催化剂结构与焦油模型化合物裂解行为的关联性

On the relation between the structure of catalysts and the cracking behavior of tar model compound

以Ni(NO_3)_2·6H_2O为镍源,分别以HZSM-5(Si/Al=25)、HZSM-5(Si/Al=50)、HZSM-5(Si/Al=200)、USY、Al_2O_3为载体制备了5种镍基催化剂,采用XRD、H_2-TPR、BET、NH_3-TPD等方法对其进行了表征,在固定床反应器中考察了上述催化剂对煤焦油模型化合物甲苯+芘的催化裂解性能。结果表明,相比惰性载体石英砂,在催化剂作用下,液相产物中轻质芳烃种类明显增多。3种Ni/HZSM-5催化剂的比表面积和平均孔径较为接近,然而酸性中心数量最多的Ni/HZSM-5(Si/Al=25),对甲苯+芘的裂解能力最强,体现为液体产物收率最低(仅为15.95%),气产率和析碳率均最高,分别达16.73%和67.32%。在酸性中心数量相近的Ni/HZSM-5(Si/Al=200)与Ni/Al_2O_3作用下,液体产物收率差别较小,但后者的芘裂解率比前者高41.47%,主要是由于后者的平均孔径比前者高1.64倍,说明平均孔径大有利于重质组分芘的裂解。综合考虑液体产物收率、气产率、析碳率和芘的裂解率,Ni/Al_2O_3更适合甲苯+芘裂解反应体系。

Five kinds of Ni-based catalysts were prepared using HZSM-5(Si/Al=25),HZSM-5(Si/Al=50),HZSM-5(Si/Al=200),USY and Al2O3 as the carriers and Ni(NO3)2·6H2O as the nickel resource.All the catalysts were characterized by XRD,H2-TPR,BET and NH3-TPD.Then the performance of catalysts for cracking coal tar model compounds of toluene and pyrene were investigated in a fixed-bed reactor.The experimental results showed that the species of light aromatics in the liquid product increased obviously with catalysts compared to that with silica sand.Though the three kinds of Ni/HZSM-5 had similar specific surface area and average pore diameter,Ni/HZSM-5(Si/Al=25)showed the highest gas yield and carbon deposition of 16.73%and 67.32%,respectively and the lowest liquid product yield of 15.95%due to the highest acidity.For Ni/HZSM-5(Si/Al=200)and Ni/Al2O3 samples,the liquid product yields were almost the same,owing to their similar acidity,however,the latter had a higher pyrene cracking efficiency of 41.47%,about 1.64 times higher than the Ni/HZSM-5(Si/Al=200),indicating that the larger pore size was beneficial to the pyrene cracking.Through comprehensive consideration of the pyrene cracking efficiency and the yield of liquid,gas and carbon deposition,we think Ni/Al2O3 is more suitable for the cracking of toluene and pyrene.