Elements of Chemical Reaction ering 4th Ed - H. Scott Fogler 49

Elements of Chemical Reaction ering 4th Ed - H. Scott Fogler 49

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Sec. 1.4 Continuovs-Flow Reactors 2 7 Consequently. we see that Equation ( I - I I ) applies equally well to our model of tubular reactors of' variable and constant cross-sectional area, although ir is duubtful that one would hnd a reactor of the shape shown in Figure I-l l unIess it were designed by Pablo Picasso. The conclusion drawn from the applicarion of the design equation to Picasso's reactor is an important one: the degree of completion of a reaction achieved in an ideal plug-flow reactor (PFR) does not depend on its shape, only on its total volume. Again consider the jsornerizntion A + B, this time in a PFR. As the reac- tants proceed down the reactor. A is consumed by chemical reaction and B is produced. Consequent!y, the molar Raw rate of A decreases and that of B increases, as shown in Figure 1
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Unformatted text preview: - 1 2. Figure 1-12 Profiles of molar flow rates in a PFR. We now ask what is the reactor volume V , necessary to reduce the enter- ing molar flow rare of A from FA, to FA!. Rearranging Equation ( I - 12) in the f o rrn and integrating with limits at V = 0, then FA= FA,,, and at V = V,. then FA= FA,. V, is the volume necessary to reduce the entering molar flow rate FA, to some specified value FA1 and also the volume necessary to produce a molar flow rate o f B of FBI. 1.4.3 Packed-Bed Reactor The principal difference between reactor design calculations involving homo- geneous reactions and those involving fluid-solid heterogeneous reactions is that for the: batter, the reaction takes place on the surface of the catalyst. Con- sequently, the reaction rate is based on mass of solid catalyst. W, rather than on...
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