Effects of Phosphorus on modification of HZSM-5 zeolite synthesized with different framework aluminum distribution in catalytic transformation of LPG to light olefins

 
In this work, HZSM-5 zeolites with aluminum nitrate and aluminum hydroxide and Si/Al ratio 20 were synthesized and the effect of framework aluminum distribution on modification of HZSM-5 with phosphorous were investigated in catalytic cracking of LPG. The prepared catalysts were characterized by X-Ray Diffraction, Field Emission Scanning Electron Microscopy, Nitrogen Adsorption-desorption, X-Ray Fluorescence and NH3-Temperature Programmed Desorption analyses. Aluminum distribution in the framework of HZSM-5 was determined by chemical analysis of X-Ray Fluorescence and reflectance UV-Visible analyses. The highest proportion of single Al atoms was found to be 90.6% for HZAM-5 synthesized with aluminum nitrate and the highest proportion of close Al atoms in the zeolite framework was 47.8% for HZAM-5 synthesized with aluminum hydroxide. The catalytic cracking tests showed that the catalytic stability and the olefin yield in LPG cracking for HZAM-5 synthesized with aluminum nitrate, were greater than those of HZAM-5 synthesized with aluminum hydroxide. After 240 min,the olefin yield just decreased from 49.8% to 41.5% for P/HZSM-5 synthesized with higher single Al atoms. Also, the propylene to ethylene ratio, yield of C5+ heavy products, coke percent and deactivation rate for P/HZSM-5(Nitrate) catalyst were determined to be 0.986, 2%, 6% and 21.31%, respectively.