纳米HZSM-5的酸性调控及其催化苯和稀乙烯制乙苯

Acid Modification of Nanosized HZSM-5 for Alkylation of Benzene With Dilute Ethylene

采用硅溶胶、氯化铝、四丙基溴化铵(模板剂)为原料,在水热条件下合成纳米HZSM-5分子筛。以此为母体,在焙烧脱除模板剂前,用硝酸酸洗处理不同时间,得到一系列外表面酸量不同的纳米HZSM-5分子筛,并以此制备催化剂。采用XRD、SEM、NH3-TPD、XRF、XPS和Py-FTIR等手段对硝酸酸洗前后的纳米HZSM-5分子筛进行表征,考察纳米HZSM-5分子筛在硝酸酸洗处理后酸量、外表面酸分布的变化以及制备的催化剂对催化苯和稀乙烯烷基化反应性能的影响。结果表明:硝酸酸洗处理能改变纳米HZSM-5酸量和外表面的酸分布,与母体相比,硝酸酸洗处理16 h得到的分子筛外表面酸中心最少;以酸洗16 h的HZSM-5分子筛(Z160-N-16)制备催化剂(Z160-N-16-C),在360℃、1.4 MPa、n(Benzene)∶n(Ethylene)=1、乙烯质量空速1.5 h-1条件下催化苯和稀乙烯烷基化反应,苯的转化率、乙基(乙苯和二乙苯)的选择性和分别为37%和96%;该催化剂的积炭速率降至以母体分子筛制备催化剂的50%,副产物二甲苯的质量分数降低了20%。

Nanosized HZSM-5 was hydrothermally synthesized using tetrapropylammonium bromide as template,silica sol and aluminum chloride hexahydrate as silicon and aluminium sources,respectively.Taking this as parent zeolite,a series of nanosized HZSM-5 zeolites,serving as catalyst precursors,with different acid amount were obtained by treating with nitric acid for different time before removing organic template.The structure and acidity of samples were characterized by XRD,SEM,NH3-TPD,XRF,XPS and Py-FTIR.The acid amount and acid distribution on external surface of nanosized HZSM-5 after nitric acid treatment and the effects of catalysts on the alkylation performance of benzene with dilute ethylene were systematically investigated.Results show that nitric acid treatment changes the acid amount and external surface acidity of nanosized HZSM-5.Compared with parent material,the external surface of zeolite treated with nitric acid for 16 h exhibits the lowest acid content.The catalyst(Z160-N-16-C)prepared by Z160-N-16 was applied to alkylation reaction.Under the conditions of 360℃,1.4 MPa,n(Benzene)∶n(Ethylene)=1,and MHSV of ethylene of 1.5 h-1,benzene conversion is 37%,total selectivity of EB and DEB increases to 96%.Meanwhile,the coking rate of Z160-N-16-C is half of that of parent material,and the mass fraction of xylene in product is reduced by 20%.