WOLFRAM|DEMONSTRATIONS PROJECT

Gas Absorption with Chemical Reactions

​
liquid phase concentration of A at gas-liquid interface
liquid phase concentration of B in the bulk liquid
reaction rate constant
liquid phase diffusivity
A in D
B in D
Gas absorption is often enhanced by chemical reaction. For instance, acid gases (
CO
2
and
H
2
S
) are usually eliminated from natural gas with absorption using ethanolamine (
H
2
NC
2
H
4
OH
) as a basic solvent.
Consider the absorption of species
A
with a solvent
D
containing a species
B
such as a second-order irreversible chemical reaction,
A+BC
, taking place in the liquid film. Only species
A
is present in the gas phase since
B
has a very low vapor pressure (i.e.,
B
is a high boiling component). Species
A
is not present in the bulk liquid since all of
A
reacts with component
B
in the liquid film.
The steady state material balances within the film are given by:
D
AD
2
d
c
A
d
2
x
=k
c
A
c
B
and
D
BD
2
d
c
B
d
2
x
=k
c
A
c
B
, where the binary diffusion approximation for
A
and
B
in
D
has been used. These equations simply state that the rates of diffusion of species
A
and
B
are equal to the rate of chemical reaction.
This Demonstration displays the bulk liquid, the gas phase, and the liquid film where the concentrations of species
A
and
B
(blue and red curves, respectively) are shown as a function of position. The user can change the values of the diffusivities, the reaction rate constant, the concentration of
B
in the bulk liquid, as well as the concentration of
A
at the gas-liquid interface.
The displayed flux of species
A
, calculated at the gas-liquid interface, gets larger when the reaction rate is increased. This situation corresponds to a higher uptake of species
A
by the solvent.