Synthesis and MTO performance of SAPO-18 molecular sieves with different Si/Al ratio

SAPO-18 was hydrothermally synthesized using a template of N, N-diisopropylethylamine(DIEA). The molecular sieve was characterized by XRD, SEM, BET and FTIR. The results showed that the SAPO-18 molecular sieves could be successfully synthesized when the silica-alumina ratio (molar ratio) was between 0.2 and 0.6. The molecular sieve was evaluated in MTO process. It was found that when the silica-alumina ratio was low, the life of the molecular sieve was long, but the selectivity was low. With the Si/Al ratio increased, the life of zeolite decreased and the selectivity increased slightly. To be considered comprehensively, the SiO₂/Al₂O₃ ratio of 0.2 was the most suitable, its dilute selectivity was 76% and the lifetime was 140 min. In addition, the effects of reaction temperature and space velocity on SAPO-18 zeolites catalyzed MTO process were also investigated. It was found that the double dilute selectivity of SAPO-18 zeolites could be increased with the increase of temperature and space velocity.