硅烷化改性对纳米ZSM-5甲醇制汽油催化剂性能的影响

对比了水热处理后微米ZSM-5和纳米ZSM-5分子筛的物化性质和催化甲醇制汽油(MTG)的反应性能,发现采用纳米ZSM-5分子筛催化剂能得到较高的汽油收率和较长的寿命,但汽油中均四甲苯含量较高.对纳米ZSM-5分子筛进行硅烷化处理,利用低温N_2吸附-脱附、X射线衍射(XRD)、氨气程序升温脱附(NH_3-TPD)对改性前后的样品进行表征.在温度380℃、压力2.0 MPa、空速3.0 h~(-1)的反应条件下进行MTG反应,对硅烷化改性后的催化剂进行评价.结果表明,负载SiO_2后催化剂的强酸中心降低,比表面积和孔容降低.纳米ZSM-5分子筛合适的SiO_2负载量为2%,硅改性后用于MTG反应,催化剂的寿命和汽油收率分别由改性前的144 h和33.6%显著增加到180 h和34.4%.当SiO_2负载量继续增加时,催化剂寿命和汽油收率逐渐降低.另外,随SiO_2负载量的增加,其催化MTG所得汽油产品中的异构烷烃和芳烃含量降低,烯烃和正构烷烃含量增加,均四甲苯含量显著降低,改善了油品质量.

The Effect of Silylation on the Catalytic Performance of Nanosize ZSM-5 Zeolites for the Conversion of Methanol to Gasoline

The catalytic performances of microsize and nanosize ZSM-5 zeolites modified by hydrothermal treatment for the conversion of methanol to gasoline (MTG)were compared.The results showed that with the nanosize ZSM-5 as catalyst,a higher gasoline yield of MTG and longer catalyst lifetime were obtained,but the durene content in the gasoline was too high.Silylation method was used to treat the nanosize ZSM-5 zeolite,and the parent and modi-fied samples were characterized by N2 adsorption-desorption,XRD and NH3-TPD method.Their performances of MTG were tested at the condition of temperature 380 ℃,pressure 2.0 MPa,and methanol mass space velocity 3 .0 h-1 .The results indicated that silylation of the zeolite could decrease the concentration of strong acid sites, specific area and pore volume.When the content of SiO2 loaded on the nanosize zeolite was 2%,the catalyst life time increased from 144 h to 180 h,and the gasoline yield increased from 33.6%to 34.4%.When the SiO2 con-tent increased continuously,both the catalyst life and gasoline yield gradually decreased.In addition,i-alkane , aromatic and especially durene content in gasoline decreased with the increase of SiO2 loading,while olefin and n-alkane increased,and the gasoline quality was greatly improved.