The Molecular Sieving of Propylene and Propane on SAPO-35 Molecular Sieve

Selective adsorption is regarded as a promising alternative for propylene/propane separation. However, the similar physicochemical properties of these two components pose a challenge in developing adsorbents that simultaneously exhibit high selectivity and substantial adsorption capacity. This study aims to achieve molecular sieving of propylene and propane by precisely controlling the pore size of silicoaluminophosphate (SAPO) molecular sieve. The pore size of the eight-membered-ring SAPO-35 molecular sieve is tuned via ion exchange to fall between the kinetic diameters of propylene and propane, enabling selective adsorption of propylene while excluding propane molecules. Ion exchange treatment increased the equilibrium adsorption selectivity of the SAPO-35 from 2.2 to 11.4, placing it among the highest-performing molecular sieve-based adsorbents. This modification also substantially improved the material's regeneration capability at ambient temperature. Theoretical calculations reveal that steric hindrance effects, arising when gas molecules diffuse through the eight-membered-ring channels, contribute significantly to the high adsorption selectivity. Breakthrough experiments demonstrated that Na-SAPO-35 achieves a dynamic selectivity of 15.9 for propylene/propane separation. The development of Na-SAPO-35 adsorbents with high selectivity, substantial adsorption capacity, and robust durability is critical for advancing the industrial implementation of adsorption-based separation technologies.