核壳ZSM-5分子筛合成及其催化苯与甲醇烷基化性能

Synthesis of Core-Shell ZSM-5 Zeolite and Its Catalytic Performance in Alkylation of Benzene with Methanol

为了提高苯与甲醇烷基化中苯转化率及产物选择性,利用球磨-母液重结晶的方法得到小晶粒ZSM-5分子筛,然后在十六烷基三甲基溴化铵(CTAB)辅助下制备了以介孔二氧化硅为壳,以小晶粒ZSM-5分子筛为核的核壳结构分子筛。采用X射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、N2物理吸附、NH3程序升温脱附(NH3-TPD)和红外光谱(IR)等方法表征了催化剂的物化性质,并在固定床反应器中考察了催化剂的催化性能。结果表明:该方法成功合成了微-介孔联通良好的核壳结构分子筛,且有效覆盖了核层分子筛外表面酸位。在苯与甲醇烷基化反应中,苯转化率提高了9.92%,乙苯选择性下降了2.77%,同时二甲苯及对二甲苯选择性有所提高,核壳结构分子筛催化性能的提升主要归因于其独特的孔道结构和酸性分布。

In order to improve the conversion of benzene and products selectivity in alkylation of benzene with methanol,the small-cystal ZSM-5 zeolite was prepared by ball milling and mother liquor recrystallization.Then using cetyltrimethylammonium bromide(CTAB)as a template to generate mesoporous silica on the surface of the small-cystal ZSM-5 zeolite,whereas a core-shell structure zeolite was successfully prepared.The physicochemical properties of the samples were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),nitrogen physical adsorption,ammonia temperature programmed desorption(NH3-TPD)and infrared spectroscopy(IR).Catalytic performance of catalysts in the alkylation of benzene with methanol was evaluated in a fixed bed reactor.The results showed that the core-shell zeolite with good micro-mesoporous connectivity were successfully synthesized,and the external acid sites of the core zeolite were effectively covered.In the alkylation of benzene with methanol,the conversion of benzene was increased by 9.92%,and the selectivity of ethylbenzene was decreased by 2.77%.Meanwhile,the selectivity of xylene and p-xylene was significantly improved.The improvement of catalytic performance of the core-shell zeolite was mainly due to its unique pore structure and acidity distribution.