Gas absorption is often enhanced by chemical reaction. For instance, acid gases (
and
) are usually eliminated from natural gas with absorption using ethanolamine (
) as a basic solvent.
Consider the absorption of species
with a solvent
containing a species
such as a second-order irreversible chemical reaction,
, taking place in the liquid film. Only species
is present in the gas phase since
has a very low vapor pressure (i.e.,
is a high boiling component). Species
is not present in the bulk liquid since all of
reacts with component
in the liquid film.
The steady state material balances within the film are given by:
and
, where the binary diffusion approximation for
and
in
has been used. These equations simply state that the rates of diffusion of species
and
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
and
(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
in the bulk liquid, as well as the concentration of
at the gas-liquid interface.
The displayed flux of species
, calculated at the gas-liquid interface, gets larger when the reaction rate is increased. This situation corresponds to a higher uptake of species
by the solvent.
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