La,Ce,Th改性ZSM-5分子筛作为烷烃裂解催化剂的评价

Evalution of Rare Earth Metal Modified ZSM-5 Zeolites as Cracking Catalysts of Hydrocarbon

本文考察烷烃(正已烷烃,正庚烷,液体石蜡)在HZSM—5和稀土金属La,Ce:Th改性ZSM—5分子筛上的催化裂解行为,结果有:(1)较高的反应温度(范围:370—430℃)有利于烷烃在分子筛表面强酸中心和碱中心协同作用下,形成正碳离子,而提高烷烃的裂解转化率;(2)较低反应物进料空速,可以增大炕烃在催化剂表面的接触时间,其裂解产物(尤其是气相产物)含量增多,在相同条件下稀土金属改性的ZSM—5催化剂其裂解活性低些,这正支持了烷烃在分子筛强酸中心上裂解的机理;(3)以稀土改性ZSM—5分子筛为催化剂的裂解的烷烃油相产物中芳烃含量有较明显降低;(4)稀土改性ZSM—5分子筛具有较少的积碳现象。

The catalytic behaviour of craking hydrocarbon (n-hexane, n-heptane, liquid paraffin) on the rare earth metal (La, Ce, Th) modified ZSM-5 zeolites was inverstigated. The results shown: a) At the higher reaction temperature (range: 370--430℃) would help to raise the conversion of cracking hydrocarbon, because in this condition hydrocarbon could be easily to form the carboniogenic medium under the action of the surface active centers of the zeolite catalyst, b)With a lower weight space velocity of the reactant it would be Iound that the cracking products (especially tile gas-phase products) would be increascd, due to the contact time of hydrocarbon on the surface of catalyst. c) In the cracking liquid-phase products the component of aromatic compounds would be decreased obviously on the rare earth metal modified ZSM-5 zeolites. d) There was the less coking on the surface of the above modified zeolites. In brief, the catalytic activity of the rare earth metal modified ZSM-5 zeolites would be lower than that of HZSM-5 zeolite.