分子筛孔结构和酸性对正癸烷加氢裂化反应性能的影响

EFFECT OF PORE STRUCTURE AND ACIDITY OF ZEOLITES ON THE HYDROCRACKING PERFORMANCE OF n-DECANE

采用XRD,BET,NH3-TPD方法对不同孔结构的Beta、ZSM-5分子筛和两种不同介孔体积的Y型分子筛Y1、Y2进行表征,以正癸烷为模型化合物考察四种分子筛制备的加氢裂化催化剂的反应性能。结果表明,Beta分子筛的活性和异构选择性最高,Y型分子筛次之,ZSM-5分子筛的活性和异构选择性最低。对于Y型分子筛,介孔体积较大的Y2分子筛的异构癸烷选择性较高。在Beta和Y型分子筛上,正癸烷主要按照三支链叔碳正离子β-裂化机理生成较多的支链产物;在ZSM-5分子筛上,正癸烷主要按照单支链仲碳正离子β-裂化机理生成较多的直链产物。

The physicochemical properties of four zeolites with various pore structure and mesopore volume were characterized by XRD, BET and NH3-TPD. The hydrocracking performances of four catalysts containing zeolite Beta, ZSM-5, zeolite Y1 and Y2 respectively were investigated using n-decane as model feed. The results showed that the pore structure and acidity of zeolite strongly influenced the activity, isomerization selectivity, product distributions and reaction mechanism of n-decane hydrocraeking. Zeolite Beta showed the highest activity and isomerization selectivity, followed by zeolite Y, and ZSM-5 was the least. Within the two types of zeolite Y, zeolite Y2 with larger mesopore volume showed higher isomerization selectivity. The hydrocracking of n-decane over zeolite Beta and zeolite Y catalysts was mainly β-scission of tri-branched carbonium ions, thus their products contained more branched hydrocarbons. In contrast, over ZSM-5 catalyst, most products were normal alkanes due to the β-scission of mono branched carbonium ions.