Light hydrocarbon sorption properties of pure silica Si-CHA and ITQ-3 and high silica ZSM-58

The light hydrocarbon sorption properties of the three 8-ring zeolites, pure silica Si-CHA and ITQ-3 and high silica ZSM-58 (DDR structure type), have been measured and the adsorption rates and adsorption energies of ethene, ethane, propane and propene were determined. Of particular interest is the large difference in the rates of adsorption of propene and propane exhibited by each of these zeolites. For Si-CHA the ratio of the D's is 43,000 at 30 °C and the activation energies for diffusion of propene and propane are ∼10 and 73 kJ/mol, respectively, indicating that activated diffusion controls the diffusion rate of propane through its 8-rings. The diffusivity decreases in the order ethene ∼ ethane > propene ≫ propane > n-hexane. All three zeolites have potential for the separation of propene from propene/propane mixtures.