycle ratios. 

In Chapter 7.4, empty reactor volume determination of a perfect CSTR is described by following the discharge concentration from the sudden step-change injection of a non-adsorbing inert gas (solid line in the picture.) Next the same experiment is discussed if made with a chemisorbing gas and shown on the previous picture with a dotted line. In this second case, the reactor... 

FIGURE 1.8 Comparison of reactor volume required for a given conversion for a first-order reaction in a PFR and a CSTR. 

There is an interior optimum. For this particular numerical example, it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular post-reactor. The model reaction also demonstrates a phenomenon known as washout which is important in continuous cell culture. If kt is too small, a steady-state reaction cannot be sustained even with initial spiking of component B. A continuous fermentation process will have a maximum flow rate beyond which the initial inoculum of cells will be washed out of the system. At lower flow rates, the cells reproduce fast enough to achieve and hold a steady state. 

Reaction occurs in the loop as well as in the stirred tank, and it is possible to eliminate the stirred tank so that the reactor volume consists of the heat exchanger and piping. This approach is used for very large reactors. In the limiting case where the loop becomes the CSTR without a separate agitated vessel, Equation (5.35) becomes q/Q > 10. This is similar to the rule-of-thumb discussed in Section 4.5.3 that a recycle loop reactor approximates a CSTR. The reader may wonder why the rule-of-thumb proposed a minimum recycle ratio of 8 in Chapter 4 but 10 here. Thumbs vary in size. More conservative designers have... 

Example 6.7 Determine optimal reactor volumes and operating temperatures for the three ideal reactors a single CSTR, an isothermal PER, and an adiabatic PER. 

Determine the minimum operating cost for the process of Example 6.2 when the reactor consists of two equal-volume CSTRs in series. The capital cost per reactor is the same as for a single reactor. 

Example 4.5 Derive the state space representation of two continuous flow stirred-tank reactors in series (CSTR-in-series). Chemical reaction is first order in both reactors. The reactor volumes are fixed, but the volumetric flow rate and inlet concentration are functions of time. 

If the reaction occurs in the liquid phase at 25 °C, determine the reactor volume requirements for cascades of one and three identical CSTR s. The rate at which liquid feed is supplied is 0.278 m3/ksec. Use the graphical approach outlined previously. The following constraints are applicable. 

Figure 8.15, reproduced from Levenspiel (21), is in essence a plot of this ratio versus the fraction conversion for various values of N, the number of identical CSTR s employed. The larger the value of N, the smaller the discrepancy in reactor volume requirements between the... 

If a monomer solution at a concentration of 1 mole/liter is fed to a CSTR at 0 °C, determine the space time necessary to achieve a conversion corresponding to 90% of the equilibrium value. If the reactor volume is 100 liters, what is the corresponding volumetric flow rate ... 

A V - W where V is the desired product. These liquid phase reactions are to be carried out in a cascade of two equal volume CSTR s in series. If the reactors are to be sized so as to maximize the concentration of species V in the effluent from the second reactor, determine the reactor volumes necessary to process 500 gal/hr of feed containing 6 moles/gal of species A. No V or W is present in the feed. What fraction of the A ends up as V The rate constants kx and k2 are both equal to 0.5 hr - L... 

Consider the reaction system and production requirements discussed in Illustration 10.1. Consider the possibility of using one or more continuous stirred tank reactors operating in series. If each CSTR is to operate at 163 °C and if the feed stream is to consist of pure A entering at 20 °C, determine the reactor volumes and heat transfer requirements for... 

Continuous Stirred Tank Reactor (CSTR). The conversion degree of the azo-dye, the reaction volume (V) and the volumetric flow rate (Q) of the dye-bearing stream are related to each other through the material balance referred to the dye and extended to the reactor volume. Assuming an unstructured model for the biophase, the material balance yields... 

For the CSTR case, illustrated in Figure 7.2, suppose the feed concentration of monomer is cUo, the feed rate is q, and the reactor volume is V. Using the material-balance equation 2.3-4, we have, for the monomer ... 

A gas-phase reaction between ethylene (A) and hydrogen to produce ethane is carried out in a CSTR. The feed, containing 40 mol% ethylene, 40 mol% hydrogen, and 20% inert species (I), enters the reactor at a total rate of 1.5 mol min-1, with qg = 2.5 L min-1. The reaction is first-order with respect to both hydrogen and ethylene, with kA = 0.25 L mol-1 min-1. Determine the reactor volume required to produce a product that contains 60 md% ethane. Assume T and P ate unchanged... 

CSTR, if the volume of each CSTR is equal to one-half the reactor volume calculated in... 

For the reaction in problem 14-13, determine the minimum reactor volume required for a two-stage CSTR used to achieve 65% conversion of A. What is the volume of each tank ... 

A second-order reaction of A - B, with fcA = 2.4 L mol 1 h 1, is to be conducted in up to two CSTRs arranged in series. Determine the minimum reactor volume required to achieve 66.7% conversion of A, given that the feed rate and volumetric flow rate at the inlet are 3.75 mol min 1 and 2.5 L min 1, respectively. The feed consists of pure A... 

For exothermic, reversible reactions, the existence of a locus of maximum rates, as shown in Section 5.3.4, and illustrated in Figures 5.2(a) and 18.3, introduces the opportunity to optimize (minimize) the reactor volume or mean residence time for a specified throughput and fractional conversion of reactant. This is done by choice of an appropriate T (for a CSTR) or T profile (for a PFR) so that the rate is a maximum at each point. The mode of operation (e.g., adiabatic operation for a PFR) may not allow a faithful interpretation of this requirement. For illustration, we consider the optimization of both a CSTR and a PFR for the model reaction... 

Consider the conversion of methanol in a 50-L reactor (volume of catalyst) similar to that shown in Figure 1.2 (which operates like a CSTR). The reactor contains 800 g of catalyst (zeolite H-ZSM5), and the space time through the reactor is 0.1 h The methanol feed rate is 1.3 kg h-1. For each reaction temperature, determine the yield and selectivity to each olefin, and comment on your results. 

A liquid phase reaction, 2A = 2B, is conducted in a CSTR with 20% recycle through a heater as shown. Fresh input is at 300 K and consists of 500 kg/hr of water and 20 kgmol/hr of substance A. The recycle is at 350 K. Heat capacity of the solute is 40 kcal/gmol-K, the reaction is endothermic with AHr = +2000 cal/gmol of A converted, reactor volume is 25,000 liters and the specific rate is... 

The reversible reaction, 2A 8, is conducted in a three equal stage CSTR. Substances A and B have the same molal densities, p Ibmol/cuft. A portion B21 of the content of substance B that leaves the second stage is recycled to the first stage. The inlet stream A and the product stream B30 are specified. The stream letters identify molal flow rates. Write the equations from which the various unspecified quantities labelled on the sketch and the reactor volume Vr can be found. 

The specific rate is k = 5.2 1 iter/gmol-hr at 82 C. Equal molal quantities the reactants are to be used. They are supplied as aqueous solutions, bicarbonate as 15 wt% and the chlorhydrin as 30 wt%. Production of glycol to be 20 kg/hr at 95% conversion. Specific gravity of the feed mixture 1.02. Find the required reactor volumes of a PFR and of a CSTR. 

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