Plug flow reactors reactant

The irreversible reaction 2A—>B takes place in the gas phase in a constant temperature plug flow reactor. Reactant A and diluent gas are fed in equimolar ratio, and the conversion of A is 85 percent. If the molar feed rate of A is doubled, what is the conversion of A assuming the feed rate of diluent is... 

Continuous-Flow Stirred-Tank Reactor. In a continuous-flow stirred-tank reactor (CSTR), reactants and products are continuously added and withdrawn. In practice, mechanical or hydrauHc agitation is required to achieve uniform composition and temperature, a choice strongly influenced by process considerations, ie, multiple specialty product requirements and mechanical seal pressure limitations. The CSTR is the idealized opposite of the weU-stirred batch and tubular plug-flow reactors. Analysis of selected combinations of these reactor types can be useful in quantitatively evaluating more complex gas-, Hquid-, and soHd-flow behaviors. 

After the rates have been determined at a series of reactant concentrations, the differential method of testing rate equations is applied. Smith [3] and Carberry [4] have adequately reviewed the designs of heterogeneous catalytic reactors. The following examples review design problems in a plug flow reactor with a homogeneous phase. 

Figure 8.13. Rate of methanol synthesis of a Cu/Zn0/Al203 catalyst in a plug flow reactor as a function of time on stream. The catalyst was operated at 494 K and 63 bar in a gas steam of 5 % CO, 5 % COj, 88% H2, and 2% N2. Note the steady decrease in reactivity, which is ascribed to sintering ofthe copper particles. The CO2 was removed from the reactants for 4 h after 168 h. After reintroduction the catalyst displays a restored...

Figure 5.4a compares the profiles for a mixed-flow and plug-flow reactor between the same inlet and outlet concentrations, from which it can be concluded that the mixed-flow reactor requires a larger volume. The rate of reaction in a mixed-flow reactor is uniformly low as the reactant is instantly diluted by the product that has already been formed. In a plug-flow or ideal-batch reactor,... 

Consider the segment of tubular reactor shown in Figure 8.3. Since the fluid composition varies with longitudinal position, we must write our material balance for a reactant species over a different element of reactor (dVR). Moreover, since plug flow reactors are operated at steady state except during start-up and shut-down procedures, the relations of major interest are those in which the accumulation term is missing from equation 8.0.1. Thus... 

In order to reduce the disparities in volume or space time requirements between an individual CSTR and a plug flow reactor, batteries or cascades of stirred tank reactors ard employed. These reactor networks consist of a number of stirred tank reactors confiected in series with the effluent from one reactor serving as the input to the next. Although the concentration is uniform within any one reactor, there is a progressive decrease in reactant concentration as ohe moves from the initial tank to the final tank in the cascade. In effect one has stepwise variations in composition as he moves from onfe CSTR to another. Figure 8.9 illustrates the stepwise variations typical of reactor cascades for different numbers of CSTR s in series. In the general nonisothermal case one will also en-... 

In this case the order of the desired reaction is higher than that of the unwanted reaction so the exponent on the concentration is positive. The instantaneous selectivity is promoted by employing high concentrations of reactant. Consequently, batch or plug flow reactors are most appropriate from a selectivity viewpoint. 

If A has significant economic value then it should be separated from the reactor effluent stream and recycled for subsequent use. Since the conversion level is higher in the plug flow reactor, the recycle rate will be much smaller and the demands on the separation equipment for reclaiming species A will also be somewhat smaller. Even when species A is of relatively little economic value, there may be circumstances when the costs associated with meeting the pollution control requirements for the process effluent will dictate separation and recycle of this reactant as the most economic alternative. 

On the other hand, if it is possible to use a temperature progression scheme and if one desires to obtain the maximum amount of the desired product per unit time per finit reactor volume, somewhat different considerations are applicable. If Ex > E2, one should use a high temperature throughout, but if E2 > Eu the temperature should increase with time in a batch reactor or with distance from the reactor inlet in a plug flow reactor. It is best to use a low temperature initially in order to favor conversion to the desired product. In the final stages of the reaction a higher temperature is more desirable in order to raise the reaction rate, which has fallen off because of depletion of reactants. Even though this temperature increases the production of the undesirable product, more of the desired product is formed than would otherwise be the case. Thus one obtains a maximum production capacity for the desired product. 

Continuous reactor a reactor characterized by a continuous flow of reactants into and a continuous flow of products from the reaction system examples are the plug flow reactor (PFR) and the continuous stirred tank reactor (CSTR). 

Plug flow reactor (PFR) a tube reactor in which the reactants are fed continuously at one end and the products are removed continuously from the other end concentration and heat generation change along the length of the tube the PFR is often used for potentially hazardous reactions because of the relatively small inventory in the system. 

Cracking of pentene-2 was investigated at 670 C and 1 atm in a plug flow reactor (Kunzru et al, IECPDD 2 339, 1963). The product was a mixture of substances and was characterized simply by the number of mols produced per -mol of reactant transformed. 

It is proposed to carry out to within 90% of equilibrium a gas phase reaction, A B, which is first order, by passage through a plug flow reactor at 500 C and 1 atm. The pure reactant enters at 350 C and the available data are,... 

A liquid phase reaction, 2A = B, is conducted in a plug flow reactor. When a solution containing 10 kgmol/m of reactant is charged at the rate of... 

The very fast reaction, A + B 2C, takes place in a plug flow reactor. It has the equilibrium constant Ke = 4. Find the ratio of A to B in the charge that would minimize the total reactant cost to produce a given amount of C. Unconverted products are discarded. Cost of A is oc/lbmol, that of B is /3/lbmol. 

The volume required to convert all the reactants to products for the plug flow reactor is greater than that for the stirred reactor. The final temperature is, of course, higher than the stirred reactor temperature. 

Several continuous stirred tank reactors are often operated in series or cascade as shown in Fig. 13. In this way, the disadvantages of the relatively low reactant concentration on the one hand, and by-passing on the other, may be partially off-set. As the number of tanks in series increases, the performance of the complete system approaches that of a plug-flow reactor and, in the limit of an infinite number of tanks, becomes equal to it. 

In a plug flow reactor the composition of the fluid varies from point to point along a flow path consequently, the material balance for a reaction component must be made for a differential element of volume dV. Thus for reactant A, Eq. 4.1 becomes... 

In an isothermal batch reactor 70% of a liquid reactant is converted in 13 min. What space-time and space-velocity are needed to effect this conversion in a plug flow reactor and in a mixed flow reactor ... 

A plug flow reactor (2 m ) processes an aqueous feed (100 liter/min) containing reactant A (C o = 100 mmol/liter). This reaction is reversible and represented by... 

A specific enzyme acts as catalyst in the fermentation of reactant A. At a given enzyme concentration in the aqueous feed stream (25 liter/min) find the volume of plug flow reactor needed for 95% conversion of reactant A (Cao = 2 mol/liter). The kinetics of the fermentation at this enzyme concentration is given by... 

A stream of pure gaseous reactant A (C o = 660 mmol/liter) enters a plug flow reactor at a flow rate of AO = 540 mmol/min and polymerizes there as follows... 

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