Study on phosphorus modification of HZSM-5 zeolite and its performance in hydrowaxter cracking

A series of phosphorus modified HZSM-5 molecular sieves are prepared by impregnation method. X-ray diffraction (XRD), N₂ physical adsorption, X-ray fluorescence spectrometry, NH₃ temperature-programmed desorption, and infrared spectra of pyridine adsorption methods are used for its characterization and the different phosphorus content of HZSM-5 molecular sieve structure, acidity and the influence law on hydrogenation wax cracking are examined. The results show that with the increase of phosphorus content, the B acid site decreases, and the pore volume and specific surface area decreases. The selectivity of light olefins increases due to the decrease of strong B acid site which inhibited hydrogen transfer reaction. As the modified HZSM-5 molecular sieve pore is blocked, its activity decreases significantly with the increase of phosphorus content. Therefore, the yield of propylene presents a trend of first increasing and then decreasing. When phosphorus mass fraction is 5%, propylene yield can be up to 5.9%. It is particularly important to check the appropriate phosphorus content during the development of the productive propylene additive.