The separation of styrene/ethylbenzene mixture is of great importance in the petrochemical industry. Current technology uses distillation; this separation is difficult because of the small, 9 K, difference in the boiling points. An alternative separation method uses selective adsorption in nanoporous materials such as zeolites and metal organic frameworks. Here we present a simulation screening study for the separation of styrene/ethylbenzene mixture by adsorptive means in nanoporous materials near pore saturation conditions. Under these conditions, different entropic mechanisms can dictate the separation process. Commensurate stacking has the best trade-off between selectivity and saturation capacity and offers a geometrical solution to the separation problem. MIL-47 has the right channel size and topology for styrene to exhibit commensurate stacking offering high capacity and selectivity for styrene over ethylbenzene. Out of all the screened structures, MIL-47 was found to be the best candidate for the separation of styrene/ethylbenzene mixture.