Influence of Catalyst Binders on the Acidity and Catalytic Performance of HZSM-5 Zeolites for Methanol-to-Propylene (MTP) Process: Single and Binary Binder System

The effect of the binders, such as silica, alumina, and aluminum phosphate solution (APS), was studied on the acidity and catalytic performance of HZSM-5 zeolite (SiO₂/Al₂O₃ = 80) in methanol-to-propylene (MTP) process. The strong acidity of catalyst increased slightly with alumina binder but decreased with silica and APS binders. It is noted that the catalyst with APS binder showed the highest bulk crush strength. Catalytic performance of the alumina or silica bound catalyst was comparable to that of pure HZSM-5 catalyst while that of APS bound catalyst was completely different depending on the binder content. Low content (10 wt%) of APS resulted in a dramatically enhanced propylene selectivity (>40 C mol%) due to the decrease in strong acidity. On the other hand with high content (>20 wt%) of APS, methanol was mostly dehydrated into dimethylether without further transformation into hydrocarbons even if the mechanical strength was significantly improved. The binary binder system was proposed not only to improve the mechanical strength of catalyst with small amount of APS binder but also to keep a high propylene selectivity. The catalyst bound with APS-and-alumina or APS-and-silica showed a comparable propylene selectivity to that of HZSM-5 with the 10 wt% of APS single binder while demonstrated much higher bulk crush strengths.