Preparation Of Hierarchical SAPO-34 And Its MTO Performance

In this paper,hierarchical SAPO-34 using cheap carbohydrates as hard template and DEA as template was proposed.The hierarchical SAPO-34 was successfully synthesized.The prepared zeolites were characterized by X-ray diffraction?XRD?,N₂ isothermal adsorption,scanning electron microscopy,composition analysis and NH_3-TPD.In a fixed-bed reactor,the effects of silicon content,crystallization time and template agents,as well as hard template agents such as xylose,sucrose,starch,glucomannan and mixed sugars,on the structure of the synthesized SAPO-34 and the catalytic reaction of methanol to olefins?MTO?were studied.The results show that:?1?The specific surface area,micropore and mesoporous volume of SAPO-34 zeolite are 249.2 m²/g,0.106 cm³/g and 0.006 cm³/g,respectively.The specific surface area,micropore volume and mesoporous volume of hierarchical SAPO-34-d prepared with starch as hard template are 507.5 m²/g,0.241 cm³/g and 0.012 cm³/g,respectively.Compared with conventional SAPO-34,the specific surface area,micropore and mesoporous volume of hierarchical SAPO-34 prepared by different carbohydrate templates were significantly increased.?2?Compared with conventional SAPO-34 zeolites,MTO catalytic life of hierarchical SAPO-34 zeolites are higher.The order of the catalytic life of SAPO-34-h from high to low is SAPO-34-z>SAPO-34-h>SAPO-34-d>SAPO-34-m>SAPO-34>SAPO-p.?3?The diene selectivity of hierarchical SAPO-34 zeolite is higher than that of conventional SAPO-34 zeolite.The initial diene selectivity of SAPO-34-m zeolite is up to75.4%,3.7%higher than that of conventional SAPO-34 zeolite 71.7%,while that of SAPO-34-h,SAPO-34-d,SAPO-34-z and SAPO-34-p is 3.4,2.0,1.9 and 0.2%higher than that of conventional SAPO-34 zeolite,respectively.Initial activity of SAPO-34 zeolite can be improved by introduction of mesopores.?4?Hard template sucrose can improve the pore structure and acidity of molecular sieves.The initial diene selectivity of SAPO-34-z zeolite obtained by using sucrose as hard template is relatively high,and the MTO catalytic life is the longest?130 min?,which is 30%higher than that of conventional SAPO-34 zeolite?100 min?.?5?The SAPO-34 zeolite synthesized by high silicon-aluminium synthesis has higher crystallinity,higher acidity and longer MTO catalytic life than that of SAPO-34 zeolite synthesized by low silicon-aluminium ratio.Pure SAPO-34 zeolite could not be synthesized under 24 hours crystallization time,and the suitable crystallization time was 48 hours.