A Novel Preparation of SAPO-18 Molecular Sieve with Enhanced Stability for Dimethyl Ether to Olefins

SAPO-18 molecular sieve is an important catalyst for dimethylether-to-olefins (DTO) reaction. Although the conventional synthesized SAPO-18 using N,N'-diisopropylethylamine (DIEA) alone exhibits nanoparticles and better catalytic performance due to the weaker diffusion resistance, its high cost of preparation and difficult separation of the powder limit the industrial process of this type of molecular sieve. Therefore, reducing the cost and increasing the particle size appropriately become the key issues for its practical application. In this study, SAPO-18 catalysts were synthesized hydrothermally using mixture of triethylamine (TEA) and a small amount of DIEA as templates. The results revealed that fairly pure SAPO-18 molecular sieve with particle size of approximately 1.0 mu m could be synthesized under the initial gel composition as: xDIEA:(1.4-x)TEA: 1.0 Al2O3: 0.9 P2O5:0.6SiO(2):50H(2)O, where x varies from 0.2 to 0.6. Furthermore, the catalytic performance for DTO reaction over the novel synthesized SAPO-18 catalysts showed higher selectivities to light olefins and much lower coke deposition than the conventional synthesized SAPO-18 using DIEA alone.