Molar flow CSTRs

To develop E(B) for two CSTRs in series, we use a slightly different, but equivalent, method from that used for a single CSTR in Section 13.4.1.1. Thus, consider a small amount (moles) of tracer M, nMo = F,dt, where Ft is the total steady-state molar flow rate, added to the first vessel at time 0. The initial concentration of M is cMo = nMo/(V/2). We develop a material balance for M around each tank to determine the time-dependent outlet concentration of M from the second vessel, cM2(l). 

Figure 3-1 The continuous stirred tank reactor (CSTR) of volume V with inlet molar flow rate Fja and outlet molar flow rate F ...

We consider a reaction of type A——>P the CSTR (Figure 8.1) is continuously fed with a stream at an initial conversion X0. Thus, the concentration of the reactant A in the feed stream is CA0 and at the outlet of the reactor is at its final value Ctt = CA= CA0 (1 — XA), which is also equal to the concentration inside the reactor volume. If the reactor is operated at steady state, the molar flow rate of A, FA the mass balance can be written for the reactant A ... 

Eqs. 1 to 3 relate the rate of production Rj of the balanced reaction component y to the molar amounts or their derivatives with respect to the time variable (reaction time or space time, see above). From the algebraic eq. 2 for the CSTR reactor the rate of production, Rj, may be calculated very simply by introducing the molar flow rates at the inlet and outlet of the reactor these quantities are easily derived from the known flow rate and the analytically determined composition of the reaction mixture. With a plug-flow or with a batch reactor we either have to limit the changes of conversion X or mole amount n7 to very low values so that the derivatives or dAy/d( //y,0) or dn7/d/ could be approximated by differences AXj/ (Q/Fj,0) or An7/A, (differential mode of operation), or to measure experimentally the dependence of Xj or nj on the space or reaction time in a broader region this dependence is then differentiated graphically or numerically. 

The mole balance can now be conpleted for one CSTR. The inlet molar flow rate for propylene oxide is calculated above. The inlet molar flow rate of methanol,... 

It is interesting to compare the volumes of a CSTR and a plug-flow reactor (PFR) required for the same job. To do this we shall use the data in Figure 2-1 to learn which reactor would require the smaller volume to achieve a conversion of 60% a CSTR or a PFR. The feed conditions are the same in both cases. The entering molar flow rate is 5 mol/s. 

For the two CSTRs in series, 40% conversion is achieved in the first reactor. What is the total volume of the two reactors necessary for 80% overall conversion of the species A entering reactor 1 Fa2 s the molar flow rate of A exiting from the la.st reactor in the sequence, = 0.2Fao.)... 

Next use this polynomial and an ODE solver to plot fte conversion down Uie length (i.e., volume) of a PFR and find the CSTR volume for 80% converison for an entering molar flow rate of 5 mol/s. 

The CSTR design equation gives the reactor volume necessary to reduce the entering flow rate of species, , Fjq, to the exit flow rate Fj. We note that the CSTR is modeled such that the conditions in the exit stream (e.g., concentration, temperature) are identical to those in the tank. The molar flow rate Fj is just the product of the concentration of species J and the volumetric flow rate v ... 

What will be the exit molar flow rates of U and D from the reactor What is the CSTR reactor volume for the conditiota specified above ... 

Similarly, the xylene yield based on reaetion rates is also zero. Consequently, we see that under these eonditions (Tpp,) the instantaneous selectivity and instantaneous yield, whieh are based on reactioji rates, are not very meaningful parameters and we must use the overall seleetivity 5xt and the overall yield, which are based on molar flow rates. The yield of xylene from mesitylene based on molar flow rates exiting the CSTR for t = 0.5 is... 

N NCLD NMWD n na electrochemical reaction Molar flow rate, molar flux Number chain length distribution Number molecular weight distribution Number of stages in a CSTR battery, reaction order, number of electrons in electrochemical reaction, number of experiments Number of moles of A present kg - mol lb-mol... 

The CSTR volume necessary to achieve 80% conversion is 6.4 m when operated at 500 K, 830 kPa (8.2 atm), and with an entering molar flow rate of A of 0.4 mol/s. This volume correspond.s to a reactor about 1.5 m in diameter and 3.6 m high. It s a large CSTR. but this is a gas-phase reaction, and CSTRs are normally not used for gas-phase reactions. CSTRs ire used primarily for liquid-phase reactions. 

We divide the chapter into two parts Part 1 Mote Balances in Terms of Conversion, and Part 2 Mole Balances in Terms of Concentration, C,. and Molar Flow Rates, F,." In Pan 1, we will concentrate on batch reactors, CSTRs, and PFRs where conversion is the preferred measure of a reaction s progress for single reactions. In Part 2. we will analyze membrane reactors, the startup of a CSTR. and semibatch reactors, which are most easily analyzed using concentration and molar How rates as the variables rather than conversion. We will again use mole balances in terms of these variables (Q. f,) for multiple reactors in Chapter 6. 

The yield of xylene from mesitylene ba.sed on molar flow rales exiting the CSTR for... 

What is the Plan In the following pages we manipulate Equation (8- order to apply it to each of the reactor types we have been discussing, b PFR, PBR, and CSTR. The end result of the application of the energy bal to each type of reactor is shown in Table 8-1. The equations are used in Si of the algorithm discussed in Example E8-1. The equations in Table 8-1 r temperature to conversion and molar flow rates and to the system paramt such as the overall heat-transfer coefficient and area, Ua, and correspor ambient temperature, r. and the heat of reaction, AWr. ... 

Chemical Reaction Engineering. There is a greater emphasis on the use of mole balances in terms of concentrations and molar flow rates rather than conversion. It is introduced early in the text so that these forms of the balance equations can be easily applied to membrane reactors and multiple reactions, as well as PFRs. PBRs. and CSTRs. 

Input and output molar flows can be written as = Q jn A.m d Fa = Q Ca Note that the ratio between volume and volumetric flow designates a dynamic characteristic of a CSTR, the reaction time r. 

The inlet molar flow rate of chlorine gas is k times the inlet molar flow rate of liquid benzene, and /c = 2 is a parameter that remains constant for each simulation. The overall objective of this problem is to design a two-phase CSTR that will maximize the rate of production of monochlorobenzene. Economics should be considered from a quahtative viewpoint. Generate graphs of ... 

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