Effect of modification of HZSM-5 on dimethyl ether conversion to propylene

A HZSM-5 zeolite was prepared and modified by hydrothermal treatment and incipient wet impregnation with calcium nitrate solution,respectively.Their catalytic properties for dimethyl ether conversion to propylene(DTP) and the effects of dilution gases on the reaction were investigated in a continuous flow fixed bed reactor.The results showed that under the reaction conditions of 400 ℃,GHSV=1 440 h-1,nitrogen as dilution gas and n(DME)/n(N2)=1:5,the catalyst hydrothermally treated had better stability but lower selectivity to light olefins and the catalyst modified with calcium oxide had better stability and higher selectivity to light olefins but lower selectivity to light alkanes than the unmodified HZSM-5 catalyst;under the same conditions but carbon dioxide was used to substitute nitrogen as dilution gas,Ca-HZSM-5 catalyst exhibited better stability.