催化剂结构与焦油模型化合物裂解行为的关联性

摘要

以Ni(NO3)2·6H2O为镍源,分别以HZSM-5(Si/Al=25)、HZSM-5(Si/Al=50)、HZSM-5 (Si/Al=200)、USY、Al2O3为载体制备了5种镍基催化剂,采用XRD、H2-TPR、BET、NH3-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/Al2O3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/Al2O3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 Al2O3as 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/Al2O3samples,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/Al2O3is more suitable for the cracking of toluene and pyrene.