Reactor composition

Eig. 4. Representations of reactor compositions for modes of cell operation where A represents product and B, reactant, (a), PEER (b), batch STER and... 

Another advantage of the micro-LC approach is that the required sample size is minimal, so the sample can be drawn from a 1-1 laboratory scale reactor without influencing the reactor composition. The ISCO pLC-500 microflow syringe pump has proven to be reliable and reproducible in evaluations in our laboratory. Capillary liquid columns have been fabricated on planar devices such as silicon to form a miniaturized separation device.19... 

Fig. 10 Polymer composition as a function of reactor composition for hypothetical good and poor incorporators...

It is usual therefore to use [MeOAc] as the measure of substrate present in reactor compositions when describing either carbonylation of MeOH to AcOH or MeOAc to AC2O. 

The principal reduced C2 by-product is EtCOOH. In Ir catalysed reactions, the carbonylation rate increases with [Ir], [MeOAc], [Mel] and [CO], The rate with respect to [H2O] passes through a maximum. In contrast to Rh systems, the water gas shift in Ir catalysed MeOH carbonylation tends to be a relatively constant fraction of carbonylation rate as the reactor composition is varied, though it tends to decrease with [Mel] and [MeOAc] but increase if ionic iodides are added [9]. 

Since MeOH or MeOAc carbonylation is generally a very selective reaction, the reactor composition at any time throughout the reaction can be calculated from the amount of CO consumed. From these measurements the relationship between reaction rate and reactor composition can be established. By obtaining IR data at the same time, the nature and amount of catalyst species present can be measured to relate to rate and reaction composition. At the same time, useful data about the water gas shift reaction can be obtained from the increase in the CO2 peak. 

As with Rh catalysed carbonylation of MeOH, much enduring work on the mechanism of Ir catalysed carbonylation was carried out and reported by Forster at Monsanto [11], Combining data from catalytic reactions, synthesis and reactions of intermediates and IR studies of reaction solutions, three regimes or cycles, designated I, II and III, were identified, compared with the one for Rh. A key reactor composition variable determining which regime is operating is [H2O]. 

For exothermic reactions in mixed flow (or close to mixed flow) an interesting situation may develop in that more than one reactor composition may satisfy the governing material and energy balance equations. This means that we may not know which conversion level to expect, van Heerden (1953, 1958) was the first to treat this problem. Let us examine it. 

The effect of ATR inlet temperature on the outlet reactor compositions for the selected operating conditions (S/C = 1.5, O/C = 0.45) is given in Figure 13. The maximum hydrogen yield can be observed with the selected inlet reactor temperature of 700°C. The value is hydrogen mole fraction is 0.39 for this operating condition. 

The reactor temperature (333 K) and volume (19 m3) are fixed. The other parameter that is held constant is the volumetric flowrate of the reactor effluent (0.008754 m3/s). The rate of reaction is 0.01788 kmol/s for all reactor compositions. The product of the two reactor compositions CACK is constant at 3.8514 kmol2/m6. 

Of course, there is no guarantee that the steady-state economic optimum set of reactor compositions is the best set in terms of reactor stability. This is one of the many classical examples of the inherent engineering tradeoff between steady-state economics and dynamic controllability that occurs in many processes. 

It is quite easy to use the fsolve function in Matlab to solve for the four unknowns. Figure 2.14 gives a program that solves for the four reactor compositions given reactor temperature, reactor volume, feed conditions and kinetics. 

In the second structure, both reactor holdup VR and reactor composition z can change, so the separation section sees a smaller load disturbance. This reduces the magnitude of the resulting change in recycle flow because the effects of the disturbance can be distributed between the reaction and separation sections. 

An infinite number of operating conditions in the reactor give exactly the same reaction rate but have different reactor compositions. The only requirement is that the product of the two concentrations zA times zB) be constant. For a given reactor size and temperature, we can have any number of different reactor compositions, and these reactor compositions have a strong impact on the separation system. If zA is large and zB is small, there must be a large recycle of A and a small recycle... 

Figure 2.13 Ternary process flowsheet with incomplete conversion and two recycle streams (.heavv-out-first sequence . iai Control structure CS4 reactor composition and level control (workable. (61 control structure CS1 reactant makeup control based on component inventories t workable).

Figure 2,13a and b shows two control structures that work (CS4 and CS1), Both of these provide a mechanism for adjusting the fresh feed reactant flowrates so that the overall stoichiometry can be satisfied. In CS4 this is accomplished by measuring reactor composition. In CS1 it is accomplished by deducing the amounts of the reactants in the process from two levels in the two recycle loops. 

Control structure CS4 (Fig. 2.13a) controls reactor effluent flow, brings fresh A in to hold reactor composition zAy and brings fresh B in to control reactor level. In both columns, the base levels are controlled by manipulating bottoms flowrates and the refhtx drum levels are controlled by manipulating distillate flowrates. 

Perfect reactor level control is assumed. The reactor effluent flowrate F is fixed in control structure CS2. The two state variables of the system are the two reactor compositions zA and zB. The two nonlinear ordinary differential equations describing the system are... 

The two nonlinear ordinary differential equations can be linearized around the steady-state values of the reactor compositions zA and zs. Laplace transforming gives the characteristic equation of the system. It is important to remember that we are looking at the closed-loop system with control structure CS2 in place. Therefore Eq. (2.13) is the closed-loop characteristic equation of the process ... 

This means that it takes the fluid stream 29 times longer to cause a temperature change in the reactor than it takes to change the reactor composition. This is a sufficient difference in the propagation speeds to induce wrong-way behavior. However, a large Lewis number is not sufficient to create a problem. Another important requirement is that the reaction should be near completion at the exit of the reactor. This requirement is not met for the vinyl acetate reaction which has only a 36 percent conversion in oxygen. 

If we select temperature, we would like the reactor flow and composition to be nearly constant and we are constrained by the upper reactor temperature limit of 1300°F. If we select toluene composition, we can control it either directly or indirectly. If directly, a reactor feed composition analyzer is needed and is used to adjust either the fresh toluene feed rate or the total reactor toluene feed rate. If indirectly, the separation section is used as an analyzer for toluene. This allows us to control the total flow of toluene to the reactor (recycle plus fresh). Fresh toluene feed flow is used to control toluene inventory reflected in the recycle column overhead receiver level as an indication of the need for reactant makeup. Controlling the total toluene flow sets the reactor composition indirectly and is advantageous because it is less complicated and does not require an on-line analyzer. 

Component Molecular Weight Reactor Composition Mole Fraction ... 

The first term on the right-hand side of Eq. (7-50) is the molar feed rate of the components, which can be different for each component, hence the subscript i, and can vary with time. A typical concentration profile versus time for a reactant whose concentration is kept constant initially by controlling the feed rate is shown in Fig. 7 21). Knowledge of the reaction kinetics allows these ordinary differential equations to be integrated to obtain the reactor composition versus time. 

In an ideal continuous stirred tank reactor, composition and temperature are uniform throughout just as in the ideal batch reactor. But this reactor also has a continuous feed of reactants and a continuous withdrawal of products and unconverted reactants, and the effluent composition and temperature are the same as those in the tank (Fig. 7-fb). A CSTR can be operated under transient conditions (due to variation in feed composition, temperature, cooling rate, etc., with time), or it can be operated under steady-state conditions. In this section we limit the discussion to isothermal conditions. This eliminates the need to consider energy balance equations, and due to the uniform composition the component material balances are simple ordinary differential equations with time as the independent variable ... 

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