MTA Reaction And Coking Behaviors Of Kaolin-based CHA-MFI Zeolite

Methanol to aromatic（MTA）is a new non-oil route for low-cost synthesis of high-quality aromatics,which has attracted much attention in recent years,because of the methanol can easily be obtained from coal.The key to this technology is to develop new catalysts with high catalytic activity and stability.In this thesis,a kaolin-based SAPO-34/ZSM-5（CHA-MFI）composite zeolite catalyst for MTA reaction was proposed and the reaction performance,coke deactivation and the effect of the modified crystal layer（SAPO-34）were studied.Firstly,SAPO-34/ZSM-5 composite zeolite film was applied to MTA reaction with fixed-bed reactor.The BTX selectivity of the composite zeolite film was improved 7%compared with H-ZSM-5.Then the flash and deactivation catalysts were characterized by TG,XPS,FTIR,GC-MS and N₂ adsorption-desorption.For the result,the composite zeolite film benifited from the two-layer structure and hierarchical pore structure.On the one hand,olefine was quickly diffused to the H-ZSM-5 and converted to the aromatic,which shortened the reaction process.On the other hand,the coke deposition on the surface of SAPO-34 was removed,which greatly prolonged its reaction life.Furthermore,the location of coke was changed by hierarchical pores,which makes coke to form in mesoporous pore easily.Then,the thickness of the SAPO-34 crystal layer was controlled by changing the composition of the synthesis gel.The thick crystal layer lead to the rapid deactivation and the low concentration of synthetic solution will lead to the amorphous structure blocking the pores.The best composition of the synthesis gel was 3 Mor:1 Al₂O₃:1P₂O₅:0.6 TEOS:210 H₂O.The thickness of the modified film was about 10μm,which showed the best performance.Finally,the composite zeolite was synthesized by Zn in-site doping.Active metal species and newly acid sites improved the reaction performance.The doped zeolite presents a multi-crystal stacked flower-shaped structure with more micropores.For composite zeolite,the 2%Zn content was shown the best reaction performance.The MTA reaction selectivity and the lifetime were improved to 41%and 41h,respectively.