Synthesis And Modification Of SAPO-34 For MTO Reaction

Methanol to olefin (MTO), as a potential method instead of conventional oil route, has received wide attention in the past years. The key issue for the MTO reaction is to develop new catalyst with higher lifetime, higher selectivity to olefin, higher conversion and stability. SAPO-34 molecular sieve is a potential catalyst for MTO reaction, because of its high conversion of methanol and selectivity to ethane and propene. However, fast deactivation has been reported due to coke formation. In this paper, the synthesis and modification of SAPO-34 molecular sieve were studied to prolong the lifetime of the catalyst.The experiments were carried out to investigate the effect of Vapor Phase Transport (VPT) method and different templates such as MOR, TEA and TEAOH on SAPO-34 synthesis. The results show that the crystal grain size of catalyst synthesized with different templates is in the order: MOR-SAPO-34> TEA-SAPO-34>TEAOH-SAPO-34; the lifetime is in the the order: TEAOH-SAPO-34^TEA-SAPO-34>MOR-SAPO-34; The lifetime of SAPO-34 synthesized by VPT method is short due to without dispersion medium in the system.The experiments were carried out to investigate the effect of metal ions such as Mg, Co, Ni and Mn on lifetime of catalyst. The results show that MeSAPO-34 modified by Mg, Co, Ni or Mn metal ion has low acidity of catalyst and high of the selectivity to ethane; at different temperature, the lifetime of MnSAPO-34 shows the longest lifetime, 7.25 h, at 400℃; the MnSAPO-34 with Mn/Al₂O₃ being 0.01 shows the best selectivities to ethane and propene. In the studies, a hierarchical porous SAPO-34, synthesized with silane coupling agent TPOAC as mesopore structure directing agent, was also used for MTO reaction. Compared to the conventional SAPO-34, the hierarchical porous SAPO-34 molecular sieve has a longer lifetime, while lower selectivities to ethane and propene.The reproducibility of SAPO-34 was studied. The catalyst can be regenerated through simply calcinations in air at 550℃. The performance of regenerated SAPO-34 after 3 times is very similar to the fresh SAPO-34.