Synthesis,Modification And Catalytic Performance Of Ethanol Aromatized ZSM-5 Zeolites

In this paper,the synthesis and modification of ZSM-5 zeolites and the aromatization performance of ethanol were systematically studied by experimental evaluation,XRD,TPD,BET and other spectral characterization methods.The relationship between the physical and chemical properties of ZSM-5 molecular sieves and its catalytic performance has been preliminarily studied.Firstly,the aromatization properties of four zeolites,HZSM-5,BETA,MCM-22 and MCM-49,were compared and analyzed under atmospheric pressure,450℃ and pure ethanol feed space velocity of 4 h-1.The results showed that HZSM-5 zeolites had better aromatization performance,and the highest yield of aromatic hydrocarbons in liquid phase can reach 24%.The subsequent work would be based on HZSM-5 zeolites.The effects of Si/Al ratios(Si/Al=9,13,25,38,48,58)on the properties of HZSM-5 zeolite samples were investigated by single factor experiment.The results showed that with the increase of Si/Al ratio,the specific surface area of HZSM-5 zeolites increased first and then decreased,and the total acid content decreased monotonously.The evaluation results show that the molecular sieve synthesized under the condition of Si/Al ratio 13 has relatively better aromatization catalytic performance.Based on HZSM-5 zeolites synthesized at Si/Al ratio of 13,Cu,Zn,Ga and Ni metal modification and P nonmetal modification of HZSM-5 zeolites were studied by ion exchange method.The results show that the addition of Zn can increase the amount of weak acid and medium strong acid in HZSM-5 zeolites,and the distribution of both acids is relatively uniform.The evaluation results showed that the zeolite catalyst prepared by Zn modification in the four metal modifications had good catalytic effect,and the highest yield of liquid aromatics reached 35.3%.The relatively appropriate loading amount of Zn was 2%,and the highest yield of liquid aromatic hydrocarbons on Zn-HZSM-5 zeolite obtained under this condition could reach 37.2%.The P modification is beneficial to the improvement of thermal stability and aromatization performance of the zeolite,and the yield can be increased by 2%compared with raw powder,and the suitable loading capacity is 1%.The results of two-component modification of P and Zn showed that the modification effect of loading P before loading Zn was better than that of loading Zn before loading P and loading P and Zn simultaneously.The catalytic effect of 2%Zn-1%P-HZSM-5 zeolite prepared by loading P first and then loading Zn on ethanol was significantly improved.The yield can be increased by 19.3%on the basis of raw powder,and the best aromatic yield can reach 43.32%.The highest aromatic yield of 2%Zn+1%P-HZSM-5 zeolite prepared by Zn and P simultaneous loading was 34.18%.The 1%P-2%Zn-HZSM-5 zeolite prepared by loading Zn first and then loading P had little increase in aromatics yield,and its highest aromatics yield was only 27.92%.Based on 2%Zn-1%P-HZSM-5 molecular sieve,the effects of reaction temperature(350-500℃)and ethanol mass space velocity(3-6 h-1)on ethanol aromatization were investigated.The results show that with the increase of the reaction temperature,the yield of aromatic hydrocarbons shows a trend of first increasing and then decreasing,and the highest aromatic yield point appears at 450℃.With the increase of ethanol mass space velocity,the yield of aromatics increased first and then decreased,and the highest yield point appeared at 4 h-1.Through the evaluation experiment,the optimum process conditions were determined as follows:reaction temperature 450℃,ethanol mass space velocity 4 h-1,and the highest aromatic yield was 43.3%.