Ultrafast synthesis of SAPO-17 zeolites with excellent CO2/N2 and CO2/CH4 separation performance

Abstract

Silicoaluminophosphate (SAPO) zeolites with small pores (8-ring window), such as SAPO-34, SAPO-17, and SAPO-RHO, have attracted a lot of attention due to their unique structural features, and their applications in the field of small-molecule gas adsorption and separation. However, the fast, efficient and green synthesis of SAPO zeolites remains a great challenge. In this work, SAPO-17 zeolites were synthesized within 1 min for the first time by a seed-assisted microwave method, and the resulting samples possessed excellent performance in the application of CO₂ adsorption and separation for flue gas and natural gas. The microwave-assisted route can shorten the crystallization time of traditional hydrothermal methods from a few hours to 30 min. Furthermore, the crystallization time could be drastically shortened to 1 min with the addition of seeds, which represents the shortest time for the preparation of a SAPO-17 zeolite up to now. SAPO-17 synthesized within 1 min (SAPO-17-S-1) possessed the smallest crystal size, and the largest micropore volume and specific surface area among all the samples, which enhanced mass transfer and exposed more active sites, and thus it possessed prominent performance for CO₂ adsorption (3.47 mmol g⁻¹ at 273 K and 1 bar) and gas separation. At 298 K and 100 kPa, SAPO-17-S-1 exhibited the highest gas selectivity for CO₂/N₂ (276) and CO₂/CH₄ (63) over the other samples, which were synthesized in a relatively long time. Transient binary breakthrough experiments on SAPO-17-S-1 further verified the highly-efficient gas separation performance. This work proposes a green and ultrafast strategy for the synthesis of SAPO-17 zeolites with highly selective CO₂ adsorption over N₂ and CH₄.