Study On Effect Of Acidity Adjustment Of HZSM-5 Catalyst On Methanol-to-propylene

To improve the catalysts performance for the methanol-to-propylene(MTP)reaction,regulation on the structure and activity of HZSM-5 zeolite were studied from three aspects:acidity adjustment through the MFI-Silicalite-Ⅰ core-shell composite,acidity adjustment of MFI zeolite synthesized form Si,Al and boron,acidity adjustment through the composite of MFI structure and CHA structure zeolites,and their structure-activity relationships for catalyzing the MTP reaction.Hydrothermally prepared HZSM-5@Silicalite-1 composite zeolite showed comparable pore properties to HZSM-5 or Silicalite-1.The weak and strong acid peak temperatures by NH3-TPD were around 170℃ and 370 ℃,respectively.Silicalite-1 partially covered the acid sites of HZSM5 surface.The total acid amount lowered.The Silicalite-1 layers by different silicon sources showed distinct effects on the catalytic performance.Fixing the mass ratio of core/shell as 1:3,for the layer from TEOS,the strong acid amount of the composite lowered by 28%.For that from fumed SiO2,the weak acid amount reduced by 35%,and the propylene selectivity in the MTP reaction reached 44%.For that from Si,the thickness of the shell was thinner,relatively conducive to product diffusion.The activity with the time-on-steam reaction was stable for 26 h.Hydrothermally prepared H-[B,Al]-ZSM-5 using glucose as assist template with Su、Al、B as sources had the mesopores of 3.5 nm and 8-10 nm,and mesoporosity of 73%.The weak and strong acid peak temperatures by NH3-TPD were around 170℃ and 370℃,respectively.As the Si/Al2 of the synthetic gel was increased,the weak acid amount increased and the propylene selectivity in the MTP reaction increased.At the(Al2+B2)/Si of 0.01,the olefins selectivity and the propylene selectivity reached 84.5%and 50.1%,respectively.The catalytic performance with the time-on-stream reaction was stable for 580 h.For the composite of H-[B,Al]Z5-G(Si/Al2=200,MFI structure)with SAPO-34(CHA structure)at the Si/Al2 of 0.6 of SAPO-34 composite gel and the solid/liquid ratio of 2/30(g/mL),the weak and strong acid peak temperatures of the composite samples by NH3-TPD were around 180℃ and 425 ℃,respectively.As the B/Al ratio in H-[B,Al]Z5-G from 1 to 9,the weak acid amount of H[B,Al]Z5-G/SAPO-34 increased by 81%and the strong acid amount did by 88%.Furthermore,for the composite of H-[B,Al]Z5-G with SAPO-18 at SAPO-18 Si/Al2=0.6 and the solid/liquid ratio of 2/30 g/mL,the weak and strong acid peak temperatures of the composite samples by NH3-TPD were around 170℃ and 400℃,respectively.as the B/Al ratio in H-[B,Al]Z5-G,the total acid amount of H-[B,Al]Z5-G/SAPO-18 was markedly increased.The propylene selectivity was 51.3%,the C5+selectivity was 9.3%,and the activity with the time-on-stream reaction was stable for 70 h.