Synthesis And Modification Of SAPO-34 Zeolites And Theirs Application In The Conversion Of Syngas Into Lower Olefins

Lower olefins(ethylene,propylene and butene)are important chemical raw materials.Due to the depletion of crude oil resources and and the urgent demand for the lower olefins,the novel route for the synthesis of lower olefins from non-petroleum carbon resources via syngas platform has attracted much attention.Recently,our group has developed a bifunctional catalyst combined Zr-Zn oxide with SAPO-34 zeolite,which showed good catalytic performances for the synthesis of lower olefins from syngas.In the reaction,syngas is converted to methanol/dimethyl ether intermediates and further converted to lower olefins in SAPO-34 zeolite.The acid properties and pore structure of SAPO-34 have a significant effect on the catalytic performances.In this dissertation,we aimed to develop a high-performance catalyst for synthesis of olefins from syngas.We focused on the synthesis of microporous and hierarchical SAPO-34 zeolites and the modification of SAPO-34 zeolites by metal-ions,and examined their catalytic performances in the reaction of syngas conversion.We deeply studied the key factors of the synthesis methods and synthesis parameters.We first prepared the microporous SAPO-34 zeolites with TEA/TEAOH dual-template via hydro-thermal method.The effects of different aluminum sources,crystallization time,and the amount of template agent TEA on the properties of SAPO-34 zeolites were investigated.We obtained an optimized conditions for the synthesis of zeolites.On the other hand,the HF solution was used to replace TEAOH as the additive.The results showed that the introduction of HF could increase the crystallinity of SAPO-34,and it was easier to form zeolite grains with more uniform size.The SAPO-34-HF zeolites coupled with Zr-Zn oxides are used for the conversion of syngas into lower olefins.The catalytic performance and stability are greatly improved.After 320 h test,the CO conversion and C2?4= selectivity are maintained at 23%and 75%,respectively.These results indicatethat the addition of HF promotes the catalytic performance and stability of the bifunctional catalysts.We further introduced the mesoporous templating agents TPOAC and CTAB into the hydrothermal synthesis process,and we successfully synthesized the mesoporous SAPO-34 zeolites.The external surface area of SAPO-34-TPOAC zeolite is as high as 233.3 m2,g-1,and the mesoporous volum is 0.36 cm3 g-1,which distinctly formed a mesoporous structure.The mesopores in the SAPO-34-CTAB is not as significant as that of SAPO-34-TPOAC,but it still has a mesoporous structure compared to microporous SAPO-34.Compared to microporous SAPO-34 zeolites,The hierarchical SAPO-34-TPOAC zeolites coupled with Zr-Zn oxides didn't showed better catalytic performances,while the Zr-Zn/SAPO-34-CTAB exhibited high CO conversion and C2-4= selectivity.After 110 h of reaction,CO conversion and C2?4=selectivity were maintained at 25%and 75%,respectively.This thesis also focused on the modification of microporous SAPO-34 zeolite by metal-ions.The results show that the solid-state ion exchange method can introduce the metal ion into the framework of SAPO-34 without changing the intrinsic properties of the zeolites.The catalytic performances of syngas conversion were also investigated.We found that Sr2+,Ga3+,Ni2+,Zn2+ could increase the selectivity of lower olefins,effectively regulate the olefins/paraffins ratio of the product,and suppress the carbon deposition during the reaction.