Successive desilication and dealumination of HZSM-5 in catalytic conversion of waste cooking oil to produce aromatics

An integrated modified HZSM-5 was prepared by sodium hydroxide leaching and followed by hydrothermal process in series, and the co-modified zeolites were then used to conduct the catalytic fast pyrolysis of waste cooking oil to investigate whether an enhanced production of aromatics could be obtained. X-ray diffraction, N₂ adsorption–desorption, TEM and NH₃-TPD were utilized to characterize the modified zeolites. Experimental results indicated that the crystal structure of HZSM-5 was damaged as alkali treatment time was beyond 4 h, and a micro-mesopore hierarchical system was created inside the zeolites. Simultaneously, the strong acid sites decreased with the increment of modification time, while the weak acid sites performed an opposite inclination. The relative yields of aromatics and olefins presented deviation when alkali treatment time exceeded the specific limitation, and a moderate alkali treatment time of 4 h was beneficial for promoting the yield of aromatics.