环状ZSM-5分子筛在苯和乙醇烷基化反应中的应用

Application of cyclic ZSM-5 zeolite in alkylation of benzene and ethanol

低温下采用水热晶化法合成了环状中空ZSM-5分子筛,并以磷酸二氢铵为前体,制备了不同磷负载量的环状中空ZSM-5催化剂,采用XRD,SEM,NH_(3)-TPD,Py-FTIR等方法对催化剂进行表征,并在气相连续流动固定床反应器上对苯和乙醇烷基化制乙苯进行性能评价和稳定性考察。实验结果表明,环状中空ZSM-5催化剂进行磷改性后,催化剂的酸强度降低,随着磷负载量的增加,乙苯选择性逐渐增加,甲苯和丙苯选择性逐渐降低;当磷负载量达到3%(w)后,催化剂外表面强酸位基本消失,此时乙苯选择性最高;在n(苯)∶n(乙醇)=8∶1、340℃、1.0 MPa、WHSV=1 h^(-1)条件下,对该催化剂进行了寿命考察,在300 h反应过程中,乙醇转化率超过99.9%,苯的转化率维持在11%左右,乙基苯的选择性最高达到98.4%,二甲苯相对含量最低达到0.11%。

Cyclic hollow ZSM-5 zeolite was synthesized by hydrothermal crystallization at low temperature.And cyclic hollow ZSM-5 catalysts with different P loads were prepare using ammonium dihydrogen phosphate as precursor.The catalysts were characterized by XRD,SEM,NH_(3)-TPD and Py-FTIR,and their performances and stabilities for alkylation of benzene and ethanol to ethylbenzene were evaluated in a gas-phase continuous flow fixed bed reactor.The experimental results show that the acid strength of the catalyst decreases after P modification of the cyclic hollow ZSM-5 zeolite,and with the increase of P loading,the selectivity for ethylbenzene increases while that for toluene,propylbenzene decreases.When P loading reaches 3%(w),the strong acid site on the surface of the catalyst basically disappears,and the selectivity to ethylbenzene is the highest.Under the conditions of n(benzene)∶n(ethanol)=8∶1,340℃,1.0 MPa,WHSV=1 h^(-1) and reaction time 300 h,the conversion of ethanol is more than 99.9%,the conversion of benzene is maintained at about 11%,the highest selectivity for ethylbenzene is 98.4%,and the minimum relative content of xylene reaches 0.11%.