Page 85 - Elements of Chemical Reaction Engineering 3rd Edition

Sec. 2.5 Some Further Definitions 57
we see that for (every mole of A that is consumed, cla moles of C appear. In
other words,
c
rate'lof formation of C = - (rate of disappearance of A)
a

Similarly, the rellationship between the rate of formation of C and D is

The relationship can be expressed directly from the stoichiometry of the
reaction,

aA+bB - cCtdD (2- 1)
for which
Remember this
very important
relationship for the (2-20)
relative rates of
reaction.
Space Time. The space time, T, is obtained by dividing reactor volume by
the volumetric flow rate entering the reactor:

(2-21)

The space time is the time necessary to process one reactor volume of
fluid based on entrance conditions. For example, consider the tubular reactor
shown in Figure 2-10, which is 20 m long and 0.2 m3 in volume. The dashed
line in Figure 2-10 represents 0.2 m3 of fluid directly upstream of the reactor.
The time it takes for this fluid to enter the reactor completely is the space tiime.
It is also called the holding rime or mean residence time.

Space time or mean
residence time,
T = v/u, -------I______

Figure 2-10

/
If both sides of the plug-flow reactor design equation (2-16) are divided
by the entering volumetric flow rate and then the left-hand side is put in terms
of space time, the equation takes the form