Page 182 - Elements of Chemical Reaction Engineering 3rd Edition

1 54 isothermal Reactor Design Chap. 4

and the rate law can be written as

(4-20)

Note from Equation (4-20) that the larger the pressure drop @e., the smaller P)
from frictional losses, the smalier the reaction rate!
Combining Equation (4-20) with the mole balance (2-17) and assuming
isothermal operation (T = To) gives

Dividing by FAo (Le,, U~C,,) yields

For isothermal operation (T = To) the right-hand side is a function of only
conversion and pressure:
hother Equation
dx
is needed. -- - F,(X, P) (4-21)
(e&, P f(wN dW
We now need to relate the pressure drop to the catalyst weight in order to
determine the conversion as a function of catalyst weight.

4.4.2 Flow Through a Packed Bed

The majority of gas-phase reactions are catalyzed by passing the reactant
through a packed bed of catalyst particles. The equa~on used most to calculate
pressure drop in a packed porous bed is the Ergun equation:2

Ergun equation

R. B. Bird, W. E. Stewart, and E. N. Lightfoot, Transport Phenomena (New York:
Wiley, 1960), p. 200.