Study On The Effect Of Acidity Modification Of HZSM-5 Catalyst On Methanol To Olefib Reaction Activity

In order to improve the propylene selectivity and activity stability in methanol to olefins(MTO)reaction,the effects of element modification and composite modification on the acidity and activity of HZSM-5 zeolite catalyst were studiedBoron modificationAt SiO2/Al2O3?400 and B/Al=1,the acid strength of BHZSM-5 retained unchanged compared with that of HZSM-5.The weak Br(?)nsted(B)acid amount was increased whereas the strong B acid amount decreased by 50%and the total acid amount increased.The propylene selectivity rose by 4%.The hydrogen transfer reaction was suppressed and the activity durability improved.Subjected to hydrothermal circumstances,more acid amount of BHZSM-5 maintained.The framework A1 in the straight and sinusoidal channels was not easy to remove compared with those in the channel intersections,which is conducive to the alkene-based cycle mechanism.The propylene selectivity reached 37.4%.At SiO2/Al2O3?400 and B/Al=1,9,the weak B acid amount was increased by 1 times whereas the amount strong B acid remained.The activity durability BHZSM-5-4000-9 extended for 50 h.ZSM-11 cocrystallization compositeZSM-5/ZSM-l1 zeolite was synthesized using hydrothermal cocrystallization.The charging SiO2/Al2O3 ratio was 180 and the ZSM-11 content was 15%.The cocrystal zeolite showed similar crystallinity,morphology,porosity,weak and medium strong B acid amount as HZSM-5,but more strong B acid amount.The propylene selectivity was raised by 10%.The A1 in the straight channels was increased,beneficial to the formation of propylene via the alkene-based cycle mechanism.SAPO-n compositeSAPO-11(SiO2/Al2O3=0.2)was composited with HZSM-5(SiO2/Al2O3=160)using hydrothermal crystallization.The propylene selectivity was improved.With increase of the HZSM-5/SAPO-11 ratio from 0.65 to 1.08,the strong acid amount was decreased by 61%.When the ratio was 1.08,the propylene and ethylene selectivity was 27.6%and 43.8%,respectively,and the C5+ selectivity 9.1%,relating to enhanced cracking.SAPO-18(SiO2/Al2O3=0.2)was composited with HZSM-5 in the ratio of 1.22.The strong acid amount was markedly increased.With further strengthened cracking,propylene was increased up to 42.5%and C5+ reduced to 8.6%.The activity stabilized for 64 h.