Study On MTP Catalytic Performance Of Si Modified ZSM-5 And SAPO-34 Molecular Sieves

Propylene is an organic chemical intermediate with high added value,which is mainly produced by steam cracking and catalytic cracking of crude oil.In view of the increasing shortage of crude oil resources,it is of great significance to develop new routes to prepare propylene.Methanol to propylene(MTP)technology is currently the most feasible method.The design and synthesis of a molecular sieve catalyst with high propylene selectivity and catalytic stability is the key technology of the MTP reaction process.Composite molecular sieves,as new catalytic materials,which can combine with pore structures and acidic properties of different molecular sieves,had attracted significant attention for their excellent catalytic performance owing to the synergistic effects of their property in recent years.In this paper,firstly choose the chemical liquid deposition method and the sol-gel modify HZSM-5 with Si,and mechanically mix it with SAPO-34 molecular sieve to make MTP catalyst.Then XRD,SEM,TEM,FT-IR,BET and NH3-TPD were used to characterize and analyze the physical properties of the molecular sieve samples,and to investigate the catalytic performance of the molecular sieve catalyst in the MTP reaction.The research contents and experimental results of this paper are as follows:(1)Use tetraethylorthosilicate(TEOS)as the silicon source,the HZSM-5molecular sieve is modified by chemical liquid deposition(CLD).The amorphous Si O2deposited on the HZSM-5 molecular sieve can adjust the acidity and the pore-opening size.The results of the MTP reaction showed that on the sample 4Si/HZ with TEOS deposition of 4%,the conversion of methanol was 100%,the selectivity of light olefins was 78.16%,and to the selectivity of propylene was 39.88%.(2)A sol-gel self-assembly method was used to synthesize a core-shell molecular sieve HZ@x Si O2 with HZSM-5 molecular sieve as the core and Si O2 as the shell.The thickness of the shell layer and the acidity of molecular sieve can be adjusted by changing the mass ratio of TEOS/HZSM-5.Regular and ordered mesoporous Si O2shell grow directly on the anisotropic surface of molecular sieve single crystal to form a core-shell structure.The mesoporous channel is vertically connected to the crystal surface of the anisotropic molecular sieve to form a hierarchical pore structure are closely related at the junction and can maintain good diffusion efficiency.In the MTP reaction,the selectivity of propylene of core-shell structure molecular sieve HZ@2.0Si O2 was 41%,which is about 10%higher than that of HZSM-5.(3)Select the best molecular sieve HZ@2.0Si O2 for propylene in the core-shell structure,mechanically mix it with SAPO-34 molecular sieve to obtain molecular sieve samples with different mass ratios,and the test its catalytic performance in the MTP reaction.The results show that when the mass fraction of SAPO-34 in the mechanically mixed catalyst is 85%,the selectivity of propylene in the MTP reaction is the highest,reaching 47.8%,the selectivity of light olefins reaches 73.6%,and C3~=/C2~=ratio up to6.48.(4)Two HZSM-5 molecular sieve modified by Si were mechanically composited SAPO-34,and the effect of the HZSM-5 modification methods on the catalytic performance of the molecular sieve MTP was compared.The results show that these two different Si modification method have a greater impact on the catalytic performance of MTP.The molecular sieve catalyst prepared by mechanically mixing core-shell structure HZ@2.0Si O2 and SAPO-34 molecular sieve has higher propylene selectivity.