不同硅铝比Al-MCM-41介孔分子筛的表征及催化合成氯乙酸正辛酯

摘要

以十六烷基三甲基溴化铵( CTAB)为模板剂,正硅酸乙酯(TEOS)为硅源,乙二胺为碱性介质,当n(TEOS)∶n( NaAl02)∶n(CTAB)∶n(H2NCH2CH2NH2)∶n(H2O)=1∶x∶0.12∶ 3.5∶130,其中x=0.1,0.033,0.02,0.01,0.006 7时,水热法合成了Al - MCM - 41介孔分子筛.通过XRD,N2吸附-脱附,NH3 - TPD和TEM等手段对不同硅铝比(n(Si)/n(Al))的Al - MCM -41介孔分子筛进行了表征.结果表明,当n(Si)/n( Al)由150减小至30时,Al - MCM -41介孔分子筛仍具有典型的六方介孔结构特征,但当n( Si)/n(Al)=10时,样品结构有序性下降.Al - MCM - 41介孔分子筛酸量随着n( Si)/n( Al)减小而增大.将Al - MCM - 41介孔分子筛用于催化合成氯乙酸正辛酯,相同反应条件下,n( Si) /n( Al) =30的Al - MCM - 41介孔分子筛为催化剂时酯化率最高,由此表明,Al - MCM - 41介孔分子筛作为催化剂,反应酯化率不仅取决于样品酸量,也与其晶体结构相关.当Al - MCM - 41介孔分子筛用量为氯乙酸质量的3％,反应温度为120～140℃,n(氯乙酸)∶n(正辛醇)=1∶1.2时,酯化率可达94.34％.%Mesoporous molecular sieve MCM -41 containing Si and Al with Si/Al molar ratio equal to 10,30, 50,100 and 150 were synthesized under hydrothermal conditions using cetyltrimethylammonium bromide (CTAB) as template and tetraethylorthosilicate (TEOS) as silica source and ethylenediamine as alkaline medium. The optimum molar ratio was n(TEOS): n{ NaA102) : n( CTAB) : n( H2NCH2CH2NH2): n( H20) = 1: x: 0. 12: 3. 5: 130, where x = 0. 1,0. 033 ,0. 02,0. 01 and 0. 006 7 respectively. The structure and physical and chemical surface properties of the samples were characterized by XRD, N2 adsorption - desorption, NH3 -TPD,TEM,et al. The results indicated that when Si/Al molar ratio of the samples drops from 150 to 30,the mesoporous molecular sieve MCM - 41 keeps its characteristics of typical hexagonal mesoporous structure. However,as the Si/Al molar ratio declines further to 10, the ordered mesoporous structure of the molecular sieve is partly diminished. The acid amount of Al - MCM -41 increases with decrease of Si/Al molar ratio. Al - MCM -41 molecular sieve was used in the preparation of n - octyl chloroacetate as catalyst. Under same conditions,when the Si/Al molar ratio is 30, the conversion can achieve a highest value. This phenomenon indicated that the esterification not only depends upon the chloroacetic acid/n - octanol ratio, but also the crystal structure of the Al - MCM -41 molecular sieve. When chloroacetic acid reacted with octanol with molar ratio of 1: 1. 2 at 120 ~ 140 ℃ and the dosage of Al - MCM - 41 ( Si/Al = 30) is 3% ( mass fraction) , the esterification achieves 94. 34% .