Gas absorption is often enhanced by a chemical reaction. For instance, acid gases (
) are usually eliminated from natural gas by 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,
, that takes place in a 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.
he steady state material balances within the film are given by
, where the binary diffusion approximation for
has been used. These equations simply state that the rates of diffusion of species
are equal to the rate of the chemical reaction. The concentration of
in the bulk liquid is arbitrarily set to 2 while the concentration of
at the gas-liquid interface is set to 1.
This Demonstration displays the liquid film concentrations of species
(blue and orange curves, respectively) as a function of position. You can change the values of the diffusivities,
, the reaction rate constant,
, as well as the number of Chebyshev collocation points,
. Excellent agreement is obtained between the numerical solutions given by Chebyshev orthogonal collocation (blue and orange dots) and by NDSolve
(blue and orange curves).