低硅铝比ZSM-5分子筛上C_4烃的催化裂解反应

Catalytic Cracking of C_4 Hydrocarbons on ZSM-5 Molecular Sieves with Low SiO_2/Al_2O_3 Molar Ratio

以低硅铝比(n(SiO2)/n(Al2O3)=20-45)的ZSM-5分子筛为催化剂,研究了混合C4烃的催化裂解反应,并对不同硅铝比的ZSM-5分子筛进行了酸性表征.混合C4烃的催化裂解反应结果表明,低硅铝比的ZSM-5分子筛具有较高的低温催化活性,高硅铝比ZSM-5分子筛催化剂上乙烯和丙烯的收率高于低硅铝比ZSM-5分子筛催化剂,低硅铝比ZSM-5分子筛上苯和甲苯的收率高于高硅铝比ZSM-5分子筛催化剂.在反应温度为625℃时,硅铝比为20的ZSM-5分子筛催化剂上乙烯、丙烯、苯和甲苯的总收率可达79.42%.酸性表征结果表明,硅铝比低的ZSM-5分子筛具有更多的Br觟nsted(B)酸酸量、Lewis(L)酸酸量及总酸酸量,这是低硅铝比ZSM-5分子筛具有低温高活性及高的苯和甲苯收率的原因.

The catalytic cracking of C4 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 ℃, 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 Br觟nsted （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 C4 hydrocarbons.