Encyclopedia of Environmental Science and Engineering, Volume I and II

VAPOR AND GASEOUS POLLUTANT FUNDAMENTALS 1223

where Kg and KL are overall mass transfer coefficient in gas

and liquid phase, respectively. If concentrations at equilib-

rium can be represented by Henry’s law

C H Cig*  iL,

then

N k C C k E C C

k C C K C C

i g ig igI L iLI iL

g ig ig L ig iL

   

   

( ) ( )

( *) ( * ),

whence

1 1

K k

H

Ek

H

g g L KL

  

 

.

If the gas is highly soluble in the liquid, H′ will be small and

Kg  kg. Hence the mass transfer rate is

N K C Ci g ig( ig*)

and absorption is said to be gas phase controlled.

In cleaning an effluent stream of low pollutant species

concentration physical absorption alone is often insufficient

to produce the required removal and a reactant may be added

to the absorbing solution to enhance the rate. For example

potassium permanganate has been found to be an excellent

absorbent for NO (see excellent review by C. Strombald

(1988)).

interface

liquid film

bulk gas phase bulk liquid phase

gas film

Cig

CigI

CilI

CiI

FIGURE 14 Concentration gradients (film theory).

SATURATION IN cc S.T.P PER g

PRESSURE IN mm. Hg

2 6 10

200

400 40°

0°

600

30°

20°

FIGURE 13 Adsorption isotherms for the

system CO 2 -silica gel (note that tc  31 C).

Patrick, Preston and Owens: J. Phys. Chem.

29, 421 (1925) (Fig. 1).

NVs × 103 cc/gm

RTV

s

fs fg

ln

cal/cc.

20°C 100°F

60°C

90°C 200°F

150°F

250°F

Ray and Box

CARBON DIOXIDE

Szepesy

10

40

60

80

100

1 100 500

FIGURE 12

C022_001_r03.indd 1223 11/18/2005 2:32:55 PM