Catalytic Cracking of C4 Hydrocarbons on ZSM-5 Molecular Sieves with Low SiO2/Al2O3 Molar Ratio

The catalytic cracking of C-4 hydrocarbons was investigated using ZSM-5 with low SiO2/Al2O3 molar ratio (n(SiO2)/n(Al2O3)=20-45) as a catalyst. The reaction results indicated that the catalyst with lower SiO2/Al2O3 molar ratio exhibited higher catalytic activity at low temperatures. The yield of propylene and ethylene over ZSM-5 with low SiO2/Al2O3 molar ratio was lower than that over the catalyst with high SiO2/Al2O3 molar ratio. However the yield of benzene and toluene was reversed. At 625 degrees C, the total yield of ethylene, propene, benzene, and toluene was as high as 79.42% over the catalyst with n(SiO2)/n(Al2O3)=20. The acidity characterization by temperature-programmed desorption of ammonia and pyridine adsorption FT-IR showed that ZSM-5 with lower SiO2/Al2O3 molar ratio had more Bronsted (B) and Lewis (L) acid sites. This accounted for the higher activity at low temperature and higher yield of benzene and toluene in the cracking of C-4 hydrocarbons.