Second-Order Reaction in a CSTR

For a second-order liquid-phase reaction being carried out in a CSTR. the combination of the rate law and the design equation yields 

Conversion for a second-order liquid-phase reaction in a CSTR 

Example 4-2 Producing 200 Million Pounds per Year in a CSTR 

Close to 12.2 billion metric tons of ethylene glycol (EG) were produced in 2000, which ranked it the twenty-sixth most produced chemical in the nation that year on a total pound basis. About one-half of the ethylene glycol is used for antifreeze while the other half is used in the manufacture of polyesters. In the polyester category, 88% was used for fibers and 12% for the manufacture of bottles and films. The 20( 4 selling price for ethylene glycol was 0.28 per pound. 

Assumption Ethylene glycol (EG) is the only reaction product formed. 

---

Figures 1.6 and 1.7 display the conversion behavior for flrst-and second-order reactions in a CSTR and contrast the behavior to that of a piston flow reactor. It is apparent that piston flow is substantially better than the CSTR for obtaining high conversions. The comparison is even more dramatic when made in terms of the volume needed to achieve a given conversion see Figure 1.8. The generalization that...

Automatic controllers can produce small oscillations of the controlled variable. The effect of sinsoidal variations in concentration, temperature or feed rate on the effluent concentration of a second order reaction in a CSTR will be examined. The unsteady material balance is... 

Figure 11. Equivalence between the droplet diffusion model (81) and the IEM model for a zero-order reaction and a second-order reaction in a CSTR. The Damkohler numbers are such that f = 0.5 for perfect micromixing. The agreement is excellent for the second-order reaction, more approximate for the zero-order one.

Figure 4-6 Conversion as a function of ihc Oamkohler number (titCjio) for a. second-order reaction in a CSTR.

Figure 5A.1. Conversion of a second order reaction in a CSTR with perfect RTD, for various ratios of micromixing and reaction times, as a function of Da = kc T.

For a second order reaction in a two stage CSTR, find the size ratio for a minimum total residence time. 

Compare conversions of first and second order reactions in a four stage CSTR with segregated flow in a Gamma vessel having the same variance. For... 

The degree of conversion of a second order reaction in a perfectly mixed CSTR, for constant density is found from... 

For a liquid-phase, second-order reaction in a batch reactor, CaC ) = Cao/(1 + kCAot), and for an ideal CSTR, E t) = e / /T. Substituting these expressions into Eqn. (10-23),... 

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... 

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. 

For a second-order reaction in an ideal CSTR with complete micro-mixing, the design equation for the calculation of space time is... 

Fig. 5 Second-order reaction in CSTR/Separator/Recycle a) Control structure not relying on self-regulation b) production rate changes manipulating reactor-inlet flow rate.

A second order reaction is conducted in two equal CSTR stages. The residence time per stage is T = 1 and the specific rate is /cCq = 0.5. Feed concentration is Cq. Two cases are to be examined (1) with pure solvent initially in the tanks and (2) with concentrations Cq initially in both tanks, that is, with Cio = Coq = Cq. 

Example 1.6 Apply Equation (1.54) to calculate the mean residence time needed to achieve 90% conversion in a CSTR for (a) a first-order reaction, (b) a second-order reaction of the type A - - B — Products. The rate constant... 

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. 

For the gas-phase, second-order reaction C2H4 + C4H6 - CgHio (or A + B - C) carried out adiabatically in a 2-liter experimental CSTR at steady-state, what should the temperature (T/K) be to achieve 40% conversion, if the (total) pressure (P) is 1.2 bar (assume constant), the feed rate (q0) is 20 cm3 s-1, and.. the reactants are equimolar in the feed. The Arrhenius parameters are EA = 115,000 J mol-1 and A =3.0x 107L mol-1s-1 (Rowley and Steiner, 1951 see Example 4-8). Thermochemical data are as follows (from Stull et al., 1969) ... 

Two stirred tanks are available, one 100 m3 in volume, the other 30 m3 in volume. It is suggested that these tanks be used as a two-stage CSTR for carrying out a liquid phase reaction A + B product. The two reactants will be present in the feed stream in equimolar proportions, the concentration of each being 1.5 kmol/m3. The volumetric flowrate of the feed stream will be 0.3 x 10-3 m3/s. The reaction is irreversible and is of first order with respect to each of the reactants A and B, i.e. second order overall, with a rate constant 1.8 x 10-4 m3/kmols. 

Conversion data are obtained in a CSTR at several residence times and two temperatures. Verify that the reaction is second order and find the Arrhenius constants, f = C/C0... 

A second order reaction conducted in a three stage CSTR undergoes 88% conversion. Inlet concentration is C0 = 2 and the residence time per stage is 6 minutes. The specific rate is to be found. 

A second order reaction is conducted in a CSTR that is provided with a pumparound heat exchanger as sketched. Heat transfer rate in the exchanger is Q - 15000(AT) lm Btu/hr, The reactor is to be kept at 200 F. Other temperatures are shown on the sketch. Feed rate is V = 100 cfh, inlet concentration is 0.5 lbmol/cuft Also AHr= -50000, p = 50, Cp = 0.8. 

A second order reaction is done adiabatically in a CSTR. Data for the system are ... 

Values of E(tr) of a reactor are tabulated. The residence time is t = 5. Find the conversion in segregated flow of a second order reaction with kC0 = 0.04. Interpret the fact that the variance is greater than unity and that the performance is poorer than that of a single stage CSTR. 

A second order reaction undergoes conversion under three conditions falunder segregated flow, with E(tr) = 4tr exp(-2tr) (bl in a two stage CSTR ... 

The model of a reactor consists of two equal sized CSTRs joined by a PFR whose residence time equals that of the combined CSTRs. A second order reaction with kC0t = 2 is to be studied by the maximum mixedness mechanism. More details of this problem are in problem P5.04.09 where the RTD is developed as... 

A series of tests of a second order reaction were made in a rotating basket CSTR with several sizes of catalyst pellets. All runs were made with the same residence time and with inlet C0 = 4. Effluent concentrations were measured. Beyond R = 0.1 cm, there were no differences in conversion. 

---