Liquid Phase CSTRs

In order to allow integration of countercurrent relations like Eq. (23-93), point values of the mass-transfer coefficients and eqiiilibrium data are needed, over ranges of partial pressure and liquid-phase compositions. The same data are needed for the design of stirred tank performance. Then the conditions vary with time instead of position. Because of limited solubihty, gas/liquid reactions in stirred tanks usually are operated in semibatch fashion, with the liquid phase charged at once, then the gas phase introduced gradually over a period of time. CSTR operation rarely is feasible with such systems. 

When liquid content of the feed is high, a condenser and a separator are needed. The liquid-to-gas ratio can be as high, so that even at reaction temperatures a liquid phase is present. The reactor still performs as a CSTR, however the response time for changes will be much longer than for vapor phase alone. Much lower RPM will be needed for liquid-phase studies (or liquid and gas phase experiments) since the density of the pumped fluid is an order-of-magnitude greater than for vapor phase alone. In this case a foamy mixture or a liquid saturated with gas is recirculated. 

Example 4.1 Suppose a liquid-phase CSTR is used for consecutive, first-... 

Example 11.5 Suppose that the liquid phase in a gas-liquid CSTR contains a catalyst for the hrst-order reaction of a compound supplied from the gas phase. The reaction is... 

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... 

Example 11.18 Consider a gas-sparged CSTR with reaction occurring only in the liquid phase. Suppose a pilot-scale reactor gives a satisfactory product. Propose a scaleup to a larger vessel. 

Continuous flow stirred tank reactors are normally just what the name implies—tanks into which reactants flow and from which a product stream is removed on a continuous basis. CFSTR, CSTR, C-star, and back-mix reactor are only a few of the names applied to the idealized stirred tank flow reactor. We will use the letters CSTR as a shorthand notation in this textbook. The virtues of a stirred tank reactor lie in its simplicity of construction and the relative ease with which it may be controlled. These reactors are used primarily for carrying out liquid phase reactions in the organic chemicals... 

ILLUSTRATION 8.6 DETERMINATION OF REQUIRED CSTR VOLUME UNDER ISOTHERMAL OPERATING CONDITIONS—LIQUID PHASE REACTION... 

Variations in fluid density on reaction can have significant effects on the size ratio, but the effects are secondary when compared to the variations in reaction order. For positive values of the expansion parameter SA, the volume ratio is increased, for negative values of 8a, the volume ratio decreases. However, the fact that in practice CSTR s are used only for liquid phase reactions makes this point academic. 

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. 

A combination of two identical CSTR s in series is to be used, to prepare a mixture of polysulfonated aromatic compounds. The reaction will occur isothermally in the liquid phase and may be represented as... 

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... 

The main conclusions to be drawn from this study are that the reactor design works well, and that steady state continuous flow operation requires excellent mixing of the gases and two liquid phases and high conversions. Improvements in the catalyst (ligand) are required to reduce leaching still further, but commercialisation will also require a different reactor design or more than one CSTR in series. 

The classical CRE model for a perfectly macromixed reactor is the continuous stirred tank reactor (CSTR). Thus, to fix our ideas, let us consider a stirred tank with two inlet streams and one outlet stream. The CFD model for this system would compute the flow field inside of the stirred tank given the inlet flow velocities and concentrations, the geometry of the reactor (including baffles and impellers), and the angular velocity of the stirrer. For liquid-phase flow with uniform density, the CFD model for the flow field can be developed independently from the mixing model. For simplicity, we will consider this case. Nevertheless, the SGS models are easily extendable to flows with variable density. 

A continuous stirred-tank reactor (CSTR) is normally used for liquid-phase reactions,... 

Far a liquid-phase reaction of the type A +. . . products, an experimental CSTR of volume 1.5 L is used to measure the rate of reaction at a given temperature. If the steacty-state feed rate is 0.015 L s 1, the feed concentration (cAo) is 0.8 mol L-1, and A is 15% converted on flow through the reactor, what is the value of (- rA) ... 

Consider a constant-density reaction with one reactant, A - products, as illustrated for a liquid-phase reaction in a CSTR in Figure 3.6. One experiment at steady-state generates one point value of (—rA) for the conditions (cA, q, T) chosen. This value is given by the material balance obtained in Section 2.3.2 ... 

Suppose the liquid-phase reaction AB + C was studied in a 3-L CSTR at steady-state, and the following results were obtained ... 

Consider a liquid-phase reaction taking place in a CSTR according to the following kinetics scheme ... 

As in the case of a batch reactor for commercial operation, a CSTR is normally used for a liquid-phase reaction. In the laboratory, it may also be used for a gas-phase reaction for experimental measurements, particularly for a solid-catalyzed reaction, as in Figure 1.2. The operation is normally one of steady-state, except for startup, shutdown, and operational disturbances or upsets, in which cases unsteady-state operation has to be taken into account. 

A liquid-phase reaction A B is to be conducted in a CSTR at steady-state at 163°C. The temperature of the feed is 20°C, and 90% conversion of A is required. Determine the volume of a CSTR to produce 130 kg B h 1, and calculate the heat load (Q) for the process. Does this represent addition or removal of heat from the system ... 

Consider the startup of a CSTR for the liquid-phase reaction A products. The reactor is initially filled with feed when steady flow of feed (q) is begun. Determine the time (t)... 

A first-order liquid-phase reaction, A - products, is conducted in a 2000-L CSTR. The feed contains pure A, at a rate of 300 L min-1, with an inlet concentration of 4.0 mol L-1. The following additional data are available ... 

Consider the liquid-phase reaction A +. . . products taking place in a two-stage CSTR. If the reaction is first-order, and both stages are at the same T, how are the sizes of the two stages related to minimize the total volume V for a given feed rate (FAo) and outlet conversion (/A2) ... 

Suppose the liquid-phase hydration of ethylene oxide (A) to ethylene glycol, CzHtOiA) + H2O - C2H6O2, takes place in a CSTR of volume (V) 10,000 L the rate constant is fcA = 2.464 X10-3 min-1 (Bronsted et al., 1929 see Example 4-3). 

The liquid-phase reaction A - B + C takes place in a single-stage CSTR The rate law for... 

A fust-order, liquid-phase endothermic reaction, A -> B + C, takes place in a CSTR oper-... 

A liquid-phase reaction, A + 2B - C, is to be conducted in two equal-sized CSTRs. The... 

A liquid-phase reaction takes place in two CSTRs operating (at steady-state) in parallel at... 

In this chapter, we develop the basis for design and performance analysis for a plug flow reactor (PFR). Like a CSTR. a PFR is usually operated continuously at steady-state, apart from startup and shutdown periods. Unlike a CSTR, which is used primarily for liquid-phase reactions, a PFR may be used for either gas-phase or liquid-phase reactions. 

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