Computing adsorption isotherms for benzene, toluene, and p-xylene in heulandite zeolite

When computer simulations were performed in the grand canonical ensemble, adsorption isotherms for benzene, toluene, and p-xylene in Heulandite zeolite were constructed. Nitrogen adsorption was simulated to test a feasible computational strategy. Simulations were performed at three temperatures (200, 298, and 473 K), at pressures ranging from 0 to 200 kPa, and at water contents ranging from 0% to 4%, It was found that the adsorption of the organic species was not significantly affected by increasing the pressure over 10 kPa. Also, increasing the water content of the zeolite reduced the adsorption of these aromatics significantly. On the other hand, as the temperature was increased the amount of adsorbed material was only slightly affected. To access adsorption selectivity information, various mixtures of the aromatics were studied. Results from the simulations show that adsorption of benzene was higher than that of toluene, and toluene adsorption was higher than that of p-xylene. A relation between the electronic environment; of the molecular species and the amount of adsorbed material was established. The results obtained are compared with experimental data available on other synthetic and natural zeolites.