426
Chapter 10
Figure 10.2. Concentration profiles in gas and liquid films for the transfer of the gaseous compound A into
the liquid phase. The composition of the gas bulk and of the bulk liquid are assumed to be constant.
described as the product of the concentration difference across the film layer, i.e., a linear driving
force, and a mass transfer coefficient, k. Thus the flux across the gas film is given by
J A,g = ks(PA - Р ал)
(
10
.
1
)
where
pA
is the partial pressure of compound A in the gas bubble. Index і refers to the concentration
at the gas-liquid interface. Similarly, for the flux across the liquid film
J
лл
= k !(c A
,i
~ ca )
(10.2)
In the dilute aqueous solutions normally used as fermentation media, the concentrations on each
side of the gas-liquid interface can be related to each other by
Henry's law:
P aj = H Ac Ai
(10.3)
where
HA
is Henry’s constant for compound A (unit: atm L mole'1). Table 10.1 lists the values of
Henry's constant for a few components.
Commund A
H ä
fatm L mole'll
Ammonia1
17.1 10'3
Methane
745.5
Ethane
545.1
Carbon dioxide
29.7
Oxygen
790.6
Hvdrogen
1270.0
*At a concentration of 0.2 g L'1
in the aqueous phase.
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