Interaction between binder and high silica HZSM-5 zeolite for methanol to olefins reactions

Aluminum phosphate (AlPO4) bound HZSM-5 extrudates were prepared with different Al/P ratios, and characterized with respect to the species chemical state, surface morphology, pore structure, and acidity, in comparison to conventional alumina bound and as-received HZSM-5 zeolite catalyst. The binder results in decrease in micropore volume implying blockage of micro channels within the zeolite crystal. AlPO4 binder forms dense amorphous matrix, while alumina forms a porous matrix with significant increase in mesopore volume and surface area. Moreover, both of the bound samples exhibit decreases in acidity strength and sites number, while the alumina bound one shows an increase in strong acidity strength which implies an enhancement of the acid stability of the strong acid sites. The reaction performance experiments on the simulated MTP operating conditions show that compared to alumina bound catalyst the AlPO4-bound type exhibits much lower paraffins and aromatics yields, and particularly that the polymer grade propylene may be easily obtained without C3 splitter, though the lifetime assessment reveals that alumina is much superior to AlPO4 as the binder.