F-T模型化合物在ZSM-5沸石催化剂上的反应研究

Study of F-T model compounds reactiong over HZSM—5 zeolites

采用F-T合成产物的主要组分α-烯烃和n-烷烃模型化合物,研究不同的合成方法,不同SiO_2/Al_2O_3比及不同质子化预处理的HZSM-5,对催化转化活性和产物选择性的影响。预处理方法不同对沸石表面酸性和酸强度分布影响不同,n-烷烃与α-烯烃的催化活性中心不同,烷烃活性中心是沸石表面强酸中心。产物选择性与分子链长有关,在相同反应条件下,同碳数α-烯烃转化可获得比烷烃高出10%～20%(wt)汽油和烃产率。当沸石SiO_2/Al_2O_3比大于50时,孔道结构将有利于对二甲苯扩散,p/m、p/o值超出平衡值。

The effects of different synthetic methods,different SiO_2/Al_2O_3 ratios and HZSM-5 pretreated with different protonation methods on the catalytic conversion activity and the selectivity to the product were studied by use of the model—compounds of alkenes and alkanes which are the main components in Fischer—Tropsch synthesis. The defferent pretreatment methods affected the acidity and acid strength distribution on the surface of zeolites. The catalytic active sites of alkanes were different to that of alkenes. The active sites of alkanes were the strong acid sites on the zeolite surface. The selectivity to the products was related to the chain length of molecule. Under the same reaction condition, the yield of gasoline fraction and aromatics for alkenes was about 10%-20% (wt) higher than that for alka nes with the same number of carbon atoms. When the SiO_2/Al_2O_3 ratio of zeolite was above 50,the cavity structure was of benefit to the diffusion of xylene and the values for p/m, p/o exceeded the equilibrium values.