Synthesis of Silicoaluminophosphate SAPO-56 Molecular Sieves for Efficient CO₂ Adsorption and Separation

Capturing CO₂ from flue gas and natural gas is crucial for energy production and environmental protection, and the development of efficient adsorbents is the key. In this study, we systematically investigated the factors influencing the hydrothermal synthesis of silicoaluminophosphate SAPO-56 molecular sieve, including the molar ratio of raw materials, crystallization time, and temperature. A seed-assisted synthesis strategy was employed to significantly reduce the crystal size of SAPO-56 from over 30 μm to below 1 μm. The resulting submicron-sized SAPO-56 exhibited a markedly enhanced CO₂ uptake (5.94 mmol g^-1 at 0 °C) compared to conventional SAPO-56 samples (4.77 mmol g^-1), surpassing most previously reported zeolitic adsorbents. Significantly, the submicron-sized SAPO-56 was utilized for the first time as a filler to prepare mixed matrix membranes (MMMs) with benzimidazole-based polyimide (BIMPI) as the polymer matrix for natural gas purification. The membrane with 50% SAPO-56 loading demonstrated a promising CO₂ permeability of 151.23 Barrer, significantly higher than that of the pure BIMPI membrane (18.00 Barrer). This work provides valuable insights into the ratio synthesis of SAPO-56 molecular sieves and advances their application in CO₂ adsorption and separation, as well as in MMMs for natural gas purification.