Problem 4

Adsorption from mixtures

In this problem, you will investigate the selective adsorption of one component of a mixture on the surface.

1. Confirm the derived relationship (see Multicomponent):

$$\frac{\theta_A}{\theta_B} = \frac{P_A}{P_B}\frac{K_A}{K_B}$$

by simulating a mixture of two components (A and B) at log $P_A$ = log $P_B$ = -4.0, T = 1.0, with $\epsilon_A = 7.5$ and $\epsilon_B = 5.0$. In your analysis, you need to first show that $K \propto e^{-\epsilon/kT}$.

2. Repeat (1.) at higher pressures. Does this relationship hold outside of the Henry's Law region? How high can you raise the pressure before it starts to break down? Why do you think this happens?

3. For a gas mixture where $P_A = 10\times P_B$, what ratio of $\epsilon_A / \epsilon_B$ is necessary to achieve a 1:1 ratio of A:B in the adsorbed layer? Comment on how such an adsorbate might be used in gas separations.