Energetics and siting of sorbed molecules in zeolites by computer simulations. Comparison with calorimetric and structural results. I — Aliphatics and aromatics in faujasite and mordenite

Sorbent/sorbate interactions corresponding to FAU(foujasite)/sorbate and MOR (mordenite)/sorbate systems have been investigated by using the theoretical exp-6-1 Buckingham model. In FAU/sorbate systems this simple molecular mechanics model correctly simulates the salient structural and energetical features corresponding to known sorbate complexes; it is furthermore established that in case of saturated hydrocarbons the coulombic interactions might be neglected, the correct sorption heats being calculated without considering any hypothetical local relaxation of the zeolitic framework. In the case of MOR/alkane systems, it is shown that for methane and ethane, possible sorption sites exist in the side pockets, whereas longer n-alkanes essentially reside in the main 12-ring channel. In all cases the calculated sorption energies for the n-alkanes vary linearly versus the aliphatic carbon chain-length. It is found that hexane isomers have comparable sorption heats.