448
Chapter 10
10.1.5. Gas-Liquid Oxygen Transfer
Due to the importance of aerobic fermentation processes, gas-liquid mass transfer is almost
synonymous with oxygen transfer from gas bubbles to the liquid medium. Since the volumetric rate
of mass transfer is proportional to the difference between the equilibrium (saturation) concentration
cB
and the actual value of the dissolved oxygen concentration in the medium
ca,
it is necessary to
know the saturation concentration. The solubility of oxygen, i.e.
c j,
decreases with increasing
temperature (see Table 10.8), and it decreases with the concentration of various solutes present in
the medium (see Table 10.9). The solubility is also related to the partial pressure of oxygen in the
gas phase. When Henry's law [Eq. (10.3)] can be applied, a change in the partial pressure will lead
to a proportional change in the saturation concentration.
Table 10.8. Solubility of oxygen in pure water at an oxygen pressure of 1 atm.
Temperature (°С)
Solubility of 0 ; (mmoles L'1)
0
2.18
10
1.70
15
1.54
20
1.38
25
1.26
30
1.16
40
1.09
Table 10.9. Solubility of oxygen at 25 °C and 1
atm 0 2 in various aqueous solutions.
Component
Concentration (g L 1)
Solubility of 0-> (mmoles L'1)
Glucose
20
1.233
50
1.194
90
1.133
180
0.990
Citric acid
25
1.242
100
1.137
200
0.983
Gluconic acid
25
1.210
100
1.121
200
0.991
Com steep liquor
10
1.205
50
1.189
100
1.154
Yeast extract
5
1.255
10
1.228
Xanthan
1
1.250
5
1.251
Pullulan
1
1.266
10
1.241
20
1.240
The data are taken from Popovic er
al.
(1979).
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